Disposable devices for sensing biomarkers like Na+ ion in sweat was developed using UV-Ozone irradiated laser-induced graphene (LIG) based electrodes. Solid-state ion-selective electrodes (ISEs) sensitive to Na+ ions were fabricated by a two-step drop-coating process of polyvinyl chloride solution containing plasticizer, ionophore and ion-exchanger on LIG electrode. Hydrophobic to hydrophilic transition induced by UV-Ozone treatment reduced the contact angle, resulting in better permeation of the ion-selective membrane into the ozonized LIG film. Raman spectroscopy and IR absorption studies indicate physisorption of ozone on LIG. Performance of ozonized LIG (O-LIG) electrodes was much better than pristine LIG and screen-printed carbon electrodes. 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 devices were around 1 min.