Nitrogen and sulfur co-doped carbon dots: A facile and green fluorescence probe for free chlorine

•A sensitive and green fluorescence probe was developed for the detection of free chlorine.•The assay was based on fluorescence quenching of nitrogen and sulfur co-doped carbon dots.•The assay is high sensitivity and selectivity for detection of free chlorine in tap water.

Nitrogen and sulfur co-doped carbon dots (N,S-CDs) emitted strong blue fluorescence in aqueous solution, and it was found that the free chlorine could efficiently quench the fluorescence of the N,S-CDs, which was utilized as a sensitive, low-cost and green fluorescence probe for the detection of free chlorine. Under optimal conditions, a linear relationship between the decreased fluorescence intensity of N,S-CDs and the concentration of free chlorine in the range from 0.01 to 100 μM was obtained with a detection limit of 5 nM (3σ). The proposed method was successfully applied for the determination of free residual chlorine in tap water and swimming pool with quantitative recovery (91–106%). The developed N,S-CDs fluorescence probe provides a new and promising tool for the water quality monitoring in the environmental analysis fields with low cost and excellent performance.

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