Printed pH Sensors for Textile-Based Wearables: A Conceptual and Experimental Study on Materials, Deposition Technology, and Sensing Principles

In this article, organic and polymeric materials, printing technology, and sensing principles are investigated toward a reliable printed wearable pH sensor realized on textiles. A literature study and experimental work of three different organic and polymeric material-based pH sensors and their corresponding measurement methods are systematically made. Initially, the three different sensors, a conductometric PEDOT:PSS sensor, a voltametric carbon-alizarin sensor, and a potentiometric graphene/polyaniline (PANI) sensor are selected based on specific established criteria and are reproduced on foils for a feasibility study. Mass production and feasibility for fabrication on textile substrates are also the objectives of this work, and lead to the deployment of printing and coating techniques for the sensor fabrication. These three sensors are printed on flexible foils and tested and verified for sensor performances. Based on the experimental results and literature study, a conclusive comparison between the sensing principles regarding device fabrication, functionality, and wearability is performed. As per this analysis, a potentiometric PANI sensor is printed on a textile substrate and tested for a buffer solution of pH ranging from 4 to 9.5. The potentiometric PANI sensor shows a sensitivity of 45 mV pH(-1) with linear sensor responses and repeatable characteristics.