Potassium Ion-selective Membrane Research Articles

A Fiber Sensor for Long-Term Monitoring of Extracellular Potassium Ion Fluctuations in Chronic Neuropsychiatric Diseases.

The extracellular potassium ion concentration in the brain exerts a significant influence on cellular excitability and intercellular communication. Perturbations in the extracellular potassium ion level are closely correlated with various chronic neuropsychiatric disorders including depression. However, a critical gap persists in performing real-time and long-term monitoring of extracellular potassium ions, which is necessary for comprehensive profiling of chronic neuropsychiatric diseases. Here, a fiber potassium ion sensor (FKS) that consists of a soft conductive fiber with a rough surface and a hydrophobic-treated transduction layer interfaced with a potassium ion-selective membrane is found to solve this problem. The FKS demonstrates stable interfaces between its distinct functional layers in an aqueous environment, conferring an exceptional stability of 6 months in vivo, in stark contrast to previous reports with working durations from hours to days. Upon implantation into the mouse brain, the FKS enables effective monitoring of extracellular potassium ion dynamics under diverse physiological states including anesthesia, forced swimming, and tail suspension. Using this FKS, tracking of extracellular potassium ion fluctuations that align with behaviors associated with the progression of depression over months is achieved, demonstrating its usability in studying chronic neuropsychiatric disorders from a new biochemical perspective.

A graphene-based electrochemical detection platform for monitoring the change of potassium content in sweat during exhaustive exercise

In this investigation, we developed an ion-selective electrode-based potassium ion sensor for the detection of potassium ions in sweat, and evaluated its selectivity and stability. The sensor was fabricated through in-situ polymerization of 3,4-ethylenedioxythiophene (EDOT) monomer on a graphene-modified glassy carbon electrode using a constant current method. This was followed by the application of a potassium ion-selective membrane to form a poly(3,4-ethylenedioxythiophene) (PEDOT) modified potassium ion sensing electrode. The physical morphology and electrochemical properties of the sensor were characterized using scanning electron microscopy (SEM) and an electrochemical workstation. The results indicated that the conductivity of the PEDOT modified electrode was significantly enhanced, and the potassium ion sensor exhibited a near-Nernstian response over the range of 1–40 mM potassium ion concentration. The sensor demonstrated good repeatability, reproducibility, long-term stability, and high selectivity against interference from sodium ions, glucose, dopamine, and urea.

Dependence of the potentiometric response of PEDOT(PSS) on the solubility product of silver salts

The potentiometric response of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) deposited on glassy carbon (GC), i.e. GC/PEDOT(PSS), was studied before and after conditioning in silver nitrate solution. The deposition of silver in the PEDOT(PSS) film was characterized by SEM/EDAX and cyclic voltammetry. The potentiometric response of the Ag-conditioned GC/PEDOT(PSS) electrode was dependent on the nature of the anion present in the calibration solutions. In cases where anions do not form sparingly soluble silver salts, a cationic response was observed for GC/PEDOT(PSS), as expected. However, an anionic response was observed in solutions containing anions (X−) that can form sparingly soluble salts with silver ions (AgX). Furthermore, the measured potentials in X− solutions followed the solubility product values of AgX. The agreement between the experimental and thermodynamic data was excellent. This validates the hypothesis of equilibrium existing between Ag+ ions in the polymer film (due to conditioning) and Ag+ ions in the solution. The Ag-conditioned GC/PEDOT(PSS) electrode covered with a potassium ion-selective membrane (GC/PEDOT(PSS)/K+-ISM) showed a cationic response in KCl solutions with close to Nernstian slope value.

