N, P and S co-doped red fluorescent carbon dots sensing for nitrite by fluorescent/colorimetric/smart phone/test strip methods through diazo coupling reaction in food samples.

Nitrite is limited to apply in meat products as colorant, which probably leads to food poisoning and increased cancer risk when excessively consumed. Consequently, the development of simple and sensitive methods for the detection of nitrite is indispensable. N, P and S co-doped carbon dots emitting red fluorescence (R-CDs) are prepared by the one-step hydrothermal strategy with o-phenylenediamine, p-aminobenzoic acid, sulfuric acid and phosphoric acid as precursors. The optimal excitation and emission wavelengths of R-CDs are 567 nm and 632 nm (the fluorescence quantum yield of 0.23), respectively. And the prepared R-CDs have satisfactory photostability at room temperature. The R-CDs are in possession of high selectivity for nitrite with the response time of 5 min that could be applied to fluorescence and ratiometric absorption spectra dual-mode detection for nitrite with the fluorescence detection range of 5.00-67.50 µM and the detection limit (LOD) of 0.89 µM. The fluorescence of R-CDs at 632 nm could be statically quenched by NO. Subsequently, the detection range of ratio absorption method is 10.00-180.00 µM whose correlation coefficient is 0.9999 and the LOD is calculated to be 0.27 µM. Ultimately, the R-CDs-based smart phone and strip sensing methods are established to achieve the simple detection for nitrite. The constructed fluorescence and absorption spectroscopy-based sensing methods have expansive application prospect as a rapid and improvised strategy for the detection of nitrite in daily life.