Classifications

• • 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
  • G01N21/47—Scattering, i.e. diffuse reflection
• • 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

Definitions

• the present disclosure relates broadly to sensors, and more particularly to surface plasmon resonance sensors, and methods for their manufacture and use.
• the interface between the media is coated with a thin layer of metal (e.g., gold), and light is monochromatic and p-polarized (i.e., polarized parallel with respect to a plane on which the light is incident), the intensity of the reflected light is sharply reduced at a specific incident angle (called surface plasmon resonance (SPR)) due to the resonance energy transfer between the evanescent wave and surface plasmons.
• SPR surface plasmon resonance
• the resonance conditions are influenced by the material adsorbed onto the thin metal film.
• Surface plasmons also termed “surface plasmon polaritons" are surface electromagnetic waves that propagate in a direction parallel to a metal/dielectric (or metal/vacuum) interface. Since the wave is on the boundary of the metal and the dielectric, these oscillations are very sensitive to any change of this boundary, such as the adsorption of molecules to the metal surface.
• the thin metallic layer is disposed onto a transparent substrate (e.g., glass). Light illuminates the thin metallic layer through the transparent substrate, and an evanescent wave penetrates through the thin metallic layer. The plasmons are excited at the opposite side of the film thin metallic layer.
• the present disclosure provides a surface plasmon resonance sensor element comprising:
• an optical construction disposed on the thin metallic layer for directing light to and away from the thin metallic layer
• the absorptive layer disposed on the thin metallic layer opposite the optical construction, the absorptive layer comprising a polymer of intrinsic microporosity having an average pore volume of at least 0.4 cubic nanometers (nm ⁇ ).
• the present disclosure provides a surface plasmon resonance sensor comprising:
• a vapor delivery chamber comprising an inlet port, an outlet port, and a sampling port, wherein the sampling port and at least a portion of the absorptive layer are hermetically sealed together;
• a detector for detecting an image corresponding to a minimal intensity of light reflected from the thin metallic layer, thereby measuring a resonance angle.
• SPR sensor elements according to the present disclosure have increased sensitivity for analyte vapors as compared to previous SPR sensors (e.g., those using MAKROLON-type polycarbonate).
• absorptive and absorptive in reference to the absorptive layer include both absorption and adsorption;
• the term "monomelic unit” refers to a recurring group of atoms present in the structure of a polymer, including the polymer backbone, and corresponding to a single monomer molecule (whether actual or theoretical).
• a polymer (exclusive of end groups) may consist of one or more different monomelic units.
• Fig. 1 is a schematic cross-sectional view of an exemplary SPR sensor element according to the present disclosure
• Fig. 2 is a schematic cross-sectional view of an exemplary SPR sensor according to the present disclosure
• Fig. 3 is a plot of reflected light amplitude versus pixel location of a CCD array for various toluene vapor concentrations from Example 1 ;
• Fig. 4 is a plot of reflected light valley positions in pixels of a CCD array versus various toluene vapor concentrations from Example 1.
• exemplary SPR sensor element 100 comprises thin metallic layer 1 10, optical construction 120, and absorptive layer 130.
• Optical construction 120 is disposed on thin metallic layer 1 10 and serves to directing light to and away from thin metallic layer 1 10.
• Optical construction 120 comprises optical prism 122, transparent plate 126, and transparent fluid 124 sandwiched therebetween.
• Optical prism 122, transparent plate 126, and transparent fluid 124 have substantially the same (i.e., matched) indexes of refraction.
• Absorptive layer 130 is disposed on thin metallic layer 1 10 opposite optical construction 120.
• Absorptive layer 130 comprises a polymer of intrinsic microporosity having an average pore volume of at least 0.4 nm ⁇ .
• the thin metallic layer typically comprises a metal such as, for example, gold, silver, aluminum, or copper, although other metals (e.g., titanium or chromium) may be used if desired. Combinations of metals may also be used.
• the combination of metals comprises a bilayer construction wherein a metal layer furthest from the optical construction comprises a metal such as, for example, gold, copper, or silver and contacts a tie layer (in contact with the optical construction) which comprises a metal or metal-containing compound such as, for example, titanium, chromium, nickel, copper, cobalt, molybdenum, tantalum nitride, or an alloy thereof.
• the thickness of the thin metallic layer should be sufficiently thin that is less than the effective length of the evanescent wave. Typically, thicknesses of the thin metallic layer in a range of from about from 10 nm to about 100 nm may be effective, although other thicknesses may be used.
• the metal layer may be deposited according to any suitable technique, including, for example, thermal vapor deposition and sputtering techniques.
• the optical construction directs light to and away from the thin metallic layer.
