Membranes

Editorial

5 pages, 201 KiB

Open AccessEditorial

Special Issue “Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs, and Applications for Ion Measurement”

by Andrzej Lewenstam and Krzysztof Dołowy

Membranes 2020, 10(12), 427; https://doi.org/10.3390/membranes10120427 - 15 Dec 2020

Cited by 3 | Viewed by 1860

Abstract

Ion sensors, conventionally known as ion-selective membrane electrodes, were devised 100 years ago with the invention of a pH electrode with a glass membrane (in 1906 Cremer, in 1909 Haber and Klemensiewicz) [...] Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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14 pages, 5523 KiB

Open AccessArticle

Understanding Bidirectional Water Transport across Bronchial Epithelial Cell Monolayers: A Microfluidic Approach

by Miroslaw Zajac, Slawomir Jakiela and Krzysztof Dolowy

Membranes 2023, 13(12), 901; https://doi.org/10.3390/membranes13120901 - 6 Dec 2023

Viewed by 1834

Abstract

Deciphering the dynamics of water transport across bronchial epithelial cell monolayers is pivotal for unraveling respiratory physiology and pathology. In this study, we employ an advanced microfluidic system to explore bidirectional water transport across 16HBE14σ bronchial epithelial cells. Previous experiments unveiled electroneutral multiple [...] Read more.

Deciphering the dynamics of water transport across bronchial epithelial cell monolayers is pivotal for unraveling respiratory physiology and pathology. In this study, we employ an advanced microfluidic system to explore bidirectional water transport across 16HBE14σ bronchial epithelial cells. Previous experiments unveiled electroneutral multiple ion transport, with chloride ions utilizing transcellular pathways and sodium ions navigating both paracellular and transcellular routes. Unexpectedly, under isoosmotic conditions, rapid bidirectional movement of Na⁺ and Cl⁻ was observed, leading to the hypothesis of a substantial transport of isoosmotic solution (145 mM NaCl) across cell monolayers. To validate this conjecture, we introduce an innovative microfluidic device, offering a 500-fold sensitivity improvement in quantifying fluid flow. This system enables the direct measurement of minuscule fluid volumes traversing cell monolayers with unprecedented precision. Our results challenge conventional models, indicating a self-regulating mechanism governing water transport that involves the CFTR channel and anion exchangers. In healthy subjects, equilibrium is achieved at an apical potential of Δφ_ap = −30 mV, while subjects with cystic fibrosis exhibit modulation by an anion exchanger, reaching equilibrium at [Cl] = 67 mM in the airway surface liquid. This nuanced electrochemical basis for bidirectional water transport in bronchial epithelia sheds light on physiological intricacies and introduces a novel perspective for understanding respiratory conditions. Full article

(This article belongs to the Special Issue Advances in Artiﬁcial and Biological Membranes, Volume II)

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(A) A comprehensive illustration of the measurement system is presented, with detailed descriptions provided in the legend. (B) The physical manifestation of the polycarbonate chamber, designed to house the epithelial cell insert, is depicted. (C) An actual representation of the microfluidic chip, featuring two T-arms designed for measuring the mobility of an oil droplet within a KHS fluid environment. (D) A graphical representation illustrating the relationship between oil-droplet mobility and length for three distinct capillary numbers. In this specific experiment, the continuous phase was represented by KHS1. (E) A graphical depiction of the dependence of oil-droplet mobility on capillary numbers <math display="inline"><semantics> <mrow> <mtext> </mtext> <mi>C</mi> <mi>a</mi> <mo>=</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>4</mn> </mrow> </msup> </mrow> </semantics></math> across different continuous phases: KHS1, KHS2, KHS3. (Mobility (β) is defined as the velocity of the droplet phase relative to the average velocity of the continuous phase.) Full article ">Figure 2
The figure delineates water transport across the 16HBE14σ cell monolayer under the influence of chloride gradients. Panel (A) demonstrates water transport across cell monolayers with the apical chamber filled with a low-chloride solution (KHS3) and the basolateral chamber filled with a high-chloride solution (KHS1). In Panel (B), water transport occurs in the reversed chloride gradient, with the apical chamber filled with a high-chloride solution (KHS1) and the basolateral chamber filled with a low-chloride solution (KHS3). The data are presented as mean ± SD (n = 5). Positive values indicate basolateral to apical water flux, while negative values indicate apical to basolateral water flux. Full article ">Figure 3
Water transport across 16HBE14σ cell monolayers was assessed under sodium gradients. (A) Water transport was examined in cell monolayers with the apical chamber filled with a low-sodium solution (KHS2), while the basolateral chamber contained a high-sodium solution (KHS1). (B) Conversely, water transport was studied in cell monolayers with a reversed sodium gradient. In this case, the apical chamber was filled with a high-sodium solution (KHS1), and the basolateral chamber contained a low-sodium solution (KHS2). The data are presented as mean ± SD (n = 4). Positive values indicate basolateral to apical water flux, while negative values denote apical to basolateral water flux. Full article ">Figure 4
The study investigated the initial and final concentrations of sodium, chloride, choline, and gluconate ions on either side of the cell layer, as well as the direction of solution transport across epithelial cell monolayers. The experiments were conducted under the influence of different gradients: (A) basolateral-to-apical sodium gradient; (B) apical-to-basolateral sodium gradient; (C) basolateral-to-apical chloride gradient; (D) apical-to-basolateral chloride gradient. Final concentrations were determined in the 5th minute after the cessation of solution flow. Full article ">Figure 5
Ionic transport direction in the CFTR channel relative to apical potential difference. Full article ">Figure 6
Directional preference of the Cl/HCO3 exchanger in response to varied chloride concentrations in the airway surface liquid (ASL) or medium. Full article ">

11 pages, 2904 KiB

Open AccessArticle

Changes in Ion Transport across Biological Membranes Exposed to Particulate Matter

by Jakub Hoser, Adrianna Dabrowska, Miroslaw Zajac and Piotr Bednarczyk

Membranes 2023, 13(9), 763; https://doi.org/10.3390/membranes13090763 - 29 Aug 2023

Viewed by 1097

Abstract

The cells of living organisms are surrounded by the biological membranes that form a barrier between the internal and external environment of the cells. Cell membranes serve as barriers and gatekeepers. They protect cells against the entry of undesirable substances and are the [...] Read more.

