WO2022234533A1 - Metallic nanohole array on nanowell sensing element - Google Patents

Metallic nanohole array on nanowell sensing element Download PDF

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Publication number
WO2022234533A1
WO2022234533A1 PCT/IB2022/054209 IB2022054209W WO2022234533A1 WO 2022234533 A1 WO2022234533 A1 WO 2022234533A1 IB 2022054209 W IB2022054209 W IB 2022054209W WO 2022234533 A1 WO2022234533 A1 WO 2022234533A1
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WIPO (PCT)
Prior art keywords
nanowells
layer
article
array
deposition
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PCT/IB2022/054209
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French (fr)
Inventor
Myungchan Kang
Jeffrey L. Solomon
Christopher S. Lyons
Caleb T. NELSON
Matthew R.D. SMITH
Karl K. STENSVAD
James A. Phipps
Mary I. Buckett
Bing HAO
Henrik B. VAN LENGERICH
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3M Innovative Properties Company
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Publication of WO2022234533A1 publication Critical patent/WO2022234533A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N21/552—Attenuated total reflection
    • G01N21/553—Attenuated total reflection and using surface plasmons
    • G01N21/554—Attenuated total reflection and using surface plasmons detecting the surface plasmon resonance of nanostructured metals, e.g. localised surface plasmon resonance

Definitions

  • Nanostructures such as nanohole or nanowell arrays on substrates can exhibits extraordinary properties. For example, it was discovered that there is extraordinary optical transmission through nanohole arrays (“Extraordinary optical transmission through sub wavelength hole arrays,” Nature 391, 667-669 (1998)).
  • SPR Surface plasmon resonance
  • spectroscopy typically utilizes a thin metallic layer disposed onto an optically transparent substrate (e.g., glass).
  • Electromagnetic radiation e.g., ultraviolet light, visible light or infrared light
  • the detector analyzes the light reflected off the surface of the metal.
  • the metallic layer includes a periodic array of nanoholes (i.e., nanohole array) having subwavelength dimensions, and the detector analyzes the electromagnetic radiation transmitted through the metallic layer on the side opposite the source of electromagnetic radiation.
  • nanohole array i.e., nanohole array
  • the present disclosure describes an article including an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; an array of nanowells formed into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof, the nanowells each having a ratio of depth to opening size greater than about 0.5; and a metallic layer disposed at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells.
  • the metallic layer extends from the land areas into the nanowells along the sidewalls to form a wrapping portion to wrap a comer of the opening of the nanowells.
  • the present disclosure describes a sensor including an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; an array of nanowells formed into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof, the nanowells each having a ratio of depth to opening size greater than about 0.5; a metallic layer disposed at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells; a light source disposed on a first side of the optically transparent dielectric layer, and configured to emit a detection light toward the article; and a detector disposed on a second side of the optically transparent dielectric layer opposite the first side, and configured to receive the detection light transmitted through the article.
  • the present disclosure describes a method of making a sensor.
  • the method includes providing an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; forming an array of nanowells into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof, the nanowells each having a ratio of depth to opening size greater than about 0.5; and disposing a metallic layer at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells.
  • One such advantage of exemplary embodiments of the present disclosure is that the configuration of various sensor elements can be controlled to provide desired SPR spectral features or changes, which can be distinctively measured for detection of organic fluids.
  • FIG. 1A is a schematic cross-sectional view of an article, according to one embodiment.
  • FIG. IB is a schematic cross-sectional view of a portion of the article of FIG. 1A, according to one embodiment.
  • FIG. 1C is a schematic top view of an article, according to some embodiments.
  • FIG. 2 is a schematic diagram of a sensor including a sensor element, according to one embodiment.
  • FIG. 3A is a schematic cross-sectional view of a sensing element, according to one embodiment.
  • FIG. 3B is a schematic cross-sectional view of a sensing element, according to one embodiment.
  • FIG. 4A is a schematic diagram of a process to make the article of FIG. 1A, according to one embodiment.
  • FIG. 4B is a schematic diagram of a process to make the article of FIG. 1A, according to another e
  • FIG. 6A is a cross-sectional TEM image of EX1.
  • FIG. 5 is schematic diagrams of various structure types for Examples or Comparative Examples.
  • FIG. 6B is a cross-sectional TEM image of EX2.
  • FIG. 6C is a cross-sectional TEM image of CE3.
  • FIG. 7 is normalized transmission spectra in water for CE1, EX1, EX2, and EX3.
  • FIG. 8 is normalized transmission spectra in air and water for CE2, CE3, and EX4.
  • FIG. 9 is normalized transmission spectra in air and water for EX5, EX6, and EX8.
  • FIG. 10 is normalized simulated transmission spectra in air for EX11, CE4, CE5, and CE6.
  • FIG. 11A is cross-sectional Electric-field maps at the wavelength of 658 nm, obtained from
  • FIG. 1 IB is cross-sectional Electric -field maps at the wavelength of 658 nm, obtained from
  • FIG. 11C is cross-sectional Electric -field maps at the wavelength of 642 nm, obtained from
  • FIG. 1 ID is cross-sectional Electric-field maps at the wavelength of 658 nm, obtained from
  • FIG. 12A is overlaid representative normalized spectra at 0, 10, 20, 30, and 40 (v/v %) of Ethanol in water obtained from EX8.
  • FIG. 12B is the shift of peak position around 635nm obtained from EX8 with respect to time at various Ethanol concentrations.
  • FIG. 13A is the shift of peak position around 635nm obtained from EX17 with respect to time.
  • FIG. 13B is the shift of peak position around 748nm obtained from EX 18 with respect to time at various Acetone concentrations.
  • the present disclosure provides methods of forming metallic nanohole arrays on nanowells with a controlled depth.
  • a mesh pattern of metal layer having an array of nanoholes is provided on an array of nanowells, aligned with the openings of the respective nanowells.
  • the aspect ratio of the nanowells are controlled to be sufficiently high to prevent a substantial deposition of metal into the nanowells.
  • the metal deposition thicknesses can be tuned on both the tops of the array features and on the bottoms of the nanowells. Embodiments of this disclosure allow for the metal deposition thickness on the top of the array to be much greater than that in the nanowells.
  • FIG. 1A is a schematic cross-sectional view of an article 10, according to one embodiment.
  • FIG. IB is a schematic cross-sectional view of a portion of the article of FIG. 1A.
  • FIG. 1C is a schematic top view of the article 10.
  • the article 10 includes an optically transparent dielectric layer 3 having a first major surface 31 and a second major surface 32 opposite the first major surface 31.
  • An array of nanowells 22 formed into the first major surface 31 of the transparent dielectric layer 3.
  • the array of nanowells 22 each includes an opening 23 being interspersed between land areas 32 thereof.
  • the nanowells 22 each have a base 36 and a sidewall 34 connecting the base 36 and the land areas 32.
  • the nanowells 22 each may have an aspect ratio (e.g., the ratio of well depth D to well opening size W as shown in FIG. IB) greater than about 0.5.
  • the openings 23 of the nano wells 22 may have various regular or irregular shapes.
  • An opening size of a circular opening is the diameter of the opening.
  • An opening size for an oval opening is the length of its minor axis.
  • An opening size for a polygonal opening is based upon the length of the shortest line that can be drawn from one vertex, through the center of the opening, to the opposite side of the opening.
  • An opening size for an irregular shape is a shorter dimension of a minimum bounding rectangle of the irregular shape.
  • the minimum bounding rectangle is defined as a rectangle whose sides are respectively parallel to two orthogonal axes (e.g., x and y axes in Cartesian coordinates) and minimally enclose the shape.
  • the nanowells 22 each may have the aspect ratio of depth to opening size in a range, for example, from about 0.5: 1 to about 50:1, from about 1 to about 20: 1, from about 1.5:1 to about 10:1, from about 2:1 to about 10:1, optionally, from about 3:1 to about 10: 1.
  • nanowells may have an aspect ratio sufficiently high (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to substantially prevent a sputtering deposition of metal into the nanowells.
  • the array of nanowells has an average pitch in a range from 100 nm to 2500 nm, from 100 nm to 1000 nm, from 250 nm to 1000 nm, or optionally from 300 nm to 900 nm.
  • the term “pitch” refers to the distance from the center of one opening to the center of the next nearest opening.
  • the openings of the nano wells have an average opening size in a range from 10 to 90 percent, 15 to 85 percent, or optionally, from 20 to 80 percent of the pitch.
  • the nanowells have an average depth in a range, for example, from 50 nm to 5000 nm, from 100 nm to 2000 nm, optionally, from 200 nm to 1000 nm.
  • the optically transparent dielectric layer 3 may include at least one optically transparent inorganic layer or optically transparent polymeric layer.
  • Exemplary inorganic layers include at least one of glass, SiN and S1O2.
  • Exemplary polymeric layers include polyethylene terephthalate, poly(methyl methacrylate), polyvinyl chloride, polyethylene, polypropylene, styrene methyl methacrylate, polycarbonate, polystryrene, and copolymers thereof.
  • the optically transparent dielectric layer 3 may be provided on an optically transparent, dielectric supporting layer adjacent the dielectric layer.
  • An exemplary support layer may include, for example, a glass made of fused silica, or a polymeric layer.
  • the support layer may include the same, or different optically transparent inorganic or polymer materials of the dielectric layer.
  • the optically transparent dielectric layer may include at least one of the reaction products of a curable composition, monomer, or solution coatable polymer or resin.
  • dielectric layers include polyacylates, polymethacrylates, soluble polymers such as polyvinyl alcohol, polymer resins such as polyvinyl butyral, thermosetting polymers such as polyurethanes, thermoplastic polymers such as polypropylene.
  • the dielectric layer 3 can be formed by any suitable processes such as, for example, casting, coating, deposition, dry film lamination and printing, etc. Coating methods include spin coating, die coating, roll coating, spray, and evaporation. Printing methods include inkjet, gravure, flexographic and screen printing. After the dielectric layer is applied, it can be cured by actinic radiation or heat.
  • the dielectric layer can also be a solution resin where the solvent is evaporated to form a dried fdm.
  • a metallic layer 8 is disposed at least on the land areas 32 of the optically transparent dielectric layer 3.
  • the metallic layer 8 forms a mesh pattern having an array of nanoholes 82 aligned with the openings 23 of the respective nanowells 22.
  • the mesh pattern of the metallic layer 8 can be a repeating pattern including at least one of a square lattice, a rectangular lattice, a hexagonal lattice, a rhombic lattice, or a parallelogrammic lattice.
  • One exemplary mesh pattern of the metallic layer 8 is illustrated in FIG. 1C.
  • the metallic layer 8 forms the mesh pattern having an array of nanoholes 82 aligned with the openings 23 of the respective nanowells of the transparent dielectric layer 3.
  • the openings 82, 23 typically have a pitch 223 in a range from 100 nm to 2500 nm, from 100 nm to 1000 nm, from 250 nm to 1000 nm, or optionally from 300 nm to 900 nm.
  • the openings 82, 23 may have any suitable regular or irregular shape including, for example, spherical, oval, trigonal, rectangular, polygonal, etc.
  • the openings 82, 23 typically have an opening size 221 in a range from 5 to 95 percent of the pitch 223. In some embodiments, the opening size 221 is in a range from 10 to 90, 15 to 85, or even 20 to 80 percent of the pitch.
  • the opening size 221 is a shorter dimension of a minimum bounding rectangle of the irregular shape.
  • the minimum bounding rectangle is defined as a rectangle whose sides are respectively parallel to two orthogonal axes (e.g., x and y axes in Cartesian coordinates) and minimally enclose the shape.
  • the opening size 221 of a circular opening is the diameter of the opening.
  • the opening size 221 for an oval opening is the length of its minor axis.
  • the opening size 221 for a polygonal opening is based upon the length of the shortest line that can be drawn from one vertex, through the center of the opening, to the opposite side of the opening.
  • the metallic layer 8 has a first portion 81 on the land areas 32 with a first thickness Tl, a second portion 84 on the base 36 of the nanowell with a second thickness T2, and a third portion 86 on the sidewall 34 of the nanowell with a third thickness T3.
  • the first and third portions 81, 86 are connected at the comer of the nanowell opening 23 to wrap around the comer.
  • the thickness ratio of T2 over Tl is no greater than 70%, no greater than 60%, no greater than 50%, no greater than 40%, no greater than 30%, no greater than 20%, no greater than 10%, optionally, no greater than 5%.
  • the thickness ratio of T2 over Tl can be controlled by controlling the aspect ratio of the nanowells and/or a metal deposition process.
  • the metallic layer may include at least one of gold, silver, aluminum, copper, platinum, mthenium, nickel, palladium, rhodium, iridium, chromium, iron, lead, tin, zinc, a combination or alloy thereof.
  • the metallic layer on the land area may have an average thickness in a range from 20 nm to 500 nm, from 30 nm to 200 nm, optionally, from 30 nm to 150 nm.
  • the metal deposition thicknesses can be tuned on both the land areas and on the bottoms of the nanowells. Some embodiments of this disclosure allow for the metal deposition thickness on the top of the array to be much greater than that in the nanowells.
  • a metal deposition process described herein can be controlled such that the second thickness T2 on the base 36 of the nanowells is no greater than 70 nm, no greater than 60 nm, no greater than 50 nm, no greater than 40 nm, no greater than 30 nm, no greater than 20 nm, no greater than 10 nm, or no greater than 5 nm.
  • the metallic layer 8 may extend from the land areas 32 into the nanowells 22 along the sidewalls 34 to form the sidewall portion 86 with a depth d and a thickness T3 and form a wrapping around structure. In other words, the metallic layer 8 may wrap around the comers of the nanowell openings 23 that connect to the land areas 32.
  • the original opening size W of the nanowell opening 23 may decrease to the opening size W’ of the metallic nanohole 82.
  • the opening size W’ may be l%to 97%, 5% to 95%, 10% to 90%, 45% to 90%, or 50% to 90% of the opening size W.
  • the metallic layer 8 may have the thickness T1 on the land area 32 in the range, for example, from 20 nm to 500 nm, from 30 nm to 200 nm, optionally, from 30 nm to 150 nm.
  • the sidewall portion 86 may not have a uniform thickness.
  • the thickness T3 may decrease when the sidewall portion 86 extends away from the nanowell opening 23 toward the nanowell bottom surface 36.
  • the thickness T3 may be in the range, for example, from 3% to 48% of nanowell opening size, from 5% to 45% of nanowell opening size, from 10% to 40% of nanowell opening size.
  • the wrapping portion may have an average thickness T3 of at least 2 nm, at least 3 nm, at least 5 nm, at least 10 nm, at least 20 nm, or even at least 30 nm.
  • the depth d of the sidewall portion 86 may be no less than 1%, no less than 2%, no less than 3%, no less than 5%, or no less than 10% of a nanowell depth D. In some embodiments, the depth d may be no greater than 95%, no greater than 50%, no greater than 30%, or no greater than 20% of a nanowell depth D.
  • the nanowells 22 have an average depth D in a range, for example, from 50 nm to 5000 nm, from 100 nm to 2000 nm, optionally, from 200 nm to 1000 nm.
  • the depth d of the sidewall portion 86 may be no less than 10 nm, no less than 20 nm, no less than 50 nm, or no less than 90 nm.
  • the article 10 can be applied as a nanohole array sensing element for a plasmon resonance sensor that can be used to quantitatively detect and measure analytes based upon the refraction of transmitted light.
  • the nanohole array sensor elements of the present disclosure are configured to measure the electromagnetic radiation transmitted by the sensing element.
  • the sensors in the present disclosure are simpler, more compact, able to use single and multiple wavelength sources, and exhibit greater sensitivity to target analytes.
  • a plasmon resonance sensor may include a light source disposed on a first side of the nanohole array sensing element, and configured to emit a detection light toward the article.
  • a detector is disposed on a second side of the nanohole array sensing element opposite the first side, and configured to receive the detection light transmitted through the article.
  • the light source can be positioned on the same side of the metallic nanoholes, or the opposite side of the metallic nanoholes.
  • the light source can be positioned on the side of metallic layer, and the detector can be positioned on the opposite side.
  • the detector can be positioned on the side of metallic layer, and the light source can be positioned on the opposite side.
  • FIG. 2 illustrates one embodiment of a sensor including a sensor element 10 of the present disclosure.
  • the sensor 40 includes a chamber 42, an inlet port 44, and outlet port 46, a first optical window 48 and a second optical window 50.
  • the sensor 40 further includes a light source 52 proximate the first optical window 48 and a detector 54 proximate the second optical window 50, where the light source 52 and detector 54 are in optical alignment.
  • the light source can be a single wavelength light source, such as a single wavelength light emitting diode (LED) or laser. Alternatively, the light source can be a multiple wavelengths light source, such as a white light source. In some embodiments, the light source emits at least one wavelength of ultraviolet (UV) light (i.e., 10 to 400 nanometers). In other embodiment, the light source emits at least one wavelength of visible light (i.e., greater than 400 to less than 700 nanometers). In yet other embodiment, the light source emits at least one wavelength of infrared (IR) light (i.e., 700 to 1,000,000 nanometer). The detector senses the optical transmission through the sensor element, and obtains spectra of transmission versus wavelength based on the detected light.
  • UV ultraviolet
  • IR infrared
  • the dielectric constant of the absorptive layer will change, resulting in the change of distinctive spectral features.
  • the distinctive spectral features include peak/valley positions, measured intensity at specified wavelengths, some mathematic processes using several intensities at various wavelengths (e.g. relative intensity ratio at two wavelengths), hue, and so on.
  • the detector response can be correlated to the concentration of analyte vapor present in the vapor delivery chamber.
  • the detector includes at least one photodetector, such as a photodiode, a monochromator, a photoresistor, a phototransistor, a charge-coupled device, a complementary metal-oxide-semiconductor image sensor, a photomultiplier tube, and a phototube.
  • a photodetector such as a photodiode, a monochromator, a photoresistor, a phototransistor, a charge-coupled device, a complementary metal-oxide-semiconductor image sensor, a photomultiplier tube, and a phototube.
  • a sensing element may further include a sensing layer at least partially covering its metallic layer.
  • a sensing layer 5 is provided to substantially, conformally cover the metallic layer 8, but not filling the nanowell 22.
  • the sensing layer 5 is configured to recognize and immobilize target molecules through chemical or physical bonding. When the sensing layer recognizes and immobilizes target molecules, a change of the spectrum of transmission can be detected by the sensing element.
  • affinity groups can be provided on the metallic layer through covalent or noncovalent bonding.
  • the affinity groups can selectively bind the target analytes and yield shift of resulting spectra through nanohole arrays.
  • affinity group refers to a covalently or noncovalently attached group that is capable of specifically binding another molecule.
  • specifically binding and specific binding mean that an affinity group complexes with another molecule (i.e., its complementary molecule) with greater affinity than it complexes with other molecules under the specified conditions.
  • Noncovalent bonding includes electrostatic bonding, ionic bonding, hydrogen bonding, hydrophobic bonding, van der Waals bonding, and so on.
  • the affinity group is an antibody.
  • antibody includes antibody fragments, and are defined as polypeptide molecules that contain regions that can bind target analytes. Appropriate antibodies can be selected by one of skill in the art.
  • the affinity group is an aptamer, i.e., a short polynucleotide.
  • the affinity group is a target analyte molecule, such as a heavy metal or a small organic molecule.
  • a small organic molecule is one having a molecular weight of no greater than 5000 grams/mole.
  • the affinity group includes target- analyte-molecule-immobilized proteins, such as cortisol linked BSA.
  • binding and “specific binding” mean that an affinity group complexes with another molecule (i.e., its complementary molecule) with greater affinity than it complexes with other molecules under the specified conditions.
  • a target analyte molecule is complementary to a bound antibody.
  • An antibody is complementary to a bound target analyte molecule.
