Solid-State Ion-Selective pH Sensor

pH sensors are widely used in various applications such as agriculture, wastewater monitoring, and biomedical engineering. Solid-state ion-selective electrodes (ISEs) have been developed to enable the miniaturization of pH sensors. This paper evaluated the pH sensing electrodes based on hydrogen ionophores or pH-sensitive emeraldine-polyaniline. A miniaturized leak-free reference electrode was integrated with pH sensing electrodes. A multiple-channel electromotive force recording unit was built to facilitate the measurement of multiple ISEs. The sensitivity and dynamic range were assessed using the pH solutions from pH 1.3 to pH 10. The conductance and capacitance of different ISEs were measured and compared. We evaluated the longevity and stability of the emeraldine-polyaniline-based pH sensor, and the drifting was less than 4 mV/day.