Study of chemical processes involved in silver staining of gold nanostructures by Raman scattering

Strong Raman enhancement contributed by "hot spots" in directly fused gold dimers offer a selective and sensitive tool for understanding the surface processes involved in the silver staining of gold nanostructures. These processes include the interactions of cations, effects of surface adsorbed Cl(-) ions, surface replacement of ligands, and reduction of silver ions on the surface of the gold nanocrystals. Results show that in the commonly applied silver staining scheme for gold nanostructures, i.e., the addition of the Raman probe after the deposition of the silver shell, the Raman signals of the probe (p-mercaptobenzoic acid) were weakened greatly, due to the pre-existence of the Cl(-)-Ag(+)-citrate bridges on the surface of the gold. A new scheme was developed for silver deposition after pre-adsorption of the probe, which achieved a Raman enhancement factor as high as ∼5 × 10(8).