• the optical construction may be a unitary body or an assemblage of component parts.
• the optical construction may be an optical prism (e.g., a triangular prism or a cylindrical lens), or it may be a combination of optical elements (e.g., as shown in Fig. 1).
• the absorptive layer comprises a polymer of intrinsic microporosity (PIM) having an average pore volume of at least 0.4 nm ⁇ .
• PIM intrinsic microporosity
• the PIM has an average pore volume of at least 0.45 nrr .
• Pore volume may be determined by positron annihilation lifetime spectroscopy (PALS); for example, as described by de Miranda et al. in Physical Status Solidi RRL, 2007, vol. 1 , No. 5, pp. 190- 192.
• PIMs tend to pack poorly causing intrinsic porosity (void spaces) on the order of two nm or less that cannot be eliminated.
• Such polymers can be prepared by step-growth polymerization where at least one bis-catechol (A) is allowed to react with at least one fluormated arene (B) under basic conditions as shown in Scheme I (below) according to the procedure reported by Budd et al. in Chemical
• these polymers Due to the rigidity and contorted nature of the backbone of the resulting polymers, these polymers are unable to pack tightly in the solid state and thus have at least 10 percent free volume and are intrinsically microporous.
• the PIM may be a homopolymer having a monomelic unit selected from the group consisting of
• PIM homopolymers having monomeric unit A can be formed by step-growth polymerization as described by Budd et al. in Advanced Materials, 2004, vol. 16, No. 5, pp. 456 -459.
• PIM homopolymers having monomeric unit B can be formed according to the method described by Budd et al. in Journal of Membrane Science, 2005, vol. 251, pp. 263-269.
• the absorptive layer may be deposited by any suitable technique.
• One useful technique involves spin coating a solution of the PIM material in a suitable solvent, for example, as shown in the examples hereinbelow.
• the absorptive layer may comprise one or more additional components such as, for example, antioxidants, fillers, residual solvent, wetting aids, leveling agents.
• the thickness of the absorptive layer is typically in a range of from 0.1 micron to 10 microns, although other thickness may also be used.
• exemplary SPR sensor 200 comprises source of p-polarized light 210, SPR sensor element 100, vapor delivery chamber 220, and detector 230.
• SPR sensor element 100 may optionally be located on a rotation stage (not shown) in order to control the incident angle of light.
• Source of p-polarized light 210 provides light that is p-polarized (i.e., electric field component is polarized in the same plane as the incident ray and the surface normal of the thin metallic layer). This may be accomplished using a light source such as a laser, or a collimated white light source in combination with a polarizer and optional collection optics.
• a collimated white light source is generally more desirable than a laser due to interference fringes that may result in the resultant SPR image.
• the polarizer is used to light, and the optional collection optics (used with white light sources) consist of a narrow band pass filter, typically centered in the near-infrared region, that is used to select the excitation wavelength for the experiment.
• Vapor delivery chamber 220 comprises inlet port 222, outlet port 224 and sampling port 226. Sampling port 226 and at least a portion of the absorptive layer 130 are hermetically sealed together using o-ring 228. In typical use, analyte vapor to be analyzed is introduced into vapor delivery chamber 220 through inlet port 222. Vapor delivery chamber 220 may be made of any gas impermeable material such as for example metal, glass, or plastic.
• the analyte vapor comprises a volatile organic compound; however, this is not a requirement.
• suitable analyte vapors include aliphatic hydrocarbons (e.g., n-octane or cyclohexane), ketones (e.g., acetone or methyl ethyl ketone), aromatic hydrocarbons (benzene, toluene, chlorobenzene, or naphthalene), nitriles (e.g., acetonitrile or benzonitrile), chlorinated aliphatic hydrocarbons (e.g., chloroform, dichloroethane, methylene chloride, carbon tetrachloride, or tetrachloroethylene), esters 5 (e.g., vinyl acetate, ethyl acetate, butyl acetate, or methyl benzoate), sulfides (e.g., phenyl mercaptan),
• Detector 230 detects an image corresponding to a minimum intensity of light reflected from the thin metallic layer, thereby measuring a resonance angle. Depending on the amount of analyte vapor absorbed by the absorptive layer, its dielectric constant will change resulting a corresponding change in the angle of reflected light. The detector response can be correlated to the concentration of analyte vapor present in the vapor delivery chamber. Suitable detectors include, for example, photomultiplier tubes, photodiodes, photoconductors, phototransistors, and charge -coupled detectors (CCDs). For example, a linear CCD array may be used.
• the sensor element may be heated to an elevated temperature (e.g., in a range of from 50°C to 70°C). This may lessen humidity effects in the sensor element response.
