PhD Oral Exam - Duraichelvan Raju, Mechanical Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Breast cancer is the leading cause of death in Canada. This thesis aims to develop sensing nanoplasmonic platforms for early diagnosis of breast cancer through detection of exosomes. The adsorption of bio or organic molecules on metallic nanoparticles leads to a plasmon band shift towards longer wavelengths; a phenomenon central to Localized Surface Plasmon Resonance (LSPR). This study aims to develop nano-structured arrays of plasmonic platforms for the highperformance detection of sub-micron biological entities such as viruses, exosomes, and other extracellular vesicles (EVs) ranging from 30 nm to 1000 nm. This thesis particularly focuses on developing and optimizing unique plasmonic platforms for the detection of EVs/exosomes derived from breast cancer cell lines. These EVs/exosomes are nano-sized (30 nm s- 150 nm), cargo-bearing vesicles secreted by almost all cell types, consisting of a lipid bilayer encasing a semi-fluid core of cytoplasmic materials, including proteins, nucleic acids, and exhibit significant heterogeneity, reflecting their cellular origin. Despite their potential as biomarkers for diseases like cancer, their heterogeneity and overlapping physicochemical properties with other vesicles pose challenges for effective detection, separation and purification. In the beginning, two different types of platforms, one fabricated by an ex-situ method and the other one, by an in-situ method were investigated to find out the most convenient in terms of sensitivity for the detection of EVs/exosomes. Different fabrication conditions have been explored and the sensitivity of the platforms has been measured. A sensing protocol involving several steps has been developed and optimized for the detection of EVs/exosomes. It has been found that the platform prepared by an ex-situ method, that is by convective assembly of gold colloidal particles, was significantly more sensitive than the silver (Ag)-PDMS and gold (Au)-PDMS nanocomposite platforms fabricated by an in-situ method. In the case of gold (Au)-PDMS, gold is segregated under the surface of the polymer, without direct contact with the environment thus not suitable for the detection. Additionally, to improve the refractive index sensitivity, novel platforms have been investigated. This thesis is further dedicated to developing and characterizing new plasmonic platforms, based on nano-islands/particles, fabricated from thin gold films e-beam deposited on an adhesion layer. The nano-islands/particles fabricated by the dewetting of the uniform gold films deposited on Chromium (Cr) (Cr-Au) and Indium Tin Oxide (ITO) adhesion layers (ITO-Au), respectively. These platforms, have been characterized by a plethora of methods (UV-Vis spectroscopy, FESEM, EDS, AFM, XRD,). Subsequently, based on the characterization results, the Cr-Au platform has been identified for the detection of EVs/exosomes. In addition, a direct detection method as well was developed without any surface chemistry modification of the plasmonic platform. The detection results obtained by using this novel platform and method were compared with the results of the ex-situ, and in-situ platform studied earlier in this thesis work. It was found that, with the novel platform and method, the sensitivity of detection improved around 1.5 times and with the time taken for the detection reduced around one fourth of the earlier method time. This work also provided invaluable information, regarding the adhesion layers, and their characteristics, especially stability, in association with very thin gold films. The phenomena of interdiffusion and oxidation during the deposition and heat treatment and their effect on detection have been studied as well. Overall, this work contributes to the development of cost-effective, high-performance nano-plasmonic platforms, for early diagnosis of breast cancer establishing a foundation for their broader application in detecting and analyzing diverse biological and environmental samples.