UC Irvine

Ionic current transport and nanopores go hand in hand. Ionic current has been used to investigate properties of nanopores and vice versa for many years. Nanopores are simply holes which contain dimensions on the nanoscale and ionic current is produced through them by placing the pores in a solvent containing an electrolyte. Ionic transport is investigated typically using current-voltage or current-time measurements. In this thesis ionic transport is studied and manipulated through three separate projects. We begin using cylindrical polymer pores ~700 nm in diameter and 11 μm in length to investigate the effect of organic solvents on ionic transport and thus electrochemical properties of polymer/liquid interfaces. Current-voltage measurements were taken in solutions with varying solvent type and varying concentration of LiClO4. These measurements probed electroosmotic flow and allowed us to deduce surface charge properties of the pores. It was found that the carboxlyated surface of PET can flip charge polarity dependent on solvent type and concentration of LiClO4. This work helped overall understanding of the origin of the effective xii surface charge in organic solvents and its impact on ionic transport. Another method of ionic transport manipulation which was investigated utilized an ionic bipolar junction transistor. Nanopores in silicon nitride were sandwiched together with a thin film of Nafion which also contained a gate electrode. Current-voltage measurements were taken across the device while varying voltage at the gate. It was successfully demonstrated through this system that an ionic transistor with fully ionic inputs and outputs can easily be rearranged into amplifying units providing amplifications up to 300 times. Finally, this document goes on to investigate interpore effects by using arrays of nanopores with a gate electrode placed near one of the pores within the array. Ionic transport is investigated through modeling currentvoltage characteristics both with and without application of voltage at the gate electrode. In this system complex interactions were revealed which allow for different pores to exhibit different ionic transport properties though subject to the same bulk solution concentration and voltage configuration. Findings from these projects could be useful in a variety of applications including preparation of artificial biocircuits or spatially controllable drug delivery devices.