A nanozyme catalysis‐diazotization reaction cascaded ratiometric colorimetric assay probing the dynamics of nitrite in leftovers

Abstract As a common food additive, excessive nitrite poses a great threat to human health, and monitoring its content in food products is of importance for healthy diet. Currently, the detection of nitrite content in food is primarily focused on fresh dishes, and there is a lack of research on monitoring the variations of nitrite in different foods under various storage conditions. In this study, we cascaded nanozyme catalysis with diazotization reaction and developed a ratiometric colorimetric assay to dynamically analyze nitrite in leftovers. First, nanoscale MnFe 2 O 4 was synthesized as an oxidase mimic to catalyze colorless 3,3 ′ ,5,5 ′ ‐tetramethylbenzidine (TMB) oxidation to blue TMBox. Then, a diazotization process of the produced TMBox took place under the stimulation of nitrite, lowering the ultraviolet‐visible absorption signal (652 nm) assigned to TMBox and simultaneously generating a new signal at 445 nm ascribed to diazotized TMBox. Thus, a ratiometric colorimetric method could be constructed based on the above reversed variations of the two signals for high‐selectivity nitrite determination, providing a linear range of 1.76–180 μM and a detection limit of 0.12 μM. By employing the established assay to dynamically monitor nitrite in food products, it was found that the nitrite content in overnight leftovers was higher than that in fresh dishes, presenting an increasing trend with storage time. In addition, potential impacts of storage factors on the dynamics of nitrite content were investigated, providing some implications for food preservation and daily consumption.