  • “specifically binding” may mean that an affinity group complexes with a complementary molecule with at least a 106-fold greater affinity, at least a 10 7 -fold greater affinity, at least a 10 8 -fold greater affinity, or at least a 10 9 -fold greater affinity than it complexes with molecules unrelated to the target molecule.
  • the affinity group may be further complexed with, or noncovalently bonded.
  • the average thickness of exemplary sensing layers is typically in a range of from 1 nm to 200 nm. In some embodiments, the average thickness is in the range from 2 nm to 100 nm, 3 nm to 50 nm, or 4 nm to 30 nm.
  • a sensing layer 7 is provided to at least partially fill the nanowell 22.
  • the sensing layer 34 may act as an absorptive layer including, for example, a polymer of intrinsic microporosity (PIM).
  • PIM intrinsic microporosity
  • Exemplary absorptive layers including a PIM were described in U.S. Patent Application No. 62/951,535 (Attorney Docket No. 81665US002, to Kang et ah), which is incorporated herein by reference.
  • An article or sensing element described herein such as, for example, the article 10 of
  • FIGS. 1A-C can be made by any suitable processes.
  • FIG. 4A is a schematic diagram of a process 100 to make the article 10 of FIGS. 1A-C, according to one embodiment.
  • FIG. 4B is a schematic diagram of another process 200 to make the article 10 including metallic nanohole arrays on nanowell arrays, according to another embodiment.
  • a pattern layer 6 is provided on a first major surface 31 of a polymeric layer 3.
  • a hard mask layer 4 is disposed on the first major surface 31 of the polymeric layer 3, being sandwiched between the pattern layer 6 and the polymeric layer 3.
  • the pattern layer 6 has a first surface 61 adjacent to the hard mask layer 4, and a second surface 63 opposite the first surface 61.
  • the second surface 63 includes a pattern 62 characterized by feature dimensions of width, length, and height.
  • the pattern layer 6 can be produced, for example, by replication, molding, or photolithography.
  • the pattern layer 6 can include polymeric materials including at least one of the reaction products of, for example, radiation curable, dissolvable polymer, thermoplastic or thermosetting polymer.
  • a second pattern transfer layer can be patterned using reactive ion etching (RIE) with a variety of different chemistries and specified conditions.
  • RIE reactive ion etching
  • the pattern layer 6 can include a nano-replicated resin layer formed by a nanoreplication method.
  • nanoreplication refers to a process of molding a nanostructured surface from another nanostructured surface using, for example, curable or thermoplastic materials. Nanoreplication is further described, for instance, in “Micro/Nano Replication”, Shinill Kang, John Wiley & Sons, Inc., 2012, Chapters 1 and 5-6.
  • the pattern layer can be formed by applying a curable composition onto a nanostructured surface and replicating a pattern therefrom.
  • the curable composition can include any suitable materials that can be solidified by radiation or heat.
  • the curable composition may include a UV-curable acrylate.
  • Exemplary curable compositions for a nanoreplication method are described in PCT Patent Application No. PCT/IB2020/058611 (Attorney docket No. 81875W0003), which is incorporated herein by reference. It is to be understood that the pattern layer 6 may be prepared by any suitable processes other than a nanoreplication method. The pattern layer 6 can be built up from a variety of materials depending on the technique used to generate the pattern layer.
  • a reactive ion etching (RIE) can be carried out to etch, from the second surface 63 of the pattern layer 6, into the first major surface 31 of the polymeric layer 3 to form an array of nanowells 22 including openings 23 being interspersed between land areas 32 thereof.
  • the etching process is used to transfer a pattern from the pattern layer 6 to the polymeric layer 3 beneath. It is to be understood that any suitable selective etching process other than RIE can be used.
  • Exemplary selective etching can be carried out using reactive ion etching, high density RF inductive plasma etching, high density linear ion plasma etching, microwave plasma etching, linear microwave plasma etching, helicon wave plasma etching, ion-beam milling, pulsed ion beam etching, pulsed reactive ion etching, or a combination thereof.
  • Transferring the pattern of a masking layer (e.g., the pattern layer 6) into the underlying layers (e.g., the polymeric layer 3) can be achieved by plasma etching.
  • ion-assisted plasma processing is conveniently used.
  • Methods for achieving anisotropic etching include reactive ion etching (RIE), high density ion source processing, or a combination of high-density ion source processing along with RIE.
  • RIE reactive ion etching
  • High density plasmas can be generated by inductive RF, or microwave coupling, or by helicon ion sources. Linear high-density plasma sources are particularly advantageous for generating high aspect ratio features.
  • Combining high density plasmas with RIE enables the decoupling of the ion generation (by high density plasma) from the ion energy (by RIE bias voltage).
  • the RIE method includes etching portions of the major surface not protected or less protected by the masking layer to form a nanostructure on a layer underneath the masking layer.
  • the provided method can be carried out using a continuous roll-to-roll process referred to as "cylindrical reactive ion etching" (cylindrical RIE).
  • Cylindrical RIE utilizes a rotating cylindrical electrode to provide anisotropically etched nanostructures on the surface of a substrate or article.
  • cylindrical RIE can be described as follows.
  • a rotatable cylindrical electrode (“drum electrode”) powered by radio-frequency (RF) and a grounded counter-electrode are provided inside a vacuum vessel.
  • the counter-electrode can include the vacuum vessel itself.
  • An etchant gas is fed into the vacuum vessel, and a plasma is ignited and sustained between the drum electrode and the grounded counter-electrode.
  • a continuous substrate including a patterned masking layer can then be wrapped around the circumference of the drum and the substrate can be etched in the direction substantially normal to the plane of the substrate.
  • the exposure time of the substrate can be controlled to obtain a predetermined etch depth of the resulting nanostructure.
  • the process can be carried out at an operating pressure of approximately 1-10 mTorr. Cylindrical RIE is disclosed, for example, in U.S. Patent No. 8,460,568 (David et ah).
  • the chemistry of the plasma environment can be controlled to achieve selectivity of etching when multiple materials are present.
  • Oxygen, and mixtures of oxygen with fluorinated gases are used to etch carbon-containing materials such as polymers, diamond-like carbon, diamond, and the like.
  • concentration of the fluorine in the plasma is critical to optimize the etching rate and selectivity.
  • a small amount of fluorinated gas is used to dramatically increase the etching rate of hydrocarbon polymers by as much as 300%.
  • silicon-containing materials silicon dioxide, SiOx, diamond-like glass, silicon nitride, silicon carbide, silicon oxycarbide, polysiloxane, silicone, silicone acrylates, silsequioxane (SSQ) resins, etc
  • fluorocarbons such as CF 4 , C 2 F 6 , C 3 F 8 and the like
  • the etch selectivity between silicon-containing materials and hydrocarbon polymers may be carefully tailored by obtaining the etching profdes of these materials as a function of the F/O atomic ratio in the plasma feed gas mixture.
  • Oxygen rich conditions provide excellent selectivity of etching hydrocarbon polymers and diamond-like carbon (DLC) while using silicon materials as the masking layer. Additional materials for the masking layer are upper hard mask layer materials described in PCT Patent Application No. PCT/IB2020/058611 (Attorney docket No. 81875W0003), incorporated herein by reference.
  • fluorine rich conditions provide excellent selectivity of etching silicon-containing materials while using hydrocarbon polymer-based masking materials.
  • Fluorinated plasma chemistries may be used for etching other masking materials such as tungsten, whose fluorides are volatile. Chlorine -containing gas mixtures may be used to etch materials whose chlorides are volatile, such as aluminum, and titanium. Oxide, nitrides and carbides of these etchable metals can also be etched by using chlorine-based chemistries. Silicon nitride, aluminum nitride, and titanium oxide are high index materials that may be etched with chlorine chemistries. Typical gases used for etching includes, for example, oxygen, nitrogen trifluoride (NF 3 ), CF 4 , C 2 F 6 , C 3 F 8 , SFr,. CF, CH 4 , and the like.
  • NF 3 nitrogen trifluoride
  • a pattern of the pattern layer 6 is first transferred to the hard mask layer 4 by etching through the hard mask layer 4 to form a pattern onto the hard mask layer 4 directly beneath using the engineered nanostructures of the pattern layer 6 as a mask.
  • An array of shallow nanowells are formed including openings being interspersed between land areas thereof.
  • the land areas may include a residual pattern layer and the hard mask layer directly beneath.
  • the hard mask layer 6 includes a silicon-containing material and is reactive-ion etched using a fluorine-containing gas.
  • the polymeric layer 6 may include a hydrocarbon polymer and is resistant to the fluorine etch.
  • a reactive ion etching step (RIE) to etch the hard mask layer may be carried out using an etching chemistry that can be chosen based on the etching selectivity on the pattern layer on the top, the hard mask layer itself, and the etchable polymeric layer directly beneath.
  • RIE reactive ion etching step
  • a pattern formed on the hard mask layer 6 is then transferred to the polymeric layer 3 directly beneath by etching into the polymeric layer 3 using the pattern on the hard mask layer 4 as a mask.
  • the polymeric layer 3 may include a hydrocarbon polymer and is reactive-ion etched using oxygen.
  • the hard mask layer 4 may include a silicon-containing material and is resistant to the oxygen etch. It is to be understood that a reactive ion etching step (RIE) to etch the polymeric layer may be carried out using an etching chemistry that can be chosen based on the etching selectivity on the pattern layer on the top, the hard mask layer underneath the pattern layer, the polymeric layer itself, and an optional hard mask layer directly beneath.
  • RIE reactive ion etching step
  • the nanowells 22 can be etched to a desired depth, therefore controlling an aspect ratio (e.g., the ratio of depth D to opening size W as shown in FIG. IB) of the nanowells 22.
  • an aspect ratio e.g., the ratio of depth D to opening size W as shown in FIG. IB
  • the time of oxygen etching can be varied to allow for controllable nanohole arrays to be formed before metallization. It is possible that there can be a run-to-run variation that has the possibility to impact the consistency of etching of the polymeric layer to the same depth each time.
  • an etch stop layer 5 is provided adjacent to a second major surface of the polymeric layer 3 on the side opposite the first major surface 31 of the polymeric layer 3.
  • a support film 2 is provided to support the polymeric layer 3.
  • the etch stop layer 5 is sandwiched between the polymeric layer 3 and the support film 2.
  • the etch stop layer 5 may include a silicon-containing material and is resistant to the oxygen etch.
  • Exemplary materials for an etch stop layer may include hard mask layer materials described in PCT Patent Publication No. WO 2020/095258 (Lengerich et al.), which is incorporated herein by reference.
  • the etching of the polymeric layer 3 is automatically stopped at the etch stop layer 5 such that the nanowells 22 each have the base thereof reaching the etch stop layer 5.
  • the process allows for a desired thickness or aspect ratio to be achieved by controlling the layer thickness of the polymeric layer 3. This may enable run-to-run consistency, by removing the need to precisely time the oxygen etching step.
  • the polymeric layer 3 and the support film 2 can include the same or different materials.
  • the polymeric layer and the support film may include a polymeric material that is in the form of a flat sheet and is sufficiently flexible and strong to be processed in a roll-to- roll fashion.
  • Polymeric films used as a polymeric layer or a support film in articles described herein are sometimes referred to as base films.
  • roll-to-roll what is meant is a process where material is wound onto or unwound from a support, as well as further processed in some way. Examples of further processes include coating, slitting, blanking, and exposing to radiation, or the like.
  • Polymeric films can be manufactured in a variety of thicknesses, ranging in general from, for example, 5 micrometers to 1000 micrometers.
  • polymeric film thicknesses range from 10 micrometers to 500 micrometers, or from 15 micrometers to 250 micrometers, or from 25 micrometers to 200 micrometers.
  • Roll-to-roll polymeric films may have a width of at least 6 inches, 24 inches, 36 inches, or 48 inches.
  • Polymeric films can include, for example, poly(ethylene terephthalate) (PET), poly(butylenes terephthalate) (PBT), polyethylene naphthalate) (PEN), polycarbonate (PC), cyclic olefin copolymer (COP), polypropylene (PP), biaxially oriented polypropylene (BOPP), cellulose triacetate, a combination thereof, etc.
  • the support film 2 may include a dielectric substrate including at least one of an optically transparent inorganic layer or an optically transparent polymeric layer.
  • Exemplary inorganic layers may include at least one of glass, SiN, S1O2, amorphous SiC x O y H z , etc.
  • Exemplary polymeric layers include polyethylene terephthalate, poly(methyl methacrylate), polyvinyl chloride, polyethylene, polypropylene, styrene methyl methacrylate, polycarbonate, polystryrene, and copolymers thereof.
  • the polymeric layer 3 may include at least one of the reaction products of a curable composition, monomer, or solution coatable polymer or resin.
  • the polymeric layer 3 is applied onto the etch stop layer 5, as shown in FIG. 4B.
  • the polymeric layer 3 can be applied by any suitable processes such as, for example, casting, coating, deposition, dry film lamination and printing. Coating methods include spin coating, die coating, roll coating, spray, and evaporation. Printing methods include inkjet, gravure, flexographic and screen printing. After the polymeric layer is applied, it can be cured by actinic radiation or heat.
  • the polymeric layer can also be a solution resin where the solvent is evaporated to form a dried film.
  • polymeric layers include polyacylates, polymethacrylates, soluble polymers such as polyvinyl alcohol, polymer resins such as polyvinyl butyral, thermosetting polymers such as polyurethanes, thermoplastic polymers such as polypropylene.
  • An array of nanowells 22 is formed by etching into the first major surface 31 of the polymeric layer 3.
  • the array of nanowells 22 include openings 23 being interspersed between land areas 32 thereof.
  • the nanowells each have a base 36 and a sidewall 34 connecting the base 36 and the land areas 32 thereof.
  • the nanowells each have the aspect ratio of depth D to opening size W in a range, for example, from about 0.5: 1 to about 50: 1, from about 1 to about 20: 1, optionally, from about 1.5: 1 to about 10:1.
  • the nanowells each may have an aspect ratio high enough (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to substantially prevent a sputtering deposition of metal into the nanowells on the sidewalls and the bases thereof.
  • nanowell arrays One traditional way to create nanowell arrays is through a UV-nanoreplication, or continuous cast and cure process.
  • a nano-post mold By using a nano-post mold, high-fidelity nanowells can be directly replicated onto a flexible substrate, enabling a lower cost fabrication of nanoholes from the methods mentioned above.
  • the traditional nanoreplication processes may have limitations in the aspect ratio of structures that can be replicated. When the aspect ratio of the nanwells gets larger, it becomes increasingly difficult to peel the replication resin out without tearing, due to increased surface area contact of the resin with the mold.
  • Embodiments of the present disclosure provide nanowells having an aspect ratio sufficiently high (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to substantially prevent a sputtering deposition of metal into the nanowells.
  • an aspect ratio sufficiently high (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to substantially prevent a sputtering deposition of metal into the nanowells.
  • the metal deposition thicknesses can be tuned on both the tops of the array features and on the bottoms of the nanowells.
  • Embodiments of this disclosure allow for the metal deposition thickness on the top of the array to be much greater than that in the nanowells.
  • the array of nanowells has an average pitch in a range from 100 nm to 2500 nm, from 100 nm to 1000 nm, from 250 nm to 1000 nm, or optionally from 300 nm to 900 nm.
  • the openings of the nanowells have an average opening size in a range from 5 to 95 percent, 10 to 90 percent, 15 to 85 percent, or optionally, from 20 to 80 percent of the pitch.
  • the nanowells have an average depth in a range from 50 nm to 5000 nm, from 100 nm to 2000 nm, optionally, from 200 nm to 1000 nm.
  • the metallic layer 8 is deposited on the etched first major surface 31 of the polymeric layer 3 to form a mesh pattern of metal having an array of nanoholes aligned with the openings 23 of the respective nanowells 22.
  • the nanowells 22 each may have an aspect ratio of depth to opening size high enough (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to prevent a substantial deposition of metal into the nanowells on the sidewalls and the bases thereof.
  • the metallic layer 8 can be deposited by vapor coating techniques such as Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) processes.
  • PVD processes include sputter deposition and evaporation (thermal and ebeam).
  • PVD processes are preferred due to the ease in which the upper surfaces of nanowell structures (e.g., the land areas 32 in FIG. 4) are coated with little deposition on the lower surfaces of nanowell structures (e.g., the base 36 and the sidewall 34 of a nanowell in FIG. 4).
  • CVD and the related processes plasma-assisted CVD and atomic layer deposition (ALD) may be more difficult to control the deposition preferentially to the upper surfaces of nanowell structures.
  • ALD atomic layer deposition
  • a suitable sputter deposition process can use conventional cathode or magnetron sputter sources with targets of the metal to be deposited.
  • DC, pulsed-DC, AC, or RF power supplies can be used to power the plasma that provides the energetic ions and electric field necessary to sputter deposit the atoms from the target onto the substrate.
  • the sputtering is done in a vacuum process with an inert gas such as Ar at a pressure in the range of 0.133 Pa to 2 Pa.
  • nanowell structures with depth/opening size aspect ratios (AR) greater than, for example, about 1:1, about 2:1, or about 3:1, can be preferentially coated on the upper surfaces (e.g., the land areas 32 in FIG.
  • nanowell structures can be preferentially coated on the upper surfaces (e.g., the land areas 32 in FIG. IB) with a sputter target set to the side of and at an angle relative to the substrate (sometimes referred to as angle deposition or glancing angle deposition) to enhance shadowing effects.
  • Exemplary sputtering processes for preferentially coating nanowell structures are described in Atty. Docket No. 83726US002, which is incorporated herein by reference.
  • the evaporation process is also a vacuum process using pressures in the range of 10 4 to
  • the source material (metal to be coated) is heated via resistance heating, inductive heating, or ebeam bombardment to vaporize the metal atoms.
  • the atoms travel to the substrate in a line-of-sight process.
  • the metallic layer is preferably deposited by DC sputtering in a gaseous environment of Ar.
  • Nanopattemed molds were purchased from Eulitha AG. These silicon molds were crated via a proprietary lithography process and were subsequently Ni plated and micro-welded into cylindrical sleeves for roll-to-roll UV replication.
  • the first mold, Mold 1 contained a square-packed array of about 100 nm diameter holes on a 200 nm pitch, with the holes being 165 nm deep at an 8.5° draft angle.
  • the second mold, Mold 2 contained a square-packed array of 200 nm holes on a 400 nm pitch, with the holes being 310 nm deep at a 6.3° draft angle.
  • Sample 1 200 nm diameter nanopost on a 400 nm pitch
  • Sample 1 was prepared by die coating a urethane acrylate mixture onto a 125 -micrometer- thick polycarbonate film. The urethane acrylate mixture was then pressed against Mold 2 under pressure and exposed to UV radiation to lock the structure in place. The structure was subsequently peeled from the Nickel mold, leaving a nanostructured pattern on the polycarbonate film. The resultant pattern on the polycarbonate film was the inverse of Mold 2, a square-packed array of 200 nm diameter nanoposts on a 400 nm pitch. The height of nanopost was 300 nm.
  • Sample 2 200 nm diameter nanopost on a 400 nm pitch
  • Sample 2 was produced using the same procedure described above for Sample 1 with the following exceptions: a 75 -micrometer-thick polyethylene terephthalate (PET) film with a primed acrylic adhesion promoter were used in place of the polycarbonate film.
  • PET polyethylene terephthalate
  • the height of nanopost was 300 nm.
  • Sample 3 100-nm-diameter nanopost on a 200 nm pitch
  • Sample 3 was produced using the same film and process as Sample 1 with the exception of using Mold 1. This yielded a polycarbonate film with a nanopattem of a square-packed array of 100 nm diameter nanoposts on a 200 nm pitch. The height of nanopost was 160 nm.
  • Patterning method B Preparation of direct replicated nanowell structure Sample 4: 200 nm diameter nanowell on a 400 nm pitch
  • Sample 1 was plasma treated and attached to a steel roller.
