WO2007064390A1 - Detection d'analytes a l'aide de nanofils produits par lithographie sur fils - Google Patents

Detection d'analytes a l'aide de nanofils produits par lithographie sur fils Download PDF

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Publication number
WO2007064390A1
WO2007064390A1 PCT/US2006/037503 US2006037503W WO2007064390A1 WO 2007064390 A1 WO2007064390 A1 WO 2007064390A1 US 2006037503 W US2006037503 W US 2006037503W WO 2007064390 A1 WO2007064390 A1 WO 2007064390A1
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nanodisk
nanowire
analyte
gap
nanodisks
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PCT/US2006/037503
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English (en)
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Chad A. Mirkin
Lidong Qin
Can Xue
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Northwestern University
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Publication of WO2007064390A1 publication Critical patent/WO2007064390A1/fr

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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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y15/00—Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures

Definitions

  • the present invention relates to methods of using nanowires and Raman spectroscopy to detect an analyte.
  • the present invention relates to on-wire lithographic methods of forming nanodisk arrays and methods of using these nanodisk arrays in Raman spectroscopy detection of an analyte.
  • SERS Surface-Enhanced Raman Scattering
  • the present invention relates to methods of detecting analytes employing nanowires having nanodisk arrays.
  • one aspect of the present invention is to provide methods for detecting the presence and/or concentration of an analyte of interest in a sample using nanowires having nanodisk arrays and various spectroscopy techniques.
  • the nanowires are synthesized using on-wire lithography (OWL) such that the nanodisk thicknesses and the gaps between the nanodisks are precisely controlled to achieve a highly ordered and tailorable nanowire.
  • OTL on-wire lithography
  • the nanowire can be specifically tuned for detection of that analyte.
  • the analyte of interest can be detected either directly or indirectly via a detection reagent or probe.
  • the spectroscopic method employed is Raman spectroscopy and the nanowire enables surface-enhanced Raman scattering (SERS).
  • the spectroscopic method is fluorescence. Microwave detection can also be used.
  • kits comprising nanowires having different nanodisk arrays such that different analytes of interest can be detected by selection of a proper nanowire.
  • the kit comprises nanowires having repeating units of nanodisk arrays having the same characteristics (e.g., disk thickness, gap spacing between disks, and separation spacing between nanodisk arrays), in addition to a plurality of nanowires having different characteristics from one another.
  • the kit comprises nanowires having different nanodisk arrays along the same nanowire.
  • the kit also can comprise nanowires having repeating nanodisk arrays and nanowires of varying nanodisk arrays.
  • FIG. 1 is a schematic of the on-wire lithography (OWL) process
  • FIG- 2 is a schematic of a nanowire 10, showing a nanodisk 12, a gap 14 between nanodisks to form a nanodisk array 16, a separation gap 18 between nanodisk arrays, a coating 20 to hold the nanodisks together, and two capping nanodisks 22 at each end of the nanowire 10;
  • FIG. 3A is a field emission scanning electron microscopy (SEM) image of a nanowire having gold (Au) and nickel (Ni) segments prepared using OWL, wherein the nickel segments are darker than the gold segments;
  • FIG. 3B is a scanning electron microscopy (SEM) image of the wire of FIG. 3A after treatment with nitric acid to remove the Ni segments, wherein the Au segments remain as arrayed nanodisks/rods;
  • FIG. 3C is a scanning micro Raman image (SMRI) of gapped nanowires functionalized with a Raman probe, methylene blue (MB), wherein the inset is a schematic representation of the nanowire;
  • FIG. 3D is a three-dimensional representation of the SMRI of FIG. 3C, wherein the peak intensities are in arbitrary units;
  • FIG. 4A is an SEM image of a nanowire prior to etching and having 120 ⁇ 10 nm Au disks with varying numbers of 30 ⁇ 5 nm Ni segments between the Au nanodisks;
  • FIG. 4B is an SEM image of a nanowire prior to etching having identical 30 ⁇ 5 nm Ni segments with varying Au disk thicknesses of 40 ⁇ 5, 80 ⁇ 8, 120 ⁇ 10, or 200 ⁇ 15 nm (from top to bottom);
  • FIG. 4C is an SEM image of a nanowire prior to etching having identical Au disks of 120 ⁇ 10 nm and Ni segments of 160 ⁇ 10, 80 ⁇ 10, 30 ⁇ 5, 15 ⁇ 5, and 5 ⁇ 2 nm;
  • FIG. 4D is an SEM image of the nanowire of FIG. 4A after etching;
  • FIG. 4E is an SEM image of the nanowire of FIG. 4B after etching;
  • FIG. 4F is an SEM image of the nanowire of FIG. 4C after etching;
  • FIG. 5 A is a confocal Raman microscope image of the gapped nanowire structure of FIG. 4D functionalized with a monolayer of MB;
  • FIG. 5B is a confocal Raman microscope image of the gapped nanowire structure of FIG. 4E functionalized with a monolayer of MB;
  • FIG. 5 C is a confocal Raman microscope image of the gapped nanowire structure of FIG. 4F functionalized with a monolayer of MB;
  • FIG. 5D is a three dimensional (3D) Raman image corresponding to the two dimensional (2D) image of FIG. 5 A, with peak intensities in arbitrary units;
  • FIG. 5E is a 3D Raman image corresponding to the 2D image of FIG. 5B, with peak intensities in arbitrary units;
  • FIG. 5F is a 3D Raman image corresponding to the 2D image of FIG. 5C, with peak intensities in arbitrary units;
  • FIG. 6 contains the electric field enhancement for disk dimmers composed of identical Au disks having different thicknesses and gap distances
  • FIG. 7A is a SEM image of a silver-nickel nanowire
  • FIG. 7B is an optical scattering image of silver nanodisk arrays having (from bottom to top) 50, 100, and 150 nm silver disks;
  • FIG. 8A is a SEM image of silver-nickel nanowires.
