We demonstrate rectification of ionic transport in a nanofluidic diode fabricated by introducing a surface charge discontinuity in a nanofluidic channel. Device current-voltage (I-V) characteristics agree qualitatively with a one-dimensional model at moderate to high ionic concentrations. This study illustrates ionic flow control using surface charge patterning in nanofluidic channels under high bias voltages.

In this tutorial review, recent developments in modeling and experimental studies on nanofludics were reported. Nanofluidic studies were categorized into two groups depending on the characteristic length scale. When the size of the nanochannels and pores is 5-100 nm, electrostatic interactions are dominant, and ion and fluid flow can be analyzed by continuum dynamics. Various nanofluidic devices were proposed to manipulate aqueous solutions and biomolecules at the nanoscale. The successful development of such systems has major implications for technologies focusing on water purification and processing of complex biological solutions. When the size is less than 5 nm, steric interactions and hydration affect ion and fluid flow, which is analyzed by stochastic and/or molecular dynamics.

Theoretical modeling of ionic distribution and transport in a nanochannel containing a surface charge on its wall, 30 nm high and 5 microm long, suggests that ionic current can be controlled by locally modifying the surface charge density through a gate electrode, even if the electrical double layers are not overlapped. When the surface charge densities at the right and left halves of a channel are the same absolute value but of different signs, this could form the basis of a nanofluidic diode. When the surface charge density at the middle part of a channel is modified, this could form the basis of a nanofluidic bipolar transistor.