EP1754046A2 - Method and apparatus for performing sers analysis using a chemical reference - Google Patents
Method and apparatus for performing sers analysis using a chemical referenceInfo
- Publication number
- EP1754046A2 EP1754046A2 EP05804843A EP05804843A EP1754046A2 EP 1754046 A2 EP1754046 A2 EP 1754046A2 EP 05804843 A EP05804843 A EP 05804843A EP 05804843 A EP05804843 A EP 05804843A EP 1754046 A2 EP1754046 A2 EP 1754046A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- chemical
- containment means
- raman
- solution
- analyte
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
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
- G01N21/62—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
Definitions
- SERS Surface-enhanced Raman spectroscopy
- SERS involves the absorption of incident laser photons, generating surface plasmons within nanoscale metal structures, which then couple with nearby molecules (the analyte chemical), to thereby enhance the efficiency of Raman scattering by six orders of magnitude or more (Jeanmaire, D.L., and R.P. Van Duyne, "Surface Raman Spectroelectrochemistry", /. Electroanal. Chem., 84, 1-20 (1977) or Weaver, M.J., Farquharson, S., Tadayyoni, M.A., "Surface-enhancement factors for Raman scattering at silver electrodes. Role of adsorbate- surface interactions and electrode structure", J.
- colloids are prepared by reducing a metal salt solution to produce metal particles, which in turn form aggregates. Particle size and aggregate size are strongly influenced by initial chemical concentrations, temperature, pH, and rate of mixing, and again therefore the desired features are not reproducible.
- the third teclinique mentioned uses substrates that are prepared by depositing the desired metal onto a surface having the appropriate roughness characteristics. To pennit the analysis, the sample is preferably dried on the surface to concentrate the analyte on the active metal, and once again replication is difficult to achieve.
- the relative merits of the three methods for preparing SER-active surfaces, described above, have been further reviewed by K.L. Norrod, L.M. Sudnik, D. Rousell, and K. L.
- the particle size and aggregation state of the metal dopant are stabilized, once the sol-gel has formed, and that the sample and/or solvent will not alter the plasmon-generating capabilities of the trapped metal particles.
- changes in pH may still result in variable Raman signal intensities, such as in the case of weak acids and bases where the relative concentrations of the ionized and non-ionized forms may be influenced, Farquharson et al.
- a measurement of the intensity of such bands, as either peak height or peak area, for a chemical of known concentration can therefore be used to calculate the concentration of the same chemical in an unknown sample, by measuring its corresponding spectral band intensities. Variations in laser power, detector response, ambient temperature, etc. can however influence the intensity of the spectral bands and thereby introduce significant error in the quantitative calculation.
- a useful method of overcoming such variation errors involves the inclusion of a chemical of known concentration in the unknown sample, and using its Raman spectral band intensity as a reference to the band intensity of the chemical of unknown concentration (Pelletier, M.J., Ed. "Analytical Applications of Raman Spectroscopy,” Blackwell Science Ltd., London, 1999, p. 20).
- the choice of internal reference chemical employed depends somewhat upon the nature of the sample that is to be measured, but it is important that the spectral bands of the reference chemical that are to be used for quantifying the concentration should not overlap the spectral bands of the unknown sample to a degree that would interfere with the quantitative calculation.
- the prior art does not address the variability of amount of Raman scattering enhancement produced by surface-enhanced Raman-active media and, in any event, does not disclose reference chemicals, or provide suitable referencing techniques, that are specific to SERS or to measurement and analytical methods based thereupon.
- apparatus for use in effecting surface-enhanced Raman spectros- copy comprising first and second containment means, the first containment means having a liquid-flow entrance thereinto and an exit therefrom and containing a known quantity of a reference chemical having an effective surface-enhanced Raman factor.
- the reference chemical may be in the form of a solution with which the analyte chemical-containing solution is completely soluble to form a homogeneous test solution.
- the apparatus will normally additionally include liquid transport means operatively connected to the entrance into the first containment means, for injecting or drawing the analyte chemical-containment solution thereinto, and/or to the exit from the second containment means for effecting evacuation thereof, such liquid transport means advantageously comprising a syringe.
- liquid transport means advantageously comprising a syringe.
- positive and/or negative pressure is applied so as to cause a known volume of a solution containing at least one analyte chemical, in an unknown concentration, to be introduced into the first containment means of the apparatus; so as to cause a reference chemical contained in the first containment means to disperse homogeneously with the analyte-containing solution; and so as to cause the homogeneous test solution to be transported into the second containment means and to permeate the surface-enhanced Raman-active medium contained therein.
