Hollow Mn/Co‐MOF as a Powerful Oxidase‐Like Nanozyme for Detection of Total Antioxidant Capacity and Black Tea Fermentation Degree

The detection of total antioxidant capacity (TAC) in teas and its vital indicator for monitoring the fermentation degree during black tea processing are of great significance for intelligent manufacturing of the tea industry. Here, highly dispersed manganese species on Co-MOF with hollow structures (HS-Mn/Co-MOF) nanozyme with superior oxidase-like activity is constructed for colorimetric detection of ascorbic acid (AA) and TAC. Owing to the Mn doping and unique hollow structures, the HS-Mn/Co-MOF nanozyme possesses more surface active oxygen species, negative surface charges and rapid mass transport, thus resulting in 20-times higher catalytic activity and 30-times higher reaction rate than that of pure Co-MOF. Thanks to the remarkable oxidase-like catalytic activity, the HS-Mn/Co-MOF nanozyme-based colorimetric sensor exhibits a wide linear range of 0.01-120 µm, along with a low detection limit of 3 nm for AA detection. Additionally, the determination of TAC levels in real tea samples is further achieved and different tea types can be effectively distinguished by utilizing HS-Mn/Co-MOF nanozyme. Identification and prediction of the fermentation quality during the black tea fermentation process using nanozyme combined with machine learning are realized for the first time.