Abstract
Neurotransmitters are chemical messengers that are useful for transmission of signals across a synapse from one neuron to another. Dopamine and epinephrine are the most important neurotransmitters in the brain and human body. Previous studies reported the abnormal levels of these neurotransmitters are associated with illnesses such as Parkinson’s, Huntington’s, hypertensive crisis, depression, and others. Many researchers have been working towards finding ways to monitor the levels of these neurotransmitters in the human body. Amongst other methods, electrochemical methods have been used for the development of electrochemical sensors towards the determination of dopamine and epinephrine. This is because electrochemical methods allow the detection of these neurotransmitters in living organisms and are easy, simple and inexpensive compared to other methods. However, there are challenges associated with the use of electrochemical methods such as the selectivity and sensitivity which results from interferences with coexisting electroactive species such as ascorbic acid and uric acid which possess similar oxidation or reduction of potentials. To overcome these challenges, nanomaterials as modifiers have been reported to be successful. Thus, nanomaterials such as gold nanoparticles, carbon nanofibers and poly (propylene imine) have been used in this study.
This dissertation is based on the development of aptamer-based biosensors and electrochemical sensors for neurotransmitters. This study reports two developed electrochemical sensors for each neurotransmitter - dopamine and epinephrine and a biosensor for the detection of dopamine. Gold nanoparticles (AuNPs), poly(propylene imine) dendrimer (PPI) and carbon nanofibers (CNF) were used as nanomaterials for the fabrication of the sensors.
The first electrochemical sensor was developed for dopamine using poly(propylene imine) dendrimer - gold nanoparticle modified glassy carbon electrode. A glassy carbon electrode was modified using poly(propylene imine) dendrimer and gold nanoparticles (GCE/PPI/AuNPs). A 10 mM poly (propylene imine) (PPI) dendrimer solution was electrochemically deposited onto a glassy carbon electrode by cyclic voltammetry and left to dry. After drying, gold nanoparticles (AuNPs) were electrodeposited on the PPI layer from a 10 mM gold (III) chloride solution...