Colorimetric sensor for pH monitoring of liquid samples using bubble wrap and mobile phone camera

In this study, we utilized low cost and easily available bubble wrap, homemade indicator solution (cabbage juice), and custom built mobile app based on color detection to find pH values of common liquid samples. We studied two common color definition models i.e. the Red, Green, Blue (RGB) and Hue, Saturation, and Light (HSL) to extract pH values of eight different liquids upon color change after reaction with cabbage juice. Our results show that the HSL based color definition model performs better than the RGB model for both calibration liquids (vinegar with pH=3 and bicarbonate soda pH=9) and eight target liquids with the pH range spanning from 2 to 13.