Electrochemical studies on liquid properties in extended nanospaces using mercury microelectrodes

We developed a novel nanofluidic chip equipped with mercury microelectrodes, which enables electrochemical measurements to be made in 10-100 nm scale spaces (called extended nanospaces), and evaluated the performances. The effects of both space sizes and concentrations on the conductance (G) values of KCl solutions in extended nanospaces (216-5000 nm) were examined using impedance spectrometry. We found that the experimental G values in the extended nanospaces decreased non-linearly with decreasing KCl concentrations in the range of 10^-2 to 10^-7 M and could be explained by theoretical model taking account of surface charge density of on a glass surface. This was found to result from enhancement of proton concentrations of the confined solution owing to fast proton exchange between SiOH groups on surfaces and water. Moreover, the G values provided the specific resistance and capacitance of KCl solutions in the extended nanospaces. These results showed that the viscosity of KCl solutions increased by size-confinement and that the viscosity of solution in 216 nm-sized extended nanospaces became about 2.8 times as large as that of bulk solution. We concluded that the developed nanofluidic chip becomes a new experimental tool for demonstrating confinement-induced nanospatial electrochemical properties of liquids.