Development of Improved Ion-Selective and Reference Electrodes for In Situ Monitoring of Ion Concentrations

Abstract

This dissertation is focused on the application of electrochemistry for the fundamental understanding, development, and application of electrochemical sensors. In particular, my research focused on the development and understanding of reference electrodes and ion-selective electrodes for potentiometric sensing applications. Recently, following the needs of point-of-care and wearable sensors, electrode designs have transitioned from bulky devices with an aqueous inner filling solution (e.g. pH electrodes) to planarizable solid-contact electrodes. However, unless their polymeric sensing and reference membranes are held in place mechanically, delamination of the physically adhering membranes limits sensor lifetime, as even minimal external mechanical stress or thermal expansion can result in membrane delamination and, thereby, device failure. To address this problem, we designed a sensing platform based on inexpensive polymers to which membranes are attached covalently through photopolymerization. Even extreme mechanical stress does not result in the delamination of the sensing and reference membranes from the underlying polymer, which results in electrodes that exhibit much improved long-term performance and greatly reduced size. This method of sensor preparation is broadly applicable to a wide range of electrode types and allows for long-term measurements of numerous ions that are of environmental and medical significance. Moreover, the applicability of these ion-selective electrodes for long-term measurements requires reference electrodes that also provide stable responses. Reported here are two types of improved reference electrodes based on capillaries and ionic liquids.