Monodisperse Noble-Metal Nanoparticles and Their Surface Enhanced Raman Scattering Properties

Monodisperse Au, Ag, and Au3Pd nanoparticles (NPs) with narrow size distribution are prepared by direct reaction of the related metal salt with oleylamine in toluene. Oleylamine serves as both a reducing agent and a surfactant in the synthesis. The sizes and shape of these NPs are tuned by reaction temperatures. The hydrophobic oleylamine-coated NPs can be made water soluble by replacing oleylamine with 3-mercaptopropionic acid. Both surface plasmonic resonance (SPR) and surface enhanced Raman scattering (SERS) observed from the Au and Ag NPs are found to be NP size- and surface-dependent.