Portable analysis of tract mercury ions by a hydrogel-based ratiometric fluorescence sensor using C3N4-CdTe0.16S0.84 QDs nanocomposites

The portable detection of trace mercury ions (Hg2+) in water is crucial for preventing and controlling mercury pollution. In this study, graphitic carbon nitride nanoparticles (CNNPs) with green fluorescence as the self-calibration signal were synthesized by a one-pot solvothermal method. Cadmium telluride sulfide quantum dots (CdTe0.16S0.84 QDs) with red fluorescence as a response signal were prepared using an oxidation-reduction method. Thus, a new ratiometric fluorescence sensor based on CNNPs-CdTe0.16S0.84 QDs was constructed for the visual detection of trace Hg2+. The linear range of the sensor was from 0.05 to 2525 nM, with a detection limit of 0.009 nM. The sensor displayed higher sensitivity to Hg2+ compared to copper ions and silver ions. The fluorescence quenching behavior and the source of sensitivity for the three metal ions were investigated using the Stern-Volmer equation and density functional theory. The results suggest that the high sensitivity to Hg2+ may arise from electron transfer and electrostatic interactions between Hg2+ and CdTe0.16S0.84 QDs. Building on this proposed strategy, a new smartphone-assisted CNNPs-CdTe0.16S0.84 QDs hydrogel-based fluorescence sensor was constructed for portable on-site analysis of trace Hg2+. This new method will facilitate the on-site monitoring of hazardous substances in environmental water.