Applying smartphone camera, spectrophotometry, or ocular analysis-based dipsticks for the detection of glutathione level as a cancer biomarker

This study provides simple sensitive and selective spot tests and spectrophotometric methods for quantifying l-glutathione (GSH) as a cancer biomarker. The dipsticks are based on filter paper containing a Cu(II)-murexide complex which was prepared in phosphate buffer pH 6.0 and then incorporated inside a filter paper matrix. On addition of GSH, the spots' color progressively changed from yellow to orange through pink to violet before gradually vanishing. The indicator is released when GSH is injected because GSH displaces murexide dye from the murexide-Cu2+ complex. This enables the determination of glutathione in human serum visually using the reflectometric Red-Green-Blue (RGB) interpretation of the dipstick image data. In the spectrophotometric method, the Cu2+-murexide complex absorbance band is gradually red-shifted upon interaction with different concentrations of glutathione due to the displacement reaction.Glutathione can be determined from 0.01 to 500 μg mL−1 visually and from the evaluation of the smartphone images. The limit of detection for glutathione determination using dipsticks is 0.01 μg mL−1, which is the lowest value to date. This technique has been successfully used with positive outcomes to identify low concentrations of glutathione in samples of human serum.