  • Sample 4 was prepared using the procedure described above for Sample 1 with the exception that the plasma treated section of Sample 1 was used as the mold.
  • the resultant film was a polycarbonate film with a square-packed array of 200 nm diameter nanowells on a 400 nm pitch. The depth of nanowell was 300 nm.
  • Patterning method C Preparation of high aspect ratio nanowell structure through one hard mask layer process
  • a PET film was first plasma coated with a silicon- containing hard mask layer.
  • the films created in Sample 1 (posts) and Sample 4 (wells) were plasma treated with a release chemistry and were coated with a urethane acrylate mixture from a coating die.
  • the urethane acrylate coated fdms were laminated to the hard mask coated PET and cured via UV radiation.
  • a nanopost or nanohole array was left on top of the silicon-containing hard mask layer.
  • the films were exposed to a fluorine-containing reactive ion etching process to break through the thin areas of the mold, and break through the silicone-containing hard mask layer, leaving a patterned layer of an oxygen hard maskant layer.
  • the film was exposed to an oxygen etching step.
  • This oxygen etching step continued to etch into the underlying polymer film, while stopping at the remaining patterned etch resistant layer.
  • the depth of the resulting hole or well film was dependent on the conditions and time that the film was exposed to the oxygen etching step.
  • Patterning method D Preparation of high aspect ratio nanowell structure through one hard mask and one etch stop process
  • a PET film was sputtered with a silicon-containing etch stop layer, followed by a coating of an acrylate layer to a desired thickness, with an additional sputtered silicone-containing hard mask layer on top to create a 3 -layer film on PET.
  • the films created in Sample 1 (posts) and Sample 4 (wells) were plasma treated with a release chemistry and were coated with a urethane acrylate mixture from a coating die.
  • the urethane acrylate coated films were laminated to the 3-layer coated PET and cured via UV radiation. After separating the films, a nanopost or nanohole array was left on top of the top-most silicone-containing hard mask layer on the PET stack.
  • the films were exposed to a fluorine -containing reactive ion etching process to break through the thin areas of the replicated mold and into the top silicone-containing hard mask layer. This creates a patterned hard mask layer on the top etch-resistant layer.
  • the film was exposed to an oxygen etching step. This etch step etches through the coated acrylate layer between etch-resistant layers, creating a controlled- depth nanohole or nanohole film. The depth of the resultant feature was set by the coating thickness of the acrylate layer between etch-resistant layers.
  • a section of Sample 4 was plasma treated with a release chemistry and was coated with a urethane acrylate from a coating die.
  • the urethane acrylate coated film was put in contact with a PET film and was cured via UV radiation. After separating the films, a nanopost array was left on top of the PET film.
  • this PET film was coated with a silicon-containing acrylate resin, enough to completely fill the space between the nanoposts with a thin layer of resin over the top and was UV cured.
  • the film was then exposed to a fluorine-containing etch to break through the thin layer of silicon-containing resin on top of each of the nanoposts, while leaving a silicon-containing etch- resistant layer between the posts.
  • the film was then exposed to an oxygen-containing etch process, ablating the exposed post structures to create a well-structure in the film.
  • the depth of these wells was dependent on the conditions and exposure time of the film during the oxygen etch.
  • the area between the posts was unetched during the oxygen-containing etching step, as there was still a remaining etch-block layer in the spaces between the posts.
  • the substrate film with nanowell or nanopost structures was vapor coated with Au using a batch dc sputtering system (PVD75 from Kurt J. Lesker Co.)
  • the deposition targets were Au with dimensions of 3-inch diameter and 0.125-inch thickness, from Kurt J. Lesker Co.
  • the metal layers were deposited at an Argon pressure of 3 mTorr and a power of 200W.
  • the substrate normal was pointed directly at the source.
  • the exposure time was varied per sample to realize the desired thickness. The thickness was based on the measured thickness of deposited Au on planar polymer films using variable angle spectroscopic ellipsometry and cross-sectional TEM images.
  • the substrate film with nanowell or nanopost structures was vapor coated with Ag/Au using a roll-to-roll dc sputtering system with the target parallel to the substrate film during deposition.
  • the sputtering target was 85%Ag/15%Au with dimensions 3.85” x 21” x 0.25” (9.78cm x 53.34 cm x 0.64cm).
  • the Ag/Au was deposited at an Argon pressure of 2.9 mTorr (0.36 Pa) and a power of 3.8 kW.
  • the line speed was varied from 2.44fpm (0.744 m/min) (resulting thickness of 200 nm) to 24.38fpm (7.43 m/min) (resulting thickness of 20 nm) to create samples of different Ag/Au thicknesses.
  • the thickness was based on the measured thickness of deposited Ag/Au on plane polymer films using variable angle spectroscopic ellipsometry and cross-sectional TEM images.
  • Substrate films with nanowell or nanopost structures were coated with Au within an ultra- low vacuum “electron-beam evaporation” chamber.
  • This chamber was a custom build by the Kurt J. Lesker Co.
  • the sample was held down with KaptonTM tape onto a 10”xl0” (25cm x 25cm) metal plate and placed face down in the load lock chamber(deposition was from the lower part of the main chamber and the sample was approx. 18” (45.7cm) above the source material).
  • the load lock was pumped down to a range ⁇ lxl0 5 torr (1.33xl0 3 Pa), then the plate was moved into the main chamber.
  • the main chamber pressure was in the range ⁇ 3x10 6 torr (4xl0 4 Pa).
  • the substrate normal was pointed directly at the source.
  • the deposition was carried out by turning on the power supply and the source and controller gauges.
  • the rate of deposition was controlled via an internally written software program connected to the “INFICON XTC/2 THIN FILM DEPOSITION CONTROLLER”(INFICON of East Syracuse, New York) at a rate of 0.1 nm per second until 100 nm of metal was deposited.
  • the thickness was monitored by an INFICON 6MHz Au coated crystal with a feedback loop to the XTC/2 controller.
  • the power supply shut down once the target thickness was reached.
  • the sample was then transferred back to the load lock chamber and evacuated. The sample was removed from the plate.
  • Microcontact printing Power method FI Nanohole arrays were produced in gold layers coated on PET substrates via a microcontact printing process.
  • PDMS was cast against an e-beam written master containing the target pattern.
  • the resulting PDMS stamp was then inked in 6.5 mM octadecanethiol dissolved in ethanol for 16 hours. Following this inking step, the stamp was blown off with nitrogen and allowed to dry overnight.
  • the stamp was then mounted in the microcontact printing device. PET with 100 nm (nominal thickness) evaporated gold was loaded onto the drum of the printer, and the stamp was contacted to the fdm in order to transfer a self-assembled monolayer of the octadecanethiol.
  • this octadecanethiol was used as an etch resist in an immersed rotational wet etch using an aqueous solution 20 mM in ferric nitrate and 30 mM in thiourea for approximately 25 minutes.
  • the samples were rinsed thoroughly with deionized water, dried, and kept in a dry chamber under nitrogen gas prior to subsequent characterization and testing.
  • SEM images were obtained using a Hitachi 4700 Field Emission SEM under conditions found to minimally affect structure size and shape. To ensure conductivity between samples and the specimen holders all samples were DC sputter coated with Au/Pd alloy target in a Denton coater. Typical conditions for sputter coating were 20mA current for 25 -30s, which produced Au/Pd at a thickness of less than 1 nm. Both cross sectional and top down images were obtained in areas thought be representative of the samples in general. SEM images were analyzed using a computer program Image J (software available from National Institutes of Health, v 1.37). The average post/well diameter and post height/well depth were measured.
  • Cross-sectional (CX) structure, morphology, and elemental composition of the metal-coated nanowells was carried out with transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and quantitative x-ray microanalysis (EDS). These samples were in the form of a planar sheet, with the nanowells located on the side-of-interest. As the nanowells were patterned in a square-grid pattern, the cross-sectional samples were cut out such that the observation plane in CX was along one axis of the grid pattern. Thus, the maximum number of nanowells would be intersected in CX.
  • TEM transmission electron microscopy
  • STEM scanning transmission electron microscopy
  • EDS quantitative x-ray microanalysis
  • TEM samples were prepared using room-temperature ultramicrotomy ((Leica, model FC7) and a diamond knife (Diatome USA, P.O. Box 410, 1560 Industry Rd., Hatfield, PA 19440).
  • TEM data was acquired in the FEI Osiris transmission electron microscope (ThermoFisher Scientific, Hillsboro, OR 97124) operating at 200 kV. Instrument magnification range used was from 1.1 kX to 360 kX.
  • Quantitative, high resolution x-ray microanalysis was carried using the proprietary X-FEG high brightness electron source of the FEI Osiris TEM and the Bruker Quantax Super-X x-ray microanalysis system (Bruker Nano, Inc., 312 N. Harvey Ave., Oak Park, IL 60302). This x-ray microanalysis system is based on Silicon Drift Detector (SDD) technology and accompanying
  • a piece of 4mm x 4mm nanohole array film was placed on a transparency film (copier transparency film, item number 21828, Staples).
  • One layer of 3M electrical tape red tape, polymer film
  • a circular hole (2.83mm diameter) was placed on the top of nanohole array film.
  • the hole was aligned in the center of the piece to expose nanohole arrays while the red tape was holding the nanohole array film down to the transparency film.
  • the 2.83mm hole was generated in the tape using a disc cutter.
  • the sensor strip with nanohole array was placed and fixed inside an acrylic cuvette (Sarstedt, acryl, Ref 67.755, 10x10x45mm) with the nanohole array facing to inside cuvette and PET substrate layer facing to the cuvette wall.
  • the cuvette was inserted into a cuvette holder (model CUV-UV, Ocean Optics).
  • the area of nanohole array was aligned with a light source and a detector.
  • the nanohole array layer’s normal was pointed directly at the light source and the detector.
  • Two optical fiber probes (Part number: QP600-025-UV, Ocean Optics) were connected to the cuvette holder to measure transmission spectra through the nanohole array film.
  • One optical probe was connected to a light source and the other probe to a spectrometer.
  • One of two sets of light source-detectors was used for measurements.
  • One set consisted of a light source ((Model HL-2000-FHSA, Ocean Optics) and a detector (Jaz spectrometer, Ocean Optics) and the other set consisted of a light source (Model DH-2000-BAL, Ocean Optics) and a detector (FX-100, Ocean Optics).
  • Transmitted white light without nanohole array films was taken for a reference spectrum to convert acquired scope mode spectra to transmission spectra.
  • the transmission spectra were normalized by the reference intensity, which is the maximum transmission intensity between 400 nm and 800 nm.
  • Spectra were acquired and processed using a customized Fabview program (software available from National Instruments of Austin, TX) and OMNI driver (software available from Ocean Optics).
  • the obtained transmission spectra were converted to color (RGB color space) as follows.
  • the measured reflection spectrum was constructed to International Commission on Illumination (or “CIE”) XYZ color space using color matching the CIE 1931 2o Standard Observer function.
  • the nanohole array fdm Due to the size scale (in nm range) and the high dispersion of the metals in use, the nanohole array fdm is only correctly modeled using the FDTD (Finite Difference Time Domain) approach, which takes into account of the metal light interaction and the near field effect.
  • FDTD Finite Difference Time Domain
  • a commercially available software FDTD Solutions from Lumerical was used. After setting up the model, parameter sweeps involving metal film thickness, nanohole diameter, ambient refractive index (water or air) etc. were carried out to study the trend and compare against experimental data.
  • Activation buffer contained 0.1M MES and 0.5M NaCl with adjusted pH 6.
  • PBS buffer was prepared by diluting concentrate phosphate buffered saline solution.
  • PBS-Tween 20 was prepared by adding proper amount Tween 20 (0.02% v/v) to PBS buffer.
  • a piece of nanohole array film was immersed in ethanol and sonicated for 5 minutes using a sonicator (Model 1510, Branson, Brookfield, CT). After rinsing the film with ethanol, the piece was incubated into ImM 11-mercaptoundecanoic acid in ethanol for 30 minutes with an orbital shaker (Mophom, 40rpm). After the immobilization of thiols, the piece of nanohole array film was rinsed with ethanol, deionized water, and MES buffer (pH 6.0) sequentially. The piece was immersed into mixture of 2.5mM EDC in MES buffer and 5mM NHS in MES buffer for 15 minutes with the orbital shaker.
  • This mixture was made by mixing the same volume of 5mM EDC and lOmM NHS right before the treatment.
  • the piece was rinsed with deionized water and PBS buffer.
  • the piece was incubated in 20 pg/ml Cortisol-BSA in PBS buffer (pH 7.4) for 2 hours with the orbital shaker.
  • About 60mM ethanolamine in water was added to quench the coupling reaction for 15 minutes.
  • the final ethanolamine concentration was 12 mM.
  • the piece was rinsed with copious deionized water, dried in air, and kept in the dry chamber under nitrogen gas.
  • a sensor strip with sensing layer immobilized nanohole arrays was fabricated as described above.
  • the sensor strip was placed and fixed inside a cuvette.
  • a stirring bar (Catalog number 58948-400, 3mm x 6.3mm, VWR, Radnor, PA) was inserted into the cuvette.
  • the cuvette holder was placed on a stirrer (Model VMS-C7, VWR, Radnor, PA). After adding PBS-Tween 20 buffer to the cuvette, the solution was stirred at 750rpm during the optical measurements.
  • PIMs solid dissolved in chlorobenzene was used.
  • 130 g of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-l,r-spirobisindane Part number B22170 from Alfa Aesar, Tewksbury, MA
  • 77.1 g of tetrafluoroterephthalonitrile Part number H61326 from Alfa Aesar
  • 322.83 g potassium carbonate Part number H61326 from Alfa Aesar
  • 3380 g of N,N-dimethylformamide was reacted at 68 °C for 72 hours.
  • the polymerization mixture was poured into water, and the precipitate was isolated by filtration.
  • the resulting polymer was twice dissolved in tetrahydrofuran, precipitated from methanol, and air dried at room temperature.
  • a yellow solid product obtained was dissolved in chlorobenzene and 4.0-4.4% (wt/wt) PIMs solution was prepared.
  • the viscosity of solution was 3.0-7.0 cP using a Rheometer.
  • Nanohole array film was cut in the size of 2 cm x 2 cm and placed on a glass slide. About 30 pL of 1% wt/wt PIMs solution in chlorobenzene was applied using a micropipette on the nanohole array side. Sharply cut edges of polymer film were used to spread the solution uniformly on the entire area.
  • the coated film was dried in oven for 1 hour at 80 °C. After baking, the film was kept in the dry chamber under nitrogen before measurements.
  • the absorbance spectra were collected using optoelectronic measurement described above.
  • the absorbance at 425.47 nm is related to the thickness of PIMs layer.
  • a calibration curve relating the thickness of PIMs layers and absorbance at 425.47 nm of PIMs layer coated to various thicknesses on glass slides was measured.
  • PIMs layers were coated on glass slides using a spin coater (Model WS 400B-8NPP/LITE spin coater, Laurell Technologies Corporation, North Wales, PA) at various conditions and the thickness of PIMs layer was measured using a stylus profilometer (XP-1, Ambios Technology, Santa Cruz, CA).
  • Absorbance at 425.47 nm was linearly proportional to the thickness of PIMs layer measured from the profilometer. From the linear calibration curve, the coated thickness of PIMs layer on the nanohole array was approximately 650 nm.
  • VOCs levels were generated using a syringe pump obtained from KD Scientific, Holliston, MA fitted with a gas tight syringe (obtained from Hamilton Company of Reno, Nevada). The syringe pump delivered the VOCs onto a piece of filter paper suspended in a 500 mL three necked flask. The flow of dry air passed over the paper and vaporized the solvent. Controlling the rate of delivery of VOCs from the syringe pump generated concentrations of VOCs.
  • the syringe pump was controlled by a LAB VIEW program. All measurements were done at room temperature. The concentration of VOCs in air was verified by measurement using an IR analyzer obtained under the trade designation MIRAN from THERMO FISHER SCIENTIFIC, Waltham, MA.
  • Sensor strips with PIMs layer coated nanohole arrays were fabricated and placed inside a cuvette.
  • Several 4 mm-diameter holes were made in the cuvette using a drill.
  • a hole was made in the center of cuvette lid.
  • a gas tube was inserted through the hole of cuvette lid and connected between VOCs control chamber and the cuvette to deliver VOCs vapor.
  • the VOCs vapor entered through the cuvette lid and existed through the holes of the cuvette during optical measurements.
  • Examples and Comparative Examples The mesh pattern of Examples or Comparative Examples here is a repeating pattern of a square lattice.
  • Table 1 below lists a summary of structure types of various Examples or Comparative Examples as shown in FIG. 5.
  • the structure types include structure type “A” through “EL”
  • Table 2 summarizes the structure type of various Examples (EX) and Comparative Examples (CE).
  • Tl is the thickness of top layer metal deposition
  • T2 is the thickness of bottom layer metal deposition
  • T3 is the thickness of side layer metal deposition
  • W-W is the reduction of well opening size after metal deposition.
  • CE1 and EX 1-3 shows the effect of base structures (post vs. well) and the effect of well depth.
  • Planar Equivalent Metal deposition thickness in Tables is based on the metal thickness measured on planar surfaces.
  • roll-to-roll sputtering process was used to deposit metal on the nanostructures.
  • the cross-sectional TEM topological from EX1 shows that thicker Ag/Au deposition was observed on the top layer of nanowell structures in comparison with the Ag/Au deposition on the bottom layer as shown in FIG.6A.
  • the dark area was confirmed to be Ag/Au deposition through elemental analysis in TEM.
  • the measured thickness of Ag/Au deposition on the bottom layer was around 42nm. T2/T1 ratio is equal to 0.42.
  • FIG. 6B shows cross-sectional TEM images of EX2. Almost no metallic deposition was observed on the bottom of nanowells in FIG.6B, while some metallic deposition was observed on the bottom of nanowells in FIG.6A. The scarce metallic deposition on the bottom of nanowells in FIG.6B formed discontinuous metallic films having grains with discrete boundaries. In FIG.6B, the deposition along the side wells was observed and the metallic deposition was thinner as the location was closer to the bottom of nanowells. The metal was deposited preferentially on the top or along the side of nanowells instead of the bottom of nanowells in sputtered samples with the increase of well depth.
  • FIG. 7 shows a normalized transmission spectrum in water from CE1, which had sputtered 100-nm-thick Au/Ag (85/15) deposition on three-dimensional nanopost structures. Due to the preferential deposition on the top layer or side of posts, the plasmonic effect from nanodot array structures was dominant with some of the plasmonic effect from nanohole array structure. High light absorption was observed in the wavelength range between 550 nm and 750 nm due to nanodot array structures.
  • FIG. 7 also shows a normalized transmission spectrum in water from EX1 which had sputtered 100-nm-thick Au/Ag (85/15) deposition on nanowell array structures. Due to the preferential deposition on the top layer or side of wells, the plasmonic effect from nanohole array structures was dominant with some of the plasmonic effect from nanodot array structures in resulting transmission spectra. Several transmission peaks from nanohole array structures were observed with slight light absorption in the wavelength range between 650 nm and 750 nm due to nanodot array structures which results from some metal deposition on the bottom of nanowell structures. This result is consistent with the observation of cross-sectional TEM images (FIG. 6A). FIG.
  • FIG. 7 shows a normalized transmission spectrum in water from EX2 which had the well depth of 500 nm.
  • FIG. 7 shows normalized transmission spectrum in water from EX3 which had the well depth of 800 nm.
  • the spectrum features from EX3 were almost identical to those from EX2. This similarity of the spectra between EX2 and EX3 means that from the certain depth, almost no metal deposition on the bottom of nano well structures took place through sputtering.
  • Nanohole array structures (Structure type: E, F, and C) were fabricated with similar nanohole configuration (diameter of hole, pitch size, type of metal, and metal thickness) but by different patterning methods and metallization methods. All samples were from similar master patterns (square array, 200 nm hole size and 400 nm pitch size). From the top view SEM images, the measured average hole or well diameters from SEM images were 237nm, 244nm, and 195nm for CE2, CE3, and EX4, respectively.
