Fluorescent/ratiometric colorimetric dual-node sensor based on Fe/N co-doped carbon dots for nitrite detection

Nitrite (NO₂^-) has been extensively utilized in the food industry as a preservative and colorant; however, excessive intake can lead to serious health issues, highlighting the need for accurate and efficient detection methods. In this work, blue fluorescent iron and nitrogen co-doped carbon dots (Fe/N-CDs) were synthesized via a one-step hydrothermal method using ferric chloride, ethylenediaminetetraacetic acid (EDTA), and diethylenetriamine (DETA) as precursors. The prepared Fe/N-CDs exhibited excellent peroxidase-like activity. By leveraging the catalytic activity of Fe/N-CDs and the oxidation and diazotization reactions induced by NO₂^-, we developed a dual-mode fluorescent and ratiometric colorimetric sensor for nitrite detection. The fluorescence and colorimetric methods had linear detection ranges of 2.5-75 μM and 2.5-100 μM, with detection limits of 0.68 μM and 1.19 μM, respectively. The developed dual-mode sensing platform was successfully applied to detect NO₂^- in both pickled vegetable and cured pork samples, demonstrating its feasibility in practical applications. Furthermore, the color of the reaction changed from blue to yellow as the NO₂^- concentration increased. Quantitative nitrite analysis was further achieved by capturing RGB values with smartphone-assisted color-recognition software, using the green-to-red (G/R) ratio as the analytical signal.