Probing glutathione reductase activity with graphene quantum dots and gold nanoparticles system

Abstract

Graphene quantum dots (GQDs) and gold nanoparticles (AuNPs) were combined for probing glutathione reductase (GR) activity. The main probing mechanism is based on the following facts: (1) The fluorescence of GQDs can be quenched by AuNPs through fluorescence resonance energy transfer (FRET). (2) Reduced glutathione (GSH) can protect AuNPs from being aggregated and enlarge the inter-particle distance between GQDs and AuNPs, which subsequently produces the fluorescent signal recovery. (3) AuNPs has much weaker affinity towards oxidized glutathione (GSSG) in contrast to GSH. (4) GR can catalyze the reduction of GSSG into GSH in the presence of coenzyme β-nicotinamide adenine dinucleotide 2′-phophate hydrate (NADPH). Based on these facts, a turn-on fluorescent assay for GR has thus been developed based on the GQDs-AuNPs system. The proposed assay can allow for the evaluation of GR activity in the range of 0.0050–0.13 mU/mL, with a minimum detectable concentration of 0.0050 mU/mL, which was more than one order of magnitude lower than most of the current sensing platforms. Besides, this GQDs-AuNPs based GR assay was successfully applied for screening the inhibitor of GR activity by using 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) as a model.