Flexible Laser-Induced Graphene Microelectrochemical Sensor on Sustainable Cellulosic Paper Substrate for Sensitive Detection of Uric Acid and Tyrosine in Sweat

Graphene-based flexible electrochemical sweat sensors have garnered significant attention in both medical and athletic application fields due to their ability to provide critical insights into the body's physiological condition. Herein, we employed a green laser-induced graphene (LIG) technique using a CO₂ laser on a cellulose-based paper substrate to fabricate a microelectrochemical sensor capable of detecting tyrosine and uric acid in sweat samples. Electrochemical analysis determined the heterogeneous electron transfer (HET) rate constant (<i>k</i>₀) to be 4 × 10^-3 cm/s and confirmed that the LIG sensor maintained stability across various pH levels. For tyrosine detection, the sensor exhibited a broad linear detection range from 30 to 1000 μM, with a limit of detection (LOD) of 12.4 μM and a sensitivity of approximately 9 mAM^-1. For uric acid, the working range extended from 5 to 100 μM, with an LOD of 2.9 μM and a sensitivity of around 1 mAM^-1. These results demonstrate performance comparable to or surpassing existing flexible graphene-based sensors. Selectivity tests confirmed the sensor's ability to distinguish tyrosine and uric acid in the presence of common sweat interferents such as glucose, lactic acid, and ascorbic acid. Additionally, the mechanism of LIG formation on the cellulosic substrate was validated using molecular dynamics simulations with the ReaxFF force field, showing strong agreement with experimental data. The developed microelectrochemical sensor exhibited reliable and effective performance, underscoring its potential for sustainable, noninvasive health monitoring, and clinical diagnostics.