  • FIG. 8B is a magnified SEM image of silver-nickel nanowires, indicating the silver and nickel segments.
  • the present invention is directed to methods of detecting analytes using spectroscopy methods, such as Raman, fluorescence, UV, and the like.
  • spectroscopy methods such as Raman, fluorescence, UV, and the like.
  • the following disclosure is primarily directed to Raman but can be readily extended to other spectroscopic methods.
  • the present invention provides methods of detecting analytes via Raman spectroscopy using nanodisk arrays having various electronic, chemical, and physical characteristics. Nanodisk arrays having the appropriate characteristics allow for the enhancement of Raman signals.
  • the enhanced Raman signal can be correlated to the presence or concentration of an analyte in a test sample.
  • the photon emitted is at a lower energy or longer wavelength than that retained. This is referred to as Stokes-shifted Raman scattering. If a molecule is already at a higher vibrational state before it retains a photon, it can impart this extra energy to the remitted photon thereby returning to the ground state. In this case, the radiation emitted is of higher energy (and shorter wavelength) and is called anti-Stokes-shifted Raman scattering. In any set of molecules under normal conditions, the number of molecules at ground state is always much greater than those at an excited state, so the odds of an incident photon hitting an excited molecule and being scattered with more energy than it carried upon collision is very small. Therefore, photon scattering at frequencies higher than that of the incident photons (anti- Stokes frequencies) is minor relative to that at frequencies lower than that of the incident photons (Stokes frequencies). Consequently, it is the Stokes frequencies that are usually analyzed.
  • the amount of energy lost to or gained from a molecule in this way is quantized, resulting in scattered photons having discrete wavelength shifts. These wavelength shifts can be measured by a spectrometer.
  • Raman spectroscopy is one useful analytical tool to identify certain molecules, and as a means of studying molecular structure.
  • Other useful spectroscopic methods include fluorescence, infrared, nuclear magnetic resonance, and the like.
  • a significant increase in the intensity of Raman light scattering can be observed when molecules are brought into close proximity to (but not necessarily in contact with) certain metal surfaces.
  • the increase in intensity can be on the order of several million-fold or more, and has been coined "surface-enhanced Raman scattering” (SERS).
  • the induction of an oscillating dipole moment in a molecule by incident light is the source of the Raman scattering.
  • the effect of the resonant oscillation of the surface plasmons is to cause a large increase in the electromagnetic field strength in the vicinity of the metal surface. This results in an enhancement of the oscillating dipole induced in the scattering molecule and hence increases the intensity of the Raman scattered light. The effect is to increase the apparent intensity of the incident light in the vicinity of the particles.
  • a second factor contributing to the SERS effect is molecular imaging.
  • a molecule having a dipole moment and in close proximity to a metallic surface will induce an image of itself on that surface of opposite polarity (i.e., a "shadow" dipole on the plasmon). The proximity of that image is thought to enhance the ability of the molecules to scatter light.
  • the coupling of a molecule having an induced or distorted dipole moment due to the surface plasmons greatly enhances the excitation probability and results in an increase in the efficiency of Raman light scattered by the surface-absorbed molecules.
  • the SERS effect can be enhanced through combination with the resonance Raman effect.
  • the surface-enhanced Raman scattering effect is even more intense if the frequency of the excitation light is in resonance with a major absorption band of the molecule being illuminated.
  • the resultant Surface Enhanced Resonance Raman Scattering (SERRS) effect can result in an enhancement in the intensity of the Raman scattering signal of seven orders of magnitude or more.
