Physically Tailoring Ion Fluxes by Introducing Foamlike Structures into Polymeric Membranes of Solid Contact Ion-Selective Electrodes

Abstract

Transmembrane ion fluxes have earlier been identified as a source of potential instability in solid contact ion-selective electrodes (SC-ISEs). In this work, foamlike structures were intentionally introduced into a potassium-sensitive plasticized poly(vinyl chloride) ion-selective membrane (ISM) near the membrane|solid contact interface by controlling the temperature during membrane deposition. Foamlike structures in the ISM were shown to be effective at physically tailoring the transport of ions in the ion-selective membrane, greatly reducing the flux of interfering ions from the sample to the membrane| solid contact interface. The drifts during a conventional water layer test were hence able to be greatly mitigated, even with SC-ISEs incorporating a relatively hydrophilic poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) solid contact. In solutions with a high background concentration of interfering ions, equilibrated ion-selective electrodes with foamlike membranes were able to reproduce their initial potentials within 0.6 mV uncertainty (n = 3) from 0 to 18 h. This was achieved despite sensor exposure to solutions exceeding the selectivity limit of the ISEs in 3 h intervals, allowing improvement of the potential reproducibility of the sensors. Since the introduction of foamlike structures into ISM is linked to temperature-controlled membrane deposition, it is envisaged that the method is generally applicable to all solid contact ion-selective electrodes that are based on polymeric membranes and require membrane deposition from the cocktail solution.

A New Discovery on the Potential Stability of Ion-Selective Membranes: The Poison from Tetrahydrofuran

“…5−7 This is because of reliable performance of the sensors, such as potentiometric response stability which is a critical aspect in long-term usage. 8,9 The origin of the potential of the electrode is linked to the formation of the phase boundary potential at the membrane | solution interface. The partitioning of ions between two phases is driven by the ionophore with a selectivity established by Donnan exclusion of the counterions by the lipophilic ionic sites (e.g., ion-exchangers) (Figure 1A).…”

Paper-Based Sandwich-Structured Wearable Sensor with Sebum Filtering for Continuous Detection of Sweat pH

“…Potentiometry is an electrochemical analytical method, and it can produce continuous electric signals based on analyte concentration using an uncomplicated circuit module with low power, making it highly relevant for developing next-generation self-powered devices. Therefore, it has been widely used in wearable sweat sensors. − The ion-selective membrane, which is the most important part of ion-selective electrodes (ISEs), is usually lipophilic. − Sebum mixed in sweat may adhere to the surface of a polymeric membrane and block the proper ion-exchange capability of ISEs at the interface, thereby reducing the analytical performance of ISEs. Moreover, sebum is difficult to remove from the electrode surface, even after thoroughly washing it with ultrapure water.…”

Ion-Electron Transduction Layer of the SnS2-MoS2 Heterojunction to Elevate Superior Interface Stability for All-Solid Sodium-Ion Selective Electrode

“…The sodium ion (Na + ), as one of the human sweat elements, has attracted much attention for its participation in human metabolism. − Among various detection technologies, such as electrochemical technology, colorimetry, and fluorescence, the all-solid sodium ion selective electrode as a new generation of potential sensors is chosen by most people due to their high sensitivity and selectivity toward target objects. − However, the asymmetry of the ion to electron transduction process generally induces the polarization of the electrode surface and potential drift, thereby causing instability of interfacial potential, which affects the reliability analysis of the actual application of the electrode, and it is an urgent problem in current research. , Introducing solid contact functional materials with excellent properties as ion-electron transduction layers is a feasible way to stabilize the interfacial potential of electrodes . Wardak et al review composites materials as transduction layers for ion selective electrodes .…”