Fabrication of high-performance artificial antioxidant enzyme (AAE) systems based on a single nanozyme possessing multi-enzymatic activities is fascinating but challenging. Here, polyvinylpyrrolidone (PVP)–platinum–copper nanoparticle clusters (PVP-PtCuNCs) are prepared by a facile one-pot chemical coreduction method. PVP-PtCuNCs possess efficient superoxide dismutase (SOD)-like, peroxidase (POD)-like, and catalase (CAT)-like activities, and the multi-enzymatic activities depend on the bimetal component and cluster structure. Compared with individual platinum nanoparticle clusters (PVP-PtNCs), PVP-PtCuNCs can effectively eliminate reactive oxygen species (ROS) including superoxide anions, hydrogen peroxide, and hydroxyl radicals. The doping of copper not only reduces the usage of Pt content but also improves the catalytic efficiency and versatility effectively through the synergistic effect of bimetal components and the nanocluster structure. The results not only demonstrate that a single bimetallic nanozyme has the potential as an efficient AAE system in the biomedical application but also demonstrate that traditional concepts of structure–activity relationships can be used to fabricate nanozymes with the desired multi-enzymatic activities.

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The single function and weak catalytic activity of nonprecious metal nanozymes distinctly hinder their practical applications, so it is intriguing to develop multifunctional nanozymes via a facile and green route. Here, for the first time, “bottom–up” strategies were used to realize the efficient synthesis of MnO2 quantum dots (QDs) with simple operation and mild reaction conditions based on proteins, avoiding the operation complexity of the traditional “up–down” approach. More interestingly, MnO2 QDs exhibit extraordinarily outstanding catechol oxidase-like activity. QD nanozymes can catalyze the oxidation of dopamine (DA) into DA quinone in just 2 min, and then DA quinone polymerizes to form PDA in more than 10 min at 37 °C over a broad pH range (above pH 7.4). Based on the catechol oxidase-like activity and the interaction between QDs with a DA quinone-induced passivation effect, a “turn-on” fluorescence sensor based on two sequential recognitions for DA with self-signal output is developed without using the commonly used chromogenic reactions. The dual recognition provides the sensor with extremely good selectivity, which removes the interference from common reducible substances and metal ions. The detection limit can reach 0.038 μM, and the sensor has good specificity and a short detection time (just 2 min) under mild conditions. This offers a flexible guide for rational design and fabrication of FL turn-on biosensors for redox-active dopamine and enriches our understanding of QD nanozymes in bioanalytical fields.