Sensitive glutathione S-transferase assay based on Fe-doped hollow carbon nanospheres with oxidase-like activity

Nanozymes, as ideal alternatives to natural enzymes, have great prospects in the biosensor field due to their remarkable catalytic activity, gratifying stability, and low cost. Herein, a new oxidase-like nanozyme with Fe-doped hollow carbon spheres (Fe/HCS) was prepared. Abundant active oxygen species (1O2) are generated by the interaction of the Fe/HCS with dissolved oxygen. Then, colorless 3,3′,5,5′-tetramethylbenzidine (TMB) is oxidized to blue oxidized TMB (oxTMB), while glutathione (GSH) can reduce oxTMB, resulting in fading of the blue color. In addition, glutathione S-transferase (GST) catalyzes the conjugation reaction between GSH and 1-chloro-2,4-dinitrobenzene (CDNB) to form an adduct, which decreases the reducibility of GSH. Therefore, a direct and sensitive colorimetric method for the detection of the glutathione S-transferase activity was established, which exhibited a linear detection range of 0.001–0.02 U·L−1 and an ultralow detection limit of 0.565 mU·L−1. This colorimetric method was successfully applied to the detection of glutathione S-transferase in human serum samples, providing a new route for the application of nanozymes in biosensing techniques.