Bioinspired iron porphyrin covalent organic framework nanozyme with peroxidase-like activity for ratiometric colorimetric and portable swab-assisted detection of nitrite in food samples.

Nitrite (NO2-), a common food additive with excess risks, requires fast reliable detection for food safety. Herein, a biomimetic iron porphyrin-based covalent organic framework (Fe-Por COF) was designed as a peroxidase-like nanozyme for colorimetric NO2- detection. It efficiently catalyzed H2O2-mediated TMB oxidation to blue oxidized TMB, which specifically reacted with NO2- under acidic conditions to form a yellow diazo compound-causing visible color change and ratiometric absorbance shift (652 nm to 450 nm). This method exhibited a wide linear of 0.5-250 μM with a low detection limit of 0.43 μM. It was also successfully validated in complex food samples (smoked pork, pickled vegetable, and sausage) with recoveries of 96.8 %-105.6 %. Integrating Fe-Por COF with swabs, a portable colorimetric platform was developed for on-site detection of NO2-. This study presents an innovative strategy for effective and on-site detection of nitrite in food industry applications.