Processing-Tuned Laser-Induced Graphene Transducers for Polyaniline pH Sensors

Abstract

Flexible pH sensors are important for wearable, biomedical, environmental, and process-monitoring applications, but achieving simple, scalable fabrication while maintaining high sensing performance remains challenging. Laser-induced graphene (LIG) has emerged as a promising transducer material because it enables direct laser patterning of porous, conductive graphitized carbon electrodes on flexible substrates. Although laser-processing conditions are known to affect LIG morphology, graphitization, and electrical properties, their influence on pH-sensitive layer formation and pH-sensing performance has not been systematically investigated. In this study, polyaniline (PANi)-modified LIG pH sensors were fabricated using four laser-processing combinations of laser power and scan speed. The resulting LIG and PANi/LIG electrodes were characterized using sheet-resistance measurements, optical microscopy, SEM, Raman spectroscopy, and XPS. PANi was electropolymerized on the LIG working electrodes under identical cyclic voltammetry conditions, and the assembled sensors were evaluated in pH 4–9 buffer solutions. The results showed that laser processing produced distinct LIG morphologies, porosities, sheet resistance, and PANi coverage, leading to different sensing performances. Among the samples, PANi/LIG-9.2–350, fabricated at 9.2 W and 350 mm/s, exhibited the best overall performance, with a near-Nernstian sensitivity of −60.04 mV/pH, a 12 h drift rate of 1.67 mV/h, hysteresis of 2.06 mV, and rapid response time of 13.2 s. These findings emphasize the significance of laser-processing-dependent LIG microstructure and electrical properties in governing PANi deposition behavior and resulting potentiometric pH-sensing performance.