New Trick from Old Dog: Probing the Light-Responsive Oxidase Mimic Activity of Au Nanoclusterzymes for Dual-Channel Biosensing

Although gold nanoclusters have been widely studied as nanoclusterzymes, their practical applications are limited by the requirement of unstable H₂O₂ when leveraging their typical peroxidase-like activity. Herein, the bovine serum albumin-protected gold nanoclusters (BSA-AuNCs) are found to exhibit visible light-responsive oxidase-like (L-OXD-like) activity, which can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to its oxidation state (ox-TMB) without requiring H₂O₂. The experimental study and theoretical calculation manifest that the photoinduced reactive oxygen species like singlet oxygen (¹O₂) and superoxide anion (•O₂^-), as well as part of the photogenerated holes, are found to be contributory to the high L-OXD-like activity. Furthermore, Förster resonance energy transfer and inner filter effects jointly quench the fluorescence of BSA-AuNCs in the oxidized TMB system. This dual-signal response (colorimetric signal from ox-TMB formation and fluorescent signal from fluorescence quenching) forms the basis of a versatile dual-mode biosensing platform. To demonstrate its utility, a proof-of-concept assay for α-glucosidase activity and the inhibitor is established using this photoexcited BSA-AuNC system. This work indicates the promise of BSA-AuNC nanoclusters in applications beyond biosensing that require controllable ROS generation.