Red-emission carbon dots as fluorescent on-off-on probe for highly sensitive and selective detection of Cu2+ and glutathione

A highly sensitive and selective fluorescent on-off-on strategy is established for the synchronous detection of Cu2+ and glutathione in aqueous solution. Red carbon dots (R-CDs) were prepared by using precursors of 4,5-difluoro-1,2-phenylenediamine and citric acid via a one-step hydrothermal strategy. R-CDs show a relatively long fluorescence lifetime of 3.47 ns under 455 nm excitation and high absolute fluorescent quantum yield of 20.1% with an excitation wavelength of 550 nm. R-CDs exhibit a marked pH-responsive fluorescence property with no significant perturbation from pH 4 to pH 13 even after five cycles. R-CDs with higher concentration of 750 mu g.mL(-1) exhibit no significant cytotoxicity and good biocompatibility on HeLa cells and A549 cells after incubation for 48 h. The fluorescence of R-CDs at 619 nm (excited at 550 nm) is quenched statically by Cu2+ and recovered by glutathione subsequently, resulting in a fluorescent on-off-on assay for the synchronous detection of Cu2+ and glutathione. Under optimal conditions, the linear response covers the Cu2+ concentration range of 1 to 50 mu M and the glutathione concentration range of 1 to 70 mu M. Detection limits of Cu2+ and glutathione are 0.16 and 0.41 mu M, respectively. This fluorescent probe is applied to the determination of Cu2+ and glutathione in authentic samples with satisfying results. Such an assay broadens the potential application of CDs in environmental areas and clinical therapy fields.

Automated summary

This study establishes a sensitive and selective fluorescent on-off-on strategy for the synchronous detection of Cu2+ and glutathione in aqueous solution. The red carbon dots (R-CDs) used in this strategy show a long fluorescence lifetime and high quantum yield. The R-CDs exhibit a pH-responsive property and have low cytotoxicity. The assay can cover a wide range of Cu2+ and glutathione concentrations with low detection limits.