Au@Ag core-shell nanocubes: epitaxial growth synthesis and surface-enhanced Raman scattering performance.

Novel Au@Ag core-shell nanocubes (NCs) were successfully prepared by the controlled epitaxial growth of Ag shells onto Au nanoellipsoids (NEs) in the presence of surfactants. The growth mechanism of the Au@Ag core-shell NCs was systematically investigated by analyzing their morphology, optical properties, and crystallography. The localized surface plasmon resonance (LSPR) characteristics and the electric field distribution of the Au@Ag core-shell NCs were studied using the finite element method (FEM) based on the plasmon hybridization theory. Compared with pure Ag NCs, the absorption spectrum of the Au@Ag core-shell NCs exhibits a red shift and a weak shoulder near 550 nm, and the notable enhancement of electric field occurs around the corners along the long-axis of the Au ellipsoidal core because of plasmonic resonant coupling. Surface-enhanced Raman scattering (SERS) of the Au@Ag core-shell NCs labeled with 4-mercaptobenzoic acid molecules reveals that the bimetallic core-shell NCs possess efficient SERS activity with an enhancement factor EF = 2.27 × 10(6), thus confirming the possibility of using the Au@Ag core-shell NCs as a stable probe for SERS-based biosensing applications.