Colloidal nanoparticles of gold and silver were used in Surface–Enhanced Raman Scattering (SERS) analysis of melamine and 4–aminobiphenyl. Gold colloids allowed the SERS detection of melamine at levels below 0.1 μg/L using a previously unreported SERS peak at 275 cm−1 and yielded better detection limits compared to silver colloids. For 4–aminobiphenyl, the detection limits were found to be similar for both colloids at 0.05–0.1 mg/L. Analysis by transmission electron microscopy showed that the morphology of both Ag and Au nanoparticles were uniformly spherical with average diameters that were 69.3 ± 23.1 nm and 41.6 ± 19.1 nm, respectively. The SERS spectral intensities of both compounds were found to increase as the sample pH increased. The optimal signals were obtained at pH = 8.5 for 4–aminobiphenyl and pH = 11.5 for melamine. The enhancement factors for the determination of melamine are in range of 3.5 × 104–6.3 × 104 for the silver colloid and 5.2 × 107–2.1 × 109for the gold colloid.
Keywords: surface–enhanced Raman scattering, SERS, gold colloids, colloidal nanoparticles, silver colloids, 4–aminobiphenyl, melamine, cyanuric acid, nanotechnology