Peroxidase-like activity of hollow sphere-like FeS2/SC boosted by synergistic action of defects and S–C bonding

Abstract

Pyrite FeS₂ 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 (FeS₂/SC-5.3%) composed of pyrite FeS₂ and sulfur-doped hollow sphere-shaped carbon was synthesized by a facile solvothermal method, where the S-doped carbon was in situ formed during FeS₂ 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 FeS₂, which enhanced the electron transfer between the Fe atom and the carbon and accelerated the conversion from Fe³⁺ to Fe²⁺. The optimum experimental conditions were obtained by the response surface methodology (RSM). The POD-like activity of FeS₂/SC-5.3% was significantly improved compared to that of FeS₂. The Michaelis–Menten constant (K_m) of FeS₂/SC-5.3% is 80 times lower than that of horseradish peroxidase (HRP, natural enzyme). FeS₂/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.