AgAu Hollow Nanoshells on Layered Graphene Oxide and Silica Submicrospheres as Plasmonic Nanozymes for Light-Enhanced Electrochemical H₂O₂ Sensing

Localized surface plasmon resonance (LSPR) is a phenomenon derived from the interaction between light and nanostructures, and its outcomes have been explored mainly for applications in surface-enhanced Raman spectroscopy (SERS), phototherapy, and catalysis. Bimetallic nanostructures are able to synergically combine the properties of two different metals to create a tuned response to LSPR according to their composition, shape, and morphology. In this study, an in situ synthesis of AgAu bimetallic hollow nanoshells (NS) over layered graphene oxide (GO) and silica submicrospheres (SiO₂) is presented. The synthesized structures acted as peroxidase-like nanozymes in the plasmon-enhanced electrochemical sensing of H₂O₂. The nanozymes were submitted to 405, 533, and 650 nm laser irradiation while performing the hydrogen peroxide reduction reaction (HPRR) with a fast response speed (4 s), exhibiting enhancements in sensitivity of 122% (for Ag₇₉Au₂₁/GO at 533 nm, 787 μA mM^–1 cm^–2), 105% (for Ag₇₉Au₂₁/GO at 405 nm, 725 μA mM^–1 cm^–2), and 119% (for Ag₅₀Au₅₀/SiO₂ at 650 nm, 885 μA mM^–1 cm^–2) compared to the dark conditions when matching the LSPR band maximum for each synthesized structure. When laser stimuli did not match LSPR band maximum, lower enhancements were achieved in both cases. According to Michaelis–Menten enzyme kinetics, the nanozymes I_max followed the same LSPR bias and K_m^app was lowered after LSPR stimuli, showing the smallest values upon 405 nm irradiation (0.599 mM for Ag₇₉Au₂₁/GO and 0.228 mM for Ag₅₀Au₅₀/SiO₂) demonstrating increased substrate affinity in comparison to values previously reported in enzymatic and nonenzymatic biosensors of H₂O₂. Thus, we propose that LSPR is the main mechanism involved in the faster electron transfer rates and the consequent enhancement of electrochemical H₂O₂ sensitivities, I_max, and K_m^app by the bimetallic nanozymes synthesized by this approach.