Direct measurement of electric double layer in a nanochannel by electrical impedance spectroscopy

Abstract

The ion distribution and physical behavior induced by applying an electric field to a nano-interfacial space are very important for investigating electric double layers (EDLs) in very confined spaces. We perform direct measurements of an EDL in a nanochannel by electrical impedance spectroscopy to experimentally evaluate the EDL thickness dependence on the ion density and the channel width. To this end, we developed a nanofluidic device consisting of a pair of sensing electrodes with a nanochannel between them. The measurement electrodes are completely embedded in a substrate to generate a uniform electric field and to provide a flat surface that can easily be used to seal the nanochannel. Using this device, we found that the EDL on one electrode expands with decreasing ion concentration and eventually merges with the EDL on the opposite electrode so that the nanochannel becomes completely filled with the EDL. The trend observed for the EDL width agrees well with that predicted by theory for the Debye length. These results provide valuable insight into the physical ionic structure in nanochannels, which will improve impedance-based electrical sensing and electrokinetic applications.

Optimized Synthesis and Antimalarial Activity of 1,2‐Dioxane‐4‐carboxamides

“…We fabricated the measurement nanofluidic device using previously published methods 21. The first step was microchannel fabrication.…”

“…To clarify electrokinetic phenomena caused by the EDL in nanochannels, we have previously developed a method to directly measure the EDL thickness using electrochemical impedance spectroscopy, where the measurement was conducted transverse to the direction of flow 21. The advantage of being transverse to the direction, which is a side‐by‐side radial current measurement, is that it should be possible to measure the dynamic EDL properties directly.…”

Nanofluidics: A New Arena for Materials Science

“…Despite the difficulty, some impressive works through bypassing the hurdles have been reported. Most of these works focused on the integration of electrical components (for example, electrodes) to enable electrical measurements (impedance and resistance), electrochemical reaction and detection, or external physical operation for nanofluidic devices.…”

Direct Evaluation of the Electrokinetic Properties of Electrolytes in a Nanochannel using Electrical Impedance Spectroscopy

“…[21] The first step was microchannel fabrication. The microchannel was fabricated using a series of conventional photolithography and wet etching techniques (Figure 7).…”

“…[21] The advantage of being transverse to the direction, which is a side-by-side radial current measurement, is that it should be possible to measure the dynamic EDL properties directly. EDL thickness should be altered by the applied potential, frequency, ions, etc.…”