  • the nanohole array structures were generated to etch Au layers which were coated on flat substrates through microcontact printing.
  • the resulting structures are two-dimensional metallic nanohole array patterns on the flat dielectric substrate (Structure type: E, FIG.5).
  • two-dimensional metallic nanohole array structures were generated by two different metallization method (evaporation, CE3 and sputtering, EX4) on three-dimensional dielectric nanowell structures.
  • FIG. 6C shows cross-sectional TEM topological and corresponding elemental (Au) maps of CE3.
  • the structure type of CE3 is F in FIG.5. Similar thickness of Au deposition on both top and bottom layers of nanowell structures was observed in CE3.
  • Au deposition on the top layer observed from EX4 wraps around the openings of three-dimensional dielectric nanowell structures due to side-wall sputtering deposition, while the deposition patterns from CE3 yields sharp edges on the top layer deposition due to highly directional evaporation deposition.
  • FIG. 8 shows normalized transmission spectra in air and in water from CE2, CE3, and EX4.
  • transmission spectral features are from two-dimensional metallic nanohole array structures on two-dimensional planar polymer substrates.
  • multiple peaks such as (1,0) Au/Polymer, (1,1) Au/Polymer, (1,0) Au/Air, and (1,0) Au/Water were identified.
  • Polymer means polymeric substrate layers underneath Au layers.
  • multiple peaks from the interface of Au/Polymer were observed. Peaks from the interface of Au/Media (Air or Water) were overlapped with peaks (Au/Polymer) and were difficult to monitor the shift of peaks (Au/Media) upon the environmental change in Au/Media interface.
  • FIG. 8 shows that spectra from EX4 yield only nanohole array plasmonic peaks from the interface of Au/Media without being interfered by other plasmonic effects.
  • This lack of nanodot and Fabry-Perot interference spectral features come from the lack of metal deposition on the bottom layer of nanowell structures.
  • plasmonic peaks of nanohole array structures from the interface of Au/Polymer were absent in FIG. 8. The resulting clear peaks (Au/Media) from nanohole array structures could be easily correlated to the refractive index of media.
  • p is the pitch size, which is center to center distance between periodically arrayed holes
  • the integers (i, j) are the Bragg resonance scattering orders
  • e 1 and s m are the real dielectric constants of the adjacent dielectric layer and metallic layer, respectively.
  • EX5-10 shows a series of samples to observe the sputtered deposition along the side well of nanowell structures with various thickness of metal deposition. From a series of top-view SEM images with EX5-10, the well diameter was reduced with the increase of sputtered metal deposition thickness. This reduction of well diameter indicates that sputtered metal was deposited along the side well of nanowell structures instead of being deposited on the bottom of nanowell structures. Table 3 shows the measured average diameter of nanowells after metal deposition. The diameter at 0 nm Ag/Au thickness was obtained using an extrapolated line from the values obtained with 20 nm, 30 nm, and 50 nm thick deposition. The calculated diameter at 0 nm Ag/Au thickness was 197.7 nm.
  • Tl is the Ag/Au thickness
  • T3 is the accumulated Side-wall deposition thickness
  • a is the additional side-wall deposition thickness from previous thickness
  • V is the additional side-wall deposition volume from previous thickness
  • b is the additional side-wall deposition length
  • Peak position is around 630 nm with DI water
  • Peak shift is with respect to RE
  • the intended deposition volume was supposed to be deposited on the bottom of nanowells, which was close to the deposition pattern with evaporation.
  • the same intended deposition volume was used to be deposited in a cylindrical form along the side-wall.
  • the intended deposition volume V’, the deposition volume V” along the side-wall were calculated using the equations below: )
  • V Intended additional metal deposition volume
  • t Intended additional metal deposition thickness on the flat surface
  • W Well diameter before additional metal deposition
  • W’ Well diameter after additional metal deposition
  • b Additional side well metal deposition length along the side well from the top layer
  • a Additional side well metal deposition thickness from previous thickness.
  • the resulting cross-sectional pattern at 200-nm-thick Ag/Au deposition was consistent with the deposition pattern observed from a cross-sectional SEM image. This consistency confirms that the metal deposition on the well area takes place along the side well from top layer to bottom layer.
  • the accumulated thickness of t and a are T1 and T3, respectively.
  • FIG.9 show a series of normalized transmission spectra in air and in water from EX5, EX6, and EX8.
  • No samples show the peaks (Ag-Au/Polymer) such as (1,0) Ag-Au /Polymer and (1,1) Ag-Au /Polymer as shown in FIG.8 (CE2).
  • Peaks from (1,0) Ag-Au/Air were shown around the wavelength of 500 nm and peaks from (1,0) Ag-Au/Water were shown around the wavelength of 650 nm.
  • EX5 the peaks were too broad to be identified.
  • With increase of deposited metal thickness from 20 nm to 100 nm the peaks in spectra were more distinctive.
  • the finite-difference time-domain (FDTD) method was used to simulate resulting transmission spectra from deposition patterns obtained from Table 3 and Comparative Examples structures as shown in Table 2.
  • FIG. 10 show simulated cross-sectional deposition patterns, normalized simulated transmission spectra in air.
  • FIGS. 11A-D show electric-field maps at the wavelength of 658nm or 642nm obtained from EX11 (Sputtering pattern from EX8, see structure type D in FIG. 5), CE4 (see structure type G in FIG. 5), CE5 (see structure type H in FIG.
  • CE4 (ex. dimension of nanoewell, depostion thickness on the top layer) is similar to that of EX11 without wrapping depostion along the side well and top layer of EX11.
  • CE5 (ex. dimension of nanoewell, depostion thickness on the top layer) is similar to that of EX11 without side deposition along the side well of EX9 but with overhanging metal deposition on the top layer.
  • the diameter of bottom well is 197 nm but the diameter of metallic hole on the top layer is 173 nm.
  • CE6 has additional deposition on the bottom of nanowell in addition to the structure of CE4.
  • the thickness of deposition on the bottom layer is same as that on the top layer in CE4.
  • FIG.10 shows nanohole array plasmonic peaks (Metal/Substrate), such as (1,0) Ag/Polymer, (1,1) Ag/Polymer and (2,0) Ag/Polymer. Peak from (1,0) Ag/Air is overlapped with peak from (2,0) Ag/Polymer.
  • FIG. 10 shows nanohole array plasmonic peaks (Metal/Substrate), such as (1,0) Ag/Polymer, (1,1) Ag/Polymer and (2,0) Ag/Polymer. Peak from (1,0) Ag/Air is overlapped with peak from (2,0) Ag/Polymer. (1,0) Ag/Polymer peak was shifted from 658nm to 642nm.
  • FIG. 10 shows more plasmonic features resulting from nanodot array structures and Fabry-Perot interference structures were convoluted into the spectrum in addtion to nanohole array structures as discussed in FIG. 8.
  • FIG. 11B and 11C cross-sectional electric field profile map
  • FIG. 11B and 11C shows the edges between Ag and Polymer layer yield high electric field (circuled area in the E-field map) at the wavelength of 658nm or 642nm due to the excitations of localized surface plasmons. These areas which yield high electric field are known as hot spots. Transmission light from hot spots of Ag/Polymer interface was mostly transmitted in FIG. 1 IB and l lC.
  • FIG. 1 ID E-field map shows similar hot spots to that of nanohole array structures of FIG.1 IB and l lC.
  • FIG.11A shows that hot spots of Ag/Polymer interface are located underneath side-wall Ag deposits and the edge of wrapped Ag deposit inside nanowell structures. Due to hidden hot spots of Ag/Polymer interface by Ag deposit, transmission of light scattering from hot spots of Ag/Polymer interface was suppressed and all peaks from the interface of Metal/Substrate were absent as shown in FIG. 11A.
  • Sensors based on nanohole array are sensitive to the change of refractive index on metal array surfaces as described in Equation 1.
  • the refractive index next to metallic surface here, Ag/Au
  • the shift of spectra can be correlated to the presence and the amount of analyte molecules.
  • the refractive index was tuned by controlling the refractive index of Media.
  • the refractive indexes of water, 10, 20, 30, 40 (v/v %) of Ethanol in water are 1.3330, 1.3358, 1.3386, 1.3414, and 1.3442, respectively.
  • FIG. 12A shows overlaid representative normalized spectra at 0, 10, 20, 30, and 40 (v/v %) of Ethanol in water obtained from EX8. The spectra were red shifted with the increase of volume percentage of Ethanol in water.
  • FIG. 12B shows the shift of peak positions with respect to time.
  • EX8 Refractive Index
  • Tl is the Ag/Au thickness
  • T3 is the accumulated Side-wall deposition thickness
  • a is the additional side-wall deposition thickness from previous thickness
  • V is the additional side-wall deposition volume from previous thickness
  • b is the additional side-wall deposition length
  • Peak position is around 450 nm with DI water
  • Peak shift is with respect to RI.
  • EX 12- 16 show a series of samples to observe the sputtered metal deposition along the side well of nanowell structures with various thickness of metal deposition. From top-view SEM images, the well diameter was reduced with the increase of sputtered metal deposition thickness. This reduction of well diameter indicates that sputtered metal was deposited along the side well of nanowell structures instead of being deposited on the bottom well of nanowell structures. Table 4 shows the average diameter of nanowells measured from SEM images. The diameter at 0 nm Ag/Au thickness was obtained using an extrapolated line from the values obtained with 20-nm-, 40-nm-, and 50-nm-thick deposition.
  • EX17 was made by immobilizing Cortisol linked BSA on metallic (Ag/Au (85/15) on EX8 as described above.
  • the sensing layer (Cortisol-BSA) was immobilized through chemical bonds (thiol) and coupling reaction (EDC-NHS) (FIG.3 A).
  • the sensor strip was fabricated after the immobilization. First, lmL of PBS Tween-20 buffer (Tween 20, 0.02% v/v) was added into a cuvette with the sensor strip.
  • FIG. 13A shows that the change of peak position around 635nm in the transmission spectra with respect to time.
  • EX 18 is an example of physically coated sensing layer on EX8. About 650 nm thick PIMs layer was coated on nanohole array structures (FIG. 3B) . EX 18 was exposed to various concentration of Acetone vapor. 10, 20, 50, 100, 200, 500, 1000 ppm Acetone vapor was delivered to the cuvette holding EX18 for 5 mins or 10 mins per each concentration. The spectra were acquired every 5 sec.
  • FIG. 13B shows the change of peak around 750 nm in the transmission spectra with respect to time. Distinctive step change of peak position was observed in FIG.13B. The saturated value of peak position at each concentration was measured from FIG.13B.
  • any distinctive spectral features can be used to quantify spectral change as shown in Table 6.
  • the distinctive spectral features include peak/valley positions, measured intensity at specified wavelengths, some mathematic processes using several intensities at various wavelengths (e.g. relative intensity ratio at two wavelengths), Hue, Saturation, and so on.
  • one or more embodiments or “an embodiment,” whether or not including the term “exemplary” preceding the term “embodiment,” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the certain exemplary embodiments of the present disclosure.
  • the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the certain exemplary embodiments of the present disclosure.
  • the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

Abstract

Sensing elements having a metallic-nanohole-array-on-nanowell structure, methods of making and using the same are provided. The sensing elements includes a mesh pattern of metallic layer having an array of nanoholes provided on an array of nanowells, aligned with the openings of the respective nanowells. The metallic layer extends into the nanowells along the sidewalls to wrap the opening of the nanowells.

Description

METALLIC NANOHOLE ARRAY ON NANOWELL SENSING ELEMENT
BACKGROUND
Nanostructures such as nanohole or nanowell arrays on substrates can exhibits extraordinary properties. For example, it was discovered that there is extraordinary optical transmission through nanohole arrays (“Extraordinary optical transmission through sub wavelength hole arrays,” Nature 391, 667-669 (1998)).
Surface plasmon resonance (SPR) spectroscopy has received recent attention as an analytical technique for detection of organic fluids. Surface plasmon resonance spectroscopy typically utilizes a thin metallic layer disposed onto an optically transparent substrate (e.g., glass). Electromagnetic radiation (e.g., ultraviolet light, visible light or infrared light) is directed at the thin metallic layer through the transparent substrate to create an evanescent wave at the surface of the thin metallic layer opposite the source of electromagnetic radiation. In one variation, termed the Kretschmann configuration, the detector analyzes the light reflected off the surface of the metal. In an alternative variation, the metallic layer includes a periodic array of nanoholes (i.e., nanohole array) having subwavelength dimensions, and the detector analyzes the electromagnetic radiation transmitted through the metallic layer on the side opposite the source of electromagnetic radiation. The latter configuration provides for a simpler sensor having a compact, collinear optical arrangement with higher analyte sensitivity
SUMMARY
Briefly, in one aspect, the present disclosure describes an article including an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; an array of nanowells formed into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof, the nanowells each having a ratio of depth to opening size greater than about 0.5; and a metallic layer disposed at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells. In some cases, the metallic layer extends from the land areas into the nanowells along the sidewalls to form a wrapping portion to wrap a comer of the opening of the nanowells.
In another aspect, the present disclosure describes a sensor including an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; an array of nanowells formed into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof, the nanowells each having a ratio of depth to opening size greater than about 0.5; a metallic layer disposed at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells; a light source disposed on a first side of the optically transparent dielectric layer, and configured to emit a detection light toward the article; and a detector disposed on a second side of the optically transparent dielectric layer opposite the first side, and configured to receive the detection light transmitted through the article.
In another aspect, the present disclosure describes a method of making a sensor. The method includes providing an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; forming an array of nanowells into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof, the nanowells each having a ratio of depth to opening size greater than about 0.5; and disposing a metallic layer at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells.
Various unexpected results and advantages are obtained in exemplary embodiments of the disclosure. One such advantage of exemplary embodiments of the present disclosure is that the configuration of various sensor elements can be controlled to provide desired SPR spectral features or changes, which can be distinctively measured for detection of organic fluids.
Various aspects and advantages of exemplary embodiments of the disclosure have been summarized. The above Summary is not intended to describe each illustrated embodiment or every implementation of the present certain exemplary embodiments of the present disclosure. The Drawings and the Detailed Description that follow more particularly exemplify certain preferred embodiments using the principles disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which:
FIG. 1A is a schematic cross-sectional view of an article, according to one embodiment.
FIG. IB is a schematic cross-sectional view of a portion of the article of FIG. 1A, according to one embodiment.
FIG. 1C is a schematic top view of an article, according to some embodiments. FIG. 2 is a schematic diagram of a sensor including a sensor element, according to one embodiment.
FIG. 3A is a schematic cross-sectional view of a sensing element, according to one embodiment.
FIG. 3B is a schematic cross-sectional view of a sensing element, according to one embodiment.
FIG. 4A is a schematic diagram of a process to make the article of FIG. 1A, according to one embodiment.
FIG. 4B is a schematic diagram of a process to make the article of FIG. 1A, according to another e FIG. 6A is a cross-sectional TEM image of EX1.
FIG. 5 is schematic diagrams of various structure types for Examples or Comparative Examples.
FIG. 6B is a cross-sectional TEM image of EX2.
FIG. 6C is a cross-sectional TEM image of CE3.
FIG. 7 is normalized transmission spectra in water for CE1, EX1, EX2, and EX3.
FIG. 8 is normalized transmission spectra in air and water for CE2, CE3, and EX4.
FIG. 9 is normalized transmission spectra in air and water for EX5, EX6, and EX8.
FIG. 10 is normalized simulated transmission spectra in air for EX11, CE4, CE5, and CE6. FIG. 11A is cross-sectional Electric-field maps at the wavelength of 658 nm, obtained from
EXIT
FIG. 1 IB is cross-sectional Electric -field maps at the wavelength of 658 nm, obtained from
CE4.
FIG. 11C is cross-sectional Electric -field maps at the wavelength of 642 nm, obtained from
CE5.
FIG. 1 ID is cross-sectional Electric-field maps at the wavelength of 658 nm, obtained from
CE6.
FIG. 12A is overlaid representative normalized spectra at 0, 10, 20, 30, and 40 (v/v %) of Ethanol in water obtained from EX8.
FIG. 12B is the shift of peak position around 635nm obtained from EX8 with respect to time at various Ethanol concentrations. FIG. 13A is the shift of peak position around 635nm obtained from EX17 with respect to time.
FIG. 13B is the shift of peak position around 748nm obtained from EX 18 with respect to time at various Acetone concentrations.
In the drawings, like reference numerals indicate like elements. While the above-identified drawing, which may not be drawn to scale, sets forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed disclosure by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure.
DETAILED DESCRIPTION
The present disclosure provides methods of forming metallic nanohole arrays on nanowells with a controlled depth. A mesh pattern of metal layer having an array of nanoholes is provided on an array of nanowells, aligned with the openings of the respective nanowells. The aspect ratio of the nanowells are controlled to be sufficiently high to prevent a substantial deposition of metal into the nanowells. By controlling the aspect ratio of the nanohole opening to the depth of the nanowells, the metal deposition thicknesses can be tuned on both the tops of the array features and on the bottoms of the nanowells. Embodiments of this disclosure allow for the metal deposition thickness on the top of the array to be much greater than that in the nanowells.
FIG. 1A is a schematic cross-sectional view of an article 10, according to one embodiment. FIG. IB is a schematic cross-sectional view of a portion of the article of FIG. 1A. FIG. 1C is a schematic top view of the article 10. The article 10 includes an optically transparent dielectric layer 3 having a first major surface 31 and a second major surface 32 opposite the first major surface 31. An array of nanowells 22 formed into the first major surface 31 of the transparent dielectric layer 3. The array of nanowells 22 each includes an opening 23 being interspersed between land areas 32 thereof. The nanowells 22 each have a base 36 and a sidewall 34 connecting the base 36 and the land areas 32.
The nanowells 22 each may have an aspect ratio (e.g., the ratio of well depth D to well opening size W as shown in FIG. IB) greater than about 0.5. The openings 23 of the nano wells 22 may have various regular or irregular shapes. An opening size of a circular opening is the diameter of the opening. An opening size for an oval opening is the length of its minor axis. An opening size for a polygonal opening is based upon the length of the shortest line that can be drawn from one vertex, through the center of the opening, to the opposite side of the opening. An opening size for an irregular shape is a shorter dimension of a minimum bounding rectangle of the irregular shape. The minimum bounding rectangle is defined as a rectangle whose sides are respectively parallel to two orthogonal axes (e.g., x and y axes in Cartesian coordinates) and minimally enclose the shape.
In some embodiments, the nanowells 22 each may have the aspect ratio of depth to opening size in a range, for example, from about 0.5: 1 to about 50:1, from about 1 to about 20: 1, from about 1.5:1 to about 10:1, from about 2:1 to about 10:1, optionally, from about 3:1 to about 10: 1.
In some embodiments, nanowells may have an aspect ratio sufficiently high (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to substantially prevent a sputtering deposition of metal into the nanowells. The array of nanowells has an average pitch in a range from 100 nm to 2500 nm, from 100 nm to 1000 nm, from 250 nm to 1000 nm, or optionally from 300 nm to 900 nm. As used herein, the term “pitch” refers to the distance from the center of one opening to the center of the next nearest opening. The openings of the nano wells have an average opening size in a range from 10 to 90 percent, 15 to 85 percent, or optionally, from 20 to 80 percent of the pitch. The nanowells have an average depth in a range, for example, from 50 nm to 5000 nm, from 100 nm to 2000 nm, optionally, from 200 nm to 1000 nm.
In some embodiments, the optically transparent dielectric layer 3 may include at least one optically transparent inorganic layer or optically transparent polymeric layer. Exemplary inorganic layers include at least one of glass, SiN and S1O2. Exemplary polymeric layers include polyethylene terephthalate, poly(methyl methacrylate), polyvinyl chloride, polyethylene, polypropylene, styrene methyl methacrylate, polycarbonate, polystryrene, and copolymers thereof.
