Internal Electrolyte Solution Research Articles

Bipolar Clark-Type Oxygen Electrode Arrays for Imaging and Multiplexed Measurements of the Respiratory Activity of Cells.

Various miniature Clark-type oxygen electrodes (COEs), which are typically used to measure dissolved oxygen (DO) concentration in cellular respiration, have been developed since the 1980s. Arrays with individually addressable electrodes that constitute the sensor were used for various applications. However, the large number of leads and contact pads required for connecting the electrodes and the external instrument complicate the electrode layout and make the operation of integrated COE arrays challenging. Here, we fabricated closed bipolar electrochemical systems comprising 6 × 8 and 4 × 4 arrays of COEs for imaging and multiplexed detection. The cathodic compartment was sealed with a hydrophobic oxygen-permeable membrane to separate the internal electrolyte solution from the sample solutions. Using the bipolar Clark-type oxygen electrode (BCOE) arrays and electrochemiluminescence (ECL), we measured the DO concentration at each cathode. The results revealed that the ECL intensity changed linearly with the DO concentration. In addition, we used ECL imaging to investigate the respiratory activity of Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) in suspensions with different cell densities. The ECL images showed that the ECL intensity changed noticeably with the bacterial density. The bacterial respiratory activity was then qualitatively analyzed based on the ECL images acquired successively over a time duration. Further, we measured the antibiotic efficacy of piperacillin, oxacillin, gentamicin, and cefmetazole against E. coli and P. aeruginosa using the BCOE. We found that the ECL intensity increased with the antibiotic concentration, thus indicating the suppression of the bacterial respiratory activity.

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

Potentiometric sensors are the largest and most commonly used group of electrochemical sensors. Among them, ion-selective electrodes hold a prominent place. Since the end of the last century, their re-development has been observed, which is a consequence of the introduction of solid contact constructions, i.e., electrodes without an internal electrolyte solution. Research carried out in the field of potentiometric sensors primarily focuses on developing new variants of solid contact in order to obtain devices with better analytical parameters, and at the same time cheaper and easier to use, which has been made possible thanks to the achievements of material engineering. This paper presents an overview of new materials used as a solid contact in ion-selective electrodes over the past several years. These are primarily composite and hybrid materials that are a combination of carbon nanomaterials and polymers, as well as those obtained from carbon and polymer nanomaterials in combination with others, such as metal nanoparticles, metal oxides, ionic liquids and many others. Composite materials often have better mechanical, thermal, electrical, optical and chemical properties than the original components. With regard to their use in the construction of ion-selective electrodes, it is particularly important to increase the capacitance and surface area of the material, which makes them more effective in the process of charge transfer between the polymer membrane and the substrate material. This allows to obtain sensors with better analytical and operational parameters. Brief characteristics of electrodes with solid contact, their advantages and disadvantages, as well as research methods used to assess their parameters and analytical usefulness were presented. The work was divided into chapters according to the type of composite material, while the data in the table were arranged according to the type of ion. Selected basic analytical parameters of the obtained electrodes have been collected and summarized in order to better illustrate and compare the achievements that have been described till now in this field of analytical chemistry, which is potentiometry. This comprehensive review is a compendium of knowledge in the research area of functional composite materials and state-of-the-art SC-ISE construction technologies.

A downhole CO2 sensor to monitor CO2 movement in situ for geologic carbon storage

This paper describes how a downhole CO2 chemical sensor was prepared for use in determining the concentration of CO2 in water, particularly in harsh, high-pressure environments such as those found in geological formations considered for the geologic storage of CO2. The sensor consisted of a pair of Ir/IrOx and Ag/AgCl electrodes, a gas-permeable membrane, a bicarbonate-based internal electrolyte solution, and porous stainless steel as supporting material. The sensor was tested in the solution with different concentrations of CO2 and displayed very good CO2 sensing performance under pressures of 1000, 2000, and 3000psi. A linear relationship between the sensor response potential and the logarithm of the CO2 concentration was obtained for the sensor under different pressures. Reproducibility of the sensor was examined and the results indicated that the sensor displayed excellent reproducibility. CO2/brine core flooding tests were carried out to evaluate the performance of the CO2 sensor in simulate CO2 storage process. The results indicated that the sensor could detect CO2 movement in the tests. Further studies showed that the sensor could be reused by brine flooding after CO2/brine flushed the core. The results of the core flooding tests demonstrated that the sensor had potential application for CO2 monitoring in carbon storage.

