Mobile Phone-based Colorimetric Detection of Perfluorocarboxylic Acids using Porphyrin Hosts

Perfluorinated carboxylic acids (PFCAs) are widespread, potentially harmful, and difficult to detect pollutants. Here we investigate the use of three colorimetric porphyrin host molecules with chain lengths derived from different PFCA precursors as visual sensors for a range of different sized perfluorocarboxylates. We found that modifications to the length of the fluorinated chains led to subtleties in binding preferences and the resultant colorimetric (RGB) response. Host-guest interactions were investigated with UV-visible spectroscopy, and ImageJ software analysis was used to relate RGB information from digital photographs with binding and perceived colors. The CIE76 formula for color difference was used for the visual estimation of PFCA concentrations from generated color charts. Color responses were also parameterized to generate calibration curves from known concentrations of perfluorooctanoic acid so that total PFCA concentrations could be estimated with less than 20% error using a phone camera across a 10 ppb (parts per billion) – 16 ppm (parts per million) range.