Dual-emission carbon dots achieved by luminescence center modulation within one-pot synthesis for a fluorescent ratiometric probe of pH, Hg2+, and glutathione

Dual-emission carbon dots were synthesized by one-pot hydrothermal pyrolysis of citric acid and polyethyleneimine in the presence of rhodamine B at 160 °C for 5 h. The carbon dots have an average diameter of 2.51 nm with rhodamine moiety on their surface. Two emission bands centered at 447 and 581 nm are exhibited in their fluorescence spectra excited at 360 nm, and the former is sensitive while the latter is insensitive to Hg2+ and pH. Glutathione (GSH) can recover the fluorescence quenched by Hg2+. Therefore, the dual-emission carbon dots were developed as a fluorescent ratiometric probe employing the ratio of the two intensities at 447 and 581 nm (RI447/I581) as the signal for the determinations of pH, Hg2+, and GSH. In the range of 5.0–10.0, a good linear relationship between RI447/I581 and pH was built with a regression equation of RI447/I581 = 11.95–0.56 pH (R2 = 0.998). In the range from 0.0 to 8.0 μM, an excellent linear relationship between RI447/I581 and the concentration of Hg2+ was obtained with a calibration equation of RI447/I581 = 6.2317–0.4458c (R2 = 0.995) and a limit of detection (LOD) of 0.24 μM. In the range from 1.0 to 10.0 μM, a linear equation, RI447/I581 = 1.9133–0.4157c (R2 = 0.995), was calibrated between RI447/I581 and the concentration of glutathione with a LOD of 0.27 μM. The recoveries for the determinations of Hg2+ and GSH in real samples were in the ranges of 94.6 to 103.8% and 94.3 to 104.2%, respectively.