Self-cascade and self-activated nanozyme based on Au quantum dot modified covalent organic framework for rapid and sensitive detection of live bacteria

Multi-enzymes-guided cascade biocatalysis plays an important role in both nature and industry. Nevertheless, the inherent defects of natural enzymes (e.g., unattractive robustness, sensitivity, and reproducibility under severe catalytic environments) have limited their wider employment. Here, a self-cascade nanozyme was synthesized via depositing Au quantum dots (Au QDs) on iron ions and cysteine-doped porphyrin covalent organic framework (Fe@cpCOF). The in situ introduction of cysteine created a beneficial microenvironment around the iron-porphyrin catalytic center, facilitating the activity of the nanozyme. Through the regulation of Au QDs deposition amount on the surface of Fe@cpCOF, the synthetic nanozyme not only possessed robust glucose oxidase (GOx) mimicking activity but also demonstrated promoted peroxidase (POD) mimicking activity. In the self-cascade system, the innocuous glucose could be constantly transformed to sufficient gluconic acid and H₂O₂ by Au QDs, preventing the direct application of noxious H₂O₂ and reducing the detrimental by-effects. In addition, the product gluconic acid decreases the pH of the microenvironment, significantly activating the POD-like bioactivity of Fe@cpCOF. The obtained Au-Fe@cpCOF nanozyme was utilized to simulate the multi-step biocatalytic process in nature, thus constructing an enzyme-free self-cascade biocatalytic sensing platform for specific and wide-spectrum analysis of live bacteria. This study provides a facile assay for pathogen detection in both clinical and daily life.

Graphical Abstract