Selenium-doped Mn-N-C single-atom nanozymes with modulated electronic structure for ultrasensitive colorimetric biosensing of total antioxidant capacity in food samples.

Herein, we report a selenium-doped manganese-based single-atom nanozyme (MnNC-Se) with engineered electronic structure, and demonstrate its application as a high-performance colorimetric sensing probe for rapid assessment of total antioxidant capacity (TAC). Comprehensive XPS characterization confirms the successful covalent incorporation of Se into the N-doped carbon matrix, which strategically increases the content of pyridinic N (from 55.55% to 68.93%). This enriched pyridinic N provides robust coordination sites that optimize the electronic structure and induce a relative shift of Mn towards lower valence states. Benefiting from this optimized electronic environment, the MnNC-Se nanozyme exhibits a remarkable 16.8-fold enhancement in peroxidase-like activity compared to its undoped counterpart, with a maximum reaction rate (Vmax) of 4.6 × 10-7 M s-1 towards H2O2. On this basis, a colorimetric biosensing platform was constructed for TAC detection using ascorbic acid (AA) as the model antioxidant. The sensor displays excellent analytical performance with a linear detection range of 2-45 μM, a detection limit of 0.721 μM, and high selectivity against common interfering substances. Practical applicability was validated through spike-recovery experiments in vitamin C beverages and supplements, yielding satisfactory recoveries of 96.78-102.57% (RSD < 3%). This work not only provides a reliable sensing tool for TAC assessment in food quality control, but also demonstrates heteroatom doping as an effective strategy for engineering high-performance single-atom nanozymes toward practical biosensing applications.