The cells of living organisms are surrounded by the biological membranes that form a barrier between the internal and external environment of the cells. Cell membranes serve as barriers and gatekeepers. They protect cells against the entry of undesirable substances and are the first line of interaction with foreign particles. Therefore, it is very important to understand how substances such as particulate matter (PM) interact with cell membranes. To investigate the effect of PM on the electrical properties of biological membranes, a series of experiments using a black lipid membrane (BLM) technique were performed. L-α-Phosphatidylcholine from soybean (azolectin) was used to create lipid bilayers. PM samples of different diameters (<4 (SRM-PM4.0) and <10 μm (SRM-PM10) were purchased from The National Institute of Standards and Technology (USA) to ensure the repeatability of the measurements. Lipid membranes with incorporated gramicidin A (5 pg/mL) ion channels were used to investigate the effect of PM on ion transport. The ionic current passing through the azolectin membranes was measured in ionic gradients (50/150 mM KCl on cis/trans side). In parallel, the electric membrane capacitance measurements, analysis of the conductance and reversal potential were performed. Our results have shown that PM at concentration range from 10 to 150 μg/mL reduced the basal ionic current at negative potentials while increased it at positive ones, indicating the interaction between lipids forming the membrane and PM. Additionally, PM decreased the gramicidin A channel activity. At the same time, the amplitude of channel openings as well as single channel conductance and reversal potential remained unchanged. Lastly, particulate matter at a concentration of 150 μg/mL did not affect the electric membrane capacity to any significant extent. Understanding the interaction between PM and biological membranes could aid in the search for effective cytoprotective strategies. Perhaps, by the use of an artificial system, we will learn to support the consequences of PM-induced damage. Full article

(This article belongs to the Special Issue Advances in Artiﬁcial and Biological Membranes, Volume II)

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Human bronchial epithelial cells were incubated in cell culture medium alone and in the presence of PM4.0 and PM10 for 24 h, 48 h and 72 h, respectively. Fragments of PM particles (<4 μm and PM < 10 μm) deposited on HBE cells are clearly visible. Blue arrows indicate healthy cell examples and black arrows indicate chosen particulate matter (PM). The pictures were taken with the DLTX1080PCMOSHDU2SD camera (DELTA optical) placed in inverted optical microscope (Olympus). Full article ">Figure 2
Black lipid membrane technique. (a) Scheme of the system used in black lipid membrane (BLM) experiments including antivibration table, Faraday’s cage, chamber with cis/trans side, amplifier, converter and PC. Buffers were at pH = 7.2 and trans side was grounded. (b) Representative recording in 50/150 mM KCl (cis/trans) gradient before and after incorporation of gramicidin A (arrow) at 0 mV—indicates the closed state. (c) Multi-channel recording in 50/150 mM KCl (cis/trans) gradient after incorporation of gA. The graph shows the method of ionic current area (pA*s) calculation over 20 s through lipid membrane with incorporated gramicidin A ion channel. Full article ">Figure 3
Effects of different PM concentrations on lipid membranes. (a) Registered current–time signals of ionic current flow through lipid bilayer membranes in control (0 μg/mL) and in the presence of 50, 100, 150 μg/mL PM4.0 and PM10 at a potential of +40 mV. (b,c) Analysis of the ionic current flow through lipid membrane at +40 and −40 mV without (control) and in the presence of PM4.0 and PM10 at concentrations of 10, 30, 50, 70, 100 and 150 μg/mL. The results are presented as mean ± SD, n = 5. Statistical significance was determined at p < 0.001 (***) using one-way ANOVA. Full article ">Figure 4
Electrical membrane capacitance changes in the presence of PM. Time-resolved effect of PM4.0 and PM10 (150 μg/mL) on electrical membrane capacitance changes. Results are presented as mean ± SD, n = 3. Statistical significance was determined at p < 0.05 (*) using one-way ANOVA. Full article ">Figure 5
Effects of PM on gramicidin A channels. (a) Registered signals of ionic current flow through azolectin bilayer membrane with incorporated gramicidin A (5 pg/mL) channels at −120 mV with and without presence 150 μg/mL of PM. (b,c) Effect of particulate matter on ionic current area through azolectin bilayer membrane with incorporated gramicidin A (5 pg/mL) channels with and without the presence of 150 μg/mL PM4.0 (b) and PM10 (c). (d,e) Effect of the particulate matter on ionic current amplitude of single gramicidin A (5 pg/mL) channel in the presence of PM4.0 (d) and PM10 (e) at a concentration of 150 μg/mL. Full article ">

19 pages, 10882 KiB

Open AccessArticle

An Electrochemistry and Computational Study at an Electrified Liquid–Liquid Interface for Studying Beta-Amyloid Aggregation

by Bongiwe Silwane, Mark Wilson and Ritu Kataky

Membranes 2023, 13(6), 584; https://doi.org/10.3390/membranes13060584 - 5 Jun 2023

Viewed by 1445

Abstract

Amphiphilic peptides, such as Aß amyloids, can adsorb at an interface between two immiscible electrolyte solutions (ITIES). Based on previous work (vide infra), a hydrophilic/hydrophobic interface is used as a simple biomimetic system for studying drug interactions. The ITIES provides a 2D interface [...] Read more.

