Self-cascade reaction catalyzed by CuO nanoparticle-based dual-functional enzyme mimics

•CuO nanoparticle-based dual-functional enzyme mimics.•CuO nanoparticle as an artificial enzyme substitute for cysteine oxidase.•CuO nanoparticle as an artificial enzyme substitute for peroxidase.•A self-organized cascade reaction system based on a single-component nanozyme.•A fluorometric assay method is established for cysteine determination.

It is desirable but challenging to assemble various biomimetic properties into a functional catalytic cascade system. In this work, cupric oxide nanoparticles were investigated as oxidase mimics for the aerobic oxidation of cysteine to cystine with the generation of hydrogen peroxide. Coupling this property with the peroxidase-like activity of CuO nanoparticles, we constructed a self-organized cascade reaction system based on a single-component nanozyme, which includes the oxidation of cysteine to yield cystine and hydrogen peroxide and the hydrogen peroxide-mediated oxidation of terephthalic acid to produce a fluorescence change. Based on this artificial enzymatic cascade reaction system, a fluorometric assay method with a low detection limit of 6.6 nM was established for cysteine determination. This platform was then applied for the detection of cysteine in pharmaceutical products and human plasma, which yielded satisfactory results. Our investigations open up a new route and holds promise for the development and applications of multifunctional nanomaterials as enzyme mimics.