Evaluation of Wearable Potassium Ion Sensor Fabricated By Heat Transfer Printing

Printable wearable sensors for monitoring biomarkers in sweat of people exercising has attracted attention. For example, wearable ion sensors in sweat based on tattoo paper has been reported1).A wearable textile-based sensor has advantages such as low cost, flexibility, and light weight. For example, a stretchable self-powered biosensor has been reported previously 2). On the other hand, when a sensor is formed by printing directly on a cloth, the problem is that the resistance value increases, and the accuracy of the sensor may decrease due to the irregularity of the electrode surface.To solve the problem, we recently reported a wearable potentiometric sodium ion sensor by transfer printing technique3). In case of transfer printing, a sensor is firstly formed on a smooth substrate. Then the sensor is transferred by heating with pressure on a textile with high accuracy irregularities. In this study, we newly produced and evaluated potassium ion sensors by transfer printing technique.Schematic diagram of electrodes and the potassium ion sensor is shown in Figure 1 (a). Electrodes of the sensor were formed on a PET film by laminating overcoat, resist ink, carbon ink, Ag/AgCl ink, and adhesive using screen printing. The potassium ion selective membrane was prepared on the carbon electrode surface by drop-casting 8 μL of the solution which valinomycin, PVC, DOS, and KTCIPB were dissolved in THF and drying overnight. The Ag/AgCl reference electrode was prepared by drop-casting 8 μL of the solution which PVB and NaCl were dissolved in methanol and drying overnight. The sensor on the PET film was formed on the cloth using a heat transfer machine, and the potential difference measurement between the potassium ion selective electrode and the reference electrode was measured using a potassium chloride solution of 10-7 ~ 10-1 M.Figure 1 (b) shows the relationship between EMF of the sensor formed on the cloth by thermal transfer and potassium ion concentration. The sensor shows a linear region proportional to the potassium ion concentration in the range of 0.1 ~ 100 mM. Since the concentration of potassium ions in general human sweat is 4 ~ 24 mM4), the calculated detection lower limit suggests that this sensor may be used to quantify potassium ions in human sweat. Furthermore, selectivity coefficients of sensors for sodium ions and ammonium ions abundant in human sweat were calculated by a single solution method. The selectivity coefficient of sodium ions is , and the selectivity of ammonium ions is . These results suggest selectively measure potassium ion levels in human sweat.References1) Guinovart et al., Anal. Chem., 138, 7031-7038 (2013).2) Jeerapan et al., J. Mater. Chem. A, 4, 18342 (2016).3) Watanabe et al., Chemical Sensors, 33 (Supplement A), 67-69 (2017).4) Sonner et al., Biomicrofluidics, 9, 031301-10 (2015).AcknowledgmentsThis work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion． Figure 1

PEDOT(PSS) as Solid Contact for Ion-Selective Electrodes: The Influence of the PEDOT(PSS) Film Thickness on the Equilibration Times.

To understand the rate determining processes during the equilibration of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-based (PEDOT(PSS)-based) solid contact (SC) ion-selective electrodes (ISEs), the surfaces of Pt, Au, and GC electrodes were coated with 0.1, 1.0, 2.0, and 4.0 μm thick galvanostatically deposited PEDOT(PSS) films. Next, potential vs time transients were recorded with these electrodes, with and without an additional potassium ion-selective membrane (ISM) coating, following their first contact with 0.1 M KCl solutions. The transients were significantly different when the multilayered sensor structures were assembled on Au or GC compared to Pt. The differences in the rate of equilibration were interpreted as a consequence of differences in the hydrophilicity of PEDOT(PSS) in contact with the substrate electrode surfaces based on X-ray photoelectron spectroscopy (XPS) and synchrotron radiation-XPS (SR-XPS) analysis of 10-100 nm thick PEDOT(PSS) films. The influence of the layer thickness of the electrochemically deposited PEDOT(PSS)-films on the hydrophilicity of these films has been documented by contact angle measurements over PEDOT(PSS)-coated Au, GC, and Pt electrode surfaces. This study demonstrates that it is possible to minimize the equilibration (conditioning) time of SC ISEs with aqueous solutions before usage by optimizing the thickness of the SC layer with a controlled ISM thickness. PEDOT(PSS)-coated Au and GC electrodes exhibit a significant negative potential drift during their equilibration in an aqueous solution. By coating the PEDOT(PSS) surface with an ISM, the negative potential drift is compensated by a positive potential drift related to the hydration of the ISM and activity changes at the PEDOT(PSS)|ISM interface. The potential drifts related to activity changes in the ISM have been determined by a novel adaptation of the "sandwich membrane" method.

