A wearable fingernail chemical sensing platform: PH sensing at your fingertips

This article demonstrates an example of a wearable chemical sensor based on a fingernail platform. Fingernails represent an attractive wearable platform, merging beauty products with chemical sensing, to enable monitoring of our surrounding environment. The new colorimetric pH fingernail sensor relies on coating artificial nails with a recognition layer consisted of pH indicators entrapped in a polyvinyl chloride (PVC) matrix. Such color changing fingernails offer fast and reversible response to pH changes, repeated use, and intense color change detected easily with naked eye. The PVC matrix prevents leaching out of the indicator molecules from the fingernail sensor toward such repeated use. The limited narrow working pH range of a single pH indicator has been addressed by multiplexing three different pH indicators: bromothymol blue (pH 6.0–7.6), bromocresol green (pH 3.8–5.4), and cresol red (pH 7.2–8.8), as demonstrated for analyses of real-life samples of acidic, neutral, and basic character. The new concept of an optical wearable chemical sensor on fingernail platforms can be expanded towards diverse analytes for various applications in connection to the judicious design of the recognition layer.