Inbuilt self-cascade catalysis of the bimetal-confined structural nanozyme CoNi@CNTs-N/GO for increased bienzymatic activity and HO-free smartphone-based visual assay of total antioxidant capacity in foods.

The level of total antioxidant capacity (TAC) reflects the overall ability of food to resist oxidative damage, maintain quality and nutritional stability. In this work, we pioneered a CoNi alloy-confined N-doped carbon nanozyme (CoNi@CNT-N/GO) with a self-cascade catalysis. Compared to other nanozymes, the synergistic effect of OXD and POD realized self-sustained generation of HO, eliminating the need of exogenous addition, and further decomposition of HO into ·OH and oxidizes colorless 3,3',5,5'- tetramethylbenzidine (TMB) to blue oxTMB as an efficient catalyst. The integration of multiple components and the built-in unique mechanism enhance bienzymatic activity. A "Thing Identify" APP was utilized to construct a smartphone-based visualization platform, demonstrating satisfactory linearity (0.01-1.2 mM) and low detection limit (3.3 μM) in TAC detection of real-world foods. This platform yielded data comparable to those from commercially colorimetric kits. Overall, it proposes a novel idea for engineering multi-functional and non-additional HO nanozymes in on-site food-quality monitoring.