Date of Graduation

5-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor/Mentor

Fritsch, Ingrid

Committee Member

Stenken, Julie A.

Second Committee Member

Wilkins, Charles L.

Third Committee Member

Paul, David W.

Keywords

Pure sciences; Electrochemical sensing; Microelectrode arrays; Microfabrication; Neurotransmitters; Redox cycling

Abstract

The electrochemical method of redox cycling was exploited to achieve new discoveries in neurotransmitter detection and to advance its suitability toward in vivo use. Redox cycling has advantages in signal amplification, selectivity of species based on their electrochemical reaction mechanisms, and limited or no background subtraction. Distinction of dopamine from norepinephrine in a mixture with an electrochemical method at unmodified electrodes was demonstrated for the first time in vitro. This ability resulted from a series of fundamental studies of redox cycling behavior of the catecholamines (dopamine, norepinephrine and epinephrine) using different electrode configurations. Taking advantage of the ECC’ mechanism associated with their electrochemical oxidation and the substantially different rate constants for the first order intramolecular cyclization reaction, the catecholamines can be distinguished by monitoring the current at collector electrodes activated at different distances from the generator. In vitro detection of dopamine in the presence of multiple electrochemically-active interfering species (ascorbic acid, uric acid, L 3,4 dihydroxyphenylalanine, homovanillic acid, 3 methoxytyramine and 5 hydroxyindoleacetic acid) has also been investigated for future in vivo applications. Selective detection of physiological concentrations of dopamine at the collector electrodes using microfabricated electrode arrays was shown (with detection limits of 0.730 ± 0.013 µM and 0.086 ± 0.002 µM for dopamine with and without the presence of interfering species, respectively). In addition, two types of unique neural probes (co-planar and vertical edge microelectrode arrays) were designed with the purpose to implement the redox cycling approach in vivo. An innovative design was used to minimize the number of masks for eight layers of electrodes. Different microfabrication procedures were evaluated, with further work still needed for optimization. Also, analysis of anodic stripping voltammetry of silver-containing nanoparticles modified on electrode surfaces, performed as an interest in expanding the detection to other important neurochemicals, showed that commonly used drop-casting techniques deposit nanoparticles non-uniformly. More reproducible modification methods are needed. The work in this dissertation demonstrates the capabilities of redox cycling for multi-neurotransmitter analysis and sets the foundation for development of novel neural probes for implementing the approach. This method may also be used to obtain mechanisms and kinetics beyond the ones investigated here.

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