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

Abstract

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.