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.

We are trying to realize electrical single −molecule detection in nanofluidie device that electrically identifies single biomolecules one by one ， as Qur continuous effort to realize sing ［ e mQlecular procossing technology ． The physical size exclusion effect of the nanechanncl serves as the underlying principle f ( 〕r thc single − molecule detectien ． Because the cross − section Qf the nanochannel can be as small as ・ the size ofa biomolecule ， only a sing 】 e molecule can pass into the nanochannel at one time ． Herein we developed a simple nano 伽 idic device having a nanometcr − height straight channel that is fhnctionalized with a pair ofe 【 ectrodes fbr electrical sensing ofaqueQus solution as the first step fbr the fUtUre single − mo 且 ecule sensing ． The fabrication method and the perf ( ) ancc Qfelectrical sensing was primitively evaluated by measuring the current when a sodium chloride solution used as a sample ． κey 歟 )rds ： D 崩 ， nanochannel ， e ' eofrode ， η aηo 〃ωd' c de レ' ce ， s1η gle −m σlec σ' θ