Electroflotation extraction of low-soluble copper compounds from PCB production flushing water

The influence of the internal phase nature and electrolyte solution on the electroflotation extraction of the low-soluble copper compounds from the PCB production flushing water of the electronic technology was specified. Electroflotation activity decreases in the series Cu(OH)2, CuCO3, Cu3PO4, CuS. The influence of the surfactants (SAT) on the kinetics of the electroflotation process, on the particle size of the internal phase and electrokinetic potential has been studied. The change in the ξ-potential (for anion and cation SAT) and particle size (1.5–2 times) was specified for SAT. The electroflotation efficiency of Cu(OH)2, Cu3PO4, and CuS under the optimum conditions is 98.5 and 90%, correspondingly.

The renewable bismuth bulk annular band working electrode: Fabrication and application in the adsorptive stripping voltammetric determination of nickel(II) and cobalt(II)

The paper presents the first report on fabrication and application of a user friendly and mercury free electrochemical sensor, with the renewable bismuth bulk annular band working electrode (RBiABE), in stripping voltammetry (SV). The sensor body is partly filled with the internal electrolyte solution, in which the RBiABE is cleaned and activated before each measurement. Time of the RBiABE contact with the sample solution is precisely controlled. The usefulness of this sensor was tested by Ni(II) and Co(II) traces determination by means of differential pulse adsorptive stripping voltammetry (DP AdSV), after complexation with dimethylglyoxime (DMG) in ammonia buffer (pH 8.2). The experimental variables (composition of the supporting electrolyte, pre-concentration potential and time, potential of the RBiABE activation, and DP parameters), as well as possible interferences, were investigated. The linear calibration graphs for Ni(II) and Co(II), determined individually and together, in the range from 1×10−8 to 70×10−8molL−1 and from 1×10−9 to 70×10−9molL−1 respectively, were obtained. The calculated limit of detection (LOD), for 30s of the accumulation time, was 3×10−9molL−1 for Ni(II) in case of a single element’s analysis, whereas the LOD was 5×10−9molL−1 for Ni(II) and 3×10−10molL−1 for Co(II), when both metal ions were measured together. The repeatability of the Ni(II) and Co(II) adsorptive stripping voltammetric signals obtained at the RBiABE were equal to 5.4% and 2.5%, respectively (n=5). Finally, the proposed method was validated by determining Ni(II) and Co(II) in the certified reference waters (SPS-SW1 and SPS-SW2) with satisfactory results.

New electrochemical sensor with the renewable silver annular band working electrode: Fabrication and application for determination of selenium(IV) by cathodic stripping voltammetry

The paper presents the first report on the fabrication of an electrochemical sensor with the renewable silver annular band working electrode (RAgABE) and its application for cathodic stripping voltammetric (CSV) determination of Se(IV) in real water samples. The sensor consists of the RAgABE, integrated with the silver annular band counter/quasi-reference electrode (AgABQRE). The sensor body is partly filled with the internal electrolyte solution, in which the RAgABE is cleaned and activated, before each measurement and the analyte is stripped. Time of the RAgABE contact with the sample solution is precisely controlled. The sensor was successfully applied for Se(IV) determination in the Surface Waters SPS-SW1 and SPS-SW2 certified reference materials.

All-Solid-State pH Sensor Based on Conducting Polymer

A solid-state (free of internal electrolyte solution) reference electrode based on metallic silver is simply fabricated via a simple electrodeposition from AgNO3. Potentiometry is carried out to study the performance of the solid-state reference electrode in comparison with the commercial Ag/AgCl reference electrode. In addition, the proposed solid-state reference electrode has been integrated with the PPy-modified pH electrode to form an all-solid-state pH sensor, showing the capability of pH measurement. Absence of the internal solution leads to the pH sensor that is convenient to use and maintenance. In addition, the proposed pH sensor is possibly applied to biochemical and medical processes as well as flow infection analysis.

