Solution-Printable PEDOT Solid-Contact for Nitrate-Selective Electrodes: Enhanced Selectivity from Anion Dopant...

Poly(3,4-ethylenedioxythiophene)-polyethylene glycol (PEDOT:PEG) is a conductive material adopted in bioelectronics due to its biocompatibility and stability. While PEDOT has established its utility in cationic solid-contact ion-selective electrodes (sc-ISEs), its anionic counterpart remains less explored. Herein, we report the first example of PEDOT:PEG as a solution-printable solid-contact for all-solid-state nitrate-selective electrodes and a simple ion exchange treatment which can significantly enhance nitrate selectivity. Electrochemical impedance spectroscopy revealed that the sc-ISEs with perchlorate (ClO₄^-)-doped PEDOT:PEG suffered a large overall resistance. Removal of the ClO₄^- dopant via ion exchange reduced the resistance, resulting in significant improvement in sc-ISE performance. The optimal sc-ISE exhibited near-Nernstian response (-55.8 mV/decade) across a wide dynamic range (0.1 M to 1.12 μM) and excellent Hofmeister selectivity, which was maintained after prolonged continuous usage. This simple drop-cast and ion-exchange protocol is amenable to the scalable preparation of flexible anion sc-ISEs.