Rectification properties of conically shaped nanopores: consequences of miniaturization

TL;DR

This study investigates how nanopore length influences ion transport and rectification, revealing that shorter conical nanopores have reduced rectification which can be enhanced by surface charge and shape modifications.

Contribution

The paper introduces MsSimPore, a novel finite element solver for PNP equations that accurately models ion transport in nanopores with reservoirs, enabling detailed analysis of rectification and selectivity.

Findings

Shorter nanopores exhibit decreased rectification ability.

Surface charge and shape tailoring can enhance rectification in short pores.

MsSimPore effectively models ion transport with detailed reservoir effects.

Abstract

Nanopores attracted a great deal of scientific interest as templates for biological sensors as well as model systems to understand transport phenomena at the nanoscale. The experimental and theoretical analysis of nanopores has been so far focused on understanding the effect of the pore opening diameter on ionic transport. In this article we present systematic studies on the dependence of ion transport properties on the pore length. Particular attention was given to the effect of ion current rectification exhibited for conically shaped nanopores with homogeneous surface charges. We found that reducing the length of conically shaped nanopores significantly lowered their ability to rectify ion current. However, rectification properties of short pores can be enhanced by tailoring the surface charge and the shape of the narrow opening. Furthermore we analyze the relationship of the rectification behavior and ion selectivity for different pore lengths. All simulations were performed using MsSimPore, a software package for solving the Poisson-Nernst-Planck (PNP) equations. It is based on a novel finite element solver and allows for simulations up to surface charge densities of -2 e/nm^2. MsSimPore is based on 1D reduction of the PNP model, but allows for a direct treatment of the pore with bulk electrolyte reservoirs, a feature which was previously used in higher dimensional models only. MsSimPore includes these reservoirs in the calculations; a property especially important for short pores, where the ionic concentrations and the electric potential vary strongly inside the pore as well as in the regions next to pore entrance.