Solid‐State Microelectrodes for Flow‐Cell Analysis Based on Planar Back‐Side Contact Transducers

AbstractThis paper presents an overview of the studies carried out in the recent years in our laboratory, on the construction of different solid‐state microelectrodes for flow‐cell analysis. The microelectrodes were based on planar transducers made from a printed circuit board and manufactured as back‐side contact structures, which facilitate their mounting in a flow‐cell. Performances of the polymeric membrane ion‐selective: coated‐wire microelectrodes and microsensors with a polyHEMA layer containing internal electrolyte are compared. Conducting polymer – polypyrrole doped with ester of sulfosuccinic acid – was added to the PVC membranes to develop all‐solid‐state microelectrodes without internal electrolyte solution, exhibiting good potential stability in time. Finally, all‐solid‐state reference microelectrodes based on back‐side contact transducers are prepared and examined. These structures were applied as reference electrodes in flow‐cell measurements with potassium‐selective planar microelectrodes.

Needle-Type Ultra Micro Silver/Silver Chloride Reference Electrode for Use in Micro-Electrochemistry

A needle-type ultra micro silver/silver chloride reference electrode having a micro capillary with outer and inner diameters of 1.0 microm and 0.5 +/- 0.2 microm, respectively, was constructed. This micro reference electrode can be stuck into a living cell, and is applicable to use in very small environments, such as an electrochemical cell of an electrochemical scanning tunneling microscope or the detection portion of a micro-TAS. Excellent stability and repeatability of the micro reference electrode potential could be obtained by filling the micro capillary with agar gel containing 3.33 mol/L potassium chloride as a salt bridge, by covering the bare part of the silver wire on which silver chloride was deposited, and by electromagnetic shielding of the measurement cell and wire lead from the electromagnetic waves. The electrode showed stable potential for 7 days after its fabrication using 3.3 mol/L potassium chloride aqueous solution containing silver chloride as an internal electrolyte solution. The electrode exhibited constant electrode potential and excellent stability in test solutions of pH 5-9. The electrode potential of a commercial pH glass electrode measured against the micro reference electrode in standard pH buffer solutions was in good accordance with the Nernst equation.

Ni(II)cyclam Catalyzed Reduction of CO2 – Towards a Voltammetric Sensor for the Gas Phase

AbstractThe detection of CO2 in the gas phase is possible in presence of oxygen with an amalgamated Au‐poly(tetrafluoroethylene) gas diffusion electrode and an internal electrolyte solution containing Ni(II)cyclam. For concentrations between 0.1 to 1% the electrochemical cell has a sensitivity of 3.58 mA %−1 and the detection limit is 500 ppm. In preliminary experiments at rotating disk electrodes the optimum pH‐range was found to be between 3.5 to 6 and a selectivity ratio of the catalyst for CO2/H+ of 5 : 1 could be determined. The relationship between reduction current and the square root of the angular speed is linear, indicating that the electrochemical process is limited by diffusion of CO2. Tl and Pb are presented as alternative electrode materials at which the Ni(II)cyclam catalyzed reduction of CO2 can be observed. Problems arise from fouling effects at the sensing electrode and a non‐linearity of the calibration plot at higher concentrations.

Rotating Ion‐Selective Membrane Electrodes for Trace‐Level Measurements

AbstractIon‐selective solvent polymeric membrane electrodes (ISEs) are shown to exhibit improved response characteristics in a rotating electrode configuration. With a rather concentrated internal electrolyte solution of primary (analyte) ions, which induces their leaching from the membrane into the sample, the detection limit of the ISEs rotating at 3000 rpm is found to be better by about one order of magnitude than that of the analogous conventional ones in a stirred solution. On the other hand, with an internal solution inducing a strong inward flux of primary ions (i.e., from the sample to the ISE membrane), the apparent super‐Nernstian response due to depletion of primary ions from the analyte solution near the membrane surface is shifted by about one order of magnitude to lower concentrations. Membranes of about 0.8 mm diameter positioned eccentrically with respect to the rotation axis give a further shift of the apparent super‐Nernstian response step by about 0.3 logarithmic units. Simultaneously, the use of rotating electrodes substantially lowers the response time at submicromolar activities. An eccentrically placed Pb2+‐selective membrane on a rotating disk electrode with optimized internal solution shows a lower detection limit of aPb=6.3×10−11 M.

