Single-Atom IronNanozymes Anchored on Graphitic N‑DopedCarbon for Visual Alkaline Phosphatase Detection

The types of nitrogen atoms in single-atom nanozymes are of paramount importance to their enzyme-like catalytic activity. Herein, we report that single-atom iron nanozymes anchored on graphitic nitrogen-doped porous carbon (g-FeN₄) could serve as efficient oxidase mimics. The g-FeN₄ was found to display 1.6 times higher catalytic activity than pyridinic nitrogen-dominated single-atom iron nanozymes (FeN₄). Combined with experiments and theoretical simulations, it is shown that graphitic nitrogen could effectively regulate the charge distribution at the Fe active site, thereby accelerating O₂ activation and thus enhancing its oxidase-like activity. As a concept verification application, we constructed an ultrasensitive alkaline phosphatase activity assay method, integrating a smartphone as a colorimetric reader, based on the superior oxidase activity of g-FeN₄. This study not only unravels the significant effect of nitrogen types on the activity of single-atom nanozymes but also provides important guidance for designing highly efficient single-atom nanozymes.