In some embodiments, the optically transparent dielectric layer 3 may be provided on an optically transparent, dielectric supporting layer adjacent the dielectric layer. An exemplary support layer may include, for example, a glass made of fused silica, or a polymeric layer. The support layer may include the same, or different optically transparent inorganic or polymer materials of the dielectric layer.
In some embodiments, the optically transparent dielectric layer may include at least one of the reaction products of a curable composition, monomer, or solution coatable polymer or resin. Examples of dielectric layers include polyacylates, polymethacrylates, soluble polymers such as polyvinyl alcohol, polymer resins such as polyvinyl butyral, thermosetting polymers such as polyurethanes, thermoplastic polymers such as polypropylene. The dielectric layer 3 can be formed by any suitable processes such as, for example, casting, coating, deposition, dry film lamination and printing, etc. Coating methods include spin coating, die coating, roll coating, spray, and evaporation. Printing methods include inkjet, gravure, flexographic and screen printing. After the dielectric layer is applied, it can be cured by actinic radiation or heat. The dielectric layer can also be a solution resin where the solvent is evaporated to form a dried fdm.
A metallic layer 8 is disposed at least on the land areas 32 of the optically transparent dielectric layer 3. The metallic layer 8 forms a mesh pattern having an array of nanoholes 82 aligned with the openings 23 of the respective nanowells 22. The mesh pattern of the metallic layer 8 can be a repeating pattern including at least one of a square lattice, a rectangular lattice, a hexagonal lattice, a rhombic lattice, or a parallelogrammic lattice. One exemplary mesh pattern of the metallic layer 8 is illustrated in FIG. 1C. The metallic layer 8 forms the mesh pattern having an array of nanoholes 82 aligned with the openings 23 of the respective nanowells of the transparent dielectric layer 3. The openings 82, 23 typically have a pitch 223 in a range from 100 nm to 2500 nm, from 100 nm to 1000 nm, from 250 nm to 1000 nm, or optionally from 300 nm to 900 nm.
The openings 82, 23 may have any suitable regular or irregular shape including, for example, spherical, oval, trigonal, rectangular, polygonal, etc. The openings 82, 23 typically have an opening size 221 in a range from 5 to 95 percent of the pitch 223. In some embodiments, the opening size 221 is in a range from 10 to 90, 15 to 85, or even 20 to 80 percent of the pitch. The opening size 221 is a shorter dimension of a minimum bounding rectangle of the irregular shape. The minimum bounding rectangle is defined as a rectangle whose sides are respectively parallel to two orthogonal axes (e.g., x and y axes in Cartesian coordinates) and minimally enclose the shape. For example, the opening size 221 of a circular opening is the diameter of the opening. The opening size 221 for an oval opening is the length of its minor axis. The opening size 221 for a polygonal opening is based upon the length of the shortest line that can be drawn from one vertex, through the center of the opening, to the opposite side of the opening.
Referring to FIG. IB, the metallic layer 8 has a first portion 81 on the land areas 32 with a first thickness Tl, a second portion 84 on the base 36 of the nanowell with a second thickness T2, and a third portion 86 on the sidewall 34 of the nanowell with a third thickness T3. The first and third portions 81, 86 are connected at the comer of the nanowell opening 23 to wrap around the comer. The thickness ratio of T2 over Tl is no greater than 70%, no greater than 60%, no greater than 50%, no greater than 40%, no greater than 30%, no greater than 20%, no greater than 10%, optionally, no greater than 5%. The thickness ratio of T2 over Tl can be controlled by controlling the aspect ratio of the nanowells and/or a metal deposition process.
The metallic layer may include at least one of gold, silver, aluminum, copper, platinum, mthenium, nickel, palladium, rhodium, iridium, chromium, iron, lead, tin, zinc, a combination or alloy thereof. The metallic layer on the land area may have an average thickness in a range from 20 nm to 500 nm, from 30 nm to 200 nm, optionally, from 30 nm to 150 nm.
In some embodiments, by controlling the aspect ratio of the nanowells, the metal deposition thicknesses can be tuned on both the land areas and on the bottoms of the nanowells. Some embodiments of this disclosure allow for the metal deposition thickness on the top of the array to be much greater than that in the nanowells. In some embodiments, a metal deposition process described herein can be controlled such that the second thickness T2 on the base 36 of the nanowells is no greater than 70 nm, no greater than 60 nm, no greater than 50 nm, no greater than 40 nm, no greater than 30 nm, no greater than 20 nm, no greater than 10 nm, or no greater than 5 nm.
The metallic layer 8 may extend from the land areas 32 into the nanowells 22 along the sidewalls 34 to form the sidewall portion 86 with a depth d and a thickness T3 and form a wrapping around structure. In other words, the metallic layer 8 may wrap around the comers of the nanowell openings 23 that connect to the land areas 32. When the metallic wrapping around structure is formed on the comer of the nanowell opening 23, the original opening size W of the nanowell opening 23 may decrease to the opening size W’ of the metallic nanohole 82. In some embodiments, the opening size W’ may be l%to 97%, 5% to 95%, 10% to 90%, 45% to 90%, or 50% to 90% of the opening size W.
In some embodiments, the metallic layer 8 may have the thickness T1 on the land area 32 in the range, for example, from 20 nm to 500 nm, from 30 nm to 200 nm, optionally, from 30 nm to 150 nm. The sidewall portion 86 may not have a uniform thickness. For example, the thickness T3 may decrease when the sidewall portion 86 extends away from the nanowell opening 23 toward the nanowell bottom surface 36. The thickness T3 may be in the range, for example, from 3% to 48% of nanowell opening size, from 5% to 45% of nanowell opening size, from 10% to 40% of nanowell opening size. The wrapping portion may have an average thickness T3 of at least 2 nm, at least 3 nm, at least 5 nm, at least 10 nm, at least 20 nm, or even at least 30 nm.
In some embodiments, the depth d of the sidewall portion 86 may be no less than 1%, no less than 2%, no less than 3%, no less than 5%, or no less than 10% of a nanowell depth D. In some embodiments, the depth d may be no greater than 95%, no greater than 50%, no greater than 30%, or no greater than 20% of a nanowell depth D. The nanowells 22 have an average depth D in a range, for example, from 50 nm to 5000 nm, from 100 nm to 2000 nm, optionally, from 200 nm to 1000 nm. The depth d of the sidewall portion 86 may be no less than 10 nm, no less than 20 nm, no less than 50 nm, or no less than 90 nm.
In some embodiments, the article 10 can be applied as a nanohole array sensing element for a plasmon resonance sensor that can be used to quantitatively detect and measure analytes based upon the refraction of transmitted light. The nanohole array sensor elements of the present disclosure are configured to measure the electromagnetic radiation transmitted by the sensing element. In contrast to devices utilizing the Kretschmann configuration, the sensors in the present disclosure are simpler, more compact, able to use single and multiple wavelength sources, and exhibit greater sensitivity to target analytes. A plasmon resonance sensor may include a light source disposed on a first side of the nanohole array sensing element, and configured to emit a detection light toward the article. A detector is disposed on a second side of the nanohole array sensing element opposite the first side, and configured to receive the detection light transmitted through the article. It is to be understood that the light source can be positioned on the same side of the metallic nanoholes, or the opposite side of the metallic nanoholes. In some embodiments, the light source can be positioned on the side of metallic layer, and the detector can be positioned on the opposite side. In some embodiments, the detector can be positioned on the side of metallic layer, and the light source can be positioned on the opposite side.
FIG. 2 illustrates one embodiment of a sensor including a sensor element 10 of the present disclosure. The sensor 40 includes a chamber 42, an inlet port 44, and outlet port 46, a first optical window 48 and a second optical window 50. The sensor 40 further includes a light source 52 proximate the first optical window 48 and a detector 54 proximate the second optical window 50, where the light source 52 and detector 54 are in optical alignment.
The light source can be a single wavelength light source, such as a single wavelength light emitting diode (LED) or laser. Alternatively, the light source can be a multiple wavelengths light source, such as a white light source. In some embodiments, the light source emits at least one wavelength of ultraviolet (UV) light (i.e., 10 to 400 nanometers). In other embodiment, the light source emits at least one wavelength of visible light (i.e., greater than 400 to less than 700 nanometers). In yet other embodiment, the light source emits at least one wavelength of infrared (IR) light (i.e., 700 to 1,000,000 nanometer). The detector senses the optical transmission through the sensor element, and obtains spectra of transmission versus wavelength based on the detected light. Depending on the amount of analyte fluid absorbed by the absorptive layer, the dielectric constant of the absorptive layer will change, resulting in the change of distinctive spectral features. The distinctive spectral features include peak/valley positions, measured intensity at specified wavelengths, some mathematic processes using several intensities at various wavelengths (e.g. relative intensity ratio at two wavelengths), hue, and so on. The detector response can be correlated to the concentration of analyte vapor present in the vapor delivery chamber. The detector includes at least one photodetector, such as a photodiode, a monochromator, a photoresistor, a phototransistor, a charge-coupled device, a complementary metal-oxide-semiconductor image sensor, a photomultiplier tube, and a phototube.
In some embodiments, a sensing element may further include a sensing layer at least partially covering its metallic layer. For example, in the embodiment depicted in FIG. 3A, a sensing layer 5 is provided to substantially, conformally cover the metallic layer 8, but not filling the nanowell 22. The sensing layer 5 is configured to recognize and immobilize target molecules through chemical or physical bonding. When the sensing layer recognizes and immobilizes target molecules, a change of the spectrum of transmission can be detected by the sensing element.
The immobilization of affinity groups can be provided on the metallic layer through covalent or noncovalent bonding. The affinity groups can selectively bind the target analytes and yield shift of resulting spectra through nanohole arrays. The term “affinity group” refers to a covalently or noncovalently attached group that is capable of specifically binding another molecule. The terms “specifically binding” and “specific binding” mean that an affinity group complexes with another molecule (i.e., its complementary molecule) with greater affinity than it complexes with other molecules under the specified conditions. Noncovalent bonding includes electrostatic bonding, ionic bonding, hydrogen bonding, hydrophobic bonding, van der Waals bonding, and so on. In one embodiment, the affinity group is an antibody. Herein, “antibody” includes antibody fragments, and are defined as polypeptide molecules that contain regions that can bind target analytes. Appropriate antibodies can be selected by one of skill in the art. In another embodiment, the affinity group is an aptamer, i.e., a short polynucleotide. In yet another embodiment, the affinity group is a target analyte molecule, such as a heavy metal or a small organic molecule. Herein, a small organic molecule is one having a molecular weight of no greater than 5000 grams/mole. In yet another embodiment, the affinity group includes target- analyte-molecule-immobilized proteins, such as cortisol linked BSA. The terms “specifically binding” and “specific binding” mean that an affinity group complexes with another molecule (i.e., its complementary molecule) with greater affinity than it complexes with other molecules under the specified conditions. A target analyte molecule is complementary to a bound antibody. An antibody is complementary to a bound target analyte molecule. In various embodiments of this disclosure, “specifically binding” may mean that an affinity group complexes with a complementary molecule with at least a 106-fold greater affinity, at least a 107-fold greater affinity, at least a 108-fold greater affinity, or at least a 109-fold greater affinity than it complexes with molecules unrelated to the target molecule. As noted above, the affinity group may be further complexed with, or noncovalently bonded.
The average thickness of exemplary sensing layers is typically in a range of from 1 nm to 200 nm. In some embodiments, the average thickness is in the range from 2 nm to 100 nm, 3 nm to 50 nm, or 4 nm to 30 nm.
In the embodiment depicted in FIG. 3B, a sensing layer 7 is provided to at least partially fill the nanowell 22. The sensing layer 34 may act as an absorptive layer including, for example, a polymer of intrinsic microporosity (PIM). Exemplary absorptive layers including a PIM were described in U.S. Patent Application No. 62/951,535 (Attorney Docket No. 81665US002, to Kang et ah), which is incorporated herein by reference. An article or sensing element described herein such as, for example, the article 10 of
FIGS. 1A-C, can be made by any suitable processes. FIG. 4A is a schematic diagram of a process 100 to make the article 10 of FIGS. 1A-C, according to one embodiment. FIG. 4B is a schematic diagram of another process 200 to make the article 10 including metallic nanohole arrays on nanowell arrays, according to another embodiment.
A pattern layer 6 is provided on a first major surface 31 of a polymeric layer 3. A hard mask layer 4 is disposed on the first major surface 31 of the polymeric layer 3, being sandwiched between the pattern layer 6 and the polymeric layer 3. The pattern layer 6 has a first surface 61 adjacent to the hard mask layer 4, and a second surface 63 opposite the first surface 61. The second surface 63 includes a pattern 62 characterized by feature dimensions of width, length, and height. The pattern layer 6 can be produced, for example, by replication, molding, or photolithography. The pattern layer 6 can include polymeric materials including at least one of the reaction products of, for example, radiation curable, dissolvable polymer, thermoplastic or thermosetting polymer. In some embodiments, a second pattern transfer layer can be patterned using reactive ion etching (RIE) with a variety of different chemistries and specified conditions.
In some embodiments, the pattern layer 6 can include a nano-replicated resin layer formed by a nanoreplication method. As used herein, “nanoreplication” refers to a process of molding a nanostructured surface from another nanostructured surface using, for example, curable or thermoplastic materials. Nanoreplication is further described, for instance, in “Micro/Nano Replication”, Shinill Kang, John Wiley & Sons, Inc., 2012, Chapters 1 and 5-6. The pattern layer can be formed by applying a curable composition onto a nanostructured surface and replicating a pattern therefrom. The curable composition can include any suitable materials that can be solidified by radiation or heat. For example, the curable composition may include a UV-curable acrylate. Exemplary curable compositions for a nanoreplication method are described in PCT Patent Application No. PCT/IB2020/058611 (Attorney docket No. 81875W0003), which is incorporated herein by reference. It is to be understood that the pattern layer 6 may be prepared by any suitable processes other than a nanoreplication method. The pattern layer 6 can be built up from a variety of materials depending on the technique used to generate the pattern layer.
A reactive ion etching (RIE) can be carried out to etch, from the second surface 63 of the pattern layer 6, into the first major surface 31 of the polymeric layer 3 to form an array of nanowells 22 including openings 23 being interspersed between land areas 32 thereof. The etching process is used to transfer a pattern from the pattern layer 6 to the polymeric layer 3 beneath. It is to be understood that any suitable selective etching process other than RIE can be used. Exemplary selective etching can be carried out using reactive ion etching, high density RF inductive plasma etching, high density linear ion plasma etching, microwave plasma etching, linear microwave plasma etching, helicon wave plasma etching, ion-beam milling, pulsed ion beam etching, pulsed reactive ion etching, or a combination thereof.
Transferring the pattern of a masking layer (e.g., the pattern layer 6) into the underlying layers (e.g., the polymeric layer 3) can be achieved by plasma etching. Where high aspect ratio structures are needed, ion-assisted plasma processing is conveniently used. Methods for achieving anisotropic etching include reactive ion etching (RIE), high density ion source processing, or a combination of high-density ion source processing along with RIE. High density plasmas can be generated by inductive RF, or microwave coupling, or by helicon ion sources. Linear high-density plasma sources are particularly advantageous for generating high aspect ratio features. Combining high density plasmas with RIE enables the decoupling of the ion generation (by high density plasma) from the ion energy (by RIE bias voltage).
The RIE method includes etching portions of the major surface not protected or less protected by the masking layer to form a nanostructure on a layer underneath the masking layer. In one embodiment, the provided method can be carried out using a continuous roll-to-roll process referred to as "cylindrical reactive ion etching" (cylindrical RIE). Cylindrical RIE utilizes a rotating cylindrical electrode to provide anisotropically etched nanostructures on the surface of a substrate or article. In general, cylindrical RIE can be described as follows. A rotatable cylindrical electrode ("drum electrode") powered by radio-frequency (RF) and a grounded counter-electrode are provided inside a vacuum vessel. The counter-electrode can include the vacuum vessel itself. An etchant gas is fed into the vacuum vessel, and a plasma is ignited and sustained between the drum electrode and the grounded counter-electrode.
A continuous substrate including a patterned masking layer can then be wrapped around the circumference of the drum and the substrate can be etched in the direction substantially normal to the plane of the substrate. The exposure time of the substrate can be controlled to obtain a predetermined etch depth of the resulting nanostructure. The process can be carried out at an operating pressure of approximately 1-10 mTorr. Cylindrical RIE is disclosed, for example, in U.S. Patent No. 8,460,568 (David et ah).
The chemistry of the plasma environment can be controlled to achieve selectivity of etching when multiple materials are present. Oxygen, and mixtures of oxygen with fluorinated gases are used to etch carbon-containing materials such as polymers, diamond-like carbon, diamond, and the like. The concentration of the fluorine in the plasma is critical to optimize the etching rate and selectivity. Typically, a small amount of fluorinated gas is used to dramatically increase the etching rate of hydrocarbon polymers by as much as 300%.
To etch silicon-containing materials (silicon dioxide, SiOx, diamond-like glass, silicon nitride, silicon carbide, silicon oxycarbide, polysiloxane, silicone, silicone acrylates, silsequioxane (SSQ) resins, etc), mixtures of fluorocarbons such as CF4, C2F6, C3F8 and the like, are used in combination with oxygen. The etch selectivity between silicon-containing materials and hydrocarbon polymers may be carefully tailored by obtaining the etching profdes of these materials as a function of the F/O atomic ratio in the plasma feed gas mixture. Oxygen rich conditions provide excellent selectivity of etching hydrocarbon polymers and diamond-like carbon (DLC) while using silicon materials as the masking layer. Additional materials for the masking layer are upper hard mask layer materials described in PCT Patent Application No. PCT/IB2020/058611 (Attorney docket No. 81875W0003), incorporated herein by reference. In contrast, fluorine rich conditions provide excellent selectivity of etching silicon-containing materials while using hydrocarbon polymer-based masking materials.
Fluorinated plasma chemistries may be used for etching other masking materials such as tungsten, whose fluorides are volatile. Chlorine -containing gas mixtures may be used to etch materials whose chlorides are volatile, such as aluminum, and titanium. Oxide, nitrides and carbides of these etchable metals can also be etched by using chlorine-based chemistries. Silicon nitride, aluminum nitride, and titanium oxide are high index materials that may be etched with chlorine chemistries. Typical gases used for etching includes, for example, oxygen, nitrogen trifluoride (NF3), CF4, C2F6, C3F8, SFr,. CF, CH4, and the like.
In the embodiments depicted in FIGS. 4A and 4B, a pattern of the pattern layer 6 is first transferred to the hard mask layer 4 by etching through the hard mask layer 4 to form a pattern onto the hard mask layer 4 directly beneath using the engineered nanostructures of the pattern layer 6 as a mask. An array of shallow nanowells are formed including openings being interspersed between land areas thereof. The land areas may include a residual pattern layer and the hard mask layer directly beneath. In some embodiments, the hard mask layer 6 includes a silicon-containing material and is reactive-ion etched using a fluorine-containing gas. The polymeric layer 6 may include a hydrocarbon polymer and is resistant to the fluorine etch. It is to be understood that a reactive ion etching step (RIE) to etch the hard mask layer may be carried out using an etching chemistry that can be chosen based on the etching selectivity on the pattern layer on the top, the hard mask layer itself, and the etchable polymeric layer directly beneath.
A pattern formed on the hard mask layer 6 is then transferred to the polymeric layer 3 directly beneath by etching into the polymeric layer 3 using the pattern on the hard mask layer 4 as a mask. In some embodiments, the polymeric layer 3 may include a hydrocarbon polymer and is reactive-ion etched using oxygen. The hard mask layer 4 may include a silicon-containing material and is resistant to the oxygen etch. It is to be understood that a reactive ion etching step (RIE) to etch the polymeric layer may be carried out using an etching chemistry that can be chosen based on the etching selectivity on the pattern layer on the top, the hard mask layer underneath the pattern layer, the polymeric layer itself, and an optional hard mask layer directly beneath.
