Carbon Pyrolized Photoresist Film and Platinum Microelectrode Chronoamperometry Using a Single and Double Potential Step Approach for Dopamine Detection and Electrode Interaction with Cottrell Equation Relations.

SOTORY, PETER ZSOLT. Carbon Pyrolized Photoresist Film and Platinum Microelectrode Chronoamperometry Using a Single and Double Potential Step Approach for Dopamine Detection and Electrode Interaction with Cottrell Equation Relations. (Under the direction of Dr. Gregory S. McCarty). Dopamine is an important molecule as part of the synaptic language governing the neuronal communications through the trillions of axonal and dendritic interconnections between nerves found in the human brain and body. It has been linked to major functions such as movement, behavior, pain perception, learning, motivation, cognition, emotions and memory. The catecholamine is also implicated with the cardiovascular, metabolic, renal, hormonal and immune systems. As a hydrochloride salt, dopamine can additionally be administered as a pharmaceutical. With such an extensive set of roles, there is a need to have sensors capable of detecting dopamine concentrations. The focus of this work was the chronoamperometric study of both microscale platinum and carbon pyrolized photoresist film sensors of similar design to electrochemically detect dopamine in solution. Previously the design had been used with Fast Scan Cyclic Voltammetry (FSCV) as a prospective method to record the extracellular volume transmission of dopamine in brains. In this current work, single and double potentiometric step approaches were utilized to characterize both sensor type oxidative response linearity and analyze the competitive shielding interaction between dual potential electrodes. The redox cycling capacity, mass transport flux, electrical current flux, and Cottrell equation relation of these sensors were additionally investigated. Initially the sensors quickly fouled and had non-linear responses. A technique was developed to electronically clean the sensors to reliably restore their sensitivity. Following this discovery, the oxidative dopamine testing response became linear and dependable, enabling the chronoamperometric study of the devices. The findings showed there was evidence for electrode competition or shielding and that redox cycling was more successful with the carbon PPF design than the platinum type of sensor. The mass transport and electrical current flux per unit area were dependent on the surface area of the electrodes. The measured oxidative current was not directly predictable by the Cottrell equation. For some of the platinum sensor testing cases the difference was merely a constant multiplier. But for the remaining platinum testing scenarios, and in all of the carbon PPF cases, the multiplier was a function inversely proportional to the square root of the concentration. The same data trend could also be successfully matched to an exponential equation. Both function forms are of a type used to characterize the potential decay from an electrode surface into an ionic solution. The Debye-like modulation of the Cottrell equation suggests the observed current is an outcome of the electrode interacting with a zone or volume of solution on a length scale influenced by the size of the electric double layer from the electrode surface. Electron tunneling, moderated by the electric double layer Debye length scale, is a candidate for the method of action. There are several favorable influences for it explored in the discussion, including dopamine’s chemical nature, sterically constrained water near the electrode surface, as well as other additional factors.