• PIM- 1 (a Polymer of Intrinsic Microporosity) was prepared from the monomers 5,5',6,6'- tetrahydroxy-3,3,3',3'-tetramethyl- 1 , 1 '-spirobisindane and tetrafluoroterephthalonitrile generally according to the procedure reported by Budd et al. in Advanced Materials, 2004, Vol. 16, No. 5, pp. 456- 459.
• the dried PIM- 1 polymer was a solid yellow product obtained having a number-average molecular weight of approximately 41,900 grams/mole as determined by gel permeation chromatography analysis using light scattering detection.
• Glass slides (glass number 0050-0050-0010-GF-CA, 50 mm x 50 mm, 1.1 mm thick, material C- 263, surface 80/50, from Precision Glass & Optics, Santa Ana, California) were cleaned by soaking for 30-60 minutes in ALCONOX LIQUI-NOX detergent solution from Alconox, Inc., White Plains, New York, then scrubbing each side of the slides with a bristle brush, rinsing under warm tap water followed by a final rinse with deionized water. The slides were allowed to air dry covered to prevent dust accumulation on the surface. The dry, clean slides were stored in 3-inch (7.6-cm) wafer carriers from Entegris, Chaska, Minnesota.
• a surface plasmon resonance sensor was set up as generally shown in Fig. 2.
• the SPR sensor mounted prism was attached to a VOC delivery chamber using an o-ring, a sensor holder, and screws.
• a filter FSR-OD 300 absorptive ND filter, 25.4 mm DIA, 3.0 OD at 546.1 nm obtained from Newport Corp. of Irvine, California
• a linear 128-pixel CCD array (model TSL1401R, obtained from TAOS of Piano, Texas) with a power supply (model 6212A, obtained from Hewett Packard of Palo Alto, California) was used.
• the pixels measure 63.5 micrometers (Height) by 55.5 micrometers (Width) with 63.5 micrometers center-to-center spacing and 8 micrometers spacing between pixels.
• the total length of CCD array was 0.813 centimeters for 128 pixels.
• the CCD array was mounted on the evaluation module (model PC404A, obtained from TAOS, Piano, Texas) and the module was attached to a 3 -way transitional stage (obtained from Line Tool, Allentown, Pennsylvania).
• the distance between the gold/polymer sensing layer and CCD array was 2.25 centimeters and the CCD array was perpendicularly oriented to the reflected radiation.
• a digital camera was used to take images of the instrumental setup and the incident radiation angles were measured analyzing the digital camera images.
• the signals from the evaluation module were acquired by an oscilloscope (model TDS 3024B, obtained from Tektronix, Beaverton, Oregon).
• a customized Labview program was used to interface with the Tektronix oscilloscope for data acquisition.
• the positions of reflection minimum were calculated using a peak/valley finder algorithm built in Labview (software available from National Instruments, Austin, Texas) program.
• VOC levels were generated using a KD Scientific syringe pump (available from KD Scientific Inc., Holliston, Massachusetts) fitted with a one-milliliter gas-tight syringe (obtained from Hamilton Company, Reno, Nevada). The syringe pump delivered a VOC solvent 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.
• the syringe pump was controlled by a LABVIEW program that allowed VOC profiles to be generated during a test run.
• a MIRAN IR analyzer from Thermo Fischer Scientific, Inc., Waltham, Massachusetts was used to verify the set concentrations. All measurements were done at room temperature.
• a 30.0 nm thick gold layer was coated onto a clean glass slide by thermal vapor deposition of gold at a rate of 0.1 nm per second (nm/sec).
• the deposition process was controlled using an Inficon XTC/2 thin film deposition controller from Inficon, East Syracuse, New York.
• a 5.5 percent by weight PIM solution was prepared by combining the PIM-1 polymer with chlorobenzene in a small jar and mixing on a roller mill (Mini Bottle Roller number 348920 from
• the gold surface of slide was spin coated with the PIM-1 solution using a Model WS 400B- 8NPP/LITE spin coater from Laurell Technologies Corporation of North Wales, Pennsylvania.
• the PIM solution was dispensed to the slide for 15 sec at 300 rpm, and then coated for 45 sec at 2000 rpm.
• the thickness of the PIM layer was 620 nm. The thickness was measured by removing a small section of the coating an acetone soaked cotton swab and measuring on a Model XP- 1 Profilometer from Ambios Technology, Santa Cruz, California.
• the parameters used in the measurement were a scan speed of 0.1 mm/sec, a scan length of 5 mm, a range of 10 micrometers, a stylus force of 0.20 mg and a filter level of 4. After measuring, the coated slides were baked for 1 hour at 100°C.
