SURFACE-ENHANCED RAMAN-SPECTROSCOPY OF P-AMINOBENZOIC ACID WITH EXCITATION IN THE VISIBLE AND NEAR-INFRARED SPECTRAL REGION

Surface-enhanced Raman spectroscopy (SERS) of p-aminobenzoic acid (PAB A) in yellow silver colloids was studied with excitation in the visibl e as well as in the near infrared spectral region by means of a conven tional scanning spectroscopic technique. Two kinds of adsorbed surface species, one binding through the carboxylate and another through the amine group to the colloidal silver surface, were deduced from the spe ctral changes before and after addition of sodium chloride solution. I t was found that the species adsorbed through the amine group was prob ably desorbed by competitive adsorption of chloride ions. The enhancem ent factor in the near infrared is larger than in the visible spectral region and the optimum conditions for near infrared (NIR)-SERS were f ound different from those for SERS with visible light excitation. Seve ral enhancement mechanisms may contribute simultaneously to the NIR-SE RS of molecules in silver colloids, two of which are presented and dis cussed in detail in this paper.