Cu-MOF derived CuO@g-C 3 N 4 nanozyme for cascade catalytic colorimetric sensing

The use of peroxidase mimics has great potential for various real applications due to their strong catalytic activity. Herein, a facile strategy was proposed to directly prepare CuO@g-C 3 N 4 by Cu-MOF derivatization and demonstrated its efficacy in constructing a multiple enzymatic cascade system by loading protein enzymes onto it. The resulting CuO@g-C 3 N 4 possessed high peroxidase-like activity, with a Michaelis constant ( K m ) of 0.25 and 0.16 mM for H 2 O 2 and 3,3’,5,5’-tetramethylbenzidine (TMB), respectively. Additionally, the high surface area of CuO@g-C 3 N 4 facilitated the loading of protein enzymes and maintained their activity over an extended period, expanding the potential applications of CuO@g-C 3 N 4 . To test its feasibility, CuO@g-C 3 N 4 /protein oxidase complex was prepared and used to sense the ripeness and freshness of fruits and meat, respectively. The mechanism relied on the fact that the ripeness of fruits increased and freshness of food decreased with the release of marked targets, such as glucose and xanthine, which could produce H 2 O 2 when digested by the corresponding oxidase. The peroxidase mimics of CuO@g-C 3 N 4 could then sensitively colorimetric detect H 2 O 2 in present of TMB. The obtained CuO@g-C 3 N 4 /oxidase complex exhibited an excellent linear response to glucose or xanthine in the range of 1.0–120 μmol/L or 8.0–350 μmol/L, respectively. Furthermore, accurate quantification of glucose and xanthine in real samples is achieved with spiked recoveries ranging from 80.2% to 120.0% and from 94.2% to 112.0%, respectively. Overall, this work demonstrates the potential of CuO@g-C 3 N 4 in various practical applications, such as food freshness detection. Graphical Abstract