- the phrase "common field of view” should be understood to mean the single field of surface-enhanced Raman-active medium at which both the reference chemical and also the analyte chemical are simultaneously irradiated by the excitation (generally, laser beam) radiation, and the field from which SER scattered radiation is also collected, and it will be understood that collection will usually occur on the same axis as the axis of irradiation.
- the term “scattering efficiency” refers to the ratio of Raman radiation energy produced per unit of excitation radiation energy delivered.
- the molecular size of the reference chemical should be substantially smaller (typically being at least two orders of magnitude smaller) than is that of the analyte chemical, and preferably the reference chemical will be of such size that it occupies no more than about one percent of the surface area of a metal constituting the surface-enhanced Raman active medium, h most instances the reference chemical will comprise a thiocyanate or cyanide compound that is soluble in the test solution, usually being a salt or an inorganic complex and desirably being selected from the group consisting of thiocyanate salts of sodium, potassium and calcium; cyanide salts of sodium, potassium and calcium; sodium ferrocyanide; potassium hexacyanoruthenate; and pentacyanoferrothiocyanate.
- the surface-enhanced Raman-active medium used will normally employ a metal selected from the group consisting of copper, gold, silver, nickel, and alloys and mixtures thereof to produce particles (normally 5 to 1000 nm diameter particles), isolated or aggregated, ordered or random, or to produce a surface of equivalent mo ⁇ hology (e.g., roughened electrodes, periodic arrays, patterned structures).
- the particles can be generated on a surface by chemical- or vapor- deposition techniques; functionally equivalent surface morphologies can be generated by chemical or electrochemical etching, and effective surface structures can be generated by photolithography or a combination of the foregoing techniques (e.g., vapor deposition on chemically deposited spheres).
- Metal particles or aggregates can be suspended in a colloidal solution, by reduction of a metal salt solution, for use as such or for application, for example, to a surface bearing the analyte chemical.
- the metal particles or aggregates can also be inco ⁇ orated into porous structures, such as polymers or sol-gels.
- Polymers can be synfliesized with at least one monomer that allows inclusion of the metal constituent, and at least one chemical functional group that maintains porosity, or provides for porosity (e.g., a polymer that expands, upon the addition of a solvent, to allow access to the metal surface by the analyte).
- the surface-enhanced Raman-active medium will com- prise a chemically synthesized sol-gel, desirably synthesized utilizing a silicia-based, titania- s based, or zirconia-bascd alkoxide and at least one surface-enhanced Raman-active mclal.
- the surface-enhanced Raman-active medium is comprised of a mixture of a porous material and at least one surface-enhanced Raman-active metal
- the porous material employed is desirably one that is effective to produce chemical separations or selective chemical extractions.
- Such a porous material may be selected from the group consisting of sol-gels, silica gels, silica stabilized by zirconia, derivatized silica-based matrices (e.g., trifunctional quanternary aiiiine, aromatic sulfonic acid), long-chain (e.g., C%, Cis) alkane particles, derivatized long-chain alkane particles (e.g., phenyl, cyano, etc.).
- sol-gels silica gels, silica stabilized by zirconia
- derivatized silica-based matrices e.g., trifunctional quanternary aiiiine, aromatic sulfonic acid
- long-chain alkane particles e.g., C%, Cis
- derivatized long-chain alkane particles e.g., phenyl, cyano, etc.
- the measured intensity of the characteristic band of the analyte chemical divided by the measured intensity of the characteristic band of the reference chemical, provides a ratio factor that is employed to eliminate the effects of parameters that cause variations in surface-enhanced Raman activity of the selected surface-enhanced Raman-active medium, and is utilized to calculate the concentration of the analyte chemical.
- the surface-enhanced Raman scattering efficiencies of the reference chemical and of the analyte chemical, relative to one another, is also utilized to calculate the analyte chemical concentration.
- the relative scattering efficiencies can be determined by measuring surface-enhanced Raman spectral band intensities of the reference and analyte chemicals, using a standard sample containing a representative surface-enhanced Raman-active medium and a standard solution containing selected concentrations of the two chemicals. Calculation of the unknown concentra- tion can be carried out by application of the following equation (Equation I):
- [AMeas] (I SER AM a S /I SER R Mcas ) x (I SER RS/I SER AS) x [RMeas], wherein AMeas stands for the analyte chemical in the test solution and [AMeas] represents the concentration thereof, I stands for the measured intensity of the surface-enhanced Raman band used for the scattering efficiency determination, RMeas stands for the reference chemical in the test solution and [RMeas] represents the concentration thereof, RS stands for the reference chemical of selected concentration, in the standard solution, and AS stands for the analyte chemical of selected concentration therein; the term (I SER RS /I SER A S) provides the relative surface- enhanced Raman scattering efficiency ratio of the reference chemical and the analyte chemical.
