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Active Electrokinetic Transport Control in a Nanofluidic Device with Embedded Surface Electrodes

Fuest, Marie
http://rave.ohiolink.edu/etdc/view?acc_num=osu1449484271

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Mechanical Engineering.
Since the 1990s, lab on-a-chip (LoC) systems, or miniaturized devices that perform several unit operations that typically require bench top sized equipment on an integrated platform have been developed for applications in biotechnology, chemical and biological reactors, energy conversion systems, separation and filtration systems, and medical, pharmaceutical, and environmental monitoring. The success of LoC technology relies on the ability to manipulate ions and molecules in increasingly small volumes of fluid (nL and less). With decreasing critical length scales for devices made possible by advances in microfabrication and nanofabrication, the device surface-area-to volume ratio has made the role of surface properties critical to operation and novel functionality of many of these devices. Of the various surface properties, surface charge presents a unique parameter with broad applicability for engineering new device functionalities. Gated nanofluidic devices, geometrically analogous to semiconductor field-effect transistors, feature a nanofluidic channel with a “gate” electrode embedded in the nanochannel wall, providing an active, tunable region for manipulation of local surface charge. Specifically, an independently controlled potential applied to the embedded gate electrode allows systematic manipulation of the surface charge density at the dielectric electrolyte interface. Fabrication protocols for gated nanofluidic devices with sub 20 nm critical length scales were developed that rely on UV lithography, wet etching, and oxygen plasma bonding techniques. Active control over ionic transport through the nanochannel was monitored by changes in current as a function of gate potential, electrolyte type, electrolyte concentration, and solution pH. The measured current was referenced with respect to the ungated or intrinsic case, or the case when only an axial potential was applied with no gate potential. In this dissertation, it was experimentally verified that the gate electrode additionally alters the electric field in the nanochannel by modifying the potential in the nanochannel near the gate electrode/dielectric/solution interface. In the surface charge governed transport regime, the gate electrode was used to switch off the measured current for a fixed axial potential, where repeatable on/off switching was demonstrated. Local variation of surface charge by the gate electrode on transport of multivalent aqueous electrolytes and electrolyte mixtures, which form the basis for biological or practical applications, was investigated as a function of cation type. In agreement with previous anomalous transport reports, no significant difference was observed for the intrinsic nanochannel conductance of KCl compared to NaCl. Conductance decreased for MgCl2 and CaCl2 at concentrations typically associated with surface charge governed transport for monovalent electrolytes, suggesting a decrease in the total surface charge due to divalent cation adsorption at the negatively charged walls. Data from KCl and CaCl2 electrolyte mixtures clearly indicated that Ca2+ in the mixture is the dominating ion as determined by a decrease in surface charge density when CaCl2 was added and a surface charge density that was independent of KCl concentration for %CaCl2 > 25%. Cation adsorption to the charged walls regulates the surface charge density thus limiting the ability of the gate electrode to alter the net surface charge and consequently modulate nanochannel conductance as a function of cation type.
Shaurya Prakash, PhD (Advisor)
A. T. Conlisk, PhD (Committee Member)
Steven Ringel, PhD (Committee Member)
Carlos Castro, PhD (Committee Member)
367 p.
Mechanical Engineering

Recommended Citations

Citations

  • Fuest, M. (2016). Active Electrokinetic Transport Control in a Nanofluidic Device with Embedded Surface Electrodes [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449484271

    APA Style (7th edition)

  • Fuest, Marie. Active Electrokinetic Transport Control in a Nanofluidic Device with Embedded Surface Electrodes. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1449484271.

    MLA Style (8th edition)

  • Fuest, Marie. "Active Electrokinetic Transport Control in a Nanofluidic Device with Embedded Surface Electrodes." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449484271

    Chicago Manual of Style (17th edition)

osu1449484271
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This open access ETD is published by The Ohio State University and OhioLINK.