Visible light enhanced peroxidase-mimetic activity of Fe-N-C functionalized Ti₃C₂T_x MXene for rapid colorimetric quantification of total antioxidant capacity

Rapid and reliable determinations of total antioxidant capacity (TAC) are critical to the assessments of food quality and safety. Traditional spectrophotometric assays are severely bottlenecked by prolonged incubation times, while conventional nanozymes frequently suffer from sluggish reaction kinetics, severely restricting their on-site rapid detection applications. This study fabricated a highly dispersed Fe-N-C functionalized Ti₃C₂T_x MXene nanozyme with highly visible light enhanced peroxidase-mimetic activity. Stable Fe-N_x active sites immobilized on conductive MXene, combined with narrowing engineered interface bandgap, achieve highly efficient reaction kinetics. Under visible light irradiation, this nanozyme catalyst accelerates electron transfer through a multi-pathway radical mechanism. It promotes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and achieves a strong signal within 1 min, which effectively eliminates the lengthy radical pre-generation time of traditional methods. Based on the competitive inhibition of TMB oxidation by antioxidants, a colorimetric platform was developed for a sensitive TAC quantification. This platform was successfully applied to typical antioxidants of ascorbic acid, glutathione, l-cysteine and Trolox. Furthermore, the proposed method showed promising consistency with the standard TEAC methods in real samples' detections, yielding a relative error of less than 5%. Overall, this work provides a paradigm to transcend nanozyme catalytic limitations via synergistic decoration and photo-activation, offering a rapid, low-cost analytical method for food safety.