Portable point-of-care testing of food glutathione enabled by a high-performance sulfur-vacancy FeS mimetic enzyme

Glutathione (GSH) is a key bioactive substance that significantly influences food nutrition and safety. In this study, a novel colorimetric sensing platform was developed based on sulfur vacancy iron sulfide (SV-FeS) mimetic enzyme for rapid and quantitative detection of GSH in food samples. The mimetic enzyme features a three-dimensional (3D) micro-flower structure with high specific surface area, exhibiting exceptional peroxidase-like (POD-like) activity. The SV-FeS (pH = 3, 1h) mimetic enzyme demonstrates high substrate affinity with a low Michaelis constant (Kₘ) of 0.052 mM toward H₂O₂. In liquid-phase GSH detection, the sensor showed excellent linearity in the range of 5-100 μM (R² = 0.998) with a limit of detection (LOD) of 0.38 μM. To meet point-of-care testing (POCT) requirements, a microfluidic paper-based analytical devices (μPADs) integrated with a SV-FeS (pH = 3, 1 h) mimetic enzyme and a smartphone-based readout system was constructed. This sensor enables one-step GSH quantification within 5 min, achieving a linear range of 35-500 μM (R² = 0.990) and a LOD of 10.4 μM. In practical applications, the sensor demonstrated satisfactory performance with spiked recoveries of 95.5 %-102.5 %, relative standard deviation (RSD) below 8 %, and maintained stability for 15 days at 4 °C. This work provides an effective solution for on-site GSH detection in food quality and safety monitoring.