Polyethylenimine-functionalized nitrogen and sulfur co-doped carbon dots as effective fluorescent probes for detection of Hg ions.

Surface modification of nitrogen and sulfur co-doped carbon quantum dots (N, S-CDs) were performed using cysteine and polyethylenimine as raw materials. The prepared N, S-CDs exhibited excitation-independent in the range of 300-380 nm. Furthermore, mercury(II) ions (Hg) can effectively quench the fluorescence intensity of the N, S-CDs. Based on this, we developed a fluorescence sensor with high sensitivity and selectivity to detect Hg. Under optimized conditions, the sensor showed good linearity in the range of 0-500 nM, and the limit of detection is 9.2 nM. Further, the sensor showed high sensitivity to Hg in lake water and rice samples. The recovery of the Hg in lake water and rice samples ranged between 98.2 % and 109.5 % with a relative standard deviation below 5.8 %. With outstanding sensitivity and selectivity, the fluorescence sensor provides a promising platform for monitoring Hg in real samples.