Systematic preparation of colloidal silver nanoparticles for effective SERS substrates

Optimized parameters to produce aggregated silver colloidal nanoparticles in solution for the effective surface-enhanced Raman scattering (SERS) substrates were systematically determined. The sizes of the prepared silver nanoparticles were identified in TEM images, which were 31 ± 5 nm and almost all of them were aggregated in three or four particles in solution. The optimum condition was determined by relative enhancement of the SERS signal in the spectra of benzoic acid. The observed SERS signals in the prepared solution were remarkably reproducible and the solution was stable for a week at least. The SERS spectrum of biphenyl carboxylic acid in Ag colloidal solution prepared in the present method was obtained for comparison to the one previously reported. In addition, the SERS spectrum of 4,4’-biphenyl dicarboxylic acid was measured for the first time in solution and spectral assignments were provided.