Engineering sulfur vacancies in NiCo2S4 flower-like structure to achieve exceptional peroxidase activity for advanced colorimetric biomedical diagnostics

NiCo 2 S 4 has garnered significant attention in biochemical analysis as an enzyme mimic due to its peroxidase-like activity. However, its catalytic properties have not been fully explored, limiting its application, particularly in biomedical diagnostics for low-abundance biomolecules. The catalytic activity of nanozymes is closely linked to their interface structure, and sulfur vacancies (SVs) have shown considerable promise in enhancing nanozyme activity. In this work, we synthesized SVs-NiCo 2 S 4 with a flower-like structure and NiCo 2 S 4 with a sphere-like structure with varying SV concentrations by modulating the reaction solvent, utilizing the NiCo-glycerate metal-organic framework as a template. The SVs-NiCo 2 S 4 demonstrated a remarkable catalytic efficiency of 3.85 times higher than NiCo 2 S 4 with fewer SVs. This nanozyme effectively facilitated the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in H 2 O 2 , leading to a strong color response. Density functional theory (DFT) calculations and hydroxyl radicals (·OH) detection confirmed that the enhanced peroxidase-mimicking activity of SVs-NiCo 2 S 4 was attributed to its efficient adsorption of H 2 O 2 and subsequent decomposition into ·OH on the SVs sites of SVs-NiCo 2 S 4 . Based on these findings, we developed an enhanced colorimetric detection method for glutathione (GSH) utilizing the peroxidase-mimicking properties of SVs-NiCo 2 S 4 . Compared to NiCo 2 S 4 , SVs-NiCo 2 S 4 exhibited greater sensitivity for GSH detection, with a linear range spanning six orders of magnitude from 5 nM to 50 nM and 70 nM to 130 μM, alongside a detection limit of 1.55 nM. A deeper understanding of the mechanisms underlying the SVs can provide valuable insights for developing high-performance nanozymes and biosensors, thereby expanding the potential applications of NiCo 2 S 4 in biosensing and medical diagnostics.