High-Activity OXD-like MnOx Nanozymes: H2O2-Free Signal Amplification Strategy for Ultrasensitive Colorimetric Assay of Antioxidants in Fruit Juice

Total antioxidant capacity represents a critical parameter for assessing food quality and freshness, while conventional detection methodologies are often constrained by operational intricacy or insufficient efficiency. Herein, we developed a rapid and user-friendly colorimetric sensing platform based on manganese oxide (MnOx) nanozymes for the quantification of antioxidants in fruit juice samples. MnOx nanozymes can efficiently catalyze the oxidation of the colorless substrate 3,3′,5,5′-tetramethylbenzidine, yielding a blue reaction product; however, the presence of antioxidants significantly suppresses this catalytic activity, inducing concentration-dependent color shifts in the reaction system. After systematic optimization of key reaction parameters (e.g., nanozyme concentration, TMB dosage, reaction temperature, and incubation time), the proposed platform achieved a detection limit of 1.79 μM, with a naked - eye visual detection limit of 5 μM and a total detection time of <10 min. Practical validation in real fruit juice samples verified the accuracy of the developed method for antioxidant quantification, as evidenced by recovery rates of 88.76%–109.10% and RSDs of all below 3.44%.This work introduces a novel, efficient, and stable approach for the rapid monitoring of TAC in food products, exhibiting considerable potential for food quality control and safety assessment.