Potentiometric sensing of potassium ion (K + ) using valinomycin supported on ZnO/rGO nanocomposites

A solid-contact ion-selective electrode (ISE) was fabricated using zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposites as an intermediate layer between glassy carbon electrode (GCE) and ionophore. The resulting solid contact acts as an ion-to-electron transducer in potassium ion-selective electrode (K + -ISE) containing valinomycin as ionophore. The new transducing layer was characterized by using scanning electron microscopy (SEM), X-ray diffraction analysis, and cyclic voltammetry (CV) techniques. Hexagonal wurtzite phase of ZnO was revealed from diffraction analysis and the SEM images showed the formation of one-dimensional nanorods with hexagonal top surfaces. Validation of the sensing material was carried out using CV studies and the experimental studies showed that ZnO/rGO has a strong capability to function as a solid contact in the fabrication of K + -ISEs. Valinomycin-based ISE developed using ZnO/rGO showed a high sensitivity of 9.95 µA (µM) −1 cm − 2 with a faster response time of ~ 2 s and limit of detection (LOD) of 0.956 mM. Interference studies, reproducibility, and long-term stability of the sensing material toward K + detection were assessed and the results showed that the ZnO/rGO redox capacitance is favorable for solid contact as K + -ISE for real-time application in soil analysis.