Superhydrophobic\nPaper Strips with Embedded Agarose-Anthocyanin\nMini-Discs for Point-of-Need Quantitative pH Measurements

Commercial pH paper is a quick and simple tool for measuring\na\nsolution’s acidity/basicity, but it only provides qualitative\nor semi-quantitative results, and the synthetic indicator dyes within\ncan be toxic or carcinogenic. Although pH meters enable more accurate\nand quantitative analysis, they are less convenient to operate and\nare tedious to calibrate. This presents a need for an alternative\npH testing method for applications where it is not easy or possible\nto use a pH meter, yet quantitative results are desired. We report\nherein the fabrication of a pH test strip made from superhydrophobic\npaper and agarose-anthocyanin film discs. In the proposed method,\ntest strips are dipped into samples and then imaged with a portable\nscanner (or a smartphone). The color of the film is extracted with\nImageJ software (or a mobile app), using the RGB color system. By\ngenerating a calibration curve relating the film color to the sample\npH using standard buffer solutions, we are able to quantify the pH\nof beverages and other liquids with an accuracy and precision comparable\nto that of a pH meter. The test strips offer the same convenience\nas conventional pH paper, with the added capabilities of quantitation\nand multiplexed testing, which presents a practical tool for point-of-need\npH analysis.