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UBC Theses and Dissertations

Development of advanced operators for enhanced on-chip biosensing in digital microfluidic platforms Samiei, Ehsan


Over the past two decades, digital microfluidics (DMF) has grown significantly as a powerful tool for lab-on-a-chip (LOC) applications. Since the introduction of DMF with its primary capabilities in sample manipulation (transport, splitting and mixing) in the droplet format, many advances have been made towards the development of platforms capable of performing entire processes of biochemical assays in an automated fashion. These advances include the progress made towards the fabrication methods, and the development of techniques for sample manipulation and integration of biosensors. Despite the general success in such developments, DMF still lacks capabilities in sample manipulation (including the droplets and their contents, e.g. cells and microbeads), specifically for biosensing, in which sample preparation and post-sensing removal of the sample are required. Therefore, in majority of the applications, DMF has been used for processing parts of the entire assay, and after biosensing, the recovery of the chip was hindered due to the contamination of the biosensor for its hydrophilic behavior. This thesis aims at the development of advanced operators for accurate pre-sensing sample preparation, biosensing and post sensing sample removal. For this purpose, an unequal droplet splitting method is developed based on the geometrical modification of one actuating electrode, which enables dispensing/splitting droplets with a wide range of volