Cascading oxidoreductases-like nanozymes for high selective and sensitive fluorescent detection of ascorbic acid

Compared with natural enzymes, nanozymes have the advantages of high stability and low cost; however, selectivity and sensitivity are key issues that prevent their further development. In this study, we report a cascade nanozymatic system with significantly improved selectivity and sensitivity that combines more substrate-specific reactions and sensitive fluorescence detection. Taking detection of ascorbic acid (AA) as an example, a cascade catalytic reaction system consisting of oxidase-like N-doped carbon nanocages (NC) and peroxidase-like copper oxide (CuO) improved the reaction selectivity in transforming the substrate into the target product by more than 1200 times against the interference of uric acid. The cascade catalytic reaction system was also applicable for transfer from open reactors into a spatially confined microfluidic device, increasing the slope of the calibration curves by approximately 1000-fold with a linear detection range of 2.5 nmol/L to 100 nmol/L and a low limit of detection of 0.77 nmol/L. This work offers a new strategy that achieves significant improvements in selectivity and sensitivity.