Specific dual-mode fluorometric and colorimetric detection of nitrite based on oxidase-like activity of carbon dots/iron alkoxide composite

Trace detection of nitrite in food has gained increasing attention due to its connection with biological and environmental processes. Herein, a dual-mode fluorometric/colorimetric sensor is established for nitrite detection by combining the oxidase-like activity of iron alkoxide (IA) with the bimodal excitation properties of nitrogen-doped carbon dots (N-CDs). IA oxidizes the colorless 3,3′,5,5′-tetramethylbenzidine into blue-colored 3,3′,5,5′-tetramethylbenzidine oxide. Subsequently, nitrite further triggers a diazotization reaction, resulting in a color change from blue to green. Simultaneously, the fluorescence intensity of N-CDs at 470 nm decreases significantly, while the signal at 371 nm remains nearly unchanged, owing to the localized inner filter effect. Satisfactory results are attained with low limits of detection of 49 nM in the fluorometric mode and 73 nM in the colorimetric mode. Furthermore, an intelligent lateral flow assay platform is established for the visual detection of nitrite. Therefore, this work provides innovative guidance for nitrite detection in food safety.