A "turn-on" fluorescent probe for glutathione detection based on the polyethylenimine-carbon dots-Cu²⁺ system

Glutathione (GSH) plays critical roles in many physiological processes usually present in live cells, and altered levels have been linked to some clinical pathological conditions. However, current techniques of GSH detection with fluorescence assay strategies remain poorly researched. In this work, branched polyethylenimine-functionalized carbon dots (PEI-CDs) are synthesized by simple hydrothermal treatment of glucose and PEI. The fluorescence of the PEI-CDs could be efficiently quenched by Cu²⁺ and then recovered by some biothiols. Basing on this, a "turn-on" fluorescent probe for detecting GSH has been developed using PEI-CDs-Cu²⁺ system. Compared with traditional probes for GSH detection, a significant advantage of the PEI-CDs-Cu²⁺ system is that it can be used for GSH detection at both low and high concentrations with different concentration combinations of PEI-CDs and Cu²⁺. More specifically, two good linear relationships are achieved in the ranges of 0-80 μM and 0-1400 μM for GSH, respectively. Correspondingly, the detection limits of GSH are 0.33 μM and 9.49 μM, respectively. The quantum yields (QYs) of PEI-CDs and PEI-CDs-Cu²⁺+GSH was 9.6% and 4.2%, respectively. Moreover, the PEI-CDs-Cu²⁺ has excellent optical stability and good biocompatibility. Additionally, it is worth noting that the developed probe has successfully realized the visualization of GSH detection in MGC-803 cells.