Nitrogen-sulfur co-doped pH-insensitive fluorescent carbon dots for high sensitive and selective hypochlorite detection.

Carbon dots (CDs) are novel fluorescent carbon nanomaterial with exceptional properties and have drawn great attention in recent years. However, the preparation and applications of high-quality carbon dots remain challenging. Here, we describe a simple hydrothermal synthesis route using citric acid as a carbon source for stable fluorescent CDs. The CDs are modified with glutathione and exhibit high fluorescent quantum yields (30.2%) and excellent photo-stability. In addition, the fluorescence intensity of CDs remains stable over a wide range of pH values (3-12). Hypochlorite (ClO) can effectively quench the fluorescence of the CDs by destroying the pyrrolic ring and conjugate structure of the CDs. Thus, the CDs can be used to detect ClO. Under optimized conditions, the fluorescence intensity changes of CDs correspond selectively to ClO in the range of 100-800 nmol/L with a LOD of 16 nmol/L. Practical applications of the proposed method for free chlorine detection in tap water show similar results and recovery compared to the standard DPD-based method. These results suggest that the pH-insensitive CDs prepared via this facile procedure are a promising chemosensor for free chlorine and have great potential in analytical applications.