Flexible Electrochemical Sensor Based on NiCu(OOH) for Monitoring Urea in Human Sweat

Abstract

Wearable and flexible electrochemical sweat analysis for monitoring health-related urea concentrations with high sensitivity and selectivity is highly required for individual medical care and disease diagnosis. Herein, we report a sensitive and selective sweat sensor based on a flexible NiCu(OOH)/polystyrene (PS) electrode to detect a urea biomarker. The non-enzymatic sensor was fabricated using electrospinning PS containing carbon nanotube as a conductive component and co-sputtering Ni-Cu alloys as a catalyst. The flexible PS provided a porous structure, leading to sufficient active sites, easy access to reactants, and adequate water wettability for effective charge transfer. The sputtered Ni-Cu alloys deposited on the PS were transformed to a Ni-Cu oxyhydroxide form by cyclic voltammetry treatment, managing the detection of the urea molecule in a neutral pH environment. This urea sensor displayed an excellent linear response with a sensitivity of 10.72 mu AmM(-1)cm(-2) toward a physiologically appropriate linear range of 2.00-30.00 mM, and negligible interferences from co-existing common species. Furthermore, bending tests demonstrated excellent mechanical tolerance where electrochemical performance was not affected under 200 cycles and 150 degrees bending. The flexible electrochemical urea sensor platform can provide noninvasive monitoring of urea levels in sweat fluids, ensuring clinical diagnosis for biomedical applications.