A novel fluorescence sensor for the detection of chloride ion in artificial sweat and environmental water with nitrogen-doped graphene quantum dots

A new fluorescent detection route for chloride ion was designed with Nitrogen-doped graphene quantum dots (N-GQDs), which were prepared by a traditional hydrothermal method with citric acid as carbon source and urea as nitrogen source. The prepared N-GQDs solution was light yellow, and the freeze-dried solid was black. It emitted blue light under ultraviolet light. Meanwhile, The N-GQDs were characterized by TEM, XRD, UV-Vis and fluorescence, the results indicated that the N-GQDs had good dispersibility, photostability and excitation independent emission fluorescence. After addition of Ag+ solution, Ag+ combined to the surface functional groups of N-GQDs, resulting in an obvious quenching of the fluorescence intensity of N-GQDs. Nevertheless, the fluorescence intensity recovered significantly with the addition of Cl- to the N-GQDs/Ag+ system, this was because of AgCl was formed due to the “soft hard acid base principle”. The change of fluorescence intensity had a linear response to the chloride ion concentration in the range of 8.5-300 μmol L-1, with a detection limit (LOD) of 0.1 μmol L-1. To authenticate the application, the proposed method has been successfully used for quantitative analysis of chloride ion in real samples, including artificial sweat and environmental water.