Voltage-Driven Translocation through a Nanopore: How can we define a/the Capture Radius?

A typical translocation event includes the following three steps: (i) the diffusion, (ii) the capture, and finally (iii) the translocation of the analyte. The capture process remains rather ill-understood because it cannot easily be visualized or inferred from the blockage current measured across the nanopore. To estimate the size of the so-called capture zone, a capture radius R_c is generally defined as the radial distance from the pore where diffusion-dominated dynamics (at large distance) cross over to drift-dominated dynamics (near the pore). However, this definition is ambiguous and the models used are often over-simplified. We investigate several approaches to defining and estimating R_c for the simple case of a charged particle diffusing in a liquid and attracted to the nanopore by an applied electric field. We present a theoretical analysis of the flux and Péclet number methods as well as 2D Lattice Monte Carlo (LMC) simulations with different simulation protocols and boundary conditions, including particle evaporation from the pore under a reversed field conditions. We compare our results to experimental estimates and we stress the fact that the boundary conditions and finite experimental times both matter in the interpretation of R_c .