Adsorption and aggregation characteristics of silver nanoparticles onto a poly(4-vinylpyridine) film: a comparison with gold nanoparticles.

The adsorption and aggregation processes of Ag nanoparticles versus Au nanoparticles onto a poly(4-vinylpyridine) (P4VP) surface has been investigated by means of quartz crystal microbalance (QCM), atomic force microscopy (AFM), and Raman scattering spectroscopy. Both the QCM and AFM data indicated that the citrate-reduced Ag and Au nanoparticles are adsorbed onto P4VP, forming only approximately 30% and approximately 17% of surface coverage, respectively, even after 6 h of adsorption in solution. The P4VP film was too thin to observe its normal Raman spectrum, but the Raman peaks of P4VP could be detected upon the adsorption of Ag (or Au) nanoparticles onto the film, due to the surface-enhanced Raman scattering (SERS) effect associated with the localized surface plasmon of Ag (or Au) nanoparticles. When in contact with the solution of Ag (or Au) nanoparticles, the SERS peaks of P4VP thus increased linearly as a function of time, in a manner similar to that shown by the QCM and AFM data. In the interim, however, as the sol solution was drained, the SERS signal of P4VP was intensified about twice probably due to the aggregation of nanoparticles. Eventually, the SERS signal derived from the Ag nanoparticles became two times stronger than that from the same number of Au nanoparticles, at least under the 632.8 nm excitation, suggesting that Ag nanoparticles must be more advantageous than Au nanoparticles in elucidating by SERS the physicochemical characteristics of organic/polymeric surfaces and suggesting their likely advantages in metallic staining in immunoassays.