Peroxidase-like single Fe atoms anchored on Ti₃C₂T_x MXene as surface enhanced Raman scattering substrate for the simultaneous discrimination of multiple antioxidants

Single-atom nanozymes (SAzymes) are emerging as promising alternatives to mimic natural enzyme, which is due to high atomic utilization efficiency, well-defined geometric, and unique electronic structure. Herein, Fe single atoms supported on Ti₃C₂T_x (Fe-SA/Ti₃C₂T_x) with intrinsic peroxidase activity is developed, further constructing a sensitive Raman sensor array for sensing of five antioxidants. Fe-SA/Ti₃C₂T_x shows excellent peroxidase-like performance in catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with colorimetric reactions. X-ray adsorption fine structure (XAFS) reveals that the electron transport between the Ti₃C₂T_x and Fe atoms occurs along Fe-O-Ti ligands, meanwhile the density functional theory (DFT) calculations confirm the spontaneous dissociation of H₂O₂ and the formation of OH radicals. Furthermore, the peroxidase-like Fe-SA/Ti₃C₂T_x was used as surface enhanced Raman scattering (SERS) substrate of oxidized TMB (TMB⁺) and achieved satisfied signal amplification performance. Using the blocking effects of free radical reactions, one-off identification of 5 antioxidants, including ascorbic acid (AA), uric acid (UA), glutathione (GSH), melatonin (Mel), and tea polyphenols (TPP), could be realized with this high identifiable catalytic property. This principle could realize 100% distinguish accuracy combined with linear discriminant analysis (LDA) and heat map data analysis. A wide detection concentration ranges from 10⁻⁸ to 10⁻³ M for five antioxidants was also achieved.