Voltage-driven translocation: Defining a capture radius.

Analyte translocation involves three phases: (i) diffusion in the loading solution, (ii) capture by the pore, and (iii) threading. The capture process remains poorly characterized because it cannot easily be visualized or inferred from indirect measurements. The capture performance of a device is often described by a capture radius generally defined as the radial distance R* at which diffusion-dominated dynamics cross over to field-induced drift. However, this definition is rather ambiguous and the related models are usually oversimplified and studied in the steady-state limit. We investigate different approaches to defining and estimating R* for a charged particle diffusing in a liquid and attracted to the nanopore by the electric field. We present a theoretical analysis of the Péclet number as well as Monte Carlo simulations with different simulation protocols. Our analysis shows that the boundary conditions, pore size, and finite experimental times all matter in the interpretation and calculation of R*.