Metal nanoclusters engineered interfacial adsorption for enhanced ROS independent oxidase-mimicking activity

Recently, reactive oxygen species (ROS)-independent mimetics of oxidase with Au nanoclusters (NCs) as the catalysts and MnO₂ as electron acceptor have gained attention. In this study, we aim to explore the oxidase-mimicking potential of bovine serum albumin (BSA)-templated metal nanoclusters (BSA-M NCs, where M = Ag, Pt, Cu, or Cd) beyond Au NCs in boosting the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by MnO₂, denoted as BM@Metal. The oxidase-mimetic activity of BM@Metal is independent of ROS and generally enhanced by the incorporation of metal nanoclusters. Notably, this enhancement varies with the metal species, with BSA-Cd exhibiting the highest activity. The X-ray photoelectron spectroscopy (XPS) analysis confirms mixed valence states (Mn(IV)/Mn(II)) in BM@Cd. Given that the catalytic activity is closely linked to the substrate adsorption, the label-free isothermal titration calorimetry was employed to probe the affinity between TMB and BSA-M NCs, which provides a robust approach for probing the interface adsorption. The results reveal that the superior catalytic performance of BSA-Cd correlates with enhanced TMB adsorption, likely facilitated by coordination and hydrophobic interactions. Finally, the superior catalytic performance of BSA-M NCs on the oxidation of TMB by MnO₂ has inspired us to fabricate the assay for analyzing α-glucosidase’s activity. This work not only demonstrates the versatility of metal NCs in constructing ROS-independent oxidase mimetics but also provides interfacial adsorption engineered strategy for the rational design of superior ROS independent mimetics of natural oxidase.