• Individual sensor elements were prepared by dicing the coated slide using a standard glass scoring cutter into four 25 mm by 25 mm elements. The slide was cut on the back (inactive side) while supporting the front (active) surface to prevent damage to it. After dicing into individual sensor elements, the sensor elements were stored in 1.5-inch (3.8-cm) wafer holders from Entegris, Chaska, Minnesota.
• the sensor element was mounted in a SPR SENSOR apparatus as described above.
• the incident radiation angle under dry air was 63.5 degrees.
• the sensor was exposed to a series of toluene
• concentrations of toluene concentrations i.e., 3, 6, 9, 12 ppm of toluene in dry air.
• Fig. 3 reports the signals obtained from CCD array. A higher pixel position represents reflected radiation at higher angles. Without toluene exposure (0 ppm toluene), a clear reflection minimum
• Fig. 4 reports the valley position change after a series of toluene exposure with respect to time. Clear steps of the valley position changes are observed at each stepped concentration. Some fluctuation of signals comes from the fluctuating toluene vapor delivery caused by the syringe pump. The fluctuation gives insight to the response time of the SPR sensors.
• the SPR sensor can spontaneously respond to spontaneously fluctuating VOC concentrations in seconds.
• a sensor element was prepared according to the procedure described in Example 1 , except that two metal layers were coated on a slide and a 3.6 percent by weight solids PIM-1 solution was used. A 5.0 nm thick layer of titanium was deposited on the PGO slide at a rate of 0.1 nm/sec followed by depositing a 30.0 nm layer of gold at rate of 0.5 nm/sec over the titanium layer.
• Example 1 was dispensed to the sensor for 15 sec at 300 rpm, and then coated for 45 sec at 4000 rpm.
• the thickness of PIM-1 layer was 203 nm.
• the radiation angle under dry air was 51.5 degrees.
• a sensor was prepared according to the procedure of Example 2, except that a 1.7 percent polycarbonate ((poly(bisphenol A carbonate) polycarbonate from Sigma Aldrich of Milwaukee, Wisconsin, and corresponding to MAKROLON polycarbonates, used without further purification) solution in chloroform was dispensed to the slide for 5 sec at 300 rpm and then coated for 40 sec at 3000 rpm. The thickness of polycarbonate layer was 221 nm. Sensor elements were tested with ethanol, MEK, and toluene described in Example 2. The radiation angle under dry air was 61.5 degrees. Results are reported in Tables 1, 2, and 3.
• the present disclosure provides a surface plasmon resonance sensor element comprising:
• an optical construction disposed on the thin metallic layer for directing light to and away from the thin metallic layer
• the absorptive layer disposed on the thin metallic layer opposite the optical construction, the absorptive layer comprising a polymer of intrinsic microporosity having an average pore volume of at least 0.4 cubic nanometers.
• the present disclosure provides a surface plasmon resonance sensor element according to the first embodiment, wherein the optical construction consists of a prism.
• the present disclosure provides a surface plasmon resonance sensor element according to the first or second embodiment, wherein the optical construction comprises a prism, a transparent plate, and a fluid sandwiched therebetween, wherein the prism, transparent plate, and fluid have matched indexes of refraction.
• the present disclosure provides a surface plasmon resonance sensor element according to any one of the first to third embodiments, wherein the polymer of intrinsic microporosity has an average pore volume of at least 0.45 cubic nanometers.
• the present disclosure provides a surface plasmon resonance sensor element according to any one of the first to fourth embodiments, wherein the polymer of intrinsic microporosity is a homopolymer having a monomeric unit selected from the group consisting of
• the present disclosure provides a surface plasmon resonance sensor element according to any one of the first to fifth embodiments, wherein the thin metallic layer comprises at least one of gold, silver, aluminum, or copper.
• the present disclosure provides a surface plasmon resonance sensor comprising:
• a surface plasmon resonance sensor element according to any of the first to seventh embodiments; a detector for detecting an image corresponding to a minimal intensity of light reflected from the thin metallic layer, thereby measuring a resonance angle.
• the present disclosure provides a surface plasmon resonance sensor according to the seventh embodiment, wherein the source of p-polarized light comprises a laser.
• the present disclosure provides a surface plasmon resonance sensor according to the seventh or eighth embodiment, wherein the detector comprises a photodiode array.
• the present disclosure provides a surface plasmon resonance sensor according to any one of the seventh to ninth embodiments, wherein the optical construction consists of a prism.
• the present disclosure provides a surface plasmon resonance sensor according to any one of the seventh to ninth embodiments, wherein the optical construction comprises a prism, a transparent plate, and a fluid sandwiched therebetween, wherein the prism, transparent plate, and fluid have matched indexes of refraction.

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• 2012
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