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.