2,4-Dinitrobenzenesulfonate-functionalized carbon dots as a turn-on fluorescent probe for imaging of biothiols in living cells

The authors describe a carbon dot-based fluorescent probe for biothiols. Green emissive carbon dots (g-CDs; with λ ex /λ em maxima of 407/505 nm) were synthesized by a one-step solvothermal method starting from 3-diethylaminophenol. They were then covalently functionalized with 2,4-dinitrobenzenesulfonyl chloride to afford 2,4-Dinitrobenzenesulfonate-functionalized CDs (g-CD-DNBS) as a nanoprobe for biothiols. The fluorescence of the g-CD-DNBS is quite weak. Upon addition of biothiols, the DNBS group of the probe is removed by thiol groups. This results in gradual restoration of the green fluorescence. The nanoprobe exhibits high selectivity for biothiols over other amino acids and biological molecules. The detection limits for cysteine, homocysteine and glutathione are 69, 74 and 69 nM (S/ N  = 3), respectively. The probe was applied to image biothiols in SMMC-7721 cells. Schematic presentation of the mechanism of 2,4-dinitrobenzenesulfonate-functionalized carbon dots (g-CD-DNBS) for the detection of biothiols. g-CDs: green emissive carbon dots.