Date of Graduation

12-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor

Ingrid Fritsch

Committee Member

Charles Wilkins

Second Committee Member

Julie Stenken

Third Committee Member

David Paul

Fourth Committee Member

Simon Ang

Abstract

Redox cycling is an electrochemical technique that cycles the reversible redox species between its oxidative states repeatedly on generator and collector electrodes. Two or more individually-addressable microelectrodes located close to each other allow redox cycling to be possible. Electrochemical behavior of a biologically important molecule, dopamine is examined under redox cycling conditions. To our knowledge, this is the first report on detection of physiological concentration of dopamine in presence of up to 100 times excess ascorbate with the use of redox cycling, without the involvement of polymer coating such as Nafion®.

Microfabrication was used to produce different geometries (parallel bands and concentric rings) with feature size of 4 µm or 25 µm and inter-electrode spacing of 4 µm or 25 µm on a single substrate (microelectrode arrays). Comparison of the individual electrochemical response of different arrangements of individually addressable elements composing generator and collector electrodes on band and ring microelectrode arrays is presented. The individually addressable nature of microelectrodes allowed the study of different combinations of anodic and cathodic electrodes and the current at the individual elements composing the generator and the collector. Reversible electroactive species hexaammineruthenium (III) chloride in a 0.5 M potassium chloride electrolyte solution was used to perform the electrochemical characterization and comparisons of the microelectrode arrays. Behavior of band and ring microelectrodes in an array format during redox cycling is compared to each other as well as to the available theory.

The optimized geometry and arrangement of microelectrodes is used to exhibit detection of dopamine with and without redox cycling. Comparison of dopamine behavior in presence and absence of redox cycling and other available methods of detection is provided. Detection of dopamine in presence of some of the common interferences (ascorbate and 3,4-dihydroxyphenylacetic acid) is shown with and without redox cycling on unmodified electrodes as well as on electrodes modified with Nafion®.

These studies indicate that redox cycling can detect dopamine at physiologically relevant concentrations in presence of interferences, but will require the coating of electrodes with Nafion in addition to broaden the range of interfering compounds that can be eliminated. Traditional voltammetric methods to detect dopamine cannot measure resting, or static dopamine concentrations where redox cycling would be of further interest. Redox cycling provides elimination from the interfering ascorbate signal, enhancing the sensitivity toward the analyte simultaneously.

Based on the knowledge gathered from comparison of different electrodes and redox cycling of dopamine, an interdigitated microelectrode probe design suitable for investigation of redox cycling of dopamine is fabricated. The probe contains array having dimensions that will be suitable for tissue insertions studies. The knowledge gained through this project will eventually lead to a new class of multi-electrode probes for in vivo studies of neurotransmitters in neurosciences.

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