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

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.

Halogen Bonding Ionophore for Potentiometric Iodide Sensing.

Iodide (I-) is an essential micronutrient for thyroid function. Hence, rapid and portable sensing is important for I- quantification in food and biological samples. Herein, we report the first example of a halogen bonding (XB) tripodal ionophore (XB1) which is selective for the I- anion. NMR binding studies of XB1 and its H-triazole analog HB2 with I- demonstrated the dominant influence of XB interactions between the ionophore and the I- analyte. The phase boundary model was applied to formulate iodide-selective electrodes with the ionophore XB1. The optimal electrode exhibited a near-Nernstian response of -51.9 mV per decade within a large dynamic range (10-1 to 10-6 M) and notably anti-Hofmeister selectivity for I- over thiocyanate (SCN-), enabling the in situ determination of I- in complex samples. This work establishes XB as a viable supramolecular interaction in the potentiometric sensing of anions.