[SERS of positive silver colloids with addition of aggregating agent]

A very strong surface-enhanced Raman scattering (SERS) spectrum was obtained when adding some aggregating agent such as HNO3 and NaNO3 in positive silver colloid reduced by citrate using 633 nm radiation. In aid of characterizing the SERS of this process, SERS from positive silver colloid with the addition of H2SO3, HCl, and NH3 recorded. It was found that the SERS come from the citrate when adding HNO3, NaNO3 and H2 SO3, from NH3 and citrate when adding NH3, and only from Ag-Cl when adding HCl through comparing the spectra. Furthermore, the surface layer of positive silver colloid particles could be Ag+ , and the diffusion layer could be citrate.