A reversible electrochemical nanosyringe pump and some considerations to realize low-power consumption

An electrochemical syringe pump was fabricated by micromachining. Two sets of thin-film three-electrode systems for actuation and sensing were formed on a glass substrate, whereas a microflow channel and a microcontainer for the internal electrolyte solution were formed on a silicon substrate. Hydrogen gas produced or consumed on a platinum black working electrode was used as a working medium. The rates of pumping for flushing and sampling could be varied by adjusting the potential of the working electrode at appropriate values to reduce and oxidize the related species. As a result, bi-directional pumping could easily be realized. During pumping repeated up to 20 times, the deviation of the pumping rates was distributed within 7% of the respective averages. The function of the micropump incorporated in a system was tested using a solution containing Cu 2+ ions and a distinct current increase accompanying the reduction of the ions was observed following the sampling. When the goal is to reduce power consumption, the material used for the auxiliary electrode is critical and Ag/AgCl was considered to be a good alternative for a platinum auxiliary electrode.

Sensitive electrochemical detection of ozone

An amperometric sensor capable of detecting ozone in the low ppb range was developed. The most suitable electrochemical cell was based on a gold-Nafion electrode with 0.5 M H 2SO 4 as internal electrolyte solution. It is demonstrated, that by careful selection of the experimental conditions such as electrode materials, electrolyte solution and applied potential the determination of low concentrations of ozone in air is possible with detection limits of 0.6 ppb. Cross-sensitivities to the major inorganic gaseous species found in the atmosphere, are also presented, and the use of a chemical filter to circumvent the interference by nitrogen dioxide is described.

Fabrication of a sensing module using micromachined biosensors

Micromachining is a powerful tool in constructing micro biosensors and micro systems which incorporate them. A sensing module for blood components was fabricated using the technology. The analytes include glucose, urea, uric acid, creatine, and creatinine. Transducers used to construct the corresponding sensors were a Severinghaus-type carbon dioxide electrode for the urea sensor and a Clark-type oxygen electrode for the other analytes. In these electrodes, detecting electrode patterns were formed on a glass substrate by photolithography and the micro container for the internal electrolyte solution was formed on a silicon substrate by anisotropic etching. A through-hole was formed in the sensitive area, where a silicone gas-permeable membrane was formed and an enzyme was immobilized. The sensors were characterized in terms of pH and temperature dependence and calibration curves along with detection limits. Furthermore, the sensors were incorporated in an acrylate flow cell. Simultaneous operation of these sensors was successfully conducted and distinct and stable responses were observed for respective sensors.

Determination of blood pO 2 using a micromachined Clark-type oxygen electrode

Variation of the performance of a micromachined Clark-type oxygen electrode in decreasing the size of the cathode was examined aiming for the measurement of pO 2 in whole blood. In the oxygen electrode, a cathode and an anode were formed as thin-film patterns on a glass substrate and a micro container for the internal electrolyte solution was formed on a silicon substrate by anisotropic etching. A silicone rubber gas-permeable membrane was formed on the sensitive area. Seven types of oxygen electrodes with cathodes whose dimensions ranged from 25 μm×25 μm to 500 μm×500 μm were fabricated. Linear calibration curves were obtained for the respective electrodes with correlation coefficients higher than 0.995. Flow dependence of the output current was suppressed from 10–11% with the 500 μm square cathode to 1–4% with the 25 μm square cathode. Furthermore, the flow dependence was reduced by approximately one order of magnitude with the existence of the gas-permeable membrane. Response time was also dependent on the size of the cathode and became shorter as the cathode became larger. The performance of the oxygen electrode was directly compared to a commercially available blood gas analyzer in the measurement of pO 2 in whole blood. Overall, the values by the oxygen electrodes microfabricated in this study were found to be within 26% of those by the blood gas analyzer. In addition, the values by the electrodes with smaller cathodes were found to be within 8% of those by the blood gas analyzer suggesting that the microfabricated oxygen electrode can actually be used in blood gas analysis if the cathode is properly designed.

