Electrophoretic Forces on Multiple DNA Molecules in a Nanopore

Abstract

As nanopore technology develops into a mature field, understanding the physics of polymer translocation through nanopores is more important now than ever before. For charged molecules such as DNA, the electrophoretic force remains the main driving force; however, its direct measurement in solid-state nanopores has been achieved only relatively recently. Our measurements rely on combining optical tweezers with glass nanopores based on nanocapillaries, in order to stall single DNA molecules in a molecular tug-of-war. The forces involved can be explained by carefully considering electrohydrodynamic effects, which are critically dependent on the boundary conditions of the system. Previous studies have concentrated on single DNA molecules; here, we present results for up to 12 DNA molecules simultaneously held in a nanopore. We find that hydrodynamic interactions between DNA molecules are important, even in the thin-Debye-layer limit. These lead to a decrease in the force per molecule as more molecules are inserted. A simple scaling argument based on a mean field theory explains our results. Our investigation highlights the effect of confinement in determining the effective force responsible for DNA translocations. The insight gained may be applicable in a wider context, such as in gel electrophoresis, where charged polymers move through a crowded network.