A feasible image-based colorimetric assay using a smartphone RGB camera for point-of-care monitoring of diabetes.

Urinary glucose determination using a glucose test strip is simple and convenient in daily self-monitoring of diabetes. However, diabetic patients exhibit acquired impaired color vision (ICV), which results in the inability to discriminate between hues. Even with the assistance of a color chart, it is still not easy for these patients to read the urinary glucose results with the naked eye. In this study, a smartphone camera using an image-based colorimetric detection method was successfully developed for quantitative analysis of urine glucose. A horseradish peroxidase-hydrogen peroxide-3,3'5,5'-tetramethylbenzidine (HRP-H2O2-TMB) system was optimized for a reliable and gradual color fading process via a glucose oxidase (GOD) catalyzed oxidation reaction. The color changes of the peroxidase-H2O2 enzymatic reactions in the 96-well microplate were captured by a smartphone RGB camera with subsequent detection of red, green, and blue (RGB) intensities decreasing at each image pixel. The highly quantitative relationships between the glucose concentrations and the color characteristic values of the blue channel of the captured images were successfully established. The high accuracy of this method was demonstrated in urine glucose measurements with a linear response over the 0.039 mg mL-1 to 10.000 mg mL-1 glucose concentration range and a 0.009 mg mL-1 detection limit. The method has great potential as a point-of-need platform for diabetic patients with defective color vision and features high accuracy and low cost.