# The effect of the charge pattern on the applicability of a nanopore as a sensor

## TL;DR

This study explores how asymmetric charge patterns on nanopores influence their sensing capabilities and rectification properties, revealing that bipolar nanopores enhance detection of analyte ions through increased ionic current.

## Contribution

It introduces a model with asymmetric charge patterns on nanopores, demonstrating improved sensing and dual functionality including rectification, expanding on previous symmetric models.

## Key findings

- Bipolar nanopores efficiently detect analyte ions via increased Cl- current.
- Asymmetric charge patterns enable dual sensing and rectification functions.
- Charge pattern influences ion transport mechanisms and device responsiveness.

## Abstract

We investigate a model nanopore sensor that is able to detect analyte ions that are present in the electrolyte solution in very small concentrations. The nanopore selectively binds the analyte ions with which the local concentrations of the ions of the background electrolyte (KCl), and, thus, the ionic current flowing through the pore is changed. Analyte concentration can be determined from calibration curves. In our previous study (M\'{a}dai et al. J. Chem. Phys., 147(24):244702, 2017.), we proposed a symmetric model (surface charge is negative all along the pore). The mechanism of sensing was a competition between K$^{+}$ and positive analyte ions, so increasing analyte concentration decreased K$^{+}$ current. Here we allow asymmetric charge patterns on the pore wall (positive/negative/neutral along the pore), thus, gaining an additional device function, rectification, resulting in a dual responsive device. We find that a bipolar nanopore is an efficient geometry with Cl$^{-}$ ions being the main charge carriers. The mechanism of sensing is that more positive analyte ions attract more Cl$^{-}$ ions into the pore thus increasing the current. Also they make the pore less asymmetric and, thus, decrease rectification. We use a hybrid computer simulation method, where a generalization of the grand canonical Monte Carlo method to non-equilibrium (Local Equilibrium Monte Carlo) is coupled to the Nernst-Planck equation with which the flux is computed.