Peroxidase-like activity of hollow sphere-like FeS/SC boosted by synergistic action of defects and S-C bonding.

Pyrite FeS has been applied as a peroxidase due to its easy preparation and low cost. However, the low peroxidase-like (POD) activity limited its wide application. A hollow sphere-like composite (FeS/SC-5.3%) composed of pyrite FeS and sulfur-doped hollow sphere-shaped carbon was synthesized by a facile solvothermal method, where the S-doped carbon was formed during FeS formation. The synergistic action such as the defects at the carbon surface and the formation of S-C bonding improved the nanozyme activity. The S-C bonding was a bridge between the carbon and the Fe atom in FeS, which enhanced the electron transfer between the Fe atom and the carbon and accelerated the conversion from Fe to Fe. The optimum experimental conditions were obtained by the response surface methodology (RSM). The POD-like activity of FeS/SC-5.3% was significantly improved compared to that of FeS. The Michaelis-Menten constant () of FeS/SC-5.3% is 80 times lower than that of horseradish peroxidase (HRP, natural enzyme). FeS/SC-5.3% can be used to detect cysteine (Cys) with a limit of detection (LOD) as small as 0.061 μM at room temperature in only 1 min.