Electroosmotic flow rectification in conical nanopores

TL;DR

This paper investigates the counterintuitive electroosmotic flow rectification in conical nanopores, revealing that concentration polarization and permselectivity cause the observed inverse relationship between flow and current.

Contribution

It provides a systematic finite-element simulation analysis explaining the mechanism behind EOF rectification in conical nanopores, highlighting the role of concentration polarization.

Findings

EOF and ionic current are inversely related inside the pore.

Rectification depends on salt concentration polarization.

Permselectivity and asymmetry are essential for rectification.

Abstract

Recent experimental work has suggested that electroosmotic flows (EOF) through conical nanopores exhibit rectification in the opposite sense to the well-studied effect of ionic current rectification. A positive bias voltage generates large EOF and small current, while negative voltages generate small EOF and large current. Here we systematically investigate this effect using finite-element simulations. We find that inside the pore, the electric field and salt concentration are inversely correlated, which leads to the inverse relationship between the magnitudes of EOF and current. Rectification occurs when the pore is driven into states characterized by different salt concentrations depending on the sign of the voltage. The mechanism responsible for this behaviour is concentration polarization, which requires the pore to exhibit the properties of permselectivity and asymmetry.