Amphiphilic peptides, such as Aß amyloids, can adsorb at an interface between two immiscible electrolyte solutions (ITIES). Based on previous work (vide infra), a hydrophilic/hydrophobic interface is used as a simple biomimetic system for studying drug interactions. The ITIES provides a 2D interface to study ion-transfer processes associated with aggregation, as a function of Galvani potential difference. Here, the aggregation/complexation behaviour of Aβ_(1-42) is studied in the presence of Cu (II) ions, together with the effect of a multifunctional peptidomimetic inhibitor (P6). Cyclic and differential pulse voltammetry proved to be particularly sensitive to the detection of the complexation and aggregation of Aβ_(1-42), enabling estimations of changes in lipophilicity upon binding to Cu (II) and P6. At a 1:1 ratio of Cu (II):Aβ_(1-42), fresh samples showed a single DPV (Differential Pulse Voltammetry) peak half wave transfer potential (E1/2) at 0.40 V. Upon increasing the ratio of Cu (II) two-fold, fluctuations were observed in the DPVs, indicating aggregation. The approximate stoichiometry and binding properties of Aβ_(1-42) during complexation with Cu (II) were determined by performing a differential pulse voltammetry (DPV) standard addition method, which showed two binding regimes. A pKa of 8.1 was estimated, with a Cu:Aβ_1-42 ratio~1:1.7. Studies using molecular dynamics simulations of peptides at the ITIES show that Aβ_(1-42) strands interact through the formation of β-sheet stabilised structures. In the absence of copper, binding/unbinding is dynamic, and interactions are relatively weak, leading to the observation of parallel and anti-parallel arrangements of β-sheet stabilised aggregates. In the presence of copper ions, strong binding occurs between a copper ion and histidine residues on two peptides. This provides a convenient geometry for inducing favourable interactions between folded β-sheet structures. Circular Dichroism spectroscopy (CD spectroscopy) was used to support the aggregation behaviour of the Aβ_(1-42) peptides following the addition of Cu (II) and P6 to the aqueous phase. Full article

(This article belongs to the Special Issue Advances in Artiﬁcial and Biological Membranes, Volume II)

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12 pages, 1594 KiB

Open AccessArticle

Directly Using Ti₃C₂T_x MXene for a Solid-Contact Potentiometric pH Sensor toward Wearable Sweat pH Monitoring

by Rongfeng Liang, Lijie Zhong, Yirong Zhang, Yitian Tang, Meixue Lai, Tingting Han, Wei Wang, Yu Bao, Yingming Ma, Shiyu Gan and Li Niu

Membranes 2023, 13(4), 376; https://doi.org/10.3390/membranes13040376 - 25 Mar 2023

Cited by 4 | Viewed by 2183

Abstract

The level of hydrogen ions in sweat is one of the most important physiological indexes for the health state of the human body. As a type of two-dimensional (2D) material, MXene has the advantages of superior electrical conductivity, a large surface area, and [...] Read more.

The level of hydrogen ions in sweat is one of the most important physiological indexes for the health state of the human body. As a type of two-dimensional (2D) material, MXene has the advantages of superior electrical conductivity, a large surface area, and rich functional groups on the surface. Herein, we report a type of Ti₃C₂T_x-based potentiometric pH sensor for wearable sweat pH analysis. The Ti₃C₂T_x was prepared by two etching methods, including a mild LiF/HCl mixture and HF solution, which was directly used as the pH-sensitive materials. Both etched Ti₃C₂T_x showed a typical lamellar structure and exhibited enhanced potentiometric pH responses compared with a pristine precursor of Ti₃AlC₂. The HF-Ti₃C₂T_x disclosed the sensitivities of −43.51 ± 0.53 mV pH^–1 (pH 1–11) and −42.73 ± 0.61 mV pH^–1 (pH 11–1). A series of electrochemical tests demonstrated that HF-Ti₃C₂T_x exhibited better analytical performances, including sensitivity, selectivity, and reversibility, owing to deep etching. The HF-Ti₃C₂T_x was thus further fabricated as a flexible potentiometric pH sensor by virtue of its 2D characteristic. Upon integrating with a solid-contact Ag/AgCl reference electrode, the flexible sensor realized real-time monitoring of pH level in human sweat. The result disclosed a relatively stable pH value of ~6.5 after perspiration, which was consistent with the ex situ sweat pH test. This work offers a type of MXene-based potentiometric pH sensor for wearable sweat pH monitoring. Full article

(This article belongs to the Special Issue Advances in Artiﬁcial and Biological Membranes, Volume II)

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11 pages, 1666 KiB

Open AccessArticle

Interactions of Surfactants with Biomimetic Membranes—2. Generation of Electric Potential with Non-Ionic Surfactants

by Nikolai M. Kocherginsky and Brajendra K. Sharma

Membranes 2023, 13(3), 353; https://doi.org/10.3390/membranes13030353 - 18 Mar 2023

Cited by 1 | Viewed by 1715

Abstract

It is discovered that noncharged surfactants lead to electric effects that interact with biomimetic membranes made of nitrocellulose filters, which are impregnated with fatty acid esters. At a surfactant concentration as low as 64 microM in one of the solutions, they lead to [...] Read more.

