Pyrolysis-free and universal synthesis of metal-NC single-atom nanozymes with dual catalytic sites for cytoprotection

Metal-nitrogen-doped carbon single-atom nanozymes (M -NC SAzymes) have tremendous prospects to replace natural enzymes for the treatment of reactive oxygen species (ROS)-related diseases. However, developing a pyrolysis-free and universal synthesis of M -NC SAzymes with robust enzyme-mimicking activity still remains a challenge. Herein, a promising cytoprotective agent (Fe-NC SAzymes) with multiple enzyme-mimicking activities was fabricated based on the reaction of Schiff bases with Fe ions via one-pot solvothermal method. In Fe-NC SAzymes, Fe-Nx moieties served as the main catalytic sites to mimick oxidase, peroxidase, and catalase; mean-while, the co-catalytic sites of the pi-conjugated nitrogen-doped carbon structure mimicked superoxide dismutase to achieve the multiple enzyme-mimicking catalysis. Owing to the dual catalytic sites and pyrolysis-free synthesis strategy, Fe-NC SAzymes showed enhanced catalytic performance and excellent biocompatibility, which could scavenge excessive intracellular ROS to alleviate oxidative stress. The viability of cells subjected to oxidative stress recovered from 1.4% to 80.3% after Fe-NC SAzymes treatment, demonstrating an outstanding cytopro-tective performance. Remarkably, this synthetic strategy can be expanded to other metal-NC SAzymes (Cu, Mn, Co, Zn, and Ni), which provides a feasible route to design specific functional SAzymes for ROS-related diseases therapy.