Colorimetric Detection of Antioxidants in Food Samples Using MnO₂/Graphene Quantum Dot Composites with Oxidase-like Activity

Recently, strategies for developing colorimetric sensors relying on nanozymes for the detection of analytes of health, food, and environmental interest have gained significant importance. Herein, a rapid and sensitive colorimetric assay based on manganese dioxide/graphene quantum dot (MnO2/GQD) composites was developed for the detection of antioxidants in food. The composite, synthesized by a hydrothermal method, served as a nanozyme with outstanding oxidase-like catalytic activity to trigger the 3,3′,5,5′-tetramethybenzidine (TMB) chromogenic reaction. Then, an assay was performed to evaluate the reducing ability of antioxidants toward oxTMB by detecting color changes during the procedure. The colorimetric method achieved high selectivity and sensitivity toward the detection of gallic acid, tannic acid, and ascorbic acid with detection limits (S/N = 3) of 0.07, 0.28, and 0.69 μmol L–1, respectively. Moreover, the assay was used to accurately measure and discriminate the antioxidants in real food samples, revealing its great promise for portable and rapid food analysis.