High-Performance Ni–N–C Single-Atom Nanozyme with Enhanced Peroxidase-like Activity for Ultrasensitive Detection of Uranyl Ions in Seawater

The development of highly active and specific nanozymes is crucial for advancing sensitive colorimetric sensing platforms. Herein, we report a rationally designed nickel single-atom nanozyme (Ni-SAzyme), derived from a Ni-doped ZIF-8 precursor, which exhibits dramatically enhanced peroxidase (POD)-like activity. Comprehensive spectroscopic characterization and density functional theory calculations reveal that the atomically dispersed Ni–N4 sites facilitate the activation of H2O2 to generate hydroxyl radicals (·OH) as the primary reactive oxygen species. This process is responsible for the superior catalytic efficiency. Based on this exceptional POD-like activity, we developed a facile and rapid colorimetric sensor for uranyl ion (UO22+) detection. The sensing strategy relies on the UO22+-enhanced catalytic oxidation of ABTS, yielding a distinct color change. This method achieves an exceptionally low detection limit of 0.031 μM (7.378 ppb), high selectivity against interfering ions, and successful application in the determination of UO22+ in complex seawater samples with satisfactory recoveries. This work not only provides a novel strategy for designing efficient SAzymes but also offers a robust and practical sensing platform for environmental monitoring.