title: ELECTROCHEMICAL ANALYSIS AND DETECTION OF DOPAMINE USING CHITOSAN-CATECHOL MODIFIED CARBON NANOTUBE AND GRAPHENE ELECTRODES
Creators: name: (:Unkn) Unknown
Publisher: name: George Mason University
Year: 2019

description: Dopamine (DA) is one of the catecholamine neurotransmitters. It plays an important role in the functioning of the central nervous, renal and hormonal systems. Dysregulation of dopaminergic neurotransmission is associated with attention deficit hyperactivity disorder, mood disorders, Parkinson’s disease, Huntington’s disease and schizophrenia. Determination of DA is a subject of great importance and finding selective methods for its quantification in the presence of high levels of ascorbic acid (AA) and uric acid (UA), Norepinephrine (NE), and Serotonin (SE) in body fluids is relatively complicated. Common instrumental techniques like electrophoresis, chromatography, high performance liquid chromatography and spectrophotometry have been widely used for the determination of DA. However, such methods of detection are often sophisticated and very expensive. As DA shows very strong electrochemical activity, electrochemical techniques appear to be strong candidates for its detection, offering advantages such as simplicity, fast response and ease of application. Since interferents such as ascorbic acid (AA) and uric acid (UA), and other neurotransmitters may have close oxidation potentials to DA, the aim of my thesis is to design a chitosan-catechol modified electrochemical sensor to achieve not only good sensitivity but also a high degree of selectivity for the determination of DA. Using a catechol-based system for the determination of DA is advantageous due to chitosan being considered as a promising material for modification of the electrode surface due to its excellent film-forming ability, good stability, high permeability toward water, and strong adherence to the electrode surface. Catechol on the other hand amplifies the detection of DA because DA is a catechol-like phenolic compound. Carbon nanotubes, graphene and gold electrodes will be coated with chitosan and catechol via electrodeposition. The novelty in our work is the coating of the substrates with chitosan-catechol (CS-CC), enhancing the dopamine response. The electrodes were prepared by electrodepositing a CS-CC composite film via cyclic voltammetry (CV). We then performed dose-response for each set of electrodes (bare CNT, bare GR, and coated CNT as well as coated GR). Finally, we tested the electrodes in cerebro-spinal fluid (artificial and human), thus demonstrating the application of the fabricated sensors for detection of lower levels of dopamine. The electrodes exhibited highly sensitive response (2.03 mA mol-1 L , 1.446 mA mol-1 L, 0.02975 mA mol-1 L, and 0.0559 mA mol-1 L respectively for modified CNT, bare CNT, modified GR and bare GR) to the oxidation of DA with enhanced current signal on the modified CNT electrodes. The oxidation peak current of CV was proportional to the concentration of DA in the range from 50×10-9 to 50x10-6 M. For the human CSF testing, dopamine recovery rates of 49-78% and 65-65% were obtained using the coated graphene and CNT electrodes respectively. Our results indicate that the CS-CC modified CNT electrodes achieved the best recovery, sensitivity, and selectivity. Cathodic charge storage capacity (cCSC), resistance and phase were also evaluated for all electrode type to analyze the behavior of the electrode over time in both dry and wet conditions. The results indicated that the CS-CC coating and the dry condition increases the cCSC of CNT (baseline being the same for each condition), making it a more electrically active material over time. The decrease in cCSC overtime reveal that the graphene electrode with or without the coating and at different conditions become less electrically active over time. The decrease in resistance at higher frequencies suggests that the CC-CNT could be a better conductor over time, a behavior that is also noticed in the phase (resistive behavior). Overall, the CC-CNT electrode not only provided a higher affinity for DA due to the higher peak current measured across all concentrations and between all electrodes, a better ability to distinguish between the UA,DA, and AA simultaneously, as well as a stable cCSC over time.