Highly sensing and transducing materials for potentiometric ion sensors with versatile applicability

It remains great challenges to fabricate advanced potentiometric sensors based on ion-selective electrodes (ISEs) with ultrasensitivity, high selectivity, long-term durability, and even reproducible potential. Sensing and transducing materials are vital components for substantial performance optimization. This review systematically summarizes the progress in ionophore, formulation, preparation, nanostructure, and electrochemical properties of state-of-the-art sensing membranes and ion-to-electron transducing layers for comprehensively stabilizing potential and enhancing the sensing performance. This article elaborates the development of cutting-edge solid-contact (SC)-ISEs including wearable chip and needle electrodes to achieve versatile applications like health and environmental monitorings, medical diagnosis, food and plant analysis. As an indispensable element in SC-ISEs, the transducing materials particularly including conducting polymers, noble metals and carbon nanomaterials for stabilizing potential are thoroughly expounded. It is suggested that the highly transducing materials with practical applicability should possess two key features including high hydrophobicity and strong adherence onto the electrode substrates and ion-selective membranes besides high ion and electron conductivity, which could be used to guide the design and fabrication of next-generation ISEs based on multifeatured composites. The current startup status and future research direction of calibration-free ISEs with excellent potential reproducibility that would become a major hotspot in the field soon are highlighted.