Sensitive and selective colorimetric detection of glutathione in human plasma with 2,2′–azino–bis(3–ethylbenzothiazoline–6–sulfonic acid) and Ag⁺ ion

Glutathione is of vital importance to human beings through involving in many cellular functions. Simple and sensitive methods capable of detecting glutathione in biological samples are significant to diagnosis and prevention of disease. Here a simple, label–free, and sensitive colorimetric method was developed for the determination of glutathione. It was observed that Ag⁺ ion could directly oxidize 2,2′–azino–bis(3–ethylbenzothiazoline–6–sulfonic acid) (ABTS), a commonly used peroxidase substrate, to produce a green solution, which possessed a maximum absorbance at 420 nm. The presence of glutathione hindered the oxidation process and decreased the absorbance at 420 nm owing to its ability to bind with Ag⁺ ion. The procedure allowed the measurement of 0.1–4.0 μM glutathione with a detection limit of 59 nM. The relative standard deviation was 1.8% in eleven replicated measurements of 1.0 μM glutathione solution. The method was applied to the determination of glutathione in human plasma with satisfactory results.