There exists a fluidic version of the electrostatic field-effect, by which the transport of ions and charged objects in solution can be controlled in nanoscale channels. In this dissertation, we present a theory of such "electrofluidic" gating, the fabrication of electrically articulated nanopore devices that can exploit it, and measurements of ionic and DNA transport that quantify the effect. The basic idea behind electrofluidic gating is that the charge on a metal electrode beneath an insulating layer can induce electric fields in a thin layer of fluid above it. The fundamental structure for electrofluidic gating is a metal-oxide-electrolyte (MOE) capacitor, whose charging grants control over the electric double layer of the fluid. In this dissertation, we first present a model for the charging behavior of the MOE capacitor. Our model emphasizes the chemistry of oxide surfaces. We next describe fabrication of nanopore devices with embedded electrodes by focused ion beam and transmission electron microscope. Studies of the milling rate and its dependence on the electron flux identified sputtering as the dominant erosion mechanism. Next we describe experiments of gating the ionic conductance of a nanopore with an embedded gate electrode. The induced swings in the conductance showed strong dependencies on the pH and the ionic strength of the solution that are well described by our model. The absence of gate leakage currents confirmed the purely electrostatic origin of this field-effect. Finally, we demonstrate field-effect control over DNA translocations in a gated nanopore. The capture of DNA from solution was facilitated by the application of a positive charge to the embedded gate electrode, and the average translocation speed increased. These effects are explained by the reduced effective size of the nanopore due to electrostatic repulsion of DNA from its charged walls and by the modified electro-osmotic flow. This picture is consistent with the reduced capture rate and the increased average translocation speed of DNA as we increased the Debye length. Gated nanopore devices thus begin to mimic the single-molecule regulatory capabilities of biological nanopores, and suggest new avenues for fundamental studies and technological applications.
Jiang, Zhijun,
"The Electrostatic Field-Effect in Electrically Actuated Nanopores"
(2011).
Physics Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z09P2ZWR
