Calibration-free Solid-State Ion-Selective Electrode Based on a Polarized PEDOT/PEDOT-S-Doped Copolymer as Back Contact

Abstract

Solid-contact ion-selective electrodes (ISEs) have the inherent advantage of being miniaturized in addition to maintaining high selectivity and sensitivity of the ionophore-based ISE. The major disadvantage of ISEs is the necessity of performing a calibration curve (varying the intercept in the linear calibration curve equation) each time before running experiments, which limits their application as one-time disposable sensors or for use in remote water sample analysis. To overcome these challenges, we designed a unique back contact made of 3,4-ethylenedioxythiophene (EDOT) and 4- (2,3-dihydrothieno[3,4-b][1,4]dioxin-2-ylmethoxy)-1-butanesulfonic acid, sodium salt (EDOT-S). The calibration-free ISEs showed near Nernstian responses of 57.2 ± 0.2 mV/log [K + ] and 28.5 ± 0.3 mV/log [Ca 2+ ], while maintaining their respective selectivity against major interfering ions. The detection limits for Ca 2+ and K + ISEs were 0.45 ± 0.01 and 1.68 ± 0.18 μM, respectively. The charging cycles of the PEDOT: PEDOT-S back contact allowed us to fix the background potential at a desired fixed intercept value across different ionophores (K + , Ca 2+ ). This protocol was used to determine the K + and Ca 2+ contents in creek water samples. The activity and concentration of [Ca 2+ ] and [K + ] in a local creek was found to be 257 ± 7.3 and 28.1 ± 1.1 μM, respectively.

Ion-Selective Electrodes with Solid Contact Based on Composite Materials: A Review

“…Application of the synthesized material EDOT-S (3,4-ethylenedioxythiophene and 4-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid, sodium salt) in the construction of SCISEs sensitive to potassium and calcium ions on a substrate with gold disk electrodes was described in [161]. Sensors with a slope of the calibration curve close to Nernst's (57.2 and 28.5 mVdec -1 for K + and Ca 2+ , respectively) were obtained.…”

Self-Calibrated Ion-Selective Electrodes

“…In recent years, a wide variety of materials and chemicals such as redox polymers/molecules, capacitive carbon materials, nanostructured noble metals, metal–organic frameworks, intercalation compounds, and their combinations have been studied as the ion-to-electron transduction layer of solid-contact ISEs with the aim of improving the electrode-to-electrode consistency and other analytical performance characteristics. , The deposited layer or suspension of redox-active solid contact materials such as conducting polymers may be further pre-polarized to unify standard potentials of multiple electrodes. − Although a few mV or less of standard deviations (SD) in E ° have been observed from the same batch of electrodes and occasionally from different batches, the reported variation is only for indicator electrodes as a shared reference electrode has been used in most studies. Since the EMF variation of reference electrodes is also a couple of mV or more, full two-electrode potentiometric sensors are unlikely to have medically acceptable precision.…”

Self-Calibrated Ion-Selective Electrodes

“…11,12 The deposited layer or suspension of redox-active solid contact materials such as conducting polymers may be further pre-polarized to unify standard potentials of multiple electrodes. [20][21][22][23][24][25] Although a few mV or less of standard deviations (SD) have been observed from the same batch of electrodes and occasionally from different batches, the reported variation is only for indicator electrodes as a shared reference electrode has been used in most studies. Since the EMF variation of reference electrodes is also a couple of mV or more, 11 full two-electrode potentiometric sensors are unlikely to have medically acceptable precision.…”