Dual-mode colorimetric/fluorescent film for visual detection of nitrite in food

A sensing film capable of reporting nitrite levels through two optical pathways was fabricated by embedding N-CDs and NED into a PVA matrix. In this sensing film, NED undergoes a Griess-type coupling reaction, resulting in a red color, while the fluorescence of N-CDs decreases as the nitrite concentration increases. These two changes can be used for both quantification and simple visual checks. Under the best conditions, the fluorescence and colorimetric methods had limit of detection of 0.204 μg/mL and 0.178 μg/mL, respectively. A visible color change occurred at about 1.5 μg/mL, allowing for evaluation without instruments. The sensing film was tested on various food samples, such as processed meats, milk products, and vegetable extracts, with results closely matching those from the Griess method. These findings show that this dual-mode platform is practical for quick and sensitive nitrite detection in food analysis.