Dissolved-O2-driven Mn single-atom enzyme for colorimetric detection of glutathione in food.

Abstract

Rapid, low-cost measurement of glutathione (GSH) is valuable for judging food freshness. However, many colorimetric assays depend on natural enzymes or added H2O2, which limits stability and use in real samples. We developed a manganese single-atom enzyme (Mn/SAE) with intrinsic oxidase-like activity to build an enzyme-free, H2O2-free colorimetric system for GSH. Mn/SAE uses dissolved O2 to oxidize TMB to blue oxTMB; GSH reduces oxTMB back to TMB, producing a decrease in color and absorbance for readout. Under optimized conditions, both the solution assay and a paper-based analytical device (PAD) provide results within 10 min using smartphone R-channel quantification. The method shows good selectivity and performs well in real samples, tracking the expected decline of GSH in strawberries during storage. This simple, low-cost, and portable approach enables on-site GSH analysis without enzymes or H2O2. The Mn/SAE colorimetric system offers practical value for freshness monitoring and can be adapted to other redox biomarkers in food-quality assessment.