Au/Ag alloy nanostructure with built-in hotspots fabricated by galvanic-replacement-assisted growth on AgI for surface-enhanced Raman spectroscopy

Plasmonic metal nanostructures with interior nanogaps are of great interest for surface-enhanced Raman scattering (SERS) applications. Template synthesis is widely used to produce porous plasmonic metal nanostructures. However, the produced gaps strongly depend on the template size and shape; thus, nanogaps for use as hotspots for SERS applications are difficult to produce. Herein, we demonstrate that Au/Ag alloy nanostructures with efficient nanogaps were achieved on AgI nanorods with the assistance of a galvanic replacement reaction. Diethylamine played a key role in tuning the in situ reduction of Ag⁺ ions to Ag on AgI nanorods, enabling the simultaneous deposition of Au on AgI and the galvanic replacement of Ag in a controlled manner, rather than simple nonepitaxial growth. Numerical simulations and experimental results suggest that these Au/Ag alloy nanostructures possess strong internal hotspots for high sensitivity in SERS analysis. We believe that this strategy can broaden the synthesis of plasmonic metal nanostructures with efficient hotspots for a broad range of applications.