Ion-selective electrodes with 3D nanostructured conducting polymer solid contact

Until now both ion-to-electron transducers as well as large surface area nanostructured conducting materials were successfully used as solid contacts for polymer-based ion-selective electrodes. We were interested to explore the combination of these two approaches by fabricating ordered electrically conducting polymer (ECP) nanostructures using 3D nanosphere lithography and electrosynthesis to provide a high surface area and capacitive interface for solid contact ion-selective electrodes (SC-ISEs). For these studies we used poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT(PSS)) films with 750 nm diameter interconnected pores as the intermediate layer between a glassy carbon electrode and a Ag⁺ -selective polymeric membrane. We also investigated the feasibility of loading the voids created in the polymer film with a lipophilic redox mediator (1,1’-dimethylferrocene) to provide the respective ISEs with well-defined/controllable E⁰ values. These expectations were fulfilled as the standard deviation of E⁰ values were reduced with almost an order of magnitude for 3D nanostructured SC-ISEs filled with the redox mediator as compared to their redox mediator-free analogs. The detrimental effect of the redox mediator extraction into the plasticized PVC-based ion-selective membrane (ISM) was efficiently suppressed by replacing the PVC-based ISMs with a low diffusivity silicone rubber matrix.