Understanding Side Reactions in K–O2 Batteries for Improved Cycle Life

Superoxide based metal-air (or metal-oxygen) batteries, including potassium and sodium-oxygen batteries, have emerged as promising alternative chemistries in the metal-air battery family because of much improved round-trip efficiencies (>90%). In order to improve the cycle life of these batteries, it is crucial to understand and control the side reactions between the electrodes and the electrolyte. For potassium-oxygen batteries using ether-based electrolytes, the side reactions on the potassium anode have been identified as the main cause of battery failure. The composition of the side products formed on the anode, including some reaction intermediates, have been identified and quantified. Combined experimental studies and density functional theory (DFT) calculations show the side reactions are likely driven by the interaction of potassium with ether molecules and the crossover of oxygen from the cathode. To inhibit these side reactions, the incorporation of a polymeric potassium ion selective membrane (Nafion-K(+)) as a battery separator is demonstrated that significantly improves the battery cycle life. The K-O2 battery with the Nafion-K(+) separator can be discharged and charged for more than 40 cycles without increases in charging overpotential.

Real-Time Two-Dimensional Imaging of Potassium Ion Distribution Using an Ion Semiconductor Sensor with Charged Coupled Device Technology

Two-dimensional real-time observation of potassium ion distributions was achieved using an ion imaging device based on charge-coupled device (CCD) and metal-oxide semiconductor technologies, and an ion selective membrane. The CCD potassium ion image sensor was equipped with an array of 32 × 32 pixels (1024 pixels). It could record five frames per second with an area of 4.16 × 4.16 mm(2). Potassium ion images were produced instantly. The leaching of potassium ion from a 3.3 M KCl Ag/AgCl reference electrode was dynamically monitored in aqueous solution. The potassium ion selective membrane on the semiconductor consisted of plasticized poly(vinyl chloride) (PVC) with bis(benzo-15-crown-5). The addition of a polyhedral oligomeric silsesquioxane to the plasticized PVC membrane greatly improved adhesion of the membrane onto Si(3)N(4) of the semiconductor surface, and the potential response was stabilized. The potential response was linear from 10(-2) to 10(-5) M logarithmic concentration of potassium ion. The selectivity coefficients were K(K(+),Li(+))(pot) = 10(-2.85), K(K(+),Na(+))(pot) = 10(-2.30), K(K(+),Rb(+))(pot) =10(-1.16), and K(K(+),Cs(+))(pot) = 10(-2.05).

Preparation and Application of Potassium Ion-Selective Membrane Electrode Based on Benzo-15-Crown-5 Ether

Preparation and Application of Potassium Ion-Selective Membrane Electrode Based on Benzo-15-Crown-5 Ether

EVALUATION OF NITRATE AND POTASSIUM ION-SELECTIVE MEMBRANES FOR SOIL MACRONUTRIENT SENSING

On-the-go, real-time soil nutrient analysis would be useful in site-specific management of soil fertility. The rapidresponse and low sample volume associated with ion-selective field-effect transistors (ISFETs) make them good soil fertilitysensor candidates. Ion-selective microelectrode technology requires an ion-selective membrane that responds selectively toone analyte in the presence of other ions in a solution. This article describes: (1) the evaluation of nitrate and potassiumion-selective membranes, and (2) the investigation of the interaction between the ion-selective membranes and soilextractants to identify membranes and extracting solutions that are compatible for use with a real-time ISFET sensor tomeasure nitrate and potassium ions in soil. The responses of the nitrate membranes with tetradodecylammonium nitrate(TDDA) or methlytridodecylammonium chloride (MTDA) and potassium membranes with valinomycin were affected by bothmembrane type and soil extractant. A TDDA-based nitrate membrane would be capable of detecting low concentrations in soils to about 10-5 mole/L NO3 -. The valinomycin-based potassium membranes showed satisfactory selectivity performancein measuring potassium in the presence of interfering cations such as Na+, Mg2+, Ca2+, Al3+, and Li+ as well as provideda consistent sensitivity when DI water, Kelowna, or Bray P1 solutions were used as base solutions. The TDDA-based nitratemembrane and the valinomycin-based potassium membrane, used in conjunction with Kelowna extractant, would allowdetermination of nitrate and potassium levels, respectively, for site-specific control of fertilizer application.

