Variations in Electroosmotic Flow Outside Glass Nanopores with Species of Monovalent Cation

Abstract

Nanopores are an important technology in molecular sensing systems. Their behaviour is strongly affected by flow characteristics that are not well understood. Utilising a novel 3 dimensional combination optical tweezers and capillary nanopore measurement system, we have measured flow behaviour outside conical glass nanopores as a function of species of group 1 cation. We present a full 3 dimensional flow field about the nanopore. We use this 3 dimensional measurement system to find the flow force as a function of distance from the pore, allowing us to determine the momentum flux for each salt condition. We find strong salt dependence on the strength of momentum flux from the nanopore. Additionally we find previously reported voltage dependent flow reversal to be dictated by salt species. For a subset of species we observe EOF in the expected direction as predicted by classical electrokinetic theory, while for others the direction of the flow is reversed. We present a model explaining the observed behaviour. These data and corresponding model are key to understanding ion transport, fluid flow and translocation dynamics in voltage driven nanopore systems.