Laser-Induced Graphene-Based Potentiometric pH and Nonenzymatic Uric Acid Sensors for Urine Analysis on Baby Diaper

The fabrication of wearable sensors and their integration into real devices is an emerging demand in the field of sensor development. In this work, flexible sensors based on laser-induced graphene (LIG) were developed using a low-cost visible laser on polyimide tape for pH and uric acid monitoring in urine. A potentiometric pH sensor was fabricated by modifying the LIG surface with polyaniline, achieving a sensitivity of 56.7 ± 2.6 mV/pH across a wide pH range (4-10) with a rapid response time of <10 s. The sensor exhibited high selectivity toward proton ions and maintained stable performance for 6 weeks without the need for preconditioning or special storage conditions. In parallel, a nonenzymatic uric acid sensor based on LIG exhibited strong selectivity against common interfering species, excellent reproducibility (RSD <1%), and a sensitivity of 116.4 μAdec^-1, with a limit of detection (LOD) of 35 μM (3S/N) in the concentration range of 0.05-0.6 mM in buffer solution. Both sensors maintained almost similar sensitivities in artificial urine samples, and their performance was successfully demonstrated in baby diapers using a portable potentiostat, highlighting their potential for miniaturized wearable health monitoring applications.