Methacrylate-acrylate based polymers of low plasticiser content for potassium ion-selective membranes

Polymers prepared from of glycidyl methacrylate, methyl methacrylate and n-butyl acrylate were studied for their possible use as a valinomycin-based potassium ion-selective membrane with low or no plasticiser content. Four polymers were observed to be functional as potassium ion-selective membranes in the presence of valinomycin and lipophilic salt. All polymeric membranes gave Nernstian or near-Nemstian responses over the potassium ion concentration range of 10 −5−10 −1 M. The potassium selectivity over sodium, log K pot KM values, for all membranes were in the range −3.0 to −4.1 as measured by the mixed solution method with interfering sodium ion at 0.1 M. Interference of Na + and other cations was also studied by the separate solution method. Terpolymers prepared from methacrylate-acrylate monomers with a high n-butyl acrylate ratio, required little or no o-NPOE as plasticiser to form functional potassium ion-selective membranes with only a slight decrease in potassium ion selectivity. The monomer n-butyl acrylate appeared to act as a built-in plasticiser to lower the glass transition temperature of the polymers and allowed potassium ion-selective behaviour to occur even in the absence of plasticiser.

Potassium ion selective membranes built by the Langmuir—Blodgett technique

Spreading monolayers of the ionophore valinomycin in mixtures with methyl stearate with different molar ratios were studied at the air/water interface in the 15–30 C temperature range. The bidimensional miscibility of the two components was deduced by recording spreading isotherms, which allowed also the evaluation of the thermodynamic parameters Δ G mix, Δ H mix and TΔ S mix. Languir—Blodgett (LB) films of mixtures with various molar ratios were built by transferring spreading monolayers from the air/water interface on to hydrophobic and hydrophilic substrates, and their electrical resistance was determined using KCl and NaCl solutions in the 10 −3-5·10 −1 M concentration range. It was verified that valinomycin-containing mixtures showed K − ion selectivity in LB films, at an opportune molar ratio between the two components.

Electrochemical performance, biocompatibility, and adhesion of new polymer matrices for solid-state ion sensors.

Ammonium and potassium ion-selective membranes formulated with PVC/hydroxylated PVC, polyurethane/hydroxylated PVC, and moisture-curable silicone rubber matrices are studied in an effort to extend the lifetime of solid-state ion sensors through improved membrane adhesion. The PVC/membranes exhibit electrochemical performance equivalent to that of conventional PVC membranes in terms of slope, detection limit, and selectivity. The polyurethane- and silicone-rubber-based membranes have better adhesion to silicon nitride than do PVC or hydroxylated PVC matrices. Incorporating a silanizing reagent (silicon tetrachloride) significantly improves the adhesion of the polyurethane matrix. The use of silicon tetrachloride in membrane matrices also enhances the electrochemical stability of the interfacial potential between ion-selective polymer-matrix membranes and silver epoxy inner reference electrodes of solid-state sensors. The biocompatibility of the polymer matrices is examined via radiotracer protein adsorption studies and whole blood clotting time measurements. The polyurethane- and silicone-rubber-based membranes exhibit less overall nonspecific protein adsorption than the PVC or hydroxylated PVC matrices.

Use of a crown ether-heteropoly acid precipitate as a potassium ion-selective membrane electrode

A Potassium ion-selective electrode based on dibenzo-18-crown-6-tungstophosphoric acid precipitate membrane is prepared and conditions for the best functioning have been investigated. The working concentration and pH-range of the electrode is 2.0×10−2 to 1.3×10−6 mol/l and 2.9–6.5, respectively. The selectivity coefficient values for a large number of cations are quite low except for caesium and ammonium ions. The electrode can tolerate non-aqueous content upto 20%.

Potassium ion-selective membrane electrodes based on naphtho-15-crown-5

The potassium-selective PVC membrane electrodes based on naphtho-15-crown-5 have rapid, stable and Nernstian response in the range 10 -1–10 -5 M. The selectivity coefficient for potassium over sodium is 4 × 10 -4.