It is discovered that noncharged surfactants lead to electric effects that interact with biomimetic membranes made of nitrocellulose filters, which are impregnated with fatty acid esters. At a surfactant concentration as low as 64 microM in one of the solutions, they lead to the transient formation of transmembrane electric potential. Maximum changes of this potential are proportional to the log of noncharged surfactant concentrations when it changes by three orders of magnitude. We explain this new and nontrivial effect in terms of an earlier suggested physicochemical mechanics approach and noncharged surfactants transient changes induced by membrane permeability for inorganic ions. It could be used to imitate the interactions of non-ionic drugs with biological membranes. The effect may also be used in determining the concentration of these surfactants and other non-ionic chemicals of concern, such as pharmaceuticals and personal care products. Full article

(This article belongs to the Special Issue Advances in Artiﬁcial and Biological Membranes, Volume II)

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Structures of nonionic surfactants (a) sorbitan monolaurate Span-20, (b) other sorbitans, (c) polyethylene glycol sorbitan monolaurate, Tween 20, (d) Tergitol, and (e) Triton X-100. Full article ">Figure 2
Transmembrane potential vs. time after the addition of 0.1 w/v% of different surfactants to the measuring (K+ acceptor) chamber containing 5 mM buffer. The reference (K+ donor) chamber contains 5 mM buffer + 0.5 M KCl. Full article ">Figure 3
Transmembrane potential vs. time after the addition of Tergitol 15-S-7 in concentrations 16, 32, 64, 97, 130, 162, 800, and 3880 μM to the measuring (acceptor) chamber, containing the 5 mM buffer. The reference (donor) chamber contains 5 mM buffer + 0.5 M KCl. Full article ">Figure 4
Transmembrane potential as a function of time when Tergitol 15-S-7 was added to the reference chamber. The measuring chamber contains a 5 mM buffer, while the reference chamber contains 5 mM buffer + 0.5 M KCl, pH = 4.6. Full article ">Figure 5
Net changes of the minimum value of the transmembrane potential as a function of log C (µm) for different Tergitols: ● 15-S-5, ▲ 15-S-7 and ■ 15-S-9. Full article ">Figure 6
Transmembrane potential as a function of time for impregnated nitrocellulose filters with pore size 0.05 μm and 0.45 μm. Full article ">Figure 7
Time dependence of current through the membrane in response to 3.5 mM Tween 20. 0.45 μm nitrocellulose filter impregnated with isopropyl myristate separated by a 5 mM buffer+ 0.5 M KCl and a 5 mM buffer. Full article ">Figure 8
The half-life time of potential relaxation kinetics vs. the thickness of the membrane with 0.05-micrometer pores after the addition of 0.1 wt% Tergitol 15-S-7. Full article ">

15 pages, 2205 KiB

Open AccessArticle

Novel Experimental Setup for Coulometric Signal Transduction of Ion-Selective Electrodes

by Naela Delmo, Zekra Mousavi, Tomasz Sokalski and Johan Bobacka

Membranes 2022, 12(12), 1221; https://doi.org/10.3390/membranes12121221 - 2 Dec 2022

Cited by 4 | Viewed by 2120

Abstract

In this work, a novel and versatile experimental setup for coulometric signal transduction of ion-selective electrodes (ISEs) is introduced and studied. It is based on a constant potential coulometric measurement carried out using a one-compartment three-electrode electrochemical cell. In the setup, a potassium [...] Read more.

In this work, a novel and versatile experimental setup for coulometric signal transduction of ion-selective electrodes (ISEs) is introduced and studied. It is based on a constant potential coulometric measurement carried out using a one-compartment three-electrode electrochemical cell. In the setup, a potassium ion-selective electrode (K⁺- ISE) is connected as the reference electrode (RE). A poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS)-based electrode with a dummy membrane (DM) and a glassy carbon (GC) rod are connected as the working electrode (WE) and counter electrode (CE), respectively. Adding a non-selective dummy membrane to the structure of the WE facilitates the regulation of the measured signal and response time. The results from electrochemical impedance spectroscopy measurements carried out on the WE showed that the time constant is profoundly influenced by the dummy membrane thickness. In addition, the redox capacitance of the PEDOT:PSS film shows a better correlation with the electrode area than the film thickness. Sequential addition/dilution experiments showed the improvement of current and cumulated charge signals in the new setup studied in this work compared to the setup used in the original coulometric signal transduction method. Both conventional ISEs and solid-contact ISEs (SCISEs) were used in this work. The results showed that the coulometric response was independent of the type of ISE used as RE, confirming the versatility of the novel set-up. Full article

(This article belongs to the Special Issue Advances in Artiﬁcial and Biological Membranes, Volume II)

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15 pages, 2530 KiB

Open AccessArticle

Electrically Enhanced Sensitivity (EES) of Ion-Selective Membrane Electrodes and Membrane-Based Ion Sensors

by Jan Migdalski and Andrzej Lewenstam

Membranes 2022, 12(8), 763; https://doi.org/10.3390/membranes12080763 - 3 Aug 2022

Cited by 2 | Viewed by 2224

Abstract

The use of external electronic enforcement in ion-sensor measurements is described. The objective is to improve the open-circuit (potentiometric) sensitivity of ion sensors. The sensitivity determines the precision of analyte determination and has been of interest since the beginning of ion-sensor technology. Owing [...] Read more.

