Polymeric hydrogel integrated paper-based potentiometric ion-sensing device for the determination of sodium ions in human urine

A paper-based potentiometric sensor integrated with a polymeric hydrogel has been developed for sodium ion (Na⁺) determination in human urine. The construction of an all-solid-state ion selective electrode (s-ISE) and an all-solid-state reference electrode (s-RE) on a photo paper substrate was achieved using an inkjet printing method. For s-ISE fabrication, carbon nanotubes (CNTs) and gold nanoparticles (AuNPs) were printed on the substrate as a nanocomposite solid contact. A polymeric hydrogel containing lithium acetate (CH₃COOLi) was then prepared and used as an intermediate layer to improve the adhesion between the ion selective membrane (ISM) and the AuNP/CNT solid contact, leading to enhanced detection sensitivity. The printed s-RE consisted of a pseudo silver/silver chloride electrode (p-Ag/AgCl) coated with a polymeric hydrogel containing KCl to improve the potential stability of the sensor. Under the optimal conditions, the hydrogel-integrated paper-based potentiometric sensor provided a response toward Na⁺ over a linear range of 10^-7 M to 1 M with a near Nernstian slope of 56.42 ± 0.68 mV per decade. This sensor exhibited fast response, good sensitivity, and reasonable selectivity for Na⁺ measurement. Furthermore, the developed sensor was effectively applied for the detection of Na⁺ in urine samples with high accuracy. The presented work can be considered as a good addition to the growing field of potentiometric analytical platforms suitable for large-scale production using inkjet printing technology.