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 μAmM^–1cm^–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° bending. The flexible electrochemical urea sensor platform can provide noninvasive monitoring of urea levels in sweat fluids, ensuring clinical diagnosis for biomedical applications.