  • On-wire lithography is a nanofabrication strategy which is capable of achieving 2.5 nm, and in some instances 1 nm, resolution and 20 nm feature size on a nanowire.
  • OWL provides a method for producing nanodisk arrays which can be used for SERS applications.
  • the nanodisk array substrate can have several features that make it a unique SERS substrate, including easy functionalization on a single nanowire, easy homogeneous suspension in dye solutions for SERS studies, and large surface area and chemical potential for functionalization.
  • the high resolution and flexibility of the nanodisk array allows for systematic study of plasmon resonance of the particles.
  • the use of substrates obtained via OWL reduces the potential effect of imperfections on the metal surface, thereby allowing for a focused study on the molecular imaging effect. No other lithography technique has provided substrates for a SERS study that allows for this type of systematic study.
  • nanorods refers to small structures that are less than 10 ⁇ m, and preferably less than 5 ⁇ m, in any one dimension and that have a length to width ratio greater than one.
  • the nanorods used in the present invention are multicomponent in nature.
  • multicomponent refers to an entity that comprises more than one type of material.
  • a multicomponent nanorod refers to a nanorod having sections of different materials, e.g., a nanorod with one or more Au segments and one or more Ni segments.
  • the metal component of the nanorod can be any metal compatible with in situ electrochemical deposition.
  • metals include, but are not limited to, indium- tin-oxide, titanium, platinum, titanium tungstide, gold, silver, nickel, copper, and mixtures thereof.
  • a “nanowire,” interchangeably referred to as a “gapped nanowire,” is a nanorod that has been subjected to etching to remove certain metal segments and leave behind others.
  • FIG. 2 shows a nanowire 10 with its various components. These nanowires have electronic properties that can be tailored from their compositional components (i.e., the identities of the metals forming the nanorod). The use of metals having different chemical and electrical properties allows the creation of gaps in these nanowires when the nanowire is treated with a solution that dissolves one metal of the nanorod while the other metal is unaffected.
  • these nanogaps 14 are useful in producing nanodisk arrays 16 of various thicknesses that can be used to assess electromagnetic response for SERS experiments.
  • a nanodisk array is a series of metal segments (i.e., nanodisks) separated by a gap.
  • a nanodisk array 16 is shown in FIG. 2.
  • the gap is between about 2 nm and about 500 nm.
  • Other gap ranges contemplated include in the range of about 5 and about 160 nm.
  • gap sizes include 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, and 500 nm. In other cases, the gap is greater than 500 nm. Gaps up to an including 2 ⁇ m may also be incorporated into a nanodisk array.
  • Disk thicknesses for nanodisks include, but are not limited to, ranges of about 20 nm to about 500 nm, about 40 nm to about 250 urn, and about 50 nm to about 120 nm.
  • Specific disk thickness contemplated for use in the present invention include 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, and 500 nm.
  • the disk thickness of the nanodisk is at least 500 nm and can be up to 2 ⁇ m.
  • a series of nanodisk arrays having different characteristics may be present on the same nanowire. Separation of the nanodisk arrays on a nanowire is achieved using separation gaps 18, as illustrated in FIG. 2.
  • the length of a separation gap is dependent upon the size of the nanodisk array.
  • a separation gap is at least two times greater, preferably three times greater, than the total length of a nanodisk array.
  • a nanodisk array composed of two 120 nm disks separated by a 50 nm gap can be separated from a second nanodisk array by a separation gap of about 1 ⁇ m. For nanodisk arrays having larger disk thickness and gaps, larger separation gaps are needed.
  • Nanodisk arrays of varying characteristics on the same nanowire are illustrated, for example, in FIG. 4D.
  • the number of gaps in a nanodisk array can vary. At least one gap must be present in a nanodisk array. Gaps numbering from 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 can all be incorporated into a nanodisk array.
  • the number of gaps in a nanodisk array determines the number of nanodisks in the array. For example, one gap correlates to two nanodisks; two gaps correlate to three nanodisk; and three gaps to four nanodisks.
  • sacrificial metal refers to a metal that can be dissolved under the proper chemical conditions.
  • sacrificial metals include, but are not limited to, nickel which is dissolved by nitric acid, and silver which is dissolved by a methanol/ammonia/hydrogen peroxide mixture.
  • etching refers to a process of dissolving a sacrificial metal segment using conditions suitable for dissolving or removing the metal comprising the sacrificial segment.
  • etching solutions include, but are not limited to, nitric acid and a methanol/ammonia/hydrogen peroxide mixture.
  • coating refers to a material that is positioned to contact one side of a multicomponent nanorod, prior to the etching step.