- An underlying concept of the method of the invention concerns the use of a chemical of known concentration (the reference chemical), as a surface-enhanced Raman activity standard to which the unknown concentration of an analyte chemical can be referenced, and thereby quantitatively determined, by correlation of respective spectral band intensities.
- the surface enliancement provided by the reference chemical will advantageously be of known or measurable magnitude; generally, however, only the concentration of the reference chemical and the signal intensity associated with it need be known.
- the reference chemical must not only exhibit an effective SER factor, but it should also be of such molecular size that it occupies only a small percentage of the SER-active metal surface within the SER experimental field of view, and thereby produces a SER signal, when irradiated or illuminated, having an intensity that is indicative of the amount of SER activity within that field of view.
- the analyte chemical which necessarily also occupies a portion of the metal surface within the same, common field of view, will of course experience the same amount of SER activity.
- the intensity of a suitable SER spectral band of the analyte chemical, of unknown concentration, divided by the intensity of a suitable SER spectral band of the reference chemical, of known concentration, will thus provide a factor by which the effects of parameters that cause variations in SER-activity (such as differences in the average particle size, the particle size distribution, and the extent and variety of particle aggregation) can be minimized or negated entirely. Furthermore, this ratio factor will provide a method for calculating, quantitatively, the concentration of the analyte chemical of unknown concentration, provided the SER scattering efficiencies of the two chemicals, relative to one another, are known; the relative scattering efficiency factor is easily obtained by performing an SERS measurement of a sample in which the concentrations of both chemicals are known.
- the concentration of the analyte of unknown concentration can be calculated by application of Equation I, hereinabove set forth and defined. It is noted that the use of Equation I enables quantitative measurements to be perfonned with an exceptional level of precision.
- trace quantities typically 1-10 ppm
- of sodium or potassium thiocyanate are added to samples of unknown analyte concentration as the internal intensity reference chemical, utilizing the techniques herein described.
- Both salts dissociate completely in water, as well as in other polar solvents, to produce the linear SCN " molecule, which has only four unique molecular vibrations, two degenerate bending modes and the SC and CN stretching modes, occurring in the Raman spectrum as bands or peaks at 465 (degenerate), 750, and 2080 cm " , respectively.
- the degenerate bending modes have very little band intensity.
- a full Raman or SER spectrum covers the spectral range of 0 to 4000 cm “1 , and thus almost the entire spectrum is available to observe bands generated by other chemicals (analytes) that might be the subject of a quantitative measurement.
- the region from 600 to 1600 cm “1 most often used to identify unknown chemicals and known as the "finge ⁇ rint region,” is almost completely available for analysis, with only minor interference from the relatively weak SCN band at 740 cm “ .
- only two molecular vibrations commonly occur between 1900 and 2600 cm “1 , i.e., the C ⁇ N, and the C ⁇ C vibrations, and therefore only molecules containing these functional groups can potentially interfere with the use of the SCN " molecule as an intensity reference.
- the SER band for SCN “ at 2095 cm” is exceptionally strong, and is eas- ily observed using as little as 10 ppm (10 nucrogram of SCN " per milliliter of water). At this extremely low concentration the possibility of a reaction occurring between the reference chemical and the analyte is correspondingly unlikely.
- Furthemiore, the SCN " anion is very small, and each molecule can be shown to typically occupy only about 0.01 nm 2 of the SER-active metal surface, leaving the vast majority of the metal surface available for occupancy by the molecules to be analyzed, as is of course important to ensure that enliancement of the anlayte Raman scattering can occur.
- a SER spectral measurement of a homogeneous mixture of two chemicals, one an analyte of unknown concentration and one of SCN " of 10 ppm, will produce a spectrum of Raman bands according to the molecular structure of the analyte and the SCN " anion. More importantly, the ratio of the intensities of the analyte spectral bands and the SCN bands, preferably the CN stretch at 2095 cm " for the latter, will be constant and independent of the location in the sample at which the laser is effective to generate SER scattering.
- a measurement of a mixture of the analyte in question, and SCN " , both in known concentrations (e.g., of 10 ppm), will establish the relative SER scattering efficiencies of the two chemicals and thereby enable the unknown concentration of the same analyte, in any sample containing the reference chemical in a known concentration, to be determined.
- a trace quantity of sodium or potassium cyanide is introduced, as the internal intensity reference, into a sample containing an unknown concentration of analyte chemical.
