Design and fabrication of hollow metal-azolate framework derivatives with dual-functional nanozyme activity for dual-mode detection of total antioxidant capacity in fruits.

BACKGROUND: Total antioxidant activity (TAC) is an important indicator for evaluating the comprehensive antioxidant capacity of food, and its accurate detection is of great significance for assessing the health value of food and guiding dietary choices.

RESULTS: In this study, a colorimetric and smartphone-assisted dual-mode sensing platform was constructed for the detection of TAC based on Fe doped hollow carbon nitride compound (h-Fe@NC). Systematic characterization indicated that the formed Fe-N coordination structure significantly enhanced the catalytic performance of h-Fe@NC. The h-Fe@NC possesses both peroxidase-like and oxidase-like activities, showing high affinity for substrates TMB and H2O2. Mechanism studies revealed that h-Fe@NC could catalyze H2O2 to generate O2•- and •OH radicals, which in turn oxidized TMB to produce a significant increase in absorbance and solution color. The catalytic process was calculated using density functional theory, demonstrating that h-Fe@NC exhibits high nanozyme catalytic activity. Using ascorbic acid (AA) as a typical antioxidant to capture the above radicals could inhibit the color reaction, causing a reverse change in absorbance and color. Based on this, a dual-mode detection method based on absorbance and color signals was established, exhibiting a wide linear range of 1.0-40 μM and a low detection limit of 0.41 μM. What is more, it was successfully applied to the quantitative analysis of TAC in orange, grape, and kiwi fruit samples, and the results were in good agreement with those obtained by the standard method.

SIGNIFICANCE: This research provides a new strategy for the rapid and sensitive detection of TAC in fruits.