The use of external electronic enforcement in ion-sensor measurements is described. The objective is to improve the open-circuit (potentiometric) sensitivity of ion sensors. The sensitivity determines the precision of analyte determination and has been of interest since the beginning of ion-sensor technology. Owing to the theoretical interpretation founded by W.E. Nernst, the sensitivity is characterized by the slope and numerically predicted. It is empirically determined and validated during calibration by measuring an electromotive force between the ion sensor and the reference electrode. In practice, this measurement is made with commercial potentiometers that function as unaltered “black boxes”. This report demonstrates that by gaining access to a meter’s electrical systems and allowing for versatile signal summations, the empirical slope can be increased favorably. To prove the validity of the approach presented, flow-through ion-sensor blocks used in routine measurements of blood electrolytes (Na⁺, K⁺, Li⁺, Cl⁻) and multielectrode probes with flat surfaces, similar to those applied previously for monitoring transmembrane fluxes of Na⁺, K⁺, Cl⁻ through living biological cells, are used. Several options to serve real-life electroanalytical challenges, including linear calibration for sensors with high-resistance membranes, responses with non-Nernstian slopes, non-linear calibration, and discrimination of nonfunctional sensors, are shown. Full article

(This article belongs to the Special Issue Advances in Artiﬁcial and Biological Membranes, Volume II)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
(a) Flow through set containing four ISE electrodes with plastic membranes and a REF electrode, all from KONE. (b) Multielectrode platform with an external diameter of 10 mm containing five Au/Ag disc substrates (0.5 mm diameter). The central electrode (indicated by an arrow) is a solid-contact reference electrode. It is surrounded by four SC ISs. Full article ">Figure 2
Potential changes of three highly resistive sodium electrodes with glass membranes and their summed signals (a). Calibration curves of three highly resistive sodium electrodes with glass membranes and of their summed signals (b). Measurements were performed in 0.1–0.0001 M NaCl solutions. Full article ">Figure 3
Responses of the lithium electrodes Li1, Li2, and Li3 and their summed signals recorded during LiCl addition to 140 mmol NaCl (a). The calibration curves of the lithium electrodes Li1, Li2, and Li3 and their summed signals (b). Potential changes were measured versus the flow-through KONE REF (electrode block used as shown in <a href="#membranes-12-00763-f001" class="html-fig">Figure 1</a>a). Full article ">Figure 4
Potential changes of three potassium-sensitive electrodes (K1, K2, and K3) and the sums of their signals recorded during calibration in 0.1–0.00001 M KCl solutions (a). Calibration curves for three potassium-sensitive electrodes present in the multielectrode platform and the summed signals (b). The multielectrode platform shown in <a href="#membranes-12-00763-f001" class="html-fig">Figure 1</a>b was used. Full article ">Figure 5
Potential changes of the flow-through sodium electrode connected simultaneously to three different ion-meter channels and their summed signals recorded during calibration in 0.1–0.000001 M NaCl solutions (a). Calibration curves of the flow-through sodium electrodes connected simultaneously to three different ion-meter channels and their summed signals (b). Full article ">Figure A1
Scheme of the summing amplifier built with the Ultralow Offset Voltage Operational Amplifier OP08A (Analog Device) as well as its cooperation with a multichannel ion-meter and data acquisition card (DAC). The scheme was made with the use of free EasyEDA software. Full article ">Figure A2
Potential changes of the chloride electrode connected simultaneously to three ion-meter channels with different gains equal to 1.0, 2.0, and 3.2, recorded during calibration in 0.1–0.000001 M KCl solutions (a). Calibration curves for chloride electrode connected simultaneously to three ion-meter channels with different gains equal to 1.0, 2.0, and 3.2 (b). Potential changes were measured versus the silver chloride electrode REF 251 (Metrohm). Full article ">

17 pages, 7686 KiB

Open AccessArticle

Plasticized PVC Membrane Modified Electrodes: Voltammetry of Highly Hydrophobic Compounds

by Ernő Lindner, Marcin Guzinski, Bradford Pendley and Edward Chaum

Membranes 2020, 10(9), 202; https://doi.org/10.3390/membranes10090202 - 27 Aug 2020

Cited by 11 | Viewed by 4846

Abstract

In the last 50 years, plasticized polyvinyl chloride (PVC) membranes have gained unique importance in chemical sensor development. Originally, these membranes separated two solutions in conventional ion-selective electrodes. Later, the same membranes were applied over a variety of supporting electrodes and used in [...] Read more.

