Fluidic nanochannels are often fabricated on Si/SiO₂ substrates, using methodology similar chip manufacturing. While such approach is very convenient and allows for a substantial reduction in the channel size, a potential problem could stem from the fact that the deposited SiO₂ layer becomes conductive when in contact with aqueous solutions. Hence if electroosmosis/electrophoresis is attempted in such channels, a significant part of the current could leak across the SiO₂ layer into the Si instead of being transported along the channel by the electrolyte solution. The effect of such current leakage is that the electric field in the fluidic channel becomes non uniform, which will inevitably affect also the transport of fluid and analytes.

We present an analysis of the system Si/SiO₂/Electrolyte solution based on numerical solution of transient Maxwell electrodynamics equations. The fluidic channel with Si/SiO₂ walls is the considered as a leaky capacitor (see the Figure). Our data show that there is a relationship between the SiO2 layer thickness and the channel length above which the current leaks become significant. Generally longer channels lead to greater current leaks.

While a potential problem, the current leaks could be utilized to modify the field shape in the fluidic nanochannel. For example it is possible to create local minima or maxima in the potential distribution along the channel which could be utilized for controlled analyte transport or focusing and separation.