Capture and translocation of a rod-like molecule by a nanopore: orientation, charge distribution and hydrodynamics

TL;DR

This study uses hybrid simulations to explore how charge distribution, orientation, and hydrodynamics influence the translocation of rod-like molecules through nanopores, revealing asymmetric behaviors and the importance of electrohydrodynamic interactions.

Contribution

It introduces a comprehensive simulation approach combining Langevin Dynamics and Lattice Boltzmann methods to analyze electrohydrodynamic effects on rod translocation, extending previous models to include charge distribution impacts.

Findings

Asymmetric order parameter during capture and escape.

Charge distribution significantly affects rod orientation during capture.

Shorter capture times when rods are launched near the wall.

Abstract

We investigate the translocation of rods with different charge distributions using hybrid Langevin Dynamics and Lattice Boltzmann (LD-LB) simulations. Electrostatic interactions are added to the system using the $P^3M$ algorithm to model the electrohydrodynamic interactions (EHI). We first examine the free-solution electrophoretic properties of rods with various charge distributions. Our translocation simulation results suggest that the order parameter is asymmetric during the capture and escape processes despite the symmetric electric field lines, while the impacts of the charge distribution on rod orientation are more significant during the capture process. The capture/threading/escape times are under the combined effects of charge screening, rod orientation, and charge distributions. We also show that the mean capture time of a rod is shorter when it is launched near the wall because rods tend to align along the wall and hence with the local field lines. Remarkably, the \textit{orientational capture radius} we proposed previously for uniformly charged rods is still valid in the presence of EHI.