Electrochemistry and Surface Propertiesof Nanostructured Carbon Electrodes andInterfaces

Over the past two decades, carbon nanomaterials have received significant attention in health technologies, due to their impressive electroanalytical properties, especially in neurotransmitter detection. The death of dopaminergic neurons and resulting lower levels of dopamine (DA) severely disrup the body's motor functions, making life extremely difficult for Parkinson's patients. Electrochemical carbon sensors offer the potential to detect DA levels effectively in the brain. However, biofouling of electrode surfaces, causing surface passivation, along with a lack of sensitivity and selectivity in DA sensors, continues to hinder growth in the field of DA electrochemical sensors. Despite the extensive literature available on various approaches to tackle these challenges, such as employing multimaterial coatings on electrode surfaces and applying hemical treatments, there remains a lack of thorough understanding regarding their effectiveness. This necessitates the importance of developing methods to regulate the performance of electrochemical sensors by modulating the geometric properties of materials during fabrication and comprehensively studying the cause-and-effect relationships. This dissertation demonstrates the significance of modifying material assembly and structure to control associated electroanalytical properties. The role of surface nanostructures and interfaces towards carbon nanofiber (CNF) electrochemistry is studied, with DA as a case study due to its relevance in neurodegenerative disease treatment. To attain selectivity of neurotransmitter detection, adsorption of the analyte is crucial. However, reducing electrode fouling is also essential for optimal DA sensor performance. This dissertation demonstrates that achieving such balance is possible by modifying the nanoscale structure of carbon nanomaterials to promote favorable adsorption of target molecules, while optimizing the macroscopic geometry of the electrode to mitigate excessive fouling. CNF electrodes with increased fiber lengths are demonstrated to enhance electrochemical sensitivity and selectivity against common interferents by increasing adsorption sites for target molecules. Moreover, breaking the planar geometry of carbon electrodes and introducing macroscopic geometries is shown to reduce biofouling and electrochemical fouling susceptibility. It is demonstrated that commonly used adhesion layers in the fabrication of CNF, such as Cr and Ti, exhibit different carbon segregation dynamics upon annealing, affecting electrochemical activity. Subsequently, the presence of Ni seed layer alters these dynamics, favoring ordered graphitic carbon segregation and improving electrochemical properties. Nevertheless, based on the results presented in the dissertation, it is argued that i) modifying nanoscale and macroscopic geometries and (ii) systematic evaluation of the electroactivity of often overlooked electrode components are crucial for designing biosensors with optimized performance.