Nanopores are apertures of nanometric dimensions in an insulating matrix. They are routinely used to sense and measure properties of single molecules such as DNA. This sensing technique relies on the process of translocation, whereby a molecule in aqueous solution moves through the pore under an applied electric field. The presence of the molecule modulates the ionic current through the pore, from which information can be obtained regarding the molecule's properties. Whereas the electrical properties of the nanopore are relatively well known, much less work has been done regarding their fluidic properties. In this thesis I investigate the effects of fluid flow within the nanopore system. In particular, the charged nature of the DNA and pore walls results in electrically-driven flows called electroosmosis.

Using a setup which combines the nanopore with an optical trap to measure forces with piconewton sensitivity, we elucidate the electroosmotic coupling between multiple DNA molecules inside the confined environment of the pore. Outside the pore, these flows produce a nanofluidic jet, since the pore behaves like a small electroosmotic pump. We show that this jet is well-described by the low Reynolds number limit of the classical Landau-Squire solution of the Navier-Stokes equations. The properties of this jet vary in a complex way with changing conditions: the jet reverses direction as a function of salt concentration, and exhibits asymmetry with respect to voltage reversal. Using a combination of simulations and analytic modelling, we are able to account for all of these effects.

The result of this work is a more complete understanding of the fluidic properties of the nanopore. These effects govern the translocation process, and thus have consequences for better control of single molecule sensing. Additionally, the phenomena we have uncovered could potentially be harnessed in novel microfluidic applications, whose technological implications range from lab-on-a-chip devices to personalised medicine.