UV-Ozone Treated Modified Laser-Induced Graphene Based Electrochemical Sweat Sensor

Abstract

Recent studies shows laser-induced graphene (LIG) based electrodes can be very effective for electrochemical sensing applications. In this work, we aim to develop a stable ion selective membrane (ISM) based sweat sensor using laser-induced graphene (LIG) as the electrode material. However, the surface of pristine LIG is hydrophobic. Hence, coating these hydrophobic LIG films with ISM produces low sensitivity in sensing applications. In this study, UV-Ozone irradiated laser-induced graphene (LIG) based electrodes were explored for sensing biomarkers like ion in sweat. Solid-state ion-selective electrodes (ISEs) sensitive to ions were fabricated by a two-step drop-coating process of polyvinyl chloride solution containing plasticizer, ionophore, and ion-exchanger on the LIG electrode. We found the ozone treatment process significantly increased the electrochemical active surface area (EASA) and porosity of the pristine LIG. Hydrophobic to hydrophilic transition induced by UV-Ozone treatment reduced the contact angle (CA), resulting in better permeation of the ion-selective membrane (ISM) into the ozonized LIG film. Raman spectroscopy and IR absorption studies indicate physisorption of ozone on LIG. The concentration of the ISM solution has a great influence on attachment to the O-LIG film. Here, we report the applicability of O-LIG as an electrochemical sensor towards the detection of sodium ion () using the open circuit potential (OCP) method. The performance of ozonized LIG (O-LIG) electrodes was much better than pristine LIG and screen printed carbon electrodes. The sensitivity of 60.2 ± 0.9 mV/ decade to Na+ ions and a lower limit of detection of 1 × 10-6 M was achieved using O-LIG based ISEs. Response time of the O-LIG based electrodes were around 1 min. The current study demonstrates that the LIG-based electrodes can be used as a flexible electrochemical sensing platform and is suitable for future wearable sensing devices. Keywords Laser-induced graphene; ion-selective electrode; wearable sensors; electrochemical sensor; sweat sensor.