Electrokinetic focusing of charged species at bipolar electrode in a microfluidic device

dc.contributor.advisorCrooks, Richard M.en
dc.contributor.committeeMemberBard, Allen J.en
dc.contributor.committeeMemberStevenson, Keith J.en
dc.contributor.committeeMemberMullins, Charles B.en
dc.contributor.committeeMemberStanton, John F.en
dc.creatorPerdue, Robbyn K.en
dc.date.accessioned2012-02-14T18:42:37Zen
dc.date.available2012-02-14T18:42:37Zen
dc.date.issued2010-12en
dc.date.submittedDecember 2010en
dc.date.updated2012-02-14T18:43:31Zen
dc.descriptiontexten
dc.description.abstractThe development and characterization of bipolar electrode (BPE) focusing is described. BPE focusing is an electrokinetic equilibrium technique in which charged analytes are focused and locally enriched on an electric field gradient in the presence of a counter-flow. This electric field gradient is formed at the boundary of an ion depletion zone – the direct result of faradaic reactions occurring at the BPE in the presence of an externally applied electric field. Direct measurement of the electric field strength in the ion depletion region shows that the electric field is enhanced in this region and takes on a gradient shape, confirming the results of numerical simulations. Transient electric field measurements with simultaneous monitoring of a focused fluorescent tracer reveal that the field gradient forms rapidly upon application of the external field and remains stable over time with the tracer focused at a local field strength predicted by simple electrokinetic equations. These transient electric field measurements probe the effect of individual experimental parameters on the electric field gradient and the focused band. The results of these studies indicate that a steeper field gradient leads to enhanced concentration enrichment of the analyte. The slope of the gradient is increased with higher concentration of the running buffer and higher applied field strength. The addition of pressure driven flow across the microchannel moves the location of the field gradient and the position of the focused band. Further enhancement of enrichment is achieved through the suppression of Taylor dispersion after coating the microchannel with a non-ionic surfactant. The findings of these studies have motivated the transition of BPE focusing to smaller microchannels. A decrease in microchannel size not only decreases Taylor dispersion, but also provides access to higher buffer concentration and higher applied field strength, both of which enhance enrichment. The result is a three-order-of-magnitude increase in total analyte enrichment at a much higher enrichment rate. Furthermore, a dual channel configuration for BPE focusing is introduced which provides greater control over focusing conditions. Finally, the formation of ion depletion and enrichment zones at a BPE in a microchannel is shown to mimic ion concentration polarization (ICP) at micro-/nano-channel junctions. This is significant because this faradaic ICP provides a model to which traditional ICP can be compared and is achieved in a more easily fabricated device. In summary, the fundamental principles of BPE focusing are described. A greater understanding of the effect of experimental parameters on the focusing process leads to an unprecedented magnitude and rate of enrichment in a simple device architecture.en
dc.description.departmentChemistryen
dc.format.mimetypeapplication/pdfen
dc.identifier.slug2152/ETD-UT-2010-12-2162en
dc.identifier.urihttp://hdl.handle.net/2152/ETD-UT-2010-12-2162en
dc.language.isoengen
dc.subjectBipolar electrodeen
dc.subjectBipolar electrode focusingen
dc.subjectConcentration enrichmenten
dc.subjectMicrofluidicen
dc.subjectCounter-flow gradient focusingen
dc.subjectElectrokinetic equilibriumen
dc.subjectIon concentration polarizationen
dc.titleElectrokinetic focusing of charged species at bipolar electrode in a microfluidic deviceen
dc.type.genrethesisen
thesis.degree.departmentChemistryen
thesis.degree.disciplineChemistryen
thesis.degree.grantorUniversity of Texas at Austinen
thesis.degree.levelDoctoralen
thesis.degree.nameDoctor of Philosophyen
Files
Original bundle
Now showing 1 - 2 of 2
No Thumbnail Available
Name:
Movie 1.mpg
Size:
5.27 MB
Format:
Moving Picture Experts Group
Description:
Supplement (Video)
Loading...
Thumbnail Image
Name:
PERDUE-DISSERTATION.pdf
Size:
9.42 MB
Format:
Adobe Portable Document Format
License bundle
Now showing 1 - 1 of 1
No Thumbnail Available
Name:
license.txt
Size:
2.12 KB
Format:
Plain Text
Description: