Polymer translocation through a nanopore - a showcase of anomalous diffusion

TL;DR

This paper models the unbiased polymer translocation through a nanopore as an anomalous diffusion process, providing exact solutions and validating them with simulations, revealing the process's universal fractional dynamics.

Contribution

It introduces a fractional diffusion equation approach to describe polymer translocation, deriving universal exponents and exact solutions validated by simulations.

Findings

Translocation follows an anomalous diffusion process.

Analytic solutions match Monte Carlo simulation data.

Universal exponent characterizes the dynamics in 2D and 3D.

Abstract

The translocation dynamics of a polymer chain through a nanopore in the absence of an external driving force is analyzed by means of scaling arguments, fractional calculus, and computer simulations. The problem at hand is mapped on a one dimensional {\em anomalous} diffusion process in terms of reaction coordinate $s$ (i.e. the translocated number of segments at time $t$) and shown to be governed by an universal exponent $\alpha = 2/(2\nu+2-\gamma_1)$ whose value is nearly the same in two- and three-dimensions. The process is described by a {\em fractional} diffusion equation which is solved exactly in the interval $0 <s < N$ with appropriate boundary and initial conditions. The solution gives the probability distribution of translocation times as well as the variation with time of the statistical moments: $<s(t)>$, and $<s^2(t)> - < s(t)>^2$ which provide full description of the diffusion process. The comparison of the analytic results with data derived from extensive Monte Carlo (MC) simulations reveals very good agreement and proves that the diffusion dynamics of unbiased translocation through a nanopore is anomalous in its nature.