Polyvinylpyrrolidone-stabilized ultra-small Fe3O4 nanoparticles-functionalized graphene oxide with synergistically enhanced peroxidase-like activity for glutathione colorimetric determination in rat serum

A highly efficient colorimetric sensor was developed for detecting glutathione using polyvinylpyrrolidone-stabilized ultra-small Fe 3 O 4 nanoparticles integrated with graphene oxide (GO-Fe 3 O 4 ). These nanoparticles are highly water-dispersible and uniformly distributed, enabling extensive interaction with the analyte and enhancing detection sensitivity. The integration of Fe 3 O 4 nanoparticles on the graphene oxide surface prevents aggregation and exposes more active sites, thereby enhancing their catalytic activity significantly. The GO-Fe 3 O 4 nanocomposites exhibit a dramatically enhanced Fenton reaction, showing a fourfold increase in catalytic effect compared to bare Fe 3 O 4 nanoparticles. This is attributed to the synergistic peroxidase-like activity within the 3,3′,5,5′-tetramethylbenzidine (TMB)-hydrogen peroxide colorimetric system. Moreover, the GO-Fe 3 O 4 nanozyme has an excellent binding affinity to TMB, which is up to tenfold higher than that of horseradish peroxidase. The TMB is catalyzed by the GO-Fe 3 O 4 nanozyme to produce a blue oxidized form, and the presence of glutathione selectively inhibits this color change. This inhibition forms the basis for the quantitative determination of glutathione. Under optimal conditions, the colorimetric sensor demonstrated a linear response to glutathione concentrations ranging from 0.1 to 10 μmol/L, with a detection limit as low as 9.17 nmol/L ( S/N  = 3). The developed method showcased excellent selectivity, reproducibility, and accuracy. It was effectively used to determine glutathione in rat serum samples and monitor its pharmacokinetics in vivo. Graphical