A Simulation Analysis of Nanofluidic Ion Current Rectification Using a Metal-Dielectric Janus Nanopore Driven by Induced-Charge Electrokinetic Phenomena

Abstract

We propose herein a unique mechanism of generating tunable surface charges in a metal-dielectric Janus nanopore for the development of nanofluidic ion diode, wherein an uncharged metallic nanochannel is in serial connection with a dielectric nanopore of fixed surface charge. In response to an external electric field supplied by two probes located on both sides of the asymmetric Janus nanopore, the metallic portion of the nanochannel is electrochemically polarized, so that a critical junction is formed between regions with an enriched concentration of positive and negative ions in the bulk electrolyte adjacent to the conducting wall. The combined action of the field-induced bipolar induced double layer and the native unipolar double layer full of cations within the negatively-charged dielectric nanopore leads to a voltage-controllable heterogenous volumetric charge distribution. The electrochemical transport of field-induced counterions along the nanopore length direction creates an internal zone of ion enrichment/depletion, and thereby enhancement/suppression of the resulting electric current inside the Janus nanopore for reverse working status of the nanofluidic ion diode. A mathematical model based upon continuum mechanics is established to study the feasibility of the Janus nanochannel in causing sufficient ion current rectification, and we find that only a good matching between pore diameter and Debye length is able to result in a reliable rectifying functionality for practical applications. This rectification effect is reminiscent of the typical bipolar membrane, but much more flexible on account of the nature of a voltage-based control due to induced-charge electrokinetic polarization of the conducting end, which may hold promise for osmotic energy conversion wherein an electric current appears due to a difference in salt concentration. Our theoretical demonstration of a composite metal-dielectric ion-selective medium provides useful guidelines for construction of flexible on-chip platforms utilizing induced-charge electrokinetic phenomena for a high degree of freedom ion current control.

Simulation Analysis of Enhanced Ion Selectivity in a Single Graphene Nanopore

“…The finite element simulation technology has been conducted by many researchers to explore the theoretical issues of nanochannels. ,, In our previous studies, , we have demonstrated that the enrichment and depletion of the ion concentration in the asymmetrical nanochannel can cause ion current rectification (ICR). Other researchers have similar results.…”

“…In this case, single graphene nanopore models are constructed by finite element simulation (FEM) technology. Finite element simulation (FEM) is a popular simulation method for studying nanopores and related applications. − In addition, compared with FEM, the NOM is an excellent computational approach that can be used for modeling. The solution of partial differential equations (PDEs) plays a crucial role in various fields of science and engineering.…”

Improved Rectification and Osmotic Power in Polyelectrolyte-Filled Mesopores

“…For example, the diode-like ion current rectification (ICR) behavior, which assures ions preferentially transporting in one direction and hence amplifies ionic current, can be observed when the symmetry of ionic concentration profiles along the axis of a nanopore is broken [ 18 , 19 ]. Considerable experimental [ 20 , 21 , 22 ] and theoretical [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ] efforts have been made on ICR in nanofluidics and all these studies concluded that the ICR property only can emerge in case the pore size is comparable to the EDL thickness.…”