In the last 50 years, plasticized polyvinyl chloride (PVC) membranes have gained unique importance in chemical sensor development. Originally, these membranes separated two solutions in conventional ion-selective electrodes. Later, the same membranes were applied over a variety of supporting electrodes and used in both potentiometric and voltammetric measurements of ions and electrically charged molecules. The focus of this paper is to demonstrate the utility of the plasticized PVC membrane modified working electrode for the voltammetric measurement of highly lipophilic molecules. The plasticized PVC membrane prevents electrode fouling, extends the detection limit of the voltammetric methods to sub-micromolar concentrations, and minimizes interference by electrochemically active hydrophilic analytes. Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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Figure 1
Schematic representation of the processes during the concentration (black arrows) and stripping (red arrows) of cations using a conductive polymer/plasticized PVC membrane modified electrode. The 18-crown-6 molecule in the PVC membrane represents any selective ionophore which may be used in this arrangement. Full article ">Figure 2
Linear sweep voltammograms recorded with a bare and a membrane-coated electrode in 49.8 µmol/L ascorbic acid (AA) (left) and 117.6 µmol/L p-acetamino phenol (APAP) (right) solutions. The insets show the membrane-coated sensor signal with much higher resolution in the current scale. The PVC membrane composition is 25% PVC, 50% bis(2-ethylhexyl)sebacate (DOS), 22% tetradodecylammonium tetrakis(pentafuorophenyl)borate (TDDA-TPFPhB) and 3% sodium tetrakis[3,5bis(trifluoromethyl) phenyl] borate (NaTFPhB). Full article ">Figure 3
Three different variations of the processes during voltammetric measurements of propofol with the PVC membrane modified electrode. In all three examples, propofol preferentially partitions into the membrane, and during its electrochemical oxidation, propofol positively charged intermediates are generated. The electroneutrality in the membrane is sustained through (a) the uptake of hydrophobic counterions, e.g., (<math display="inline"><semantics> <mrow> <mi>C</mi> <mi>l</mi> <msubsup> <mi>O</mi> <mn>4</mn> <mo>−</mo> </msubsup> </mrow> </semantics></math>) from the solution; (b) the release of positively charged counterions of the cation exchanger (e.g., K+) incorporated in the membrane; (c) the generation of negatively charged species on the counter electrode. In this scenario, both the working (WE) and counter (CE) electrodes are coated with the membrane. Full article ">Figure 4
Chronoamperometric response of a PVC-membrane-coated glassy carbon (GC) electrode upon spiking the phosphate buffered saline (PBS) background electrolyte with propofol standard solutions. The concentrations in the PBS solution labeled 1 to 9 are 1.25, 2.5, 4.98, 9.9, 19.6, 38.4, 56.6, 80.5 and 111.1 μmol/L. The inset in the lower right is the calibration curve constructed from the chronoamperometric currents. The inset in the upper left corner shows linear sweep voltammograms recorded in PBS background solution and in PBS with propofol concentrations between 9.9 and 111.1 μmol/L. Membrane composition 25.5% PVC, 50.9% 2-nitrophenyl octyl ether (o-NPOE), 21.2% tetradodecylammonium tetrakis(pentafluorophenyl) borate (TDDATPFPhB), 2.4% sodium tetrakis[3,5bis(trifluoromethyl) phenyl] borate (NaTFPhB). Full article ">Figure 5
Linear sweep voltammograms recorded in sertraline (upper left), amitriptyline (upper right) and aripiprazone (middle left), sirolimus (middle right), everolimus (lower left) and citalopram (lower right) solutions. The concentration ranges are indicated in the individual pictures. Full article ">Figure 6
Chronoamperometric transients recorded with the plasticized PVC membrane-coated GC electrode in PBS solution of different sertraline concentrations. Applied potential: 1.0 V. Full article ">Figure 7
The reproducibility of the chronoamperometric measurements in a continuous flow mode of measurement of amitriptyline with the PVC membrane-coated GC electrode in PBS solution. Applied potential: 0.95 V. The standard solutions are switched between 0 and 0.25 µmol/L and 0.25 and 0.5 µmol/L in the PBS background. The blue line represents the mean value of the current in 0.25 µmol/L amitriptyline and the red dotted lines represent ±1 standard deviation range of the data around the mean. Full article ">Figure 8
Repeated LSVs of a bare (left) and PVC membrane-coated (right) GC electrode in 50 µmol/L (bare, left) and 10 µmol/L (membrane-coated, right) amitriptyline containing solutions. Full article ">Scheme 1
Electrochemical notation of a potentiometric cell with a conventional, liquid inner contact ion-selective membrane electrode as indicator electrode and a double junction reference electrode. Full article ">Scheme 2
Electrochemical notation of solid contact ion-selective electrodes. (a) Coated wire electrode; (b) Conductive polymer (CP)-based solid contact electrode. Full article ">Scheme 3
Electrochemical notation of membrane modified voltammetric working electrodes. (a) Membrane directly deposited on the substrate electrode surface; (b) A conductive polymer (CP) layer is sandwiched between the substrate electrode and the membrane; (c) Multiple membrane layer modified electrode. Full article ">

18 pages, 3374 KiB

Open AccessArticle

Optimization of Ruthenium Dioxide Solid Contact in Ion-Selective Electrodes

by Nikola Lenar, Beata Paczosa-Bator and Robert Piech

Membranes 2020, 10(8), 182; https://doi.org/10.3390/membranes10080182 - 9 Aug 2020

Cited by 20 | Viewed by 3040

Abstract

Ruthenium dioxide occurs in two morphologically varied structures: anhydrous and hydrous form; both of them were studied in the scope of this work and applied as mediation layers in ion-selective electrodes. The differences between the electrochemical properties of those two materials underlie their [...] Read more.

Ruthenium dioxide occurs in two morphologically varied structures: anhydrous and hydrous form; both of them were studied in the scope of this work and applied as mediation layers in ion-selective electrodes. The differences between the electrochemical properties of those two materials underlie their diverse structure and hydration properties, which was demonstrated in the paper. One of the main differences is the occurrence of structural water in RuO₂•xH₂O, which creates a large inner surface available for ion transport and was shown to be a favorable feature in the context of designing potentiometric sensors. Both materials were examined with SEM microscope, X-ray diffractometer, and contact angle microscope, and the results revealed that the hydrous form can be characterized as a porous structure with a smaller crystallite size and more hydrophobic properties contrary to the anhydrous form. Potentiometric and electrochemical tests carried out on designed GCD/RuO₂/K⁺-ISM and GCD/RuO₂•xH₂O/K⁺-ISM electrodes proved that the loose porous microstructure with chemically bounded water, which is characteristic for the hydrous form, ensures the high electrical capacitance of electrodes (up to 1.2 mF) with consequently more stable potential (with the potential drift of 0.0015 mV/h) and a faster response (of a few seconds). Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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29 pages, 2738 KiB

Open AccessArticle

Precipitation of Inorganic Salts in Mitochondrial Matrix

by Jerzy J. Jasielec, Robert Filipek, Krzysztof Dołowy and Andrzej Lewenstam

Membranes 2020, 10(5), 81; https://doi.org/10.3390/membranes10050081 - 27 Apr 2020

Cited by 10 | Viewed by 6711

Abstract

In the mitochondrial matrix, there are insoluble, osmotically inactive complexes that maintain a constant pH and calcium concentration. In the present paper, we examine the properties of insoluble calcium and magnesium salts, such as phosphates, carbonates and polyphosphates, which might play this role. [...] Read more.

