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, ...