Local Electric Field and Electrical Conductivity Analysis Using a Glass Microelectrode

Abstract

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.

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

“…The glass tip size may be shrunk with nanoporous structures of the agent, which is expected to increase the ion selectivity. In a previous study, we demonstrated the effectiveness of agarose gel fixed in the glass tip . On the other hand, agars usually form gels when heated, and they have to be quickly brought to the tip of a narrow glass capillary before they harden.…”

“…In a previous study, we demonstrated the effectiveness of agarose gel fixed in the glass tip. 38 On the other hand, agars usually form gels when heated, and they have to be quickly brought to the tip of a narrow glass capillary before they harden. It is difficult to put the warmed gel into the tip by tapping the glass tube.…”

“…Here, it is important to measure ion concentrations and electric fields locally in liquids. For example, it was suggested that ionic current responses, especially in dilute solutions, clearly reflect the properties of target objects. , Recently, we proposed a novel method to directly measure local electric fields and electrolyte concentrations, using glass microelectrodes, which enabled us to directly measure a concentration of 1 mM KCl with errors less than 3.7%. , On the other hand, the detailed mechanism of how ion species and low concentrations are identified has not yet been clarified. In this study, we further develop triple-barreled glass microelectrodes to detect proton transport through a narrow channel in the range from pH 1.68 to 10.01.…”