  • the purpose of the coating is to provide a bridging substrate to hold segments of the etched nanorod (i.e., a nanowire) together after removal of the intervening sacrificial metal segments in the etching process.
  • Nonlimiting examples of coatings used in this invention include a gold/titanium alloy and silica.
  • a coating with a gold/titanium alloy allows for the nanowire to conduct an electrical current, whereas a silica coating electrically isolates the various nanodisk arrays from each other.
  • Other backings may be chosen to provide other electrical, chemical, or physical characteristics to the nanowire, depending upon the end use of the nanowire.
  • OWL is based upon manufacturing segmented nanowires comprising at least two materials, one that is susceptible to, and one that is resistant to, wet chemical etching.
  • material pairs There are a variety of material pairs that can be used.
  • Au-Ag and Au-Ni are two such examples of metal pairs of differing chemical properties.
  • the sacrificial metal in these pairs are Ag and Ni, respectively.
  • any combination of metals having contrasting susceptibility to chemical etching conditions may be used.
  • the surfaces of nanodisks are clean, i.e., free from contamination of stabilizing surfactants or other organic chemicals, because the OWL synthetic process uses nitric acid which removes essentially all organic compounds from the surface of the nanodisks.
  • This clean surface allows for better functionalization and also decreases Raman scattering noise attributed to surface contaminants. Detection of small analyte concentrations or probe molecules therefore is enhanced due to the decreased scattering noise and tailorable functionalization of the nanodisks.
  • SERS substrates are interchangeably referred to as SERS active substrates herein.
  • SERS substrates include, but are not limited to, the nanogap wires/nanodisk arrays produced via OWL.
  • the sample is attached onto a SERS-active substrate (i.e., a nanowire).
  • a SERS-active substrate i.e., a nanowire.
  • An analyte can be attached to the SERS-active surface by direct adsorption, adsorption through a linker arm covalently attached to the analyte, or by the covalent attachment of the analyte to a detection reagent or probe on the SERS-active surface directly, through a linker arm, or by intercalation of the distal portion of a linker arm into the enhancing surface.
  • a radiation source is selected to generate radiation having a wavelength that causes appreciable Raman scattering in the presence of the analyte being measured. Although it is known that Raman scattering occurs at all wavelengths, the radiation typically employed will be near infrared radiation because ultraviolet radiation often causes fluorescence.
  • Detection of an analyte can proceed either directly or in combination with a detection reagent or probe.
  • the analyte does not have an appreciable Raman scattering cross section and a detection reagent or probe is needed to provide sufficient Raman scattering for detection.
  • the detection reagent or probe can be a molecule having one or more, preferably ally, of the following properties: (a) a strong absorption band in the vicinity of an excitation wavelength (extinction coefficient near 10 4 or greater); (b) a functional group which will enable it to be covalently or non-covalently bound to an analyte of interest; (c) photostability; (d) sufficient surface and resonance enhancement to allow detection limits of at least 10 ⁇ g, and preferably in the subnanogram range; (e) minimal exhibition of strong fluorescence emission at the excitation wave length used, usually denoted as having a large Stokes shift; and (f) a relatively simple scattering pattern with a few intense peaks.
  • spectral overlap is a desired characteristic because the emission spectrum from one detection reagent or probe can overlap the excitation spectrum of another, exciting the first detection reagent or probe and resulting in a "pumping" of the second.
  • detection reagents or probes include, but are not limited to, 4-(4- aminophenylazo)phenylarsonic acid monosodium salt, arsenazo I, basic fuchsin, Chicago sky blue, direct red 81, disperse orange 3, 2-(4-hydroxyphenylazo)-benzoic acid (HABA), erythrosin B, trypan blue, ponceau S, ponceau SS, l,5-difluoro-2,4-dinitrobenzene, methylene blue (MB), and p-dimethylaminoazobenzene (PMA).
  • the detection reagent or probe can be covalently attached to the analyte of interest.
  • the detection reagent or probe can be non-covalently attached to the analyte of interest, e.g., via hybridization, pi-stacking, hydrogen bonding, van der Waals interactions, chelation, and the like.
  • the radiation source can be any source that provides the necessary wavelength to excite the analyte or detection reagent or probe for detection using Raman spectroscopy.
  • a laser serves as the excitation source.
  • the laser may be of an inexpensive type, such as a helium-neon or diode laser. In some embodiments, a narrow bandwidth, high frequency, amplitude and modal stability, and no sidebands or harmonics are important characteristics of the laser. Lamps also can be used.
  • the radiation sources used can be monochromatic or polychromatic, and also can be of high intensity. In one embodiment, the radiation source provides a high enough photon flux that the Raman transitions of the analyte or detection reagent or probe are saturated, in order to maximize the SERS signal.
