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

Background Rapid, low-cost measurement of glutathione (GSH) is valuable for judging food freshness. However, many colorimetric assays depend on natural enzymes or added H 2 O 2 , which limits stability and use in real samples. Results We developed a manganese single-atom enzyme (Mn/SAE) with intrinsic oxidase-like activity to build an enzyme-free, H 2 O 2 -free colorimetric system for GSH. Mn/SAE uses dissolved O 2 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. Significance This simple, low-cost, and portable approach enables on-site GSH analysis without enzymes or H 2 O 2 . The Mn/SAE colorimetric system offers practical value for freshness monitoring and can be adapted to other redox biomarkers in food-quality assessment.