Doping-engineered CuBDC MOF nanozymes for sensitive tannic acid detection and antioxidant discrimination

Ferrocenecarboxylic acid (Fc-COOH)-doped Cu-based MOF nanozyme (CuBDC/Fc, BDC = 1,4-benzenedicarboxylic acid) was designed via a doping modulation strategy. The Fc-COOH doping regulates morphology of the acquired CuBDC/Fc, forming a mesoporous architecture to enhance active site accessibility and substrate interaction. The introduction of Fe/Cu redox couples, i.e. Cu(II)/Cu(I) and Fe(III)/Fe(II), facilitates electron transfer and promotes the reactive oxygen species (ROS) generation, amplifying catalytic efficiency. The CuBDC/Fc exhibited a 667.5-fold rise in peroxidase-like activity relative to CuBDC. Five antioxidants in tea, i.e. quercetin, catechin, caffeic acid, tannic acid and rutin, display different inhibition actions on the CuBDC/Fc-H₂O₂-TMB system. A tri-channel colorimetric sensor array was constructed, achieving discrimination of above five antioxidants in 1-100 μM levels and their mixture in complex tea products, and sensitive quantification detection of tannic acid. This work not only designed a MOF-based high-performance peroxidase-mimicking nanozyme but also provided a promising strategy for antioxidant analysis in tea.