Interaction effects on surface-enhanced Raman scattering activities in silver sols

Abstract

The presence of anions due to either the preparation process or the addition of external solution in silver sols may affect the surface-enhanced Raman scattering (SERS) of sample molecules. We have recorded a series of SERS spectra of benzoic acid (BA) and p-aminobenzoic acid (PABA) in the presence of different chloride ion concentrations, and studied their chloride ion effects on the surface-enhanced Raman scattering (SERS) activities of the borohydride-reduced silver sols. For both organic acids, SERS could be observed without the coexistence of chloride ions. In the presence of small amount of chloride ion, the intensity of the Raman scattering did not vary significantly. The UV–VIS spectra of the selected samples in the silver sols have been collected to investigate the adsorption state that might be affected by chloride ions. It was noted that the variation of the SERS intensity could arise from the change of the molecular adsorption state upon the addition of the chloride ions. The possible adsorption mechanism and the orientation of adsorbed molecules were discussed. SERS spectra of a variety of compounds in silver sols prepared with different methods have been collected. The existence of ions from the preparation process might play a role in explaining the SERS activities of the sols.