Seed-Mediated Growth of Ag@Au Nanodisks with Improved Chemical Stability and Surface-Enhanced Raman Scattering

Bimetallic Ag@Au nanoparticles (NPs) have received significant research interest because of their unique optical properties and molecular sensing ability through surface-enhanced Raman scattering (SERS). However, the synthesis of Ag@Au core-shell plasmonic nanostructures with precisely controlled size and shape remained a great challenge. Here, we report a simple approach for the synthesis of bimetallic Ag@Au nanodisks of about 13.5 nm thickness and different diameters through a seed-mediated growth process. The synthesis involves the conformal deposition of Au atoms at the corner sites of Ag nanoplate (AgNPL) seeds coupled with site-selective oxidative etching of AgNPL edges to generate Ag@Au nanodisks. The resultant Ag@Au nanodisks manifest significantly improved chemical stability and tunable localized surface plasmon resonance from the visible to the near-infrared spectral range. Moreover, in comparison to AgNPLs, the Ag@Au nanodisks showed greatly enhanced SERS performance with an enhancement factor up to 0.47 × 10⁵, which is nearly 3-fold higher than that of the original AgNPLs (0.18 × 10⁵). Furthermore, the Ag@Au nanodisks show a high sensitivity for detecting probe molecules such as crystal violet of concentration as low as 10^-9 M and excellent reproducibility, with the SERS intensity fluctuation less than 12.5%. The synthesis route adapted for the controlled fabrication of Ag@Au nanodisks can be a potential platform for maneuvering other bimetallic plasmonic nanostructures useful for plasmonics and sensing applications.