In the embodiment depicted in FIG. 4A, the nanowells 22 can be etched to a desired depth, therefore controlling an aspect ratio (e.g., the ratio of depth D to opening size W as shown in FIG. IB) of the nanowells 22. For example, the time of oxygen etching can be varied to allow for controllable nanohole arrays to be formed before metallization. It is possible that there can be a run-to-run variation that has the possibility to impact the consistency of etching of the polymeric layer to the same depth each time.
In the embodiment depicted in FIG. 4B, an etch stop layer 5 is provided adjacent to a second major surface of the polymeric layer 3 on the side opposite the first major surface 31 of the polymeric layer 3. A support film 2 is provided to support the polymeric layer 3. The etch stop layer 5 is sandwiched between the polymeric layer 3 and the support film 2. The etch stop layer 5 may include a silicon-containing material and is resistant to the oxygen etch. Exemplary materials for an etch stop layer may include hard mask layer materials described in PCT Patent Publication No. WO 2020/095258 (Lengerich et al.), which is incorporated herein by reference. With the etch stop layer 5, the etching of the polymeric layer 3 is automatically stopped at the etch stop layer 5 such that the nanowells 22 each have the base thereof reaching the etch stop layer 5. By using an etch stop layer directly beneath the polymeric layer 3, the process allows for a desired thickness or aspect ratio to be achieved by controlling the layer thickness of the polymeric layer 3. This may enable run-to-run consistency, by removing the need to precisely time the oxygen etching step.
The polymeric layer 3 and the support film 2 can include the same or different materials.
In some embodiments, the polymeric layer and the support film may include a polymeric material that is in the form of a flat sheet and is sufficiently flexible and strong to be processed in a roll-to- roll fashion. Polymeric films used as a polymeric layer or a support film in articles described herein are sometimes referred to as base films. By roll-to-roll, what is meant is a process where material is wound onto or unwound from a support, as well as further processed in some way. Examples of further processes include coating, slitting, blanking, and exposing to radiation, or the like. Polymeric films can be manufactured in a variety of thicknesses, ranging in general from, for example, 5 micrometers to 1000 micrometers. In some embodiments, polymeric film thicknesses range from 10 micrometers to 500 micrometers, or from 15 micrometers to 250 micrometers, or from 25 micrometers to 200 micrometers. Roll-to-roll polymeric films may have a width of at least 6 inches, 24 inches, 36 inches, or 48 inches. Polymeric films can include, for example, poly(ethylene terephthalate) (PET), poly(butylenes terephthalate) (PBT), polyethylene naphthalate) (PEN), polycarbonate (PC), cyclic olefin copolymer (COP), polypropylene (PP), biaxially oriented polypropylene (BOPP), cellulose triacetate, a combination thereof, etc.
In some embodiments, the support film 2 may include a dielectric substrate including at least one of an optically transparent inorganic layer or an optically transparent polymeric layer. Exemplary inorganic layers may include at least one of glass, SiN, S1O2, amorphous SiCxOyHz, etc. Exemplary polymeric layers include polyethylene terephthalate, poly(methyl methacrylate), polyvinyl chloride, polyethylene, polypropylene, styrene methyl methacrylate, polycarbonate, polystryrene, and copolymers thereof.
In some embodiments, the polymeric layer 3 may include at least one of the reaction products of a curable composition, monomer, or solution coatable polymer or resin. The polymeric layer 3 is applied onto the etch stop layer 5, as shown in FIG. 4B. The polymeric layer 3 can be applied by any suitable processes such as, for example, casting, coating, deposition, dry film lamination and printing. Coating methods include spin coating, die coating, roll coating, spray, and evaporation. Printing methods include inkjet, gravure, flexographic and screen printing. After the polymeric layer is applied, it can be cured by actinic radiation or heat. The polymeric layer can also be a solution resin where the solvent is evaporated to form a dried film. Examples of polymeric layers include polyacylates, polymethacrylates, soluble polymers such as polyvinyl alcohol, polymer resins such as polyvinyl butyral, thermosetting polymers such as polyurethanes, thermoplastic polymers such as polypropylene.
An array of nanowells 22 is formed by etching into the first major surface 31 of the polymeric layer 3. The array of nanowells 22 include openings 23 being interspersed between land areas 32 thereof. As shown in FIG. IB, the nanowells each have a base 36 and a sidewall 34 connecting the base 36 and the land areas 32 thereof. The nanowells each have the aspect ratio of depth D to opening size W in a range, for example, from about 0.5: 1 to about 50: 1, from about 1 to about 20: 1, optionally, from about 1.5: 1 to about 10:1. As to be discussed further below, the nanowells each may have an aspect ratio high enough (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to substantially prevent a sputtering deposition of metal into the nanowells on the sidewalls and the bases thereof.
One traditional way to create nanowell arrays is through a UV-nanoreplication, or continuous cast and cure process. By using a nano-post mold, high-fidelity nanowells can be directly replicated onto a flexible substrate, enabling a lower cost fabrication of nanoholes from the methods mentioned above. The traditional nanoreplication processes may have limitations in the aspect ratio of structures that can be replicated. When the aspect ratio of the nanwells gets larger, it becomes increasingly difficult to peel the replication resin out without tearing, due to increased surface area contact of the resin with the mold.
Embodiments of the present disclosure provide nanowells having an aspect ratio sufficiently high (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to substantially prevent a sputtering deposition of metal into the nanowells. By controlling the aspect ratio of the nanohole opening to the depth of the nanowells, the metal deposition thicknesses can be tuned on both the tops of the array features and on the bottoms of the nanowells. Embodiments of this disclosure allow for the metal deposition thickness on the top of the array to be much greater than that in the nanowells. The array of nanowells has an average pitch in a range from 100 nm to 2500 nm, from 100 nm to 1000 nm, from 250 nm to 1000 nm, or optionally from 300 nm to 900 nm. The openings of the nanowells have an average opening size in a range from 5 to 95 percent, 10 to 90 percent, 15 to 85 percent, or optionally, from 20 to 80 percent of the pitch. The nanowells have an average depth in a range from 50 nm to 5000 nm, from 100 nm to 2000 nm, optionally, from 200 nm to 1000 nm.
The metallic layer 8 is deposited on the etched first major surface 31 of the polymeric layer 3 to form a mesh pattern of metal having an array of nanoholes aligned with the openings 23 of the respective nanowells 22. The nanowells 22 each may have an aspect ratio of depth to opening size high enough (e.g., greater than about 0.5, greater than about 1.0, greater than about 1.5, greater than about 2, or even greater than about 3) to prevent a substantial deposition of metal into the nanowells on the sidewalls and the bases thereof.
In some embodiments, the metallic layer 8 can be deposited by vapor coating techniques such as Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) processes. Suitable PVD processes include sputter deposition and evaporation (thermal and ebeam). PVD processes are preferred due to the ease in which the upper surfaces of nanowell structures (e.g., the land areas 32 in FIG. 4) are coated with little deposition on the lower surfaces of nanowell structures (e.g., the base 36 and the sidewall 34 of a nanowell in FIG. 4). In addition, CVD and the related processes plasma-assisted CVD and atomic layer deposition (ALD) may be more difficult to control the deposition preferentially to the upper surfaces of nanowell structures.
A suitable sputter deposition process can use conventional cathode or magnetron sputter sources with targets of the metal to be deposited. DC, pulsed-DC, AC, or RF power supplies can be used to power the plasma that provides the energetic ions and electric field necessary to sputter deposit the atoms from the target onto the substrate. The sputtering is done in a vacuum process with an inert gas such as Ar at a pressure in the range of 0.133 Pa to 2 Pa. In one embodiment, nanowell structures with depth/opening size aspect ratios (AR) greater than, for example, about 1:1, about 2:1, or about 3:1, can be preferentially coated on the upper surfaces (e.g., the land areas 32 in FIG. IB) with sputter deposition at a normal angle (i.e., a sputter target being positioned substantially parallel and directly over the substrate). The sputter target and the substrate can be positioned such that the sputter deposition is within ±10 degrees, or within ±5 degrees from the normal direction. In another embodiment, nanowell structures can be preferentially coated on the upper surfaces (e.g., the land areas 32 in FIG. IB) with a sputter target set to the side of and at an angle relative to the substrate (sometimes referred to as angle deposition or glancing angle deposition) to enhance shadowing effects. Exemplary sputtering processes for preferentially coating nanowell structures are described in Atty. Docket No. 83726US002, which is incorporated herein by reference. The evaporation process is also a vacuum process using pressures in the range of 104 to
102 Pa. The source material (metal to be coated) is heated via resistance heating, inductive heating, or ebeam bombardment to vaporize the metal atoms. The atoms travel to the substrate in a line-of-sight process. To avoid deposition on the lower surfaces of nanowell structures, it is necessary to use glancing-angle evaporation deposition to shadow the lower surfaces (e.g., the base 36 and the sidewall 34 of a nanowell in FIG. IB) from the incident atoms. In some embodiments, the metallic layer is preferably deposited by DC sputtering in a gaseous environment of Ar.
The operation of the present disclosure will be further described with regard to the following detailed examples. These examples are offered to further illustrate the various specific and preferred embodiments and techniques. It should be understood, however, that many variations and modifications may be made while remaining within the scope of the present disclosure.
EXAMPLES
These Examples are merely for illustrative purposes and are not meant to be overly limiting on the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Summary of Materials
Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Table A provides abbreviations and a source for all materials used in the Examples below:
The following abbreviations are used in this section: L = liters, mL = milliliters, pi = microliters, g = grams, mol = mole, cm = centimeters, mm = millimeters, pm = micrometers, nm = nanometers, wt = weight, v = volume, sec = seconds, min=minutes, h=hours, ppm = parts per million, °C = degrees Celsius, K = Kelvin, mM = millimolar, Pa = pascals, and cP=centipoise. Abbreviations for materials used in this section, as well as descriptions of the materials, are provided in Table A.
Table A
Figure imgf000019_0001
1. Mold Preparation
Nanopattemed molds were purchased from Eulitha AG. These silicon molds were crated via a proprietary lithography process and were subsequently Ni plated and micro-welded into cylindrical sleeves for roll-to-roll UV replication. The first mold, Mold 1, contained a square-packed array of about 100 nm diameter holes on a 200 nm pitch, with the holes being 165 nm deep at an 8.5° draft angle. The second mold, Mold 2, contained a square-packed array of 200 nm holes on a 400 nm pitch, with the holes being 310 nm deep at a 6.3° draft angle.
2. Fabrication of nanopost or nanowell structures
2.1 Patterning method A: Preparation of direct replicated nanopost structure
Sample 1: 200 nm diameter nanopost on a 400 nm pitch
Sample 1 was prepared by die coating a urethane acrylate mixture onto a 125 -micrometer- thick polycarbonate film. The urethane acrylate mixture was then pressed against Mold 2 under pressure and exposed to UV radiation to lock the structure in place. The structure was subsequently peeled from the Nickel mold, leaving a nanostructured pattern on the polycarbonate film. The resultant pattern on the polycarbonate film was the inverse of Mold 2, a square-packed array of 200 nm diameter nanoposts on a 400 nm pitch. The height of nanopost was 300 nm.
Sample 2: 200 nm diameter nanopost on a 400 nm pitch
Sample 2 was produced using the same procedure described above for Sample 1 with the following exceptions: a 75 -micrometer-thick polyethylene terephthalate (PET) film with a primed acrylic adhesion promoter were used in place of the polycarbonate film. The height of nanopost was 300 nm.
Sample 3: 100-nm-diameter nanopost on a 200 nm pitch
Sample 3 was produced using the same film and process as Sample 1 with the exception of using Mold 1. This yielded a polycarbonate film with a nanopattem of a square-packed array of 100 nm diameter nanoposts on a 200 nm pitch. The height of nanopost was 160 nm.
2.2. Patterning method B: Preparation of direct replicated nanowell structure Sample 4: 200 nm diameter nanowell on a 400 nm pitch
A section of Sample 1 was plasma treated and attached to a steel roller. Sample 4 was prepared using the procedure described above for Sample 1 with the exception that the plasma treated section of Sample 1 was used as the mold. The resultant film was a polycarbonate film with a square-packed array of 200 nm diameter nanowells on a 400 nm pitch. The depth of nanowell was 300 nm.
3. Preparation of high aspect ratio nanowell structures
3.1. Patterning method C: Preparation of high aspect ratio nanowell structure through one hard mask layer process
As shown schematically in FIG. 4A, a PET film was first plasma coated with a silicon- containing hard mask layer. Next, the films created in Sample 1 (posts) and Sample 4 (wells) were plasma treated with a release chemistry and were coated with a urethane acrylate mixture from a coating die. The urethane acrylate coated fdms were laminated to the hard mask coated PET and cured via UV radiation. After separating the films, a nanopost or nanohole array was left on top of the silicon-containing hard mask layer. Next, the films were exposed to a fluorine-containing reactive ion etching process to break through the thin areas of the mold, and break through the silicone-containing hard mask layer, leaving a patterned layer of an oxygen hard maskant layer. Following the breakthrough of the etch resist layer, the film was exposed to an oxygen etching step. This oxygen etching step continued to etch into the underlying polymer film, while stopping at the remaining patterned etch resistant layer. The depth of the resulting hole or well film was dependent on the conditions and time that the film was exposed to the oxygen etching step.
3.2. Patterning method D: Preparation of high aspect ratio nanowell structure through one hard mask and one etch stop process
As shown schematically in FIG. 4B, a PET film was sputtered with a silicon-containing etch stop layer, followed by a coating of an acrylate layer to a desired thickness, with an additional sputtered silicone-containing hard mask layer on top to create a 3 -layer film on PET. Next, the films created in Sample 1 (posts) and Sample 4 (wells) were plasma treated with a release chemistry and were coated with a urethane acrylate mixture from a coating die. The urethane acrylate coated films were laminated to the 3-layer coated PET and cured via UV radiation. After separating the films, a nanopost or nanohole array was left on top of the top-most silicone-containing hard mask layer on the PET stack. Next, the films were exposed to a fluorine -containing reactive ion etching process to break through the thin areas of the replicated mold and into the top silicone-containing hard mask layer. This creates a patterned hard mask layer on the top etch-resistant layer. Following the breakthrough of the top hard mask layer, the film was exposed to an oxygen etching step. This etch step etches through the coated acrylate layer between etch-resistant layers, creating a controlled- depth nanohole or nanohole film. The depth of the resultant feature was set by the coating thickness of the acrylate layer between etch-resistant layers.
3.3. Patterning method E: Preparation of high aspect ratio nanowell structure
A section of Sample 4 was plasma treated with a release chemistry and was coated with a urethane acrylate from a coating die. The urethane acrylate coated film was put in contact with a PET film and was cured via UV radiation. After separating the films, a nanopost array was left on top of the PET film. Next, this PET film was coated with a silicon-containing acrylate resin, enough to completely fill the space between the nanoposts with a thin layer of resin over the top and was UV cured. The film was then exposed to a fluorine-containing etch to break through the thin layer of silicon-containing resin on top of each of the nanoposts, while leaving a silicon-containing etch- resistant layer between the posts. The film was then exposed to an oxygen-containing etch process, ablating the exposed post structures to create a well-structure in the film. The depth of these wells was dependent on the conditions and exposure time of the film during the oxygen etch. The area between the posts was unetched during the oxygen-containing etching step, as there was still a remaining etch-block layer in the spaces between the posts.
4. Metallization on 3D nanopost or nanowell structures
4.1 Batch sputtering process
The substrate film with nanowell or nanopost structures was vapor coated with Au using a batch dc sputtering system (PVD75 from Kurt J. Lesker Co.) The deposition targets were Au with dimensions of 3-inch diameter and 0.125-inch thickness, from Kurt J. Lesker Co. The metal layers were deposited at an Argon pressure of 3 mTorr and a power of 200W. The substrate normal was pointed directly at the source. The exposure time was varied per sample to realize the desired thickness. The thickness was based on the measured thickness of deposited Au on planar polymer films using variable angle spectroscopic ellipsometry and cross-sectional TEM images.
4.2 Roll-to-roll sputtering process
The substrate film with nanowell or nanopost structures was vapor coated with Ag/Au using a roll-to-roll dc sputtering system with the target parallel to the substrate film during deposition. The sputtering target was 85%Ag/15%Au with dimensions 3.85” x 21” x 0.25” (9.78cm x 53.34 cm x 0.64cm). The Ag/Au was deposited at an Argon pressure of 2.9 mTorr (0.36 Pa) and a power of 3.8 kW. The line speed was varied from 2.44fpm (0.744 m/min) (resulting thickness of 200 nm) to 24.38fpm (7.43 m/min) (resulting thickness of 20 nm) to create samples of different Ag/Au thicknesses. The thickness was based on the measured thickness of deposited Ag/Au on plane polymer films using variable angle spectroscopic ellipsometry and cross-sectional TEM images.
4.3 Gold coating using evaporator
Substrate films with nanowell or nanopost structures were coated with Au within an ultra- low vacuum “electron-beam evaporation” chamber. This chamber was a custom build by the Kurt J. Lesker Co. The sample was held down with Kapton™ tape onto a 10”xl0” (25cm x 25cm) metal plate and placed face down in the load lock chamber(deposition was from the lower part of the main chamber and the sample was approx. 18” (45.7cm) above the source material). The load lock was pumped down to a range <lxl05 torr (1.33xl03 Pa), then the plate was moved into the main chamber. The main chamber pressure was in the range <3x106 torr (4xl04 Pa). The substrate normal was pointed directly at the source.
The deposition was carried out by turning on the power supply and the source and controller gauges. The rate of deposition was controlled via an internally written software program connected to the “INFICON XTC/2 THIN FILM DEPOSITION CONTROLLER”(INFICON of East Syracuse, New York) at a rate of 0.1 nm per second until 100 nm of metal was deposited. The thickness was monitored by an INFICON 6MHz Au coated crystal with a feedback loop to the XTC/2 controller. The power supply shut down once the target thickness was reached. The sample was then transferred back to the load lock chamber and evacuated. The sample was removed from the plate.
5. Microcontact printing (Patterning method FI Nanohole arrays were produced in gold layers coated on PET substrates via a microcontact printing process. PDMS was cast against an e-beam written master containing the target pattern. The resulting PDMS stamp was then inked in 6.5 mM octadecanethiol dissolved in ethanol for 16 hours. Following this inking step, the stamp was blown off with nitrogen and allowed to dry overnight. The stamp was then mounted in the microcontact printing device. PET with 100 nm (nominal thickness) evaporated gold was loaded onto the drum of the printer, and the stamp was contacted to the fdm in order to transfer a self-assembled monolayer of the octadecanethiol. Finally, this octadecanethiol was used as an etch resist in an immersed rotational wet etch using an aqueous solution 20 mM in ferric nitrate and 30 mM in thiourea for approximately 25 minutes. The samples were rinsed thoroughly with deionized water, dried, and kept in a dry chamber under nitrogen gas prior to subsequent characterization and testing.
6. Characterization
6.1 Scanning Electron Microscopy (SEM)
SEM images were obtained using a Hitachi 4700 Field Emission SEM under conditions found to minimally affect structure size and shape. To ensure conductivity between samples and the specimen holders all samples were DC sputter coated with Au/Pd alloy target in a Denton coater. Typical conditions for sputter coating were 20mA current for 25 -30s, which produced Au/Pd at a thickness of less than 1 nm. Both cross sectional and top down images were obtained in areas thought be representative of the samples in general. SEM images were analyzed using a computer program Image J (software available from National Institutes of Health, v 1.37). The average post/well diameter and post height/well depth were measured.
