High Sensitivity pH Sensor Based on Liquid Droplet Motion Over Hydrophobic Polymer

This work proposes self-powered pH monitoring by studying the interfacial surface charge modulation as liquid droplets move over a pre-charged hydrophobic CYTOP polymer surface. Due to the large negative charge of CYTOP in the friction sequence, it can be used to build liquid droplet-based pH-detecting devices. Typically, chemical sensors based on the interaction of water and PTFE have a restricted pH detection sensitivity of approximately -74 mV per pH of the water droplet unit. We demonstrate that using the proposed mechanism, the developed pH sensor reaches a sensitivity of roughly -80 mV per pH unit, which is higher than that of a PTFE-based pH sensor. In this work, pH 4 was found to be the essential threshold in the interaction of CYTOP and water droplets. The CYTOP surface exhibits positive polarity when the pH value is greater than 4, whereas the water droplet exhibits negative polarity when the pH value is less than 4. Furthermore, a pH sensor can be utilized in conjunction with a water droplet motion-based energy harvester. Also, it has been observed that Receiver Operating Characteristics (ROC) are different with diverse pH values. We show as a proof-of-concept that the pH of water droplets can be continually monitored using our polymer-based pH sensor. The developed pH sensor could eventually be utilized to measure the pH of the sweat in order to monitor health conditions.