  • SERS excitation can be performed in the near infrared range, which minimizes excitation of intrinsic sample fluorescence.
  • SERS-based ligand binding assays using evanescent waves propagated by optical waveguides can also be performed.
  • the wavelength and angle are important and give rise to scattering.
  • the nanodisk array characteristics also can be tuned to provide means for detecting analytes using other spectroscopic means. Smaller disk thicknesses (e.g., less than 400 run) and gaps (e.g., less than 100 nm) are more suitable for optics detection (Raman spectroscopy, fluorescence, and the like), while larger disk thicknesses (e.g., between about 500 nm and about 2 ⁇ m) and gaps (e.g., between about 100 nm and about 1 ⁇ m) are more suitable for microwave applications.
  • the nanodisk array of the nanowire can be tailored to provide optimum characteristics. In one embodiment, the spacing of the nanodisk arrays are set at odd multiples of one-fourth the wavelength in order to produce a resonant cavity that enhances the field strength; even multiples do not enhance, but rather, suppress emissions.
  • the nanowires are selected to enhance a fluorescence signal of an analyte or a detection reagent or probe.
  • the fluorescence of the detectable molecule is measured.
  • the fluorescence signal indicates the presence or absence of an analyte.
  • the excitation and emission wavelengths are selected based upon the characteristics of the fluorescent moiety to be detected. In the case where a detection reagent or probe is needed (e.g., the analyte of interest is not fluorescent), then the wavelengths are selected such that the detection reagent or probe can fluoresce.
  • the nanodisk array characteristics are selected to enhance the fluorescent signal of the analyte or detection reagent or probe.
  • the selection of the nanowire having the proper nanodisk array is readily performed by persons skilled in the art using simple trial techniques. For example, in one embodiment, the characteristics are calculated based upon the wavelengths of radiation and the effective refractive index of the medium between the nanodisks.
  • analyte concentration In order to determine the concentration of an analyte in a test sample, it is necessary to correlate a measured signal to the analyte concentration. Quantification can be accomplished either by inclusion of known concentrations of one or more molecules (for example, an internal standard) or by referencing the signal intensity of an unknown amount of an analyte of interest with a standard curve generated from measurement of known amounts of that analyte. Techniques well known to those of skill in the art can be used in the creation of a standard curve and in the calculations of the concentration of the analyte of interest.
  • the kit comprises containers having (a) detection reagents or probes or (b) a plurality of nanowires, wherein each nanowire comprises at least one nanodisk array.
  • the nanowire comprises repeating units of the same nanodisk array.
  • the nanowire comprises nanodisk arrays of different properties, e.g., different disk thicknesses, different gap sizes, and/or different coatings. Regardless of the type of nanowire, the nanodisk arrays are separated from each other by distances sufficient to isolate each disk array from an adjacent nanodisk array.
  • the kit further comprises a container having detection reagents or probes, such as 4-(4- aminophenylazo)phenylarsonic acid monosodium salt, arsenazo I, basic fuchsin, Chicago sky blue, direct red 81, disperse orange 3, HABA, erythrosin B, trypan blue, ponceau S, ponceau SS, l,5-difluoro-2,4-dinitrobenzene, MB, and PMA.
  • detection reagents or probes such as 4-(4- aminophenylazo)phenylarsonic acid monosodium salt, arsenazo I, basic fuchsin, Chicago sky blue, direct red 81, disperse orange 3, HABA, erythrosin B, trypan blue, ponceau S, ponceau SS, l,5-difluoro-2,4-dinitrobenzene, MB, and PMA.
  • the nanowires can be used for any application wherein field intensification caused by a plasmon resonance and/or a controlled, tuned cavity is useful.
  • Such applications include photonic crystal technologies, fluorescence measurements, and coupler/translator applications, hi some cases, the nanowires are constructed such that the spacing between nanodisks is suitable for microwave wavelengths, hi other cases, the spacing is suitable for infrared wavelengths, and in still other cases, the spacing is suitable for visible or ultraviolet wavelengths.
  • the disclosed nanowires can be used in photonic crystals.
  • Photonic crystals are processed materials with periodic spatial variations of the dielectric constant. Based on a Bragg reflection, electromagnetic waves having defined frequency ranges cannot pass through the photonic crystal and, therefore, no resonant modes can occur. These frequency intervals are referred to as photonic band gaps. The energy does not spread in predefined directions within this stop band.
  • photonic crystals are artificial crystal structures that have an effect on electromagnetic waves that is similar to the effect a semiconductor crystal has on electronic waves. Light propagation in a photonic crystal can be controlled based on the material and the photonic crystal structure. As the nanowires of the present invention have periodic structures, they can be used as photonic crystals.