In the mitochondrial matrix, there are insoluble, osmotically inactive complexes that maintain a constant pH and calcium concentration. In the present paper, we examine the properties of insoluble calcium and magnesium salts, such as phosphates, carbonates and polyphosphates, which might play this role. We find that non-stoichiometric, magnesium-rich carbonated apatite, with very low crystallinity, precipitates in the matrix under physiological conditions. Precipitated salt acts as pH buffer, and, hence, can contribute in maintaining ATP production in ischemic conditions, which delays irreversible damage to heart and brain cells after stroke. Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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Full article ">Figure 1
The calculated activity coefficients for the main inorganic ions present in mitochondria, (a) in logarithmic scale and (b) in linear scale. Full article ">Figure 2
The calculated equilibrium concentrations of free calcium (a) as functions of pH at 37 °C and pCO2 = 7 kPa, (b) as a function of partial pressure of carbon dioxide at 37 °C and pH = 7.8. Full article ">Figure 3
The calculated equilibrium concentrations of free magnesium (a) as functions of pH at 35 °C and pCO2 = 7 kPa, (b) as a function of partial pressure of carbon dioxide at 35 °C and pH = 7.8. Full article ">Figure 4
The calculated equilibrium concentrations [∑Pi]eq required for the formation of calcium phosphates as functions of pH. Calcium concentration set to (a) [Ca2+] = 0.17 µM and (b) [Ca2+] = 5 µM. Full article ">Figure 5
The calculated equilibrium concentrations [∑Pi]eq required for the formation of magnesium phosphates as functions of pH. Magnesium concentration set to (a) [Mg2+] = 0.35 mM and (b) [Mg2+] = 1.5 mM. Full article ">Scheme 1
Ion channels, exchangers, pumps and oxidative phosphorylation chain of the inner mitochondrial membrane: green—uniporters, blue—exchangers, yellow—four complexes of oxidative phosphorylation chain, and red—ATP synthasome. There are more than one type of mitoBKCa, mitoKv or mitoCl channels. Full article ">

13 pages, 6597 KiB

Open AccessArticle

Measurement of Multi Ion Transport through Human Bronchial Epithelial Cell Line Provides an Insight into the Mechanism of Defective Water Transport in Cystic Fibrosis

by Miroslaw Zajac, Andrzej Lewenstam, Piotr Bednarczyk and Krzysztof Dolowy

Membranes 2020, 10(3), 43; https://doi.org/10.3390/membranes10030043 - 12 Mar 2020

Cited by 9 | Viewed by 4336

Abstract

We measured concentration changes of sodium, potassium, chloride ions, pH and the transepithelial potential difference by means of ion-selective electrodes, which were placed on both sides of a human bronchial epithelial 16HBE14σ cell line grown on a porous support in the presence of [...] Read more.

We measured concentration changes of sodium, potassium, chloride ions, pH and the transepithelial potential difference by means of ion-selective electrodes, which were placed on both sides of a human bronchial epithelial 16HBE14σ cell line grown on a porous support in the presence of ion channel blockers. We found that, in the isosmotic transepithelial concentration gradient of either sodium or chloride ions, there is an electroneutral transport of the isosmotic solution of sodium chloride in both directions across the cell monolayer. The transepithelial potential difference is below 3 mV. Potassium and pH change plays a minor role in ion transport. Based on our measurements, we hypothesize that in a healthy bronchial epithelium, there is a dynamic balance between water absorption and secretion. Water absorption is caused by the action of two exchangers, Na/H and Cl/HCO₃, secreting weakly dissociated carbonic acid in exchange for well dissociated NaCl and water. The water secretion phase is triggered by an apical low volume-dependent factor opening the Cystic Fibrosis Transmembrane Regulator CFTR channel and secreting anions that are accompanied by paracellular sodium and water transport. Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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22 pages, 2616 KiB

Open AccessArticle

Reference Electrodes with Polymer-Based Membranes—Comprehensive Performance Characteristics

by Peter Lingenfelter, Bartosz Bartoszewicz, Jan Migdalski, Tomasz Sokalski, Mirosław M. Bućko, Robert Filipek and Andrzej Lewenstam

Membranes 2019, 9(12), 161; https://doi.org/10.3390/membranes9120161 - 29 Nov 2019

Cited by 22 | Viewed by 6615

Abstract

Several types of liquid membrane and solid-state reference electrodes based on different plastics were fabricated. In the membranes studied, equitransferent organic (QB) and inorganic salts (KCl) are dispersed in polyvinyl chloride (PVC), polyurethane (PU), urea-formaldehyde resin (UF), polyvinyl acetate (PVA), as well as [...] Read more.

