Studying the effect of thread materials on the response of fiber-based organic electrochemical transistors for pH sensing

Among different conducting polymers, PEDOT:PSS has been used for making organic electrochemical transistors (OECTs) due to the remarkable stability and the electrochemical properties of the polymer. With the fast-growing market for wearable electronics, the application of OECTs has been proposed for wearable sensors. However, the majority of OECTs have a planar design. Recently, we have demonstrated the feasibility of fabricating OECTs on sewing threads. This work has focused on studying the effect of thread materials on the performance of fiber-based OECTs made for wearable pH sensors. Such sensors can be used to collect metabolic information from the body of a patient by analyzing the pH of perspiration. The three most commercially common different kinds of threads were used to make OECTs with polyvinyl alcohol (PVA) gel as the electrolyte. Using 100% cotton, 25% cotton-75% polyester, and 32% cotton-68% polyester threads were used to fabricate and then characterize the transistor. Threads were coated with PEDOT:PSS polymer to use as a channel then use a Silver coated thread as a gate and a PVA gel electrolyte. Devices were tested by applying different voltages to the transistor terminals and monitoring the current through the PEDOT:PSS. The best signal was obtained from the device made on 25% cotton-75% polyester thread. The experimental results showed a promising approach that can lead to a good wearable pH sensor on human perspiration.