  • the metal segments are electrochemically deposited in porous alumina templates in a controlled fashion from suitable plating solutions via well-established methods (Martin, Science, 266, 1961, 1994; Routkevitch et al, J. Phys. Chem., 100, 14037, 1996; Nicewarner- Pena et al, Science, 294, 137, 2001; Kowtyukhova et al, Chem. Eur. J., 8, 4354, 2002).
  • the length of each segment is tailored by controlling the charge passed during the electrodeposition process.
  • the resulting multi-metallic wires then are released from the template by dissolution of the template via known procedures (Park et al, Science, 303:348, 2004).
  • an aqueous suspension of Au-Ni nanorods is cast upon a glass microscope slide pre-treated with a piranha solution which makes the slide more hydrophilic.
  • a layer of silicon dioxide is deposited on the nanorods, using plasma enhanced chemical vapor deposition (PECVD). This resulted in one side of the nanorod being coated with silicon dioxide while the other side, which is protected by the microscope slide substrate, remained uncoated. Sonication of the substrate leads to the release of the coated nanorods into solution.
  • the final step of the OWL process involves the selective wet- chemical etching of the sacrificial segments.
  • Nickel segments can be removed from the rods by treating the rods with concentrated nitric acid for one hour (hr). This results in the generation of nanowire structures with gaps precisely controlled by the length of the original Ni segments.
  • the Au segments remaining after removal of the Ni segments are held in place by the stripe of silicon dioxide. Because silicon dioxide is an insulator, the Au segments are electrically isolated from one another. Alternatively, the Au segments can be electrically connected to one another by coating the nanowires with Au/Ti rather than silicon dioxide in this process.
  • the nanorods are comprised of Au and Ag segments, the sacrificial Ag segments are removed by treating the coated nanorods with an etching solution containing methanol, 30% ammonium hydroxide, and 30% hydrogen peroxide (4:1:1 v/v/v) for one hour.
  • an etching solution containing methanol, 30% ammonium hydroxide, and 30% hydrogen peroxide (4:1:1 v/v/v) for one hour.
  • etching solution containing methanol, 30% ammonium hydroxide, and 30% hydrogen peroxide (4:1:1 v/v/v) for one hour.
  • Numerous other combinations of materials and etchants can likewise be used for such purposes depending upon the intended use of the structures formed.
  • Multi-segment nanorods composed of Ni and Au segments were synthesized using electrochemical deposition into a porous alumina membrane.
  • Platinum wire was used as a counter electrode, and Ag/ AgCl was used as the reference electrode.
  • the nanopores were partially filled with Ag, leaving headroom to accommodate the growth of additional domains (Technic ACR silver RTU solution from Technic, Inc.) at a constant potential, -0.9 V vs. Ag/AgCl, by passing 1.5 C/cm 2 for 30 minutes.
  • An Au segment then was electroplated from Orotemp 24 RTU solution (Technic, Inc.) at -0.9 V vs. Ag/AgCl followed by a Ni segment from nickel sulfamate RTU solution (Technic, Inc.) at -0.9 V vs. Ag/AgCl. The procedure involving Au was repeated to form a second Au segment. Each segment length was controlled by monitoring the charge passed through the membrane.
  • the first 1.4 ⁇ m ( ⁇ 0.2) long segment of Au was generated by passing 1.3 C.
  • the Ag backing and the alumina membrane then were dissolved with concentrated nitric acid and 3 M sodium hydroxide solutions, respectively.
  • the rods were repeatedly rinsed with nanopure water until the solution reached at pH of 7.
  • Nanorods containing more than three segments are prepared by repeating the above steps until the desired number of segments have been constructed. These added segments may be constructed of the same or different materials than the materials used in the construction of the initial three segments, by appropriate selection of the plating materials and conditions in the manner known to those of skill in the art.
  • Preparation of segmented nanorods composed of gold (Au) and nickel (Ni) was achieved using electrochemical synthesis. The design of the structures was devised to incorporate specific distances between similar nanodisks and to separate different nanodisks beyond the diffraction of the excitation wavelength. This spatial separation allowed for discrete measurement and observation of individual classes of nanodisks.
  • Multi-segment nanorods and nanodisk arrays were prepared according to reported methods (Qin, L. et al, Science 309, 113-115 (2005)). The applied charge during electrochemical deposition was controlled to achieve designed nanorod structures. Charge and length of each sample are shown in Table 1. The resulting structures were measured by SEM (FIG. 3A, 3B, and 4A-4F).
  • FIG. 3 A is an SEM image of a nanorod having a diameter of 360 ⁇ 20 nm, composed of metal segments of, from bottom to top, 600 ⁇ 30 nm Au, 2 ⁇ m Ni, 300 ⁇ 20 nm Au, 30 ⁇ 5 nm Ni, 300 ⁇ 20 nm Au, 2 ⁇ m Ni, and then four repeating segments of 45 ⁇ 5 nm Au/30 ⁇ 5 nm Ni, and a final 45 ⁇ 5 nm Au segment.