Several types of liquid membrane and solid-state reference electrodes based on different plastics were fabricated. In the membranes studied, equitransferent organic (QB) and inorganic salts (KCl) are dispersed in polyvinyl chloride (PVC), polyurethane (PU), urea-formaldehyde resin (UF), polyvinyl acetate (PVA), as well as remelted KCl in order to show the matrix impact on the reference membranes’ behavior. The comparison of potentiometic performance was made using specially designed standardized testing protocols. A problem in the reference electrode research and literature has been a lack of standardized testing, which leads to difficulties in comparing different types, qualities, and properties of reference electrodes. Herein, several protocols were developed to test the electrodes’ performance with respect to stability over time, pH sensitivity, ionic strength, and various ionic species. All of the prepared reference electrodes performed well in at least some respect and would be suitable for certain applications as described in the text. Most of the reference types, however, demonstrated some weakness that had not been previously highlighted in the literature, due in large part to the lack of exhaustive and/or consistent testing protocols. Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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Full article ">Figure 1
Schematic diagrams of reference electrodes (REs) used. On the left side general scheme of RE, where 1) is the Ag/AgCl electrode, 2) is the internal solution or solid contact, 3) is the membrane or frit. On the right side: (i.) RE with QB (PVC) and QB (PU) membranes, (ii.) RE with remelted inorganic salts (RKCl), (iii.) urea-formaldehyde (UF) resin-based RE, and (iv.) RE with PVA membrane. More detailed characterization of (i.–iv.) type is provided in the text. Full article ">Figure 2
Stability over (a) 1 h, (b) 10 h, and (c) 20 h in 10−4 M KCl at 23 °C for 1. QB (PVC), 2. QB (PU), 3. RKCl, 4. PVA, 5. UF, 6. Sureflow, 7. REFEX, 8. Orion Ross Ultra. Full article ">Figure 2 Cont.
Stability over (a) 1 h, (b) 10 h, and (c) 20 h in 10−4 M KCl at 23 °C for 1. QB (PVC), 2. QB (PU), 3. RKCl, 4. PVA, 5. UF, 6. Sureflow, 7. REFEX, 8. Orion Ross Ultra. Full article ">Figure 3
pH titrations with the various reference electrodes tested. 1(+) QB(PVC), 2(o) QB(PU), 3(●) RKCl, 4(×) PVA, 5(■) UF, 6(□) Sureflow, 7(△) REFEX, 8(◇) Orion Ross Ultra. Full article ">Figure 4
pH titrations with the various reference electrodes tested. 1(+) QB(PVC), 2(o) QB(PU), 3(●) RKCl, 4(×) PVA, 5(■) UF, 6(□) Sureflow, 7(△) REFEX, 8(◇) Orion Ross Ultra. Full article ">Figure 5
MSP results for the experimental and commercial electrodes tested for this study. 1(+) QB(PVC), 2(o) QB(PU), 3(●) RKCl, 4(×) PVA, 5(■) UF, 6(□) Sureflow, 7(△) REFEX, 8(◇) Orion Ross Ultra. Full article ">Figure 6
Effect of aging on the 1. QB(PVC), 2. UF, and 3. PVA reference electrodes (a) soon after production and (b) after three months of semi-regular use. Full article ">

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14 pages, 593 KiB

Open AccessReview

Unintended Changes of Ion-Selective Membranes Composition—Origin and Effect on Analytical Performance

by Krzysztof Maksymiuk, Emilia Stelmach and Agata Michalska

Membranes 2020, 10(10), 266; https://doi.org/10.3390/membranes10100266 - 28 Sep 2020

Cited by 28 | Viewed by 3897

Abstract

Ion-selective membranes, as used in potentiometric sensors, are mixtures of a few important constituents in a carefully balanced proportion. The changes of composition of the ion-selective membrane, both qualitative and quantitative, affect the analytical performance of sensors. Different constructions and materials applied to [...] Read more.

Ion-selective membranes, as used in potentiometric sensors, are mixtures of a few important constituents in a carefully balanced proportion. The changes of composition of the ion-selective membrane, both qualitative and quantitative, affect the analytical performance of sensors. Different constructions and materials applied to improve sensors result in specific conditions of membrane formation, in consequence, potentially can result in uncontrolled modification of the membrane composition. Clearly, these effects need to be considered, especially if preparation of miniaturized, potentially disposable internal-solution free sensors is considered. Furthermore, membrane composition changes can occur during the normal operation of sensors—accumulation of species as well as release need to be taken into account, regardless of the construction of sensors used. Issues related to spontaneous changes of membrane composition that can occur during sensor construction, pre-treatment and their operation, seem to be underestimated in the subject literature. The aim of this work is to summarize available data related to potentiometric sensors and highlight the effects that can potentially be important also for other sensors using ion-selective membranes, e.g., optodes or voltammetric sensors. Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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24 pages, 14297 KiB

Open AccessEditor’s ChoiceReview

Solid-Contact Ion-Selective Electrodes: Response Mechanisms, Transducer Materials and Wearable Sensors

by Yan Lyu, Shiyu Gan, Yu Bao, Lijie Zhong, Jianan Xu, Wei Wang, Zhenbang Liu, Yingming Ma, Guifu Yang and Li Niu

Membranes 2020, 10(6), 128; https://doi.org/10.3390/membranes10060128 - 23 Jun 2020

Cited by 99 | Viewed by 10374

Abstract

Wearable sensors based on solid-contact ion-selective electrodes (SC-ISEs) are currently attracting intensive attention in monitoring human health conditions through real-time and non-invasive analysis of ions in biological fluids. SC-ISEs have gone through a revolution with improvements in potential stability and reproducibility. The introduction [...] Read more.

Wearable sensors based on solid-contact ion-selective electrodes (SC-ISEs) are currently attracting intensive attention in monitoring human health conditions through real-time and non-invasive analysis of ions in biological fluids. SC-ISEs have gone through a revolution with improvements in potential stability and reproducibility. The introduction of new transducing materials, the understanding of theoretical potentiometric responses, and wearable applications greatly facilitate SC-ISEs. We review recent advances in SC-ISEs including the response mechanism (redox capacitance and electric-double-layer capacitance mechanisms) and crucial solid transducer materials (conducting polymers, carbon and other nanomaterials) and applications in wearable sensors. At the end of the review we illustrate the existing challenges and prospects for future SC-ISEs. We expect this review to provide readers with a general picture of SC-ISEs and appeal to further establishing protocols for evaluating SC-ISEs and accelerating commercial wearable sensors for clinical diagnosis and family practice. Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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