Amperometric gas sensors with detection limits in the low ppb range

Amperometric gas sensors for monitoring toxic and industrially important gases down to low ppb concentrations at room temperature are described. The design of the sensors is based on a porous electrode chemically deposited onto one side of a Nafion ® cation exchange membrane, which acts as the sensing electrode for the trace gas to be determined. The electrode is mounted into the cell with the sensing side in direct contact with the gas entry chamber and the bare Nafion side in contact with an internal electrolyte solution. It is shown that by careful selection of the experimental conditions the sensor may be tailored to the analysis of traces of gases such as sulphur dioxide, ethylene, ethanol, acetaldehyde and acetylene. The properties of this cell design are discussed, and the influences of parameters such as flow rate of the gas stream and humidity on the sensing behaviour are highlighted.

Lowering the Detection Limit of Solvent Polymeric Ion-Selective Membrane Electrodes. 2. Influence of Composition of Sample and Internal Electrolyte Solution

The influence of the composition of the internal electrolyte solution on the response of Pb2+- and Ca2+-selective membrane electrodes is investigated. It is shown that the lower detection limit is improved by generating, in the membrane, ionic gradients that lead to a flux of primary ions toward the inner reference electrolyte solution. If the ion flux is too strong, it may cause analyte depletion at the membrane surface and, as a consequence, apparent super-Nernstian response. Such electrodes are not adequate to measure low analyte activities but can be used to determine unbiased selectivity factors. The results are interpreted in terms of a steady-state model, introduced in the companion paper, that describes the influence of concentration gradients generated by ion-exchange and coextraction processes on both sides of the membrane.

Amperometric detection of gaseous ethanol and acetaldehyde at low concentrations on an Au–Nafion electrode

An amperometric sensor capable of detecting mixtures of ethanol and acetaldehyde in the low ppb range without the need for prior separation is described. The electrochemical cell was based on a Au sensing electrode chemically deposited onto one side of a Nafion membrane with 1 M NaOH internal electrolyte solution. The detection was achieved by applying two potentials, –450 and –290 mV vs. a saturated mercury–mercurous sulfate electrode (MSE), at which ethanol and acetaldehyde react at different rates. Under the conditions investigated, acetaldehyde oxidation was mass transport limited at both potentials, whereas the anodic current due to the oxidation of ethanol was 40% lower at the more cathodic potential. Detection limits of 2 and 1 ppb (S/N = 3) were determined for ethanol and acetaldehyde respectively when the analyte species were detected individually. Poisoning of the working electrode was not observed for concentrations of ethanol in the ppb range. Acetaldehyde oxidation was found not to affect the sensing electrode condition, even at concentrations of several tens of ppm.

New Baw Sensors for Dissolved Gases

Novel BPES (Bulk Acoustic Wave Piezoelectric Crystal with Electrodes in Series) sensors for dissolved gases are proposed. They are based on the non-mass effect response of the sensor to the change in conductivity of the internal electrolyte solution of the sensing device, caused by the dissolved gas. Several kinds of such sensors are described for dissolved sulphur dioxide, nitrogen dioxide, carbon dioxide, and ammonia. Factors affecting the sensor performance are discussed, including buffer composition, unreacted foreign electrolyte in the internal solution, osmotic effect, and cell constant of the probe. This type of gas sensing device is advantageous over conventional potentiometric sensors for dissolved gases based on ion-selective electrodeS in their high sensitivity, fast response, not requiring either a reference electrode or a fragile glass pH electrode, and simple construction. Their applications in medicine, environmental science, food technology, and enzymology are provided.

Micromachined liquid-junction Ag/AgCl reference electrode

A liquid-junction Ag/AgCl reference electrode was fabricated using microfabrication techniques. It employed a novel thin-film Ag/AgCl structure which functioned normally even in a solution saturated with KCl. The container for the internal electrolyte solution and the liquid junction were formed by anisotropically etching a silicon substrate. A pin-hole junction and a combination of the pin-hole and a cellulose-acetate-plug junctions were tested. Although the electrode with the former junction showed constant drift of the potential to the positive side, the electrode with the latter junction could maintain a potential level within ±1 mV for several h. No dependence on pH and KCl concentration was observed for the latter type, which was also applied to pH measurement in combination with a commercial pH glass electrode.