Sulfur vacancy promoted peroxidase-like activity of magnetic greigite (Fe3S4) for colorimetric detection of serum glucose

Herein, sulfur vacancies in magnetic greigite (SVs-Fe 3 S 4 ) nanosheets were synthesized by a one-step solvothermal method by adjusting the ethylene glycol : water ratio. Electron paramagnetic resonance spectroscopy (EPR) and X-ray photoelectron spectroscopy (XPS) revealed that SV-rich Fe 3 S 4 and SV-poor Fe 3 S 4 were acquired using 100% ethylene glycol and 100% water as solvent, respectively. A peroxidase-like activity assay demonstrated that maximum reaction rates for H 2 O 2 -mediated oxidation of 3,3′,5,5′-tetramethyl-benzidine (TMB) catalyzed by the SV-rich Fe 3 S 4 was 2.3 times higher than SV-poor Fe 3 S 4 . Density functional theory (DFT) calculations and reactive oxygen species (ROS) detection confirmed that the enhanced peroxidase-like activity by SV-rich Fe 3 S 4 was attributed to efficient adsorption of H 2 O 2 and subsequent decomposition to hydroxyl radicals (•OH) on the SVs sites of Fe 3 S 4 . The SV-rich Fe 3 S 4 nanozyme was employed to develop a simple, highly sensitive and selective assay for glucose detection with a linear range of 0.5–150 μM and a detection limit of 0.1 μM (S/N = 3). A smartphone application (App) was designed and applied to efficiently detect serum glucose with the integrated analytical system based on the SV-rich Fe 3 S 4 . These new findings highlight the important role of surface defects in nanozymes on generating peroxidase-like activity for glucose detection in point-of-care diagnosis.