Dopamine is associated with many neurodegenerative diseases, including Parkinson’s disease and Schizophrenia, and is also related with the brain’s reward system and learning behaviors. To study dopamine activity under a certain disease or behavior and further provide possible treatment for neural disorders, it is essential to get the information of dopamine concentration. The low concentration and subtle activity of dopamine in the neurons requires highly sensitive detection.

The ultimate goal of this thesis is to enhance sensitivity in dopamine detection. An important step to achieve this is the design and fabrication of a carbon nanotube (CNT)-coated microelectrode array (MEA). Designing such an MEA requires a detailed understanding of the processes that occur at the interface betwee...[ Read more ]

Dopamine is associated with many neurodegenerative diseases, including Parkinson’s disease and Schizophrenia, and is also related with the brain’s reward system and learning behaviors. To study dopamine activity under a certain disease or behavior and further provide possible treatment for neural disorders, it is essential to get the information of dopamine concentration. The low concentration and subtle activity of dopamine in the neurons requires highly sensitive detection.

The ultimate goal of this thesis is to enhance sensitivity in dopamine detection. An important step to achieve this is the design and fabrication of a carbon nanotube (CNT)-coated microelectrode array (MEA). Designing such an MEA requires a detailed understanding of the processes that occur at the interface between the electrode and the electrolyte. Conventional models for the electrode’s electrical properties based on those processes are given. Factors, including electrolyte concentration, applied voltage, surface roughness and frequency, that can affect the electrode’s properties are analyzed. Furthermore, the diffusion characteristics under DC conditions in both the electron transfer-dominated region and diffusion-limited region are studied. The interfacial mechanisms form the basis for the selection of the electrode material in the dopamine detection. This introduction of the electrode’s electrical properties also helps others in the research group understand how an electrode works.

Based on the interface mechanisms, CNTs were chosen as the sensing material for dopamine detection due to their fast electron transfer property and other favorable properties. The preparation of the CNT-coated MEA includes the fabrication of a bare gold MEA, dispersion of CNTs and covalent bonding between the functional groups in the gold and those in the CNTs. The enhanced sensitivity obtained with the cyclic voltammetry (CV) technique demonstrates the potential use of this CNT-coated MEA for highly sensitive and high throughput dopamine detection. Furthermore, how the CNT coating affects the sensitivity is also investigated.

It is obvious from the enhanced sensitivity in dopamine detection and electrochemical impedance spectroscopy (EIS) measurement results that the CNT coating changes the electrode-electrolyte properties significantly. It is useful to study how the CNT coating changes the interface’s electrical properties. Thus an equivalent circuit model is proposed based on both the interface mechanisms and the experimental results. The equivalent circuit model includes the effects of the CNT coating density and CNT multilayers on the interfacial impedance. And the constant phase element, which is not standard circuit element, is converted into an RC network.