Palladium-Coated Gold Nanoparticles with a Controlled Shell Thickness Used as Surface-Enhanced Raman Scattering Substrate

Abstract

We report the synthesis and characterization of gold core palladium shell (Au@Pd) nanoparticles with thickness-controlled shell as an improved transition-metal substrate for surface-enhanced Raman scattering (SERS). By changing the molar ratio of H2PdCl4 to Au, the Pd shell thickness can be precisely controlled from a few nanometers down to ca. one monolayer. A series of characterizations were performed using transmission electron microscopy (TEM), UV−vis, SERS, and electrochemical techniques. The results confirmed the core−shell structure and the uniform and pinhole-free nature of the Pd shell, ensuring the properties of Pd without possible interference from Au. Consistent with theoretical prediction, the core−shell setting borrows high SERS activity from the Au core through the long-range electromagnetic enhancement in addition to the enhancement from the Pd shell itself. Moreover, their SERS activity can be optimized by the tunable shell thickness and core size. The nm-Au@Pd/Pd electrodes allow us to o...