Cu2+-Modified Boron Nitride Nanosheets-Supported Subnanometer Gold Nanoparticles: An Oxidase-Mimicking Nanoenzyme with Unexpected Oxidation Properties

In recent years, inorganic biomimetic nanozymes that mimic the activity of natural biological enzymes have attracted extensive research interest, and some mimic enzymes have been successfully applied in the fields of biosensing, catalysis, and oncotherapy. Herein, we report the preparation and mechanism study of a novel nanocomposite, Cu2+-modified hexagonal boron nitride nanosheets-supported subnanometer gold nanoparticles (Au NPs/Cu2+–BNNS). Interestingly, our investigation reveals that Cu2+–BNNS exhibits strong peroxidase mimetic nanoenzyme activity, while Au NPs/Cu2+–BNNS exhibits excellent oxidase-like activity, that is, it can catalyze the oxidation reaction of the substrate in the absence of an oxidant such as H2O2. For example, Au NPs/Cu2+–BNNS can efficiently and selectively oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) and 3,3′-dimethylbiphenyl-4,4′-diamine (OT) coloration without the presence of horseradish peroxidase (HRP) and H2O2. It is worthy to note that AuNPs/Cu2+–BNNS-induced TMB coloration only takes 4 min to reach the platform, while the conventional HRP–H2O2 system takes more than 30 min to reach the platform. Further mechanism study shows that the zeta potential, oxidation potential, and steric hindrance of the oxidative chromogenic substrate determine the selectivity of oxidation coloration, while the oxidase-like properties of Au NPs/Cu2+–BNNS are derived from reactive oxygen species generated by the adsorbed oxygen, and Cu2+ ion can synergistically promote the oxidation process. Compared with conventional biological enzymes, Au NPs/Cu2+–BNNS has the advantages of being HRP free and H2O2 free, having high efficiency, low cost, and good stability, and is successfully demonstrated for the detection of carcinoembryonic antigen (a universal cancer biomarker) and H2S (the third gaseous signal molecule).