A dual-mode fluorometric and colorimetric sensor based on N-doped carbon dots for selective and sensitive detection of nitrite in food samples

A highly sensitive and selective nitrite sensing platform based on nitrogen-doped carbon quantum dots (N-CDs), by means of a headspace single drop microextraction process, was constructed for dual-mode fluorometric and visual colorimetric determination of nitrite. In this system, the two-channel selective sensing of nitrite was achieved at the same time, with color ranging from colorless to red and N-CDs fluorescence quenching gradually. Meanwhile, gaseous NO was generated from the redox chemical vapor generation process and further extracted into a single drop, which effectively improving the analytical sensitivity and alleviating the matrix interference. By fluorescence and colorimetry, the limits of detection were calculated to be 0.03 and 0.08 μg mL-1, respectively, while 0.8 μg mL-1 nitrite was discernable by the naked eye. This method was utilized to analysis of diversified real food samples (vegetables, milk and ham), and the results were proved to be nearly consistent with a standard method. Furthermore, the storage conditions of vegetable juice have also been explored.