  • FIG. 3B is an SEM image of a nanowire of the nanorod of FIG. 3A after chemical etching to remove the Ni segments.
  • FIG. 4A is a nanorod of identical 120 ⁇ 10 nm Au disks with 30 ⁇ 5 nm Ni segments between them. From top to bottom, the number of Ni segments between each 120 ⁇ 10 nm Au disk is 0, 1, 2, 3, and 4. Each nanodisk array is separated by a Ni segment of 1.2 ⁇ m.
  • FIG. 4D is an SEM image of the nanowire of the nanorod of FIG. 4A after chemical etching to remove the Ni segments.
  • FIG. 4B is an SEM image of a nanorod composed of varying Au disk thicknesses. From top to bottom, the Au disk thicknesses are 40 ⁇ 5, 80 ⁇ 8, 120 ⁇ 10, and 200 ⁇ 15 nm. Each disk is repeated twice, separated by a Ni segment of 30 ⁇ 5 nm. Each array is separated by a 1 ⁇ m Ni segment.
  • FIG. 4E is an SEM image of the nanowire of the nanorod of FIG. 4B after chemical etching to remove the Ni segments.
  • FIG. 4C is an SEM image of a nanorod composed of varying Ni segments between Au segments of identical thickness, 120 ⁇ 10 nm. From bottom to top, the Ni segments are 160 ⁇ 10, 80 ⁇ 10, 30 ⁇ 5, 15 ⁇ 5, and 5 ⁇ 2 nm. The separations between nanodisk arrays is 1 ⁇ m.
  • FIG. 4F is an SEM image of the nanowire of the nanorod of FIG. 4C after chemical etching to remove the Ni segments.
  • Gapped nanowires having gold nanodisks and a silicon dioxide coating were prepared using OWL, then were mixed with 1 ⁇ M methylene blue (MB) 5 a Raman active molecule, in ethanol and stirred overnight. The solution was centrifuged and redispersed in ethanol five times to remove any non-dissociated MB. The resulting gold nanowires coated with a self-assembled monolayer of MB were concentrated by centrifugation and dried onto a pirhana-pretreated glass substrate.
  • MB methylene blue
  • FIG. 4A, 4B, and 4C present SEM images of Au-Ni mulicomponent nanowires. After performing OWL, the corresponding gapped nanowires were obtained as shown in FIG. 4D, 4E, and 4F.
  • the SEM images provided more precise sizes in FIG. 4A, FIG. 4B, and FIG. 4C than in FIG. 4D, FIG. 4E, and FIG. 4F due to the charges accumulated on the coated SiO 2 layer during electron beam scanning.
  • FIG. 5 A, 5B, and 5C are 2D Raman scattering images and FIG. 5D, 5E, and 5F are the corresponding 3D images.
  • the insets in FIG. 5A, 5B, and 5 C show the structural information for the corresponding Au disks.
  • the laser excitation wavelength was at 633 nm, which is close to the absorption energy of the MB molecule.
  • FIG. 5 A four bright spots were easily observable, which correspond to the Raman scattering signals from the nanodisk arrays having one, two, three, and four gaps.
  • the spot sizes became larger when gap number increased due to the larger gap areas and therefore increased number of dye molecules in locations with larger SERS enhancements.
  • the signal for two disks with one gap was 167 times higher than that from one disk without a gap. This provided significant insight into the electromagnetic mechanism of SERS and facilitated the design of SERS substrates, indicating that a gap is important to the ability of a metal surface to enhance Raman scattering.
  • FIG. 5B The disk thickness dependence of the intensities is shown in FIG. 5B.
  • the disk gap was fixed at 30 nm with disk thicknesses varying from 40 to 160 nm.
  • a single disk with a 40 nm thickness was also included at one end of the structure as a control.
  • a 2D image showed five spots of Raman scattering signals from the Au disks with different size and an identical gap distance (FIG. 5B).
  • the spot from the 120 ⁇ 20 nm Au disks showed the maximum enhanced Raman scattering signal.
  • the 3D image in FIG. 5E revealed the differences more clearly.
  • the working wavelength in calculating the enhanced local electric fields between the Au nanodisks was chosen to be the excitation wavelength of 633 nm, in order to mimic the experiments performed with MB.
  • the results with 669 nm (the mean of the incident and Stokes-shifted wavelengths) also was investigated, and the results were similar.
  • the grid size used in the DDA program was 5 nm.
