Figure 2.

(A) Transmission electron microscopic images of Au/Ag core-shell nanoparticle colloids (left) and composite nanoparticles with 4-mercaptobenzoic acid (right); (B) ultraviolet-visible absorption spectra of pure Au/Ag core-shell nanoparticles colloid (black curve) and Au/Ag core-shell nanoparticles with 4-mercaptobenzoic acid (red curve); (C) surface-enhanced Raman scattering spectra of 4-mercaptobenzoic acid adsorbed onto gold nanoparticles, silver nanoparticles, and Au/Ag core-shell nanoparticles, respectively.