Ion current rectification in asymmetric charged bilayer nanochannels

At present, little attention has been paid to the ion current rectification (ICR) performance in the bilayer nanochannel with non-uniform charge distribution, which has the similar asymmetrical property with the conical nanochannel. In this work, we have established the ions transport model in the bilayer nanochannel with the coupled Poisson-Nernst-Planck (PNP) equations. Four configuration types bilayer nanochannel are compared on the ion rectification performance. The results show that asymmetrical geometry without the surface charge cannot induce ICR and the existence of surface charge is necessary. Besides, the config.3 has the best ICR performance and the physical mechanisms are discussed in detail. It is found that the ICR performance can be enhanced by regulating the surface charge density, geometry parameters and ion concentration. The ICR ratio increases as the absolute surface charge density increases and the effect is more significant to the change of left nanopore. When the total length of the bilayer nanochannel is fixed, the ICR ratio increases first and then decreases with the increasing length of the left nanopore. In addition, the forward current is more sensitive to the change of diameter of left nanopore and the reverse current is more sensitive to the change of diameter of right nanopore. When the bulk concentration varies, the ICR ratio decreases with the increasing concentration. The research results provide useful information for ions transport control and optimization of micro/nano fluidic devices. (C) 2021 Elsevier Ltd. All rights reserved.