Dual-channel fluorescence detection of mercuric (II) and glutathione by down- and up-conversion fluorescence carbon dots.

The fluorescent carbon dots (CDs) with high fluorescent quantum yield (φf = 62%) and down- and up-conversion fluorescence properties were synthesized by one-pot hydrothermal treatment of citric acid and tris(hydroxymethyl)methyl aminomethane. The CDs displayed the capability to absorb excitation wavelength at 660 nm and 330 nm with fluorescence emission wavelength at 398 nm and 399 nm, respectively. The CDs showed high selectivity towards Hg2+ against various metal ions. Around 70% fluorescence was quenched by 40 µM Hg2+ through dynamic and static quenching mechanisms. Because of stronger affinity between the thiol and Hg2+, over 90% fluorescence was recovered by adding 40 µM glutathione to CDs-Hg2+ system. The calibration curves exhibited wide linear region for Hg2+ (0-4 µM) and glutathione (0-30 µM). The limits of detection with down- and up-conversion for Hg2+ were calculated to be 0.23 µM and 0.25 µM, and for glutathione were 0.28 µM and 0.29 µM, respectively. Inspired by the sensing results, logic gates with Hg2+ and glutathione as inputs were also established. Most importantly, this method was applied to detect Hg2+ and glutathione in tap water and lake water, and the recovery values were obtained to be 96.2%-110.4% and 93.4%-96.9%.