6.2 Transmission Electron Microscopy ITEM!
Cross-sectional (CX) structure, morphology, and elemental composition of the metal-coated nanowells was carried out with transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and quantitative x-ray microanalysis (EDS). These samples were in the form of a planar sheet, with the nanowells located on the side-of-interest. As the nanowells were patterned in a square-grid pattern, the cross-sectional samples were cut out such that the observation plane in CX was along one axis of the grid pattern. Thus, the maximum number of nanowells would be intersected in CX.
TEM samples were prepared using room-temperature ultramicrotomy ((Leica, model FC7) and a diamond knife (Diatome USA, P.O. Box 410, 1560 Industry Rd., Hatfield, PA 19440). TEM data was acquired in the FEI Osiris transmission electron microscope (ThermoFisher Scientific, Hillsboro, OR 97124) operating at 200 kV. Instrument magnification range used was from 1.1 kX to 360 kX.
Quantitative, high resolution x-ray microanalysis was carried using the proprietary X-FEG high brightness electron source of the FEI Osiris TEM and the Bruker Quantax Super-X x-ray microanalysis system (Bruker Nano, Inc., 312 N. Harvey Ave., Oak Park, IL 60302). This x-ray microanalysis system is based on Silicon Drift Detector (SDD) technology and accompanying
Bmker Espirit analysis software system. Quantitative elemental concentrations were calculated from background subtracted, deconvolved line intensities using the Cliff-Lorimer method in the Espirit analysis software.
6.3. Optoelectronic Measurement
6.3.1. Preparation of sensor strips
A piece of 4mm x 4mm nanohole array film was placed on a transparency film (copier transparency film, item number 21828, Staples). One layer of 3M electrical tape (red tape, polymer film) with a circular hole (2.83mm diameter) was placed on the top of nanohole array film. The hole was aligned in the center of the piece to expose nanohole arrays while the red tape was holding the nanohole array film down to the transparency film. The 2.83mm hole was generated in the tape using a disc cutter.
6.3.2. Optoelectronic measurement setup
The sensor strip with nanohole array was placed and fixed inside an acrylic cuvette (Sarstedt, acryl, Ref 67.755, 10x10x45mm) with the nanohole array facing to inside cuvette and PET substrate layer facing to the cuvette wall. The cuvette was inserted into a cuvette holder (model CUV-UV, Ocean Optics). The area of nanohole array was aligned with a light source and a detector. The nanohole array layer’s normal was pointed directly at the light source and the detector. Two optical fiber probes (Part number: QP600-025-UV, Ocean Optics) were connected to the cuvette holder to measure transmission spectra through the nanohole array film. One optical probe was connected to a light source and the other probe to a spectrometer. One of two sets of light source-detectors was used for measurements. One set consisted of a light source ((Model HL-2000-FHSA, Ocean Optics) and a detector (Jaz spectrometer, Ocean Optics) and the other set consisted of a light source (Model DH-2000-BAL, Ocean Optics) and a detector (FX-100, Ocean Optics).
Transmitted white light without nanohole array films was taken for a reference spectrum to convert acquired scope mode spectra to transmission spectra. The transmission spectra were normalized by the reference intensity, which is the maximum transmission intensity between 400 nm and 800 nm. Spectra were acquired and processed using a customized Fabview program (software available from National Instruments of Austin, TX) and OMNI driver (software available from Ocean Optics).
The obtained transmission spectra were converted to color (RGB color space) as follows. The measured reflection spectrum was constructed to International Commission on Illumination (or “CIE”) XYZ color space using color matching the CIE 1931 2o Standard Observer function. The CIE XYZ color space was linear transformed to CIE RGB space using CIE color space chromaticity coordinates (xR=0.49, yR=0.177, xG=0.310, yG=0.812, xB=0.20, yB=0.01). Then, Hue and Saturation were computed from RGB values. All mathematical processing was done by a customized LAB VIEW program (software available from National Instruments of Austin, Texas). 7. Simulation (Finite Difference Time Domain)
Due to the size scale (in nm range) and the high dispersion of the metals in use, the nanohole array fdm is only correctly modeled using the FDTD (Finite Difference Time Domain) approach, which takes into account of the metal light interaction and the near field effect. For this modeling effort, a commercially available software FDTD Solutions from Lumerical (based in Vancouver, CAN) was used. After setting up the model, parameter sweeps involving metal film thickness, nanohole diameter, ambient refractive index (water or air) etc. were carried out to study the trend and compare against experimental data.
8. Bio-sensing layer
8.1. Immobilization of sensing layer (Cortisol-BSA layer on Nanohole array)
Activation buffer contained 0.1M MES and 0.5M NaCl with adjusted pH 6. PBS buffer was prepared by diluting concentrate phosphate buffered saline solution. PBS-Tween 20 was prepared by adding proper amount Tween 20 (0.02% v/v) to PBS buffer.
A piece of nanohole array film was immersed in ethanol and sonicated for 5 minutes using a sonicator (Model 1510, Branson, Brookfield, CT). After rinsing the film with ethanol, the piece was incubated into ImM 11-mercaptoundecanoic acid in ethanol for 30 minutes with an orbital shaker (Mophom, 40rpm). After the immobilization of thiols, the piece of nanohole array film was rinsed with ethanol, deionized water, and MES buffer (pH 6.0) sequentially. The piece was immersed into mixture of 2.5mM EDC in MES buffer and 5mM NHS in MES buffer for 15 minutes with the orbital shaker. This mixture was made by mixing the same volume of 5mM EDC and lOmM NHS right before the treatment. After the activation of carboxyl group through EDC-NHS coupling treatment, the piece was rinsed with deionized water and PBS buffer. The piece was incubated in 20 pg/ml Cortisol-BSA in PBS buffer (pH 7.4) for 2 hours with the orbital shaker. About 60mM ethanolamine in water was added to quench the coupling reaction for 15 minutes. The final ethanolamine concentration was 12 mM. The piece was rinsed with copious deionized water, dried in air, and kept in the dry chamber under nitrogen gas.
8.2. Bio-interaction measurement
A sensor strip with sensing layer immobilized nanohole arrays was fabricated as described above. The sensor strip was placed and fixed inside a cuvette. A stirring bar (Catalog number 58948-400, 3mm x 6.3mm, VWR, Radnor, PA) was inserted into the cuvette. In addition to the optical measurement described above, the cuvette holder was placed on a stirrer (Model VMS-C7, VWR, Radnor, PA). After adding PBS-Tween 20 buffer to the cuvette, the solution was stirred at 750rpm during the optical measurements.
9. Chemical-sensing layer
9.1. Preparation of PIMs (Polymers of Intrinsic Microporositv) Solution
About 4.0 to 4.4% (wt/wt) PIMs solid dissolved in chlorobenzene was used. To prepare PIMs solid, 130 g of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-l,r-spirobisindane (Part number B22170 from Alfa Aesar, Tewksbury, MA) were combined with 77.1 g of tetrafluoroterephthalonitrile (Part number H61326 from Alfa Aesar), 322.83 g potassium carbonate, and 3380 g of N,N-dimethylformamide, and the mixture was reacted at 68 °C for 72 hours. The polymerization mixture was poured into water, and the precipitate was isolated by filtration. The resulting polymer was twice dissolved in tetrahydrofuran, precipitated from methanol, and air dried at room temperature. A yellow solid product obtained was dissolved in chlorobenzene and 4.0-4.4% (wt/wt) PIMs solution was prepared. The viscosity of solution was 3.0-7.0 cP using a Rheometer.
9.2 . Coating of sensing layer (PIMs layer coating on Nanohole Array)
The 4% wt/wt PIMs solution was further diluted to 1% wt/wt in chlorobenzene (Spectrophotometric Grade, Alfa Aesar). Nanohole array film was cut in the size of 2 cm x 2 cm and placed on a glass slide. About 30 pL of 1% wt/wt PIMs solution in chlorobenzene was applied using a micropipette on the nanohole array side. Sharply cut edges of polymer film were used to spread the solution uniformly on the entire area. The coated film was dried in oven for 1 hour at 80 °C. After baking, the film was kept in the dry chamber under nitrogen before measurements.
After coating PIMs on nanohole array, the transmitted color was close to green. The absorbance spectra were collected using optoelectronic measurement described above. The absorbance at 425.47 nm is related to the thickness of PIMs layer. To determine the thickness of the PIMs layer on the sample, a calibration curve relating the thickness of PIMs layers and absorbance at 425.47 nm of PIMs layer coated to various thicknesses on glass slides was measured. PIMs layers were coated on glass slides using a spin coater (Model WS 400B-8NPP/LITE spin coater, Laurell Technologies Corporation, North Wales, PA) at various conditions and the thickness of PIMs layer was measured using a stylus profilometer (XP-1, Ambios Technology, Santa Cruz, CA). Absorbance at 425.47 nm was linearly proportional to the thickness of PIMs layer measured from the profilometer. From the linear calibration curve, the coated thickness of PIMs layer on the nanohole array was approximately 650 nm.
9.3. Volatile Organic Compounds IVOCsI Control Chamber
Sensor elements were exposed to a solvent at different concentrations in air. All tests were performed in air that had been passed over Drierite to remove moisture and passed over activated carbon to eliminate organic contaminates. Vapor tests were conducted using a 5L/min dry air flow through the system. VOCs levels were generated using a syringe pump obtained from KD Scientific, Holliston, MA fitted with a gas tight syringe (obtained from Hamilton Company of Reno, Nevada). The syringe pump delivered the VOCs onto a piece of filter paper suspended in a 500 mL three necked flask. The flow of dry air passed over the paper and vaporized the solvent. Controlling the rate of delivery of VOCs from the syringe pump generated concentrations of VOCs. The syringe pump was controlled by a LAB VIEW program. All measurements were done at room temperature. The concentration of VOCs in air was verified by measurement using an IR analyzer obtained under the trade designation MIRAN from THERMO FISHER SCIENTIFIC, Waltham, MA.
Sensor strips with PIMs layer coated nanohole arrays were fabricated and placed inside a cuvette. Several 4 mm-diameter holes were made in the cuvette using a drill. A hole was made in the center of cuvette lid. A gas tube was inserted through the hole of cuvette lid and connected between VOCs control chamber and the cuvette to deliver VOCs vapor. The VOCs vapor entered through the cuvette lid and existed through the holes of the cuvette during optical measurements.
Examples and Comparative Examples The mesh pattern of Examples or Comparative Examples here is a repeating pattern of a square lattice. Table 1 below lists a summary of structure types of various Examples or Comparative Examples as shown in FIG. 5. The structure types include structure type “A” through “EL” Table 2 summarizes the structure type of various Examples (EX) and Comparative Examples (CE).
Table 1
Figure imgf000027_0001
* “Tl” is the thickness of top layer metal deposition; “T2” is the thickness of bottom layer metal deposition; “T3” is the thickness of side layer metal deposition; “W-W”’ is the reduction of well opening size after metal deposition.
Table 2
Figure imgf000027_0002
Figure imgf000028_0001
Ag/Au (85/15)-
EX16 C D 100 200 600 150 Sputtering
CE1 and EX1-3
CE1 and EX 1-3 shows the effect of base structures (post vs. well) and the effect of well depth. Planar Equivalent Metal deposition thickness in Tables is based on the metal thickness measured on planar surfaces. Here, roll-to-roll sputtering process was used to deposit metal on the nanostructures. The cross-sectional TEM topological from EX1 shows that thicker Ag/Au deposition was observed on the top layer of nanowell structures in comparison with the Ag/Au deposition on the bottom layer as shown in FIG.6A. The dark area was confirmed to be Ag/Au deposition through elemental analysis in TEM. The measured thickness of Ag/Au deposition on the bottom layer was around 42nm. T2/T1 ratio is equal to 0.42.
EX2 and EX3 have higher well depth than EX1. FIG. 6B shows cross-sectional TEM images of EX2. Almost no metallic deposition was observed on the bottom of nanowells in FIG.6B, while some metallic deposition was observed on the bottom of nanowells in FIG.6A. The scarce metallic deposition on the bottom of nanowells in FIG.6B formed discontinuous metallic films having grains with discrete boundaries. In FIG.6B, the deposition along the side wells was observed and the metallic deposition was thinner as the location was closer to the bottom of nanowells. The metal was deposited preferentially on the top or along the side of nanowells instead of the bottom of nanowells in sputtered samples with the increase of well depth.
FIG. 7 shows a normalized transmission spectrum in water from CE1, which had sputtered 100-nm-thick Au/Ag (85/15) deposition on three-dimensional nanopost structures. Due to the preferential deposition on the top layer or side of posts, the plasmonic effect from nanodot array structures was dominant with some of the plasmonic effect from nanohole array structure. High light absorption was observed in the wavelength range between 550 nm and 750 nm due to nanodot array structures.
FIG. 7 also shows a normalized transmission spectrum in water from EX1 which had sputtered 100-nm-thick Au/Ag (85/15) deposition on nanowell array structures. Due to the preferential deposition on the top layer or side of wells, the plasmonic effect from nanohole array structures was dominant with some of the plasmonic effect from nanodot array structures in resulting transmission spectra. Several transmission peaks from nanohole array structures were observed with slight light absorption in the wavelength range between 650 nm and 750 nm due to nanodot array structures which results from some metal deposition on the bottom of nanowell structures. This result is consistent with the observation of cross-sectional TEM images (FIG. 6A). FIG. 7 also shows a normalized transmission spectrum in water from EX2 which had the well depth of 500 nm. The light absorption in the wavelength range between 650 nm and 750 nm disappeared. This disappearance of light absorption means the lack of nanodot array structures and almost no metal deposition on the bottom of nanowell structures. FIG. 7 shows normalized transmission spectrum in water from EX3 which had the well depth of 800 nm. The spectrum features from EX3 were almost identical to those from EX2. This similarity of the spectra between EX2 and EX3 means that from the certain depth, almost no metal deposition on the bottom of nano well structures took place through sputtering.
CE2-3 and EX4
Various nanohole array structures (Structure type: E, F, and C) were fabricated with similar nanohole configuration (diameter of hole, pitch size, type of metal, and metal thickness) but by different patterning methods and metallization methods. All samples were from similar master patterns (square array, 200 nm hole size and 400 nm pitch size). From the top view SEM images, the measured average hole or well diameters from SEM images were 237nm, 244nm, and 195nm for CE2, CE3, and EX4, respectively.
In case of CE2, the nanohole array structures were generated to etch Au layers which were coated on flat substrates through microcontact printing. The resulting structures are two-dimensional metallic nanohole array patterns on the flat dielectric substrate (Structure type: E, FIG.5). However, in case of CE3 and EX4, two-dimensional metallic nanohole array structures were generated by two different metallization method (evaporation, CE3 and sputtering, EX4) on three-dimensional dielectric nanowell structures. FIG. 6C shows cross-sectional TEM topological and corresponding elemental (Au) maps of CE3. The structure type of CE3 is F in FIG.5. Similar thickness of Au deposition on both top and bottom layers of nanowell structures was observed in CE3. On the contrary, thicker Au deposition was observed on the top layer of nanowell structures in comparison with Au deposition on the bottom layer from the cross-sectional TEM image from EX4, which was like the TEM image from EX2 in FIG.6B. The structure type of EX4 is C in FIG.5. Some or minimum amount metallic deposition was observed on the bottom of nanowells compared to Au deposition on the top layer. The deposition along the side wells was observed and the metallic deposition was thinner as the location was closer to the bottom of nanowells. Compared to the evaporated sample (CE3), the metal was deposited preferentially on the top or along the side of nanowells instead of the bottom of nanowells in sputtered samples (EX4). Au deposition on the top layer observed from EX4 wraps around the openings of three-dimensional dielectric nanowell structures due to side-wall sputtering deposition, while the deposition patterns from CE3 yields sharp edges on the top layer deposition due to highly directional evaporation deposition.
FIG. 8 shows normalized transmission spectra in air and in water from CE2, CE3, and EX4.
In case of CE2, transmission spectral features are from two-dimensional metallic nanohole array structures on two-dimensional planar polymer substrates. As shown in FIG. 8, multiple peaks such as (1,0) Au/Polymer, (1,1) Au/Polymer, (1,0) Au/Air, and (1,0) Au/Water were identified. Here, Polymer means polymeric substrate layers underneath Au layers. As expected, multiple peaks from the interface of Au/Polymer were observed. Peaks from the interface of Au/Media (Air or Water) were overlapped with peaks (Au/Polymer) and were difficult to monitor the shift of peaks (Au/Media) upon the environmental change in Au/Media interface.
In case of CE3, since similar thickness of Au deposition on the top and bottom of nanowell structures were observed (FIG. 6C), multiple plasmonic effects were convoluted into resulting transmission spectra. The Au deposition on the top layer of three-dimensional dielectric nanowell structures yields two-dimensional metallic nanohole array structures, which generate higher transmission at the wavelength of SPR. The Au deposition on the bottom layer of nanowell structures yields two-dimensional metallic nanodot array structures, which generate higher absorption at the wavelength of SPR. Then, the reflected and transmitted light from the top and bottom metallic layers generates Fabry-Perot interference in transmission spectra. As shown in FIG. 8, all three plasmonic features were convoluted into resulting spectra from CE3.
On the contrary to CE2 and CE3, FIG. 8 shows that spectra from EX4 yield only nanohole array plasmonic peaks from the interface of Au/Media without being interfered by other plasmonic effects. This lack of nanodot and Fabry-Perot interference spectral features come from the lack of metal deposition on the bottom layer of nanowell structures. In addition, surprisingly, plasmonic peaks of nanohole array structures from the interface of Au/Polymer were absent in FIG. 8. The resulting clear peaks (Au/Media) from nanohole array structures could be easily correlated to the refractive index of media. As expected, the position of the biggest peak ((1,0) Au/Media, here) was shifted to higher wavelength as the media was changed from air (refractive index = 1) to water (refractive index = 1.33). These peak locations from the interface of Au/Media were expected from Equation 1. This shift confirms that the peaks shown in FIG. 9C come from the nanohole array plasmonic effect of the interface of Au/Media and the peaks were easily monitored to detect the change in the interface between Metal and Media.
Figure imgf000031_0001
Where p is the pitch size, which is center to center distance between periodically arrayed holes, the integers (i, j) are the Bragg resonance scattering orders, and e1 and sm are the real dielectric constants of the adjacent dielectric layer and metallic layer, respectively.
EX5-10 EX5-10 shows a series of samples to observe the sputtered deposition along the side well of nanowell structures with various thickness of metal deposition. From a series of top-view SEM images with EX5-10, the well diameter was reduced with the increase of sputtered metal deposition thickness. This reduction of well diameter indicates that sputtered metal was deposited along the side well of nanowell structures instead of being deposited on the bottom of nanowell structures. Table 3 shows the measured average diameter of nanowells after metal deposition. The diameter at 0 nm Ag/Au thickness was obtained using an extrapolated line from the values obtained with 20 nm, 30 nm, and 50 nm thick deposition. The calculated diameter at 0 nm Ag/Au thickness was 197.7 nm.
Table 3
Figure imgf000032_0002
* “Tl” is the Ag/Au thickness; “T3” is the accumulated Side-wall deposition thickness; “a” is the additional side-wall deposition thickness from previous thickness; “V”” is the additional side-wall deposition volume from previous thickness; “b” is the additional side-wall deposition length; “Peak position” is around 630 nm with DI water; “Peak shift” is with respect to RE
As discussed above, sputtered metal deposition along the side wells was observed and the metallic deposition was thinner as the location was closer to the bottom of nanowells. The intended deposition volume was supposed to be deposited on the bottom of nanowells, which was close to the deposition pattern with evaporation. In case of side-wall deposition, the same intended deposition volume was used to be deposited in a cylindrical form along the side-wall. The intended deposition volume V’, the deposition volume V” along the side-wall, were calculated using the equations below:
Figure imgf000032_0001
)
Figure imgf000033_0001
Where V’: Intended additional metal deposition volume; t: Intended additional metal deposition thickness on the flat surface; W: Well diameter before additional metal deposition; W’: Well diameter after additional metal deposition; b: Additional side well metal deposition length along the side well from the top layer; a: Additional side well metal deposition thickness from previous thickness.
