Synthesis and Characterization of Au@Co and Au@Ni Core−Shell Nanoparticles and Their Applications in Surface-Enhanced Raman Spectroscopy

Au@Co and Au@Ni core−shell nanoparticles with controllable shell thicknesses were prepared by reduction of Co2+ and Ni2+ salts with hydrazine hydrate in ethanol over preformed Au seeds. Both cyclic voltammetric and surface-enhanced Raman studies using CO as the probe molecule confirmed the core−shell structure of the synthesized nanoparticles. The Au@Co and Au@Ni nanoparticles dispersed on a glassy carbon electrode surface exhibit high surface-enhanced Raman scattering (SERS) effect for the adsorbed pyridine. High-quality SERS spectra of CO absorbed on Co and Ni have been obtained through the high enhancement of the core−shell nanoparticles. The originally low surface enhancement of the Co and Ni can be substantially improved giving total enhancement factors up to 103-104. Such a SERS-active substrate can be used as an alternative substrate for investigating adsorption and reactions occurring on the Co and Ni metal surfaces.