Date of Award

Spring 2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Shizhi Qian

Committee Member

Robert L. Ash

Committee Member

Yan Peng

Call Number for Print

Special Collections; LD4331.E535 B35 2011

Abstract

The magnitude of current through a conical nanopore filled with an electrolyte solution depends on the polarity of the applied bias, indicating an asymmetric diode-like current-voltage (I-V) curve. This kind of phenomenon refers to ionic current rectification (ICR), which is of interest because many ion-channel proteins in cellular membranes are rectifying. In addition, ICR in nanopores can be used to control ion concentrations in nano- and microfluidic systems. In this study, the ICR phenomenon through a conical nanopore simultaneously subjected to an electric field and salt concentration gradient is experimentally and numerically investigated.

The experiments were conducted in an Izon's SIOS nanopore system, which consisted of a fluid cell with two fluid wells separated by a thermoplastic polyurethane membrane containing a single conical nanopore. The ICR was studied experimentally by imposing a bias voltage ranging from -IV to IV across the two fluid wells filled with potassium chloride (KCI) solutions of two different concentrations. To elucidate the mechanism of ICR, a mathematical model consisting of the Nernst - Planck equations for the ionic mass transport, the Poisson equation for the electrostatics, and the Navier- Stokes equations for the flow field has been developed. The obtained numerical results are in qualitative agreement with the obtained experimental results.

In this research, the effect of the imposed electrolyte concentration gradient on the ICR is studied for the first time. Typically, the preferential current direction of a negatively charged nanopore directs from the tip towards the base due to the ion depletion under a negative voltage and ion enrichment under a positive voltage. Furthermore, the preferential current direction of a nanopore highly depends on the externally imposed salt concentration gradient, which makes it possible to tune ICR by altering the salt concentrations in the two fluid reservoirs.

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DOI

10.25777/7c0f-ev46

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