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/854,134 US20050266583A1 (en) | 2004-05-26 | 2004-05-26 | Method for quantitative surface-enhanced raman spectroscopy using a chemical reference |
US10/902,511 US7312088B2 (en) | 2004-05-26 | 2004-07-29 | Method and apparatus for performing SERS analysis using a chemical reference |
PCT/US2005/018498 WO2005119219A2 (en) | 2004-05-26 | 2005-05-25 | Method and apparatus for performing sers analysis using a chemical reference |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1754046A2 true EP1754046A2 (en) | 2007-02-21 |
EP1754046A4 EP1754046A4 (en) | 2008-04-02 |
Family
ID=35463519
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP05804843A Withdrawn EP1754046A4 (en) | 2004-05-26 | 2005-05-25 | Method and apparatus for performing sers analysis using a chemical reference |
Country Status (2)
Country | Link |
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EP (1) | EP1754046A4 (en) |
WO (1) | WO2005119219A2 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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CN108426868B (en) * | 2018-03-13 | 2020-11-13 | 浙江工业大学 | Method for in-situ on-line determination of solubility of carbon dioxide in pure water |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5850623A (en) * | 1997-03-14 | 1998-12-15 | Eastman Chemical Company | Method for standardizing raman spectrometers to obtain stable and transferable calibrations |
US6623977B1 (en) * | 1999-11-05 | 2003-09-23 | Real-Time Analyzers, Inc. | Material for surface-enhanced Raman spectroscopy, and SER sensors and method for preparing same |
US20030231304A1 (en) * | 2002-06-12 | 2003-12-18 | Selena Chan | Metal coated nanocrystalline silicon as an active surface enhanced raman spectroscopy (SERS) substrate |
-
2005
- 2005-05-25 EP EP05804843A patent/EP1754046A4/en not_active Withdrawn
- 2005-05-25 WO PCT/US2005/018498 patent/WO2005119219A2/en active Application Filing
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5850623A (en) * | 1997-03-14 | 1998-12-15 | Eastman Chemical Company | Method for standardizing raman spectrometers to obtain stable and transferable calibrations |
US6623977B1 (en) * | 1999-11-05 | 2003-09-23 | Real-Time Analyzers, Inc. | Material for surface-enhanced Raman spectroscopy, and SER sensors and method for preparing same |
US20030231304A1 (en) * | 2002-06-12 | 2003-12-18 | Selena Chan | Metal coated nanocrystalline silicon as an active surface enhanced raman spectroscopy (SERS) substrate |
Non-Patent Citations (6)
Title |
---|
MCLAUGHLIN C ET AL: "Quantitative analysis of mitoxantrone by surface-enhanced resonance Raman scattering" ANALYTICAL CHEMISTRY, AMERICAN CHEMICAL SOCIETY. COLUMBUS, US, vol. 74, no. 13, 1 July 2002 (2002-07-01), pages 3160-3167, XP002237472 ISSN: 0003-2700 * |
NIRODE W F ET AL: "On-column surface-enhanced Raman spectroscopy detection in capillary electrophoresis using running buffers containing silver colloidal solutions" ANALYTICAL CHEMISTRY, AMERICAN CHEMICAL SOCIETY. COLUMBUS, US, vol. 72, no. 8, 15 April 2000 (2000-04-15), pages 1866-1871, XP002250987 ISSN: 0003-2700 * |
S. FARQUHARSON ET AL.: "Chemical agent detection by surface-enhanced Raman spectroscopy" PROCEEDINGS OF SPIE, vol. 5269, March 2004 (2004-03), pages 16-22, XP002469854 * |
S. FARQUHARSON ET AL.: "Rapid Dipicolinic Acid Extraction from Bacillus Spores Detected by Surface-Enhanced Raman Spectroscopy" APPLIED SPECTROSCOPY, vol. 58, no. 3, March 2004 (2004-03), pages 351-354, XP002469666 * |
See also references of WO2005119219A2 * |
TAYLOR GORDON T ET AL: "OPTIMIZATION OF A FLOW INJECTION SAMPLING SYSTEM FOR QUANTITATIVE ANALYSIS OF DILUTE AQUEOUS SOLUTIONS USING COMBINED RESONANCE AND SURFACE-ENHANCED RAMAN SPECTROSCOPY (SERRS)" APPLIED SPECTROSCOPY, THE SOCIETY FOR APPLIED SPECTROSCOPY. BALTIMORE, US, vol. 44, no. 1, May 1990 (1990-05), pages 635-640, XP009084168 ISSN: 0003-7028 * |
Also Published As
Publication number | Publication date |
---|---|
WO2005119219A2 (en) | 2005-12-15 |
WO2005119219A3 (en) | 2007-03-08 |
EP1754046A4 (en) | 2008-04-02 |
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