Kinetic and structural control in polymer-based solid-contact ion-selective sensors for anion detection

Abstract

This dissertation presents the development of polymer-based solidcontact ion-selective electrodes (SC-ISEs) for selective and sensitive detection of environmentally relevant anions, particularly nitrate and phosphate. Motivated by the need for rapid, reliable, and field-deployable monitoring tools to address nutrient pollution and eutrophication, this work explores how membrane chemistry, electrode architecture, and measurement methodology collectively govern sensor performance. Molecularly imprinted polymers (MIPs) based on ethylene glycol dimethacrylate and 1-allyl-2-thiourea were synthesized to introduce selective binding sites for target ions, while polypyrrole (Ppy) was employed as a redox-active transducer to enable efficient ion-to-electron conversion. Traditional open-circuit measurements yielded sub-Nernstian responses; however, the application of pulsed-current (galvanostatic) operation shifted the sensing mechanism from thermodynamic equilibrium to iontransport kinetics, enabling near-Nernstian sensitivity ( 65 mV per decade) and strong kinetic selectivity for nitrate over competing ions. Template design was shown to critically influence selectivity, with isoamyl nitrate and diphenyl phosphate producing the most effective imprinting for nitrate and phosphate, respectively.