Fluorimetric evaluation of glutathione reductase activity and its inhibitors using carbon quantum dots

A highly sensitive fluorimetric assay has been developed for the evaluation of glutathione reductase (GR) activity and the screening of its inhibitors by using carbon quantum dots (CQDs) as the signal reporter. The detection mechanism is based on the following facts: (1) the fluorescence of CQDs can be quenched by Hg(II) through the strong CQDs-Hg(II) coordination; (2) GR can catalyze the reduction of oxidized glutathione (GSSG) into reduced glutathione (GSH), so that the fluorescence recovery of CQDs would take place resulting from the strong GSH-Hg(II) interaction; (3) GR can lose its catalytic reduction of GSSG in the presence of its inhibitors, which will inhibit the recovery of the quenched fluorescence of CQDs. The developed CQDs-based fluorimetric method can facilitate the sensitive evaluation of GR activity in the range of 0.10-2.0mUmL^-1 with a detection limit of 0.050 mUmL^-1. In addition, other kinds of enzymes like myoglobin, thrombin, alcohol dehyrogenase, amylase, pepsin, and trypsin could show no significant effects on the evaluation of GR activity. This work may expand the biological applications of CQDs as the fluorescent probes with low cost, easy preparation, and high photostability.