Application of a bipolar nanopore as a sensor: rectification as an additional device function

TL;DR

This paper models a bipolar nanopore sensor that detects analyte ions through ionic current modulation and exhibits rectification, combining sensing and device functions based on local electric field changes.

Contribution

It introduces a dual-function nanopore sensor model that combines ion detection with rectification, using a hybrid simulation approach to analyze its response mechanisms.

Findings

Binding of analyte ions modulates ionic current.

The asymmetric pore exhibits rectification as an additional device function.

Local electric field changes drive the sensor's response.

Abstract

We model and simulate a nanopore sensor that selectively binds analyte ions. This binding leads to the modulation of the local concentrations of the ions of the background electrolyte (KCl), and, thus, to the modulation of the ionic current flowing through the pore. The nanopore's wall carries a bipolar charge pattern with a larger positive buffer region determining the anions as the main charge carriers and the smaller negative binding region containing binding sites. This charge pattern proved to be an appropriate one as shown by a previous comparative study of varying charge patterns (M\'adai et al.\ \textit{J. Mol. Liq.}, 2019, \textbf{283}, 391--398.). Binding of the positive analyte ions attracts more anions in the pore thus increasing the current. The asymmetric nature of the pore results in an additional device function, rectification. Our model, therefore, is a dual response device. Using a reduced model of the nanopore studied by a hybrid computer simulation method (Local Equilibrium Monte Carlo coupled to the Nernst-Planck equation) we show that we can create a sensor whose underlying mechanisms are based on the changes of the local electric field as a response to changing thermodynamic conditions. The change of the electric field results in changes in the local ionic concentrations (depletion zones), and, thus, changes in ionic currents.