Simple Technique for Measuring Surface-Enhanced Fourier Transform Raman Spectra of Organic Compounds

Abstract

A silver surface, suitable for Fourier transform surface-enhanced Raman scattering (FT-SERS), has been prepared by subjecting a polished silver surface to an oxidation-reduction cycle in an electrochemical cell with KCl solution as the electrolyte. The surface produced by this method is shown, by scanning electron microscopy, to be very rough. The preparation of this surface is quite reproducible because the significant parameters of starting surface, electrolyte concentration, and potential can all be well controlled. After removal from the cell followed by washing and drying, organic compounds can be placed on the surface as solutions in aqueous or organic solvents, or by exposure of the surface to vapor. Typically, good FT-SERS spectra are obtained from 0.1–2 μg of sample, after evaporation of the solvent. These experiments were not optimized for minimum detection limits. The technique is very simple, and spectra can be obtained with ease for a wide variety of compounds. Most compounds gave FT-SERS spectra which were similar to their solid Raman spectra; however compounds containing groups expected to interact strongly with the silver surface gave FT-SERS spectra very different from their normal Raman spectra.

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“…Finally, we investigated the potential use of chloride-dipped electrodes in MEF, which are widely used in SERS to enhance signal intensities [16,17]. Our findings show no enhancement in fluorescence emission after chloride dipping, which is consistent with MEF being a through-space phenomenon as compared to SERS, which conversely is thought to be a contact (or near contact) interaction with a metallic surface [20,21].…”

“…Such a treatment of the electrode typically results in significantly large enhancements in the surface Raman intensities [16,17]. We questioned what would be observed for the fluorescence intensities.…”

“…A roughened silver cathode was also dipped in 10 −4 M NaCl for 1 h before being washed and then coated with ICG-HSA, so as to place our findings in context with the huge enhancements in Raman signals, typically obtained after chloride dipping the electrodes [16,17].…”

“…Localized silver colloid formation has been accomplished with reagents in laminar flow [12], by nanolithography [13,14], and by electroplating on insulators [15]. Given the extensive use of roughened silver electrodes for surface-enhanced Raman scattering (SERS) [16,17], we investigated their use for spatially selective MEF, given the typically high surface areas of fractal-like structures.…”

Roughened silver electrodes for use in metal-enhanced fluorescence

“…This remarkable development has its origins in 1974 with the report of an enormous enhancement of the scattered intensity for pyridine adsorbed to roughened silver electrodes. These surfaces are prepared from silver by sweeping the voltage between the electrodes by plus or minus fractions of a volt for several minutes in the presence of KCl [4,5]. been explained as due to an electromagnetic interaction between the incident light, subwavelength size silver particles and the organic molecule [6,7].…”