Sulfur-enhanced Fe-N-C single-atom Nanozymes for rapid and sensitive colorimetric detection of H₂O₂ and AA

In this study, sulfur-doped Fe-N-C single-atom nanozymes (FeNC-SO_x SAzyme) were successfully synthesized via a simple pyrolysis method. The FeNC-SO_x SAzyme exhibits exceptional peroxidase-like activity, enabling rapid detection of hydrogen peroxide (H₂O₂) and ascorbic acid (AA) in food samples. The catalytic mechanism involves the generation of hydroxyl radicals (·OH) from H₂O₂, which oxidizes colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxTMB, while AA reduces oxTMB back to TMB by scavenging ·OH. The optimized colorimetric method demonstrates high sensitivity, with detection limits of 0.479 μM for H₂O₂ and 0.5 μM for AA. It also exhibits excellent selectivity against interfering ions and biomolecules. Practical applications in milk and fruit samples yielded recoveries of 99.45-101.38 % for H₂O₂ and accurate quantification of AA in beverages and fruits. The FeNC-SO_x SAzyme-based sensor offers a rapid, cost-effective, and visually accessible platform for food safety monitoring, showing significant potential for real-world applications in clinical and environmental fields.