Public defence in Electronics integration and reliability, M.Sc. Ayesha Kousar

The title of the thesis: Electrochemistry and Surface Properties of Nanostructured Carbon Electrodes and Interfaces 

Doctoral student: Ayesha Kousar
Opponent: Prof. Xinxin Xiao, Aalborg University, Denmark
Custos: Prof. Tomi Laurila, Aalto University School of Electrical Engineering, Department of Electrical Engineering and Automation

Electrochemical carbon sensors offer the potential to detect neurotransmitter levels effectively in the brain. However, biofouling of electrode surfaces, causing surface passivation, along with a lack of sensitivity and selectivity in these sensors, continues to hinder growth in the field of electrochemical biosensors. Despite the extensive literature available on various approaches to tackle these challenges, such as employing multimaterial coatings on electrode surfaces and applying chemical 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 study 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 by taking dopamine as a case study. CNF electrodes with increased fiber lengths are demonstrated to enhance electrochemical sensitivity and selectivity of dopamine detection against common interferents by increasing adsorption sites for target molecules. Moreover, breaking the planar geometry of carbon electrodes and introducing macroscopic geometries (such as nanofibers, multiwalled nanotubes) 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. 

Therefore, this thesis emphasizes controlling bio-electrochemical sensor performance by i) modifying nanoscale and macroscopic geometries of carbon nanostructures and (ii) systematic evaluation of the electroactivity associated with often overlooked interfaces of electrodes. 

Keywords: carbon nanomaterial, cyclic voltammetry, electrochemical biosensing, adhesion metals, seed metals

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

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Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53