For example, in case of 20 nm thick metal deposition in Table 3, t=20 nm, W’= 193.1 nm, and W=197.7 nm. From 0 nm to 20 nm, additional side-wall metal deposition volume was 613826 nm3. The resulting b is equal to 439 nm and additional side-wall metal thickness(a=(W-W’)/2) is 2.3nm in Table 3. The deposition environment such as well diameter is continuously changed during the deposition. The calculation was done from the previous thickness to the next thickness and the deposition pattern was built step by step. The resulting cross-sectional pattern at 200-nm-thick Ag/Au deposition was consistent with the deposition pattern observed from a cross-sectional SEM image. This consistency confirms that the metal deposition on the well area takes place along the side well from top layer to bottom layer. The accumulated thickness of t and a are T1 and T3, respectively.
FIG.9 show a series of normalized transmission spectra in air and in water from EX5, EX6, and EX8. No samples show the peaks (Ag-Au/Polymer) such as (1,0) Ag-Au /Polymer and (1,1) Ag-Au /Polymer as shown in FIG.8 (CE2). Peaks from (1,0) Ag-Au/Air were shown around the wavelength of 500 nm and peaks from (1,0) Ag-Au/Water were shown around the wavelength of 650 nm. In case of EX5, the peaks were too broad to be identified. With increase of deposited metal thickness from 20 nm to 100 nm, the peaks in spectra were more distinctive.
EX11 and CE4-5
The finite-difference time-domain (FDTD) method was used to simulate resulting transmission spectra from deposition patterns obtained from Table 3 and Comparative Examples structures as shown in Table 2. The dielectric constant values of Ag with respect to wavelength, which were readily available, were used here.
From simulated transmission spectra in air and in water from EX11 (Sputtering pattern from EX8), the peak positions and peak shape of simulated spectra were consistent with experimentally obatined spectra (FIG. 9). This consistency indicates that the metal deposition patterns built from Table 3 reflect actual deposition patterns at given deposition conditions. FIG. 10 show simulated cross-sectional deposition patterns, normalized simulated transmission spectra in air. FIGS. 11A-D show electric-field maps at the wavelength of 658nm or 642nm obtained from EX11 (Sputtering pattern from EX8, see structure type D in FIG. 5), CE4 (see structure type G in FIG. 5), CE5 (see structure type H in FIG. 5), and CE6 (see strucutre type F in FIG. 5), respectively. The location of the nanowell without the metal layer is indicated by dashed lines. The structure of CE4 (ex. dimension of nanoewell, depostion thickness on the top layer) is similar to that of EX11 without wrapping depostion along the side well and top layer of EX11. The structure of CE5 (ex. dimension of nanoewell, depostion thickness on the top layer) is similar to that of EX11 without side deposition along the side well of EX9 but with overhanging metal deposition on the top layer. Here, the diameter of bottom well is 197 nm but the diameter of metallic hole on the top layer is 173 nm. CE6 has additional deposition on the bottom of nanowell in addition to the structure of CE4. The thickness of deposition on the bottom layer is same as that on the top layer in CE4.
In case of CE4, FIG.10 shows nanohole array plasmonic peaks (Metal/Substrate), such as (1,0) Ag/Polymer, (1,1) Ag/Polymer and (2,0) Ag/Polymer. Peak from (1,0) Ag/Air is overlapped with peak from (2,0) Ag/Polymer. In case of CE5, FIG. 10 shows nanohole array plasmonic peaks (Metal/Substrate), such as (1,0) Ag/Polymer, (1,1) Ag/Polymer and (2,0) Ag/Polymer. Peak from (1,0) Ag/Air is overlapped with peak from (2,0) Ag/Polymer. (1,0) Ag/Polymer peak was shifted from 658nm to 642nm. In case of CE6, FIG. 10 shows more plasmonic features resulting from nanodot array structures and Fabry-Perot interference structures were convoluted into the spectrum in addtion to nanohole array structures as discussed in FIG. 8.
At the wavelength of 658nm or 642nm, which is the peak positon of (1,0) Ag/Polymer, electric -field maps were obtained at corresponding spectra. FIG. 11B and 11C (cross-sectional electric field profile map) shows the edges between Ag and Polymer layer yield high electric field (circuled area in the E-field map) at the wavelength of 658nm or 642nm due to the excitations of localized surface plasmons. These areas which yield high electric field are known as hot spots. Transmission light from hot spots of Ag/Polymer interface was mostly transmitted in FIG. 1 IB and l lC. FIG. 1 ID (E-field map) shows similar hot spots to that of nanohole array structures of FIG.1 IB and l lC.
On the contrary, FIG.11A shows that hot spots of Ag/Polymer interface are located underneath side-wall Ag deposits and the edge of wrapped Ag deposit inside nanowell structures. Due to hidden hot spots of Ag/Polymer interface by Ag deposit, transmission of light scattering from hot spots of Ag/Polymer interface was suppressed and all peaks from the interface of Metal/Substrate were absent as shown in FIG. 11A.
Sensors based on nanohole array are sensitive to the change of refractive index on metal array surfaces as described in Equation 1. Upon binding the target analyte molecules to the nanohole array surfaces, the refractive index next to metallic surface (here, Ag/Au) surface is changed, and the change is shown in the shift of resulting transmission spectra. The shift of spectra can be correlated to the presence and the amount of analyte molecules. Here, the refractive index was tuned by controlling the refractive index of Media. The refractive indexes of water, 10, 20, 30, 40 (v/v %) of Ethanol in water are 1.3330, 1.3358, 1.3386, 1.3414, and 1.3442, respectively.
In order to measure the spectral shift in the various mixture of Ethanol and water, first, 2ml of water was injected into a cuvette with a piece of nanohole array film. About 10, 20, 30, 40 (v/v %) of Ethanol in water was generated by injecting proper amount of Ethanol into the cuvette step by step. The spectra were acquired every 10 seconds and the spectral shift was continuously monitored. FIG. 12A shows overlaid representative normalized spectra at 0, 10, 20, 30, and 40 (v/v %) of Ethanol in water obtained from EX8. The spectra were red shifted with the increase of volume percentage of Ethanol in water. The peak position of spectra around 650 nm, corresponding to (1,0) Ag-Au/Media, was measured with respect to time. FIG. 12B shows the shift of peak positions with respect to time. Whenever proper amount of Ethanol was injected to the cuvette to make intended volume percentage of Ethanol in water, peak position was changed stepwise and saturated at each Ethanol concentration. The shift of saturated peak position at each Ethanol concentration obtained from EX8 was linearly proportional to the corresponding Refractive Index (RI). The response was 814nm/RI. This response means that EX8 can be used to detect environmental change in the interface of Metal/Media. Similar experiments were performed for EX5, EX6, EX7, EX9, and EX 10. The results were summarized in Table 3. In case of EX5, the peak positions were difficult to identify. Other samples show spectral shifts upon the refractive index change of media.
EX12-16 Table 4
Figure imgf000035_0001
EX16 150 38.4 30.4 7.8 114218 101 421 319
* “Tl” is the Ag/Au thickness; “T3” is the accumulated Side-wall deposition thickness; “a” is the additional side-wall deposition thickness from previous thickness; “V”” is the additional side-wall deposition volume from previous thickness; “b” is the additional side-wall deposition length; “Peak position” is around 450 nm with DI water; “Peak shift” is with respect to RI.
EX 12- 16 show a series of samples to observe the sputtered metal deposition along the side well of nanowell structures with various thickness of metal deposition. From top-view SEM images, the well diameter was reduced with the increase of sputtered metal deposition thickness. This reduction of well diameter indicates that sputtered metal was deposited along the side well of nanowell structures instead of being deposited on the bottom well of nanowell structures. Table 4 shows the average diameter of nanowells measured from SEM images. The diameter at 0 nm Ag/Au thickness was obtained using an extrapolated line from the values obtained with 20-nm-, 40-nm-, and 50-nm-thick deposition.
Similar calculation process described above (Table 3) was done for this series of samples. From transmission spectra, no samples show the peaks from the interface of Ag-Au/Polymer (ex. (1,0) Ag-Au/Polymer) around the wavelength of 500 nm. Peaks from (1,0) Ag-Au/Water were shown around the wavelength of 450 nm. In case of EX12, the peaks were too broad to be identified.
Spectral response at various Ethanol concentration was measured for EX 12- 16. The results were summarized in Table 4. In case of EX 12, the peak positions were difficult to monitor the shift. Other samples show spectral shifts upon the refractive index change of media. The response sensitivity was from 319 to 459nm/RI.
EX17-18
Table 5
Figure imgf000036_0001
EX17 was made by immobilizing Cortisol linked BSA on metallic (Ag/Au (85/15) on EX8 as described above. The sensing layer (Cortisol-BSA) was immobilized through chemical bonds (thiol) and coupling reaction (EDC-NHS) (FIG.3 A). The sensor strip was fabricated after the immobilization. First, lmL of PBS Tween-20 buffer (Tween 20, 0.02% v/v) was added into a cuvette with the sensor strip. FIG. 13A shows that the change of peak position around 635nm in the transmission spectra with respect to time. At 2 minutes, 1.25pl of 2 pg/pl anti-Cortisol antibody (XM210) was injected into the PBS Tween buffer. Upon injection, anti-Cortisol antibody was mixed in the solution and started to bind cortisol which was linked on BSA through antibody-antigen interaction. The peak position of resulting transmission spectra started to increase upon binding of antibody on the sensing layer. The binding event was observed by positive peak position shift. At 6 minutes, 3.6 mΐ of ImM Cortisol was injected. 3600 pmol of Cortisol was excess amount to occupy remained anti-Cortisol antibody binding sites. No more antibodies were available to bind cortisol on sensing layer and no more positive peak position shift was observed. The change of peak position in resulting transmission spectra can be correlated to the amount of available antibody or cortisol in the solution.
EX 18 is an example of physically coated sensing layer on EX8. About 650 nm thick PIMs layer was coated on nanohole array structures (FIG. 3B) . EX 18 was exposed to various concentration of Acetone vapor. 10, 20, 50, 100, 200, 500, 1000 ppm Acetone vapor was delivered to the cuvette holding EX18 for 5 mins or 10 mins per each concentration. The spectra were acquired every 5 sec. FIG. 13B shows the change of peak around 750 nm in the transmission spectra with respect to time. Distinctive step change of peak position was observed in FIG.13B. The saturated value of peak position at each concentration was measured from FIG.13B.
Table 6
Figure imgf000037_0001
Here, the environmental change was monitored by a specific peak. Due to clear spectral features caused by current Examples, any other spectral characteristics of current Examples will be more obvious and clearer than those by Comparative Examples. In addition to this specific peak, any distinctive spectral features can be used to quantify spectral change as shown in Table 6. The distinctive spectral features include peak/valley positions, measured intensity at specified wavelengths, some mathematic processes using several intensities at various wavelengths (e.g. relative intensity ratio at two wavelengths), Hue, Saturation, and so on.
Reference throughout this specification to "one embodiment," "certain embodiments,"
"one or more embodiments" or "an embodiment," whether or not including the term "exemplary" preceding the term "embodiment," means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the certain exemplary embodiments of the present disclosure. Thus, the appearances of the phrases such as "in one or more embodiments," "in certain embodiments," "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the certain exemplary embodiments of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.
While the specification has described in detail certain exemplary embodiments, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, it should be understood that this disclosure is not to be unduly limited to the illustrative embodiments set forth hereinabove. In particular, as used herein, the recitation of numerical ranges by endpoints is intended to include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). In addition, all numbers used herein are assumed to be modified by the term "about." Furthermore, all publications and patents referenced herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. Various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims.

Claims

What is claimed is:
1. An article comprising: an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; an array of nanowells formed into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof; and a metallic layer disposed at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells, and the metallic layer extending from the land areas into the nanowells along the sidewalls to form a wrapping portion.
2. The article of claim 1, wherein the nanowells each have the aspect ratio of depth to opening size in a range from about 0.5: 1 to about 50: 1, from about 1: 1 to about 20: 1, from about 1.5: 1 to about 10:1, from about 2 : 1 to about 10:1, optionally, from about 3 : 1 to about 10:1.
3. The article of claim 1 or 2, wherein the metallic layer has a first thickness T1 on the land areas, and a second thickness T2 on the base of the nanowells, the ratio of T2 over T1 is no greater than 70%, no greater than 60%, no greater than 50%, no greater than 40%, no greater than 30%, no greater than 20%, no greater than 10%, optionally, no greater than 5%.
4. The article of claim 1, wherein the wrapping portion has a depth no less than 3%, no less than 5%, or no less than 10% of a nanowell depth, and an average thickness in a range from 3% to 48% of nanowell opening size, from 5% to 45% of nanowell opening size, or from 10% to 40% of nanowell opening size.
5. The article of any one of claims 1-4, wherein the optically transparent dielectric layer comprises a polymeric material comprising at least one reaction product of a curable composition, monomer, or solution coatable polymer.
6. The article of any one of claims 1-5, wherein the metallic layer comprises at least one of gold, silver, aluminum, copper, platinum, ruthenium, nickel, palladium, rhodium, iridium, chromium, iron, lead, tin, zinc, a combination or alloy thereof.
7. The article of any one of claims 1-6, wherein the array of nanowells has an average pitch in a range from 100 nm to 2500 nm, from 100 nm to 1000 nm, from 250 nm to 1000 nm, or optionally from 300 nm to 900 nm.
8. The article of claim 7, wherein the openings of the nanowells have an average opening size in a range from 5 to 95 percent, 10 to 90 percent, 15 to 85 percent, or optionally, from 20 to 80 percent of the pitch.
9. The article of any one of claims 1-8, wherein the nanowells have an average depth in a range from 50 nm to 5000 nm, from 100 nm to 2000 nm, optionally, from 200 nm to 1000 nm.
10. The article of any one of claims 1-9, wherein the metallic layer on the land area has an average thickness in a range from 20 nm to 500 nm, from 30 nm to 200 nm, optionally, from 30 nm to 150 nm.
11. The article of any one of claims 1-10, wherein the mesh pattern of the metallic layer is a repeating pattern including at least one of a square lattice, a rectangular lattice, a hexagonal lattice, a rhombic lattice, or a parallelogrammic lattice.
12. The article of any one of claims 1-11, further comprising a sensing layer at least partially covering the metallic layer.
13. The article of claim 12, wherein the sensing layer is configured to immobilize affinity group on the metallic layer through covalent or noncovalent bonding.
14. The article of claim 13, wherein the affinity group comprises target analyte molecules linked proteins or antibodies.
15. The article of any one of claims 1-11, further comprising: a sensing layer at least partially fills the nanowells.
16. The article of claim 16, wherein the sensing layer comprises a polymer of intrinsic microporosity (PIM).
17. A sensor comprising: an article of any one of claims 1-16; a light source configured to emit a detection light toward the article; and a detector configured to measure an optical transmission from the article.
18. The sensor of claim 17, wherein the light source is a single wavelength light source.
19. The sensor of claim 17, wherein the light source is a multiple wavelengths light source.
20. The sensor of any one of claims 17-19, wherein the light source emits (a) at least one wavelength of ultraviolet (UV) light, (b) at least one wavelength of visible light, or (c) at least one wavelength of infrared (IR) light.
21. The sensor of any one of claims 17-20, wherein the detector comprises at least one photodetector.
22. A method of detecting an analytic fluid using the sensor of any one of claims 17-21, the method comprising: emitting the detection light toward first major surface of the optically transparent dielectric layer; exposing the first major surface of the optically transparent dielectric layer to an analytic fluid; and detecting, via the detector, the detection light transmitted through the sensor.
23. A method of making a sensing element, the method comprising: providing an optically transparent dielectric layer having a first major surface and a second major surface opposite the first major surface; providing an array of nanowells formed into the first major surface of the transparent dielectric layer, the array of nanowells including openings being interspersed between land areas thereof, the nanowells each having a base and a sidewall connecting the base and the land areas thereof, the nanowells each having a ratio of depth to opening size greater than about 0.5; and disposing a metallic layer at least on the land areas, the metallic layer forming a mesh pattern having an array of nanoholes aligned with the openings of the respective nanowells.
24. The method of claim 23, further comprising providing a light source disposed on a first side of the optically transparent dielectric layer, and configured to emit a detection light toward the optically transparent dielectric layer.
25. The method of claim 23 or 24, further comprising providing a detector disposed on a second side of the optically transparent dielectric layer opposite the first side, and configured to receive the detection light transmitted through the optically transparent dielectric layer.
26. The method of any one of claims 23-25, further comprising providing a sensing layer to at least partially cover the metallic layer.
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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070090411A1 (en) * 2003-01-30 2007-04-26 Fuji Photo Film Co., Ltd. Sensor chip, process for producing the same, and sensor using the same
WO2008030666A2 (en) * 2006-07-25 2008-03-13 The Board Of Trustees Of The University Of Illinois Multispectral plasmonic crystal sensors
JP2008076313A (en) * 2006-09-22 2008-04-03 Japan Advanced Institute Of Science & Technology Hokuriku Tip for analysis, its manufacturing method, and apparatus and method for analysis
WO2012174099A1 (en) * 2011-06-16 2012-12-20 3M Innovative Properties Company Surface plasmon resonance sensor element and sensor including the same
US8460568B2 (en) 2008-12-30 2013-06-11 3M Innovative Properties Company Method for making nanostructured surfaces
WO2020058611A1 (en) 2018-09-17 2020-03-26 Compagnie Generale Des Etablissements Michelin Tire with beads comprising a specific rubber composition
WO2020095258A1 (en) 2018-11-09 2020-05-14 3M Innovative Properties Company Materials and methods for forming nano-structures on substrates
WO2022144774A1 (en) * 2020-12-31 2022-07-07 3M Innovative Properties Company Metallic nanohole arrays on nanowells with controlled depth and methods of making the same

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070090411A1 (en) * 2003-01-30 2007-04-26 Fuji Photo Film Co., Ltd. Sensor chip, process for producing the same, and sensor using the same
WO2008030666A2 (en) * 2006-07-25 2008-03-13 The Board Of Trustees Of The University Of Illinois Multispectral plasmonic crystal sensors
JP2008076313A (en) * 2006-09-22 2008-04-03 Japan Advanced Institute Of Science & Technology Hokuriku Tip for analysis, its manufacturing method, and apparatus and method for analysis
US8460568B2 (en) 2008-12-30 2013-06-11 3M Innovative Properties Company Method for making nanostructured surfaces
WO2012174099A1 (en) * 2011-06-16 2012-12-20 3M Innovative Properties Company Surface plasmon resonance sensor element and sensor including the same
WO2020058611A1 (en) 2018-09-17 2020-03-26 Compagnie Generale Des Etablissements Michelin Tire with beads comprising a specific rubber composition
WO2020095258A1 (en) 2018-11-09 2020-05-14 3M Innovative Properties Company Materials and methods for forming nano-structures on substrates
WO2022144774A1 (en) * 2020-12-31 2022-07-07 3M Innovative Properties Company Metallic nanohole arrays on nanowells with controlled depth and methods of making the same

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
"Extraordinary optical transmission through subwavelength hole arrays", NATURE, vol. 391, 1998, pages 667 - 669
MARIA JOANA ET AL: "Optimization of 3D Plasmonic Crystal Structures for Refractive Index Sensing", THE JOURNAL OF PHYSICAL CHEMISTRY C, vol. 113, no. 24, 18 June 2009 (2009-06-18), US, pages 10493 - 10499, XP055949848, ISSN: 1932-7447, DOI: 10.1021/jp9024552 *
SHINILL KANG: "Micro/Nano Replication", 2012, JOHN WILEY & SONS, INC.

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