Fabrication of laser-induced graphene-based multifunctional sensing platform for sweat ion and human motion monitoring

Abstract

Human sweat monitoring, which unlike blood monitoring can be easily performed on the skin, can provide valuable personal healthcare data, as well as being suitable for use in diagnosis of disease and other conditions. However, despite the tremendous interest in sweat sensing, the development of low-cost, high-efficiency, multi-biometric sensing-capable platforms is still required for the large-scale utilization of wearable biosensors for extensive monitoring with other physiological signals. Here, we propose a wearable multifunctional LIG-based sensor, complete with Arduino-based readout electronics, which simultaneously monitors concentrations of sodium and potassium ions in human sweat as well as strain generated by vital signals (human motion). Our elastomer substrates were fabricated according to the weight of polydimethylsiloxane (PDMS) and lignin. A wearable multifunctional sensor was developed via the formation of laser-induced graphene (LIG) on PDMS/lignin composite substrates using Laser Direct writing (LDW); PDMS/Lignin transforms into the porous structure after laser irradiation. The fabricated sodium and potassium ion-selective electrodes (ISE), and Ag/AgCl electrode on PDMS/lignin composite were used to measure the potential difference at various different concentrations of both Na+(10−1–10−7) and K+ ions (10−1–10−8), and our sensor showed high sensitivity values of 63.6 mV/dec (Na+, n = 6) and 59.2 mV/dec (K+, n = 7), respectively; these results almost completely follow Nernstian behavior (which predicts values of R2 =0.99988 and 0.99855, respectively) and indicate cyclic stability (5000 cycles, Gauge Factor of ~20). This simple fabrication of a multifunctional and cost-effective sensor platform indicates real-time changes of sodium and potassium ions in sweat and strain generated by human body motion.