Nitrogen and sulfur co-doped carbon dots for ratiometric fluorometric determination of mercury ions

Abstract Nitrogen and sulfur co-doped carbon dots (N,S-CDs) were prepared for dual-channel ratiometric fluorescence determination of mercury ions (Hg²⁺). The dual-emission N,S-CDs were synthesized using a simple one-pot hydrothermal treatment. When excited with visible light, N,S-CDs exhibited two emission peaks at 390 and 500 nm. Notably, the presence of Hg²⁺ caused a considerable decrease in the fluorescence of N,S-CDs at 500 nm, mainly due to the static quenching effect. In comparison, the fluorescence at 390 nm was almost unchanged. With a limit of detection (LOD) of 0.21 µM for Hg²⁺, the N,S-CDs were successfully applied to the unlabeled ratiometric fluorescence determination of Hg²⁺ in actual water samples with good recoveries (94.5–107.8%). In conclusion, this developed ratiometric fluorescent sensor provides a reliable, environmentally friendly, rapid, and efficient platform for detecting Hg²⁺ in environmental applications.