Temperature Correction of Printed Na+, K+, and pH Sensors with PEDOT:PSS-Based Thermistors toward Wearable Sweat Sensing

Abstract

Temperature correction for sensors is a critical aspect of ensuring accurate measurements in wearable devices, because skin and sweat temperatures vary between 20 and 40 °C depending on individual and time. Here, this study reports on the temperature dependence and correction techniques of printed Na+, K+, and pH sensors toward wearable applications. The ion sensor array is fabricated using a cost-effective printing method. To enable temperature correction, a printed thermistor of crosslinked poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is monolithically integrated with the ion sensor array on a flexible plastic substrate. Temperature dependence of the potential response of the printed ion sensors exhibits a linear behavior with a slope of 1–2 mV °C−1 in the physiological skin temperature range of 20–40 °C. Applying temperature correction to the ion sensors, the maximum relative errors are reduced from 60% to 7.8% for the Na+ sensors and from 76% to 14.6% for the K+ sensors, while the maximum absolute error is reduced from 0.88 to 0.19 for the pH sensors, indicating the critical importance of temperature correction as a technology for wearable printed ion sensors.