N-doped carbon dots for highly sensitive and selective sensing of copper ion and sulfide anion in lake water

Water contamination by copper ions (Cu2+) and sulfide anions (S2-) has been a longstanding human health hazard. The limitations of current detection strategies have created a high demand for effectively monitoring the concentrations of these ions in water systems. A facile fluorescent bioassay for Cu2+ and S2- was developed in this study based on on-off-on fluorescent nitrogen-doped carbon dots (N-CDs). N-CDs were synthesized for the first time via thermal treatment using hexamethylene-tetramine and ammonium citrate precursors. The obtained CDs were highly stable in aqueous solution, with a strong green emission and a 51.2% quantum yield. The maximum fluorescence emission peak was observed at 478 nm for a 360-nm excitation. Notably, the fluorescence intensity of N-CDs can be quenched by a factor of 6 by Cu2+, which can be applied to Cu2+ assays ranging from 0.05 to 5 mu M with a limit of detection (LOD) of 25 nM. Interestingly, further addition of S2recovered the fluorescence of the N-CD@Cu2+ nanocomplex, which can be used to quantify S2in a broad range from 0.05 to 10 mu M with an LOD of 32 nM. The N-CD and N-CD@Cu2+ nanocomplexes were also demonstrated to be highly specific towards Cu2+ and S2-, respectively. Finally, the sensor was successfully applied to lake water for detecting both Cu2+ and S2-, demonstrating excellent application prospects for analytical chemistry and environmental remediation.

Automated summary

A facile fluorescent bioassay for Cu2+ and S2- based on nitrogen-doped carbon dots was developed in this study. The method showed excellent specificity and stability, with high sensitivity for detecting both ions in lake water. This approach holds great promise for applications in analytical chemistry and environmental remediation.