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

The fluorescent carbon dots (CDs) with high fluorescent quantum yield (φ_f = 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%.