Chitosan functionalized nitrogen-doped carbon dot nanocomposites: a turn-on sensor for fluoride detection

The fluoride anion plays a vital role in human health by preventing dental caries and enhancing bone strength. However, excessive intake beyond the permissible limit poses a serious health risk. This underscores the critical need for accurate and routine monitoring of fluoride levels in water supplies. Traditional methods of fluoride detection are associated with many limitations and high hydration enthalpy of fluoride (Δ<i>H</i> = -504 kJ mol^-1), which additionally makes it challenging to design effective aqueous-phase fluorescent probes for fluoride. In this study, we report chitosan-functionalized N-doped carbon dots (N-CDs@C) as an environmentally friendly, cost-effective, and fluorescent probe for the selective and sensitive detection of fluoride ions in aqueous media. The interaction between N-CDs@C and fluoride likely occurs <i>via</i> hydrogen bonding and electrostatic interaction, which results in a fluorescence "turn-on" response for fluoride. The N-CDs@C probe exhibited a strong emission enhancement at 455 nm upon fluoride binding, with excellent selectivity, anti-interference performance, and a detection limit as low as 0.01 μM within a linear range of 0.12-0.50 μM. The practical utility of this sensor was demonstrated through successful application in real samples, including toothpaste and tap water with excellent recoveries ranging from 98.67-99.27% (RSD <2%).