Carbon dots-based dual-mode sensor for highly selective detection of nitrite in food substrates through diazo coupling reaction.

As an antioxidant and preservative agent, nitrite (NO) plays an essential role in the food industry to maintain freshness or inhibit microbial growth. However, excessive addition of NO is detrimental to health, so accurate and portable detection of NO is critical for food quality control. Notably, the selectivity of most carbon dots (CDs)-based fluorescence sensors was not enough due to the nonspecific interaction mechanism of hydrogen bond, electrostatic interaction and inner filter effect etc. Herein, a novel fluorescence/UV-vis absorption (FL/UV-vis) dual-mode sensor was developed on basis of mC-CDs, which were prepared by simple solvothermal treatment of m-Phenylenediamine (m-PDA) and cyanidin cation (CC). The fluorescence of these mC-CDs could be selectively responded by NO through the specific diazo coupling reaction between NO and amino groups on the surface of mC-CDs, thus effectively improving the selectivity of NO detection. The CDs-based fluorescence sensor possessed a low detection limit of 0.091 μM and 0.143 μM for FL and UV-vis methods and the excellent linear range of 0.0-60.0 μM. Furthermore, the mC-CDs sensor was employed to detect NO in real samples with a recovery rate of 97.11 %-104.15 % for quantitative addition. Moreover, the smartphone-assisted fluorescence sensing platform developed could identify the subtle color changes that could not be distinguished by the naked eye, and had the advantages of fast detection speed and intelligence. More importantly, the portable solid phase sensor based on mC-CDs had been successfully applied to the specific fluorescence identification and concentration monitoring of NO. Accordingly, the designed sensor provided a new strategy for the highly selective and convenient sensing of NO in food substrates, and paved the way for the wide application of CDs-based nanomaterials in the detection of food safety.