  • the polarizations both parallel and perpendicular to the interdimer axis were studied, and are indicated as the Z and Y axes, respectively. For a disk diameter of 360 nm, the resonance wavelengths for these two polarizations are similar.
  • the SERS enhancements are only large for Z polarization, and the variation of the Z-polarized resonance behavior with interdisk spacing is important to the interpretation of the experiments.
  • Contours of the electric fields (plotted as
  • the plane used for the intensity calculation is between the two disks and 5 nm above the surface of one of them (the choice does not effect the calculations).
  • Each column represents nanodisk arrays with the same thickness while each row represents nanodisk arrays with the same gap distance.
  • the disk thicknesses from left to right are 40, 80, 120, 160, and 200 nm, respectively.
  • the gap distances from top to bottom are 5, 10, 15, 30, and 80 nm, respectively.
  • the contours range from 0-50 times the incident intensity.
  • the 120 nm thick disks show the largest peak electric fields ( I E I 4 maximizes at 10 5 times the incident field intensity) and also the highest average fields ( ⁇ I E I 4 > - 1700, where the average is over the entire surface area of both particles). This dependence of the results on disk thickness is in agreement with the experimental measurements (see FIG. 5E). The magnitude of the SERS enhancement factor compared to that for an isolated disk (where ⁇
  • 4 > 18) was accurately predicted. Previous studies (Hao et al., J. Chem. Phys. 120:357 (2004)) focused on the electric fields around silver particle triangles and found that the electric fields between the particles increase dramatically with decreasing gap size.
  • Silver nanodisk arrays can be used to tune the surface plasmon resonance (SPR) in the visible region, which potentially can be used for SPR detections. Additionally, silver is one of the best materials for surface-enhanced Raman scattering (SERS). Silver-nickel nanowires were prepared using electrochemical deposition, as described above. SEM images of the resulting nanowires are shown in FIG. 8 A and FIG. 8B. The nanowires then were treated with a 1 : 1 solution of hydrochloric acid in water to remove (or etch) the nickel segments from the nanowires, producing gapped silver nanowires. FIG.
  • FIG. 7 contains an image showing the resulting gapped nanowires, which have silver nanodisk arrays with 50 nm, 100 nm, 150 nm Ag disks.
  • FIG 7A shows SEM images of Ag/Ni nanowires having a dark Ni segment and a bright Ag segment.
  • a dark field optical microscope image of the resulting silver nanodisk arrays is shown in FIG. 7B, and a color scattering difference between 50 nm (bottom), 100 nm (middle), 150 nm (top) Ag disks was observed.
  • the color scattering difference can be seen qualitatively in black and white reproduction of FIG. 7B, as the differences in color are translated into a difference in grayscale in the black and white version.

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Abstract

La présente invention concerne des procédés de détection d'analytes à l'aide de nanofils (10) qui présentent des séries (16) de nanodisques. La présente invention concerne en particulier des procédés de détection d'analytes par diffusion de Raman renforcée à la surface (SERS) et d'utilisation de nanofils (10) préparés en utilisant une lithographie sur fils (OWL). Le nanofil (10) comprend au moins une série (16) de nanodisques qui comprend au moins deux nanodisques (12) et au moins un interstice (14). Les caractéristiques de la série (16) de nanodisques peuvent être ajustées de manière à offrir un moyen de détection d'analytes à l'aide de moyens spectroscopiques.
PCT/US2006/037503 2005-12-02 2006-09-27 Detection d'analytes a l'aide de nanofils produits par lithographie sur fils WO2007064390A1 (fr)

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Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
GOKNUR Z. CAMBAZ, GLEB N. YUSHIN, YURY GOGOTSI, AND VADIM G. LUTSENKO: "Anisotropic Etching of SiC Whiskers", NANO LETTERS, vol. 6, no. 3, 11 October 2005 (2005-10-11), pages 548 - 551, XP002422174 *
JAMES A. SIOSS AND CHRISTINE D. KEATING: "Batch Preparation of Linear Au and Ag Nanoparticle Chains via Wet Chemistry", NANO LETTERS, vol. 5, no. 9, 4 August 2005 (2005-08-04), pages 1779 - 1783, XP002422173 *
LIDONG QIN ET AL: "On-Wire Lithography", SCIENCE, AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE,, US, vol. 309, no. 113, 1 July 2005 (2005-07-01), pages 113 - 115, XP001167309, ISSN: 0036-8075 *
ZOU S ET AL: "Silver nanoparticle array structures that produce giant enhancements in electromagnetic fields", CHEMICAL PHYSICS LETTERS, NORTH-HOLLAND, AMSTERDAM, NL, vol. 403, no. 1-3, 14 February 2005 (2005-02-14), pages 62 - 67, XP004727979, ISSN: 0009-2614 *

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