Construction of a CuO@PDA Nanozyme with Switchable Dual Enzyme-Mimic Activities for Colorimetric Sensing of Catechol and Hydroquinone.

The development of metal-based redox nanozymes represents a new frontier in pollutant sensing. In this field, designing highly active nanozymes and precisely regulating their enzymatic activity are key challenges. In this work, we report the construction of a copper peroxide@polydopamine (CuO@PDA) nanozyme with dual enzyme-like activity, mimicking the active centers of laccase and peroxidase. Here, CuO acts as the catalytic center, while PDA serves as a carrier to prevent CuO aggregation and promotes conversion of Cu/Cu active sites via the reduction effect of its surface catechol groups to complete the catalytic cycle. As expected, the obtained CuO@PDA nanozyme exhibits significant laccase- and peroxidase-mimetic activities. Moreover, its dual enzymatic activity can be systematically switched by adjusting pH and temperature. Specifically, laccase activity dominates near neutral pH, while CuO decomposition into Cu ions and HO at acidic pH triggers peroxidase activity. Similarly, CuO@PDA exhibits temperature-dependent dual enzymatic activity with peroxidase activity prevailing at low temperatures and laccase activity at high temperatures. According to enzymatic performance and XPS results, a possible catalytic mechanism of the dual enzymatic activity of CuO@PDA has been proposed. Then, based on the pH-dependent dual enzymatic activity of CuO@PDA, we constructed a detection system for the isomers of organic pollutants, catechol (CC) and hydroquinone (HQ). The laccase-like activity of CuO@PDA enables direct oxidation of CC into yellow o-benzoquinone, while HQ discolors the preoxidized substrate generated via the peroxidase-like activity of CuO@PDA. Moreover, selective sensing for CC and HQ with high sensitivity was achieved in real water samples. This approach can guide the design of nanozymes with multienzymatic activity and unveil their potential uses in environmental pollutant discrimination.