We prepared Au/Ag core-shell nanoparticles by growing Ag shell onto 12 nm Au core, using silver nitrate and sodium citrate as the reactants. By changing the molar ratio of Ag to Au, the shell thickness and thus the size of bimetallic particles could be controlled in convenient way. The formation of core-shell structure was proved by UV-Vis spectra, transmission electron microscopy(TEM), etc.. The core-shell particles showed a more narrow size distribution than Ag colloid prepared without Au core. The SERS activity of the core-shell particles was investigated by using 2,4-dimethylpyridine as the probe, which strongly indicated their potential application in SERS substrate materials.
