Water is the source of life, and its rich electrolytes play a pivotal role in all life on Earth. Back to human beings, the electrolyte concentration and distribution in the body are closely associated with health, thus solid-state ion-selective electrode (ISE) meet this need just perfectly to be made into a wearable sensor to monitor the concentration of various ions in the human body at any time. Although the best available ionophore-assisted ion-selective membrane (ISM) based ion-selective electrode has been developed for over a century, all-solid-contact ion-selective electrode still faces the problem of lack of stability. Many researchers have found that the electrochemical signal disruption is due to the condensation of water molecules forming a so-called water layer between the solid support of the electrode and ion-selective membrane. The addition of the lipophilic transducing material behind the membrane has indeed suppressed the water layer formation for a certain period of time.

Additionally, conventional ion-selective membrane potentiometry is a passive method for ion detection. However, the new alternative approach attracts a lot of attention, thin-film cyclic voltammetry can provide multi-ions detection, lower detection, and responding time manipulation. The fundamental theory of the ion-to-electron transfer was well understood, but in practical use, the transducing layer, commonly made of poly(3-octylthiophene) (POT) or the other derivatives (PEDOT-C₁₄), is not reproducible for the ion-selective electrode from batch to batch, as well as the voltammetric current is the contribution of electron-transfer coupled with the ion-transfer, where it is hard to analyze the deviation of ion sensing coming from the transducing layer or ionophore selectivity effect on the ion-transfer. This thesis shows the approach to separate the two transduction events at each interface (electrode/membrane and membrane/sample) with their phase boundary potentials and then we further developed the thin-film cyclic voltammetry technique in analytical chemistry. A promising practical use for solid contact thin-film ion-selective electrodes is present and pushes forward the development of this field.