Surface micro/nanostructure evolution of Au-Ag alloy nanoplates: Synthesis, simulation, plasmonic photothermal and surface-enhanced Raman scattering applications

This study reports the controllable surface roughening of Au-Ag alloy nanoplates via the galvanic replacement reaction between single-crystalline triangular Ag nanoplates and HAuCl4 in an aqueous medium. With a combination of experimental evidence and finite element method (FEM) simulations, improved electromagnetic field (E-field) enhancement around the surface-roughened Au-Ag nanoplates and tunable light absorption in the near-infrared (NIR) region (similar to 800-1,400 nm) are achieved by the synergistic effects of the localized surface plasmon resonance (LSPR) from the maintained triangular shape, the controllable Au-Ag alloy composition, and the increased surface roughness. The NIR light extinction enables an active photothermal effect as well as a high photothermal conversion efficiency (78.5%). The well-maintained triangular shape, surface-roughened evolutions of both micro- and nanostructures, and tunable NIR surface plasmon resonance effect enable potential applications of the Au-Ag alloy nanoplates in surface-enhanced Raman spectroscopic detection of biomolecules through 785-nm laser excitation.