Development of glass micro-electrodes for local electric field, electrical conductivity, and pH measurements

Doi, Kentaro; Asano, Nadja Maria Jorge

doi:10.1038/s41598-020-60713-z

Cited by 11 publications

(15 citation statements)

References 50 publications

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“…As Pergel et al 43 indicated a possibility of steady-state measurements as well as equilibrium conditions, the present study also improved the pH resolution by applying galvanostatic currents. 37 In this study, we found that PEG solutions filled in the tips effectively work to increase ΔV which contributes to high-pH resolutions compared with the case of no stuffing materials in the tips. Furthermore, stability and reproducibility of electrical potential responses were clearly improved.…”

Section: ■ Results and Discussionmentioning

confidence: 66%

pH Sensing Based on Ionic Current Rectification Using Triple-Barreled Glass Microelectrodes

Kishimoto,

Doi

2023

J. Phys. Chem. C

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Glass nanopores are known to provide proton selectivity in ionic current conditions in which silanol groups that fill glass surfaces support proton conduction along the surfaces in aqueous solutions. Negatively charged glass surfaces furthermore exclude anions from the glass nanopores. Therefore, glass electrodes are often used for the probes of pH sensors. We focused on the ion selectivity and ionic current rectification of glass nanopores. In this study, we propose triple-barreled glass microelectrodes that enable us to measure proton concentrations at local points with spatial resolution of the tip diameter. The glass microelectrodes consist of three capillaries for the working, counter, and reference electrodes filled with electrolyte and pH buffer solutions. A pH 1.68 buffer and KCl solution as a supporting electrolyte are maintained in a glass capillary for the counter electrode, and KCl solutions are in the working and reference electrodes. In galvanostatic current conditions, potential differences are measured in sample solutions. The potential difference is caused by the proton concentration gradient and proton-selective conduction, which is known as electrodiffusioosmosis. The ionic current is rectified due to the proton selectivity of the glass capillary, and as a result, the conductivity reflects the relative difference of pH values, ranging from 1.68 to 10.01 units. The temperature dependence of pH values is also investigated in the range from 303 to 333 K. The proposed glass microelectrodes achieve a pH resolution of 1.39 V/pH, which is much higher than the Nernst limit.

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Section: ■ Results and Discussionmentioning

confidence: 66%

pH Sensing Based on Ionic Current Rectification Using Triple-Barreled Glass Microelectrodes

Kishimoto,

Doi

2023

J. Phys. Chem. C

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“…Instrumentation developed to measure conductivity is based on: induction, [87][88][89][90][91] potentiometry [92] with Pt electrodes, [92] microneedles, [93,94] gold-coated glass electrodes, [95] and local electric fields. [96]…”

Section: Conductivity and Phmentioning

confidence: 99%

Experimental methods in chemical engineering: pH

et al. 2022

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All chemical, biochemical, and biological processes depend on pH. Since the 1920s, when the first electrode was introduced to determine the concentration of hydrogen ions, pH measurement techniques have been evolving to fit the application at laboratory and industrial scales. These techniques include conventional methods based on electrical and optical methods like glass electrodes and variants. Most of the current methods still require a probe to be immersed in a solution. However, biomedical applications in the development stages involve non‐invasive probes that measure hydrogen ion concentration or electrical conductivity, which is related to the concentration of all ions. Instruments also measure both these properties simultaneously for water analysis, agriculture, and electrochemistry. pH drops by as much as 90% increasing temperature from 5–45°C (for MgSO4, NaCl, and an acetate buffer). The repeatability is excellent for a glass electrodes, which continues to be the measurement technique of choice for most laboratories, with a standard deviation of better than 0.08% for low molar concentrations (0.05 M) that increases to above 0.2% at high molar concentrations (>0.7 M). Besides the standard potentiometric methods, emerging techniques include ion‐sensitive field transistors, pH imaging, conductometric, acoustic microsensors, microcantilevers, and spectroscopy. In the first 6 months of 2020, Web of Science indexed almost 10 000 articles that mentioned pH as a keyword; most were in environmental sciences, multidisciplinary chemistry, and chemical engineering. Here, we review the latest developments, including spectroscopic methods, progress towards miniaturization, in particular for bio‐medical applications like skin and bio‐fluids, unconventional sampling, repeatability, and uncertainty.

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“…The tip size of the microelectrode is 1 μm or less, and the spatial resolution is expected to be comparable to the tip size. The test section in a liquid vessel is well designed to maintain uniform electric fields . Using a motorized stage, the microelectrode is swept along the channel with a step varied from 20 to 200 μm.…”

Section: Introductionmentioning

confidence: 99%

“…The test section in a liquid vessel is well designed to maintain uniform electric fields. 25 Using a motorized stage, the microelectrode is swept along the channel with a step varied from 20 to 200 μm. This direct measurement of local electric fields enables us to evaluate the conductivity or concentration without calibration.…”

Section: Introductionmentioning

confidence: 99%

Local Electric Field and Electrical Conductivity Analysis Using a Glass Microelectrode

Kishimoto

Doi

2022

ACS Omega

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Transport phenomena in microfluidic chips are induced by electric fields and electrolyte concentrations. Liquid flows are often affected by ionic currents driven by electric fields in narrow channels, which are applied in microelectromechanical systems, microreactors, lab-on-a-chip, and so forth. Even though numerical studies to evaluate those local fields have been reported, measurement methods seem to be under construction. To deeply understand the dynamics of ions at the microscale, measurement techniques are necessary to be developed. In this study, we propose a novel method to directly measure electrical potential differences in liquids, local electric fields, and electrical conductivities, using a glass microelectrode. Scanning an electrolyte solution, for example, KCl solutions, with a 1 μm tip under constant ionic current conditions, a potential difference in liquids is locally measured with a micrometer-scale resolution. The conductivity of KCl solutions ranging from 0.56 to 100 mM is evaluated from electric fields locally measured, and errors are within 5% compared with the reference values. It is found that the present method enables us to directly measure local electric fields under constant current and that the electrical conductivity is quantitatively evaluated. Furthermore, it is suggested that the present method is available for various electrical analyses without calibration procedures before measurements.

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Development of glass micro-electrodes for local electric field, electrical conductivity, and pH measurements

Cited by 11 publications

References 50 publications

pH Sensing Based on Ionic Current Rectification Using Triple-Barreled Glass Microelectrodes

pH Sensing Based on Ionic Current Rectification Using Triple-Barreled Glass Microelectrodes

Experimental methods in chemical engineering: pH

Local Electric Field and Electrical Conductivity Analysis Using a Glass Microelectrode

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