Array of Manganese-Based Bimetallic Metal–Organic-Framework Nanozymes with Enhanced Oxidase-like Catalytic Activity Can Simultaneously Identify and Measure Antioxidants

Developing sensitive and highly active nanozymes for antioxidant analysis is of the utmost significance in medical diagnosis and health monitoring due to their essential roles as free reactive oxygen species scavengers. Here, six metal-organic frameworks (MOFs)-based nanozymes are developed as a dual-mode absorbance/image analysis colorimetric sensor array for simultaneous discrimination and determination of various antioxidants with comparable structural or chemical properties. The catalysts exhibit a wide range of highly potent oxidase-like catalytic activities, as verified by kinetic parameters, due to the presence of highly dispersed transition metallic and bimetallic redox nodes. These nanozymes efficiently catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB_ox, resulting in noticeable absorption and RGB color changes at 650 nm. Various antioxidants demonstrate different reducing capabilities to TMB_ox, leading to the generation of fingerprint-like spectral color patterns. The pattern recognition chemometrics methods including principal component analysis (PCA) and linear discriminant analysis (LDA) represent well-separated clustering and discrimination of ascorbic acid, dopamine, uric acid, cysteine, glutathione, thiocyanate, tannic acid, and gallic acid. The colorimetric assay provides a wide linear detection range (0.1-75 μM) and detection limits as low as 30 nM. The sensor array successfully discriminated antioxidants of various concentrations, mixtures, and potent interferences. Furthermore, the sensor's applicability in biologically relevant detection was validated in urine and plasma samples. Overall, the MOF-based nanozyme sensor array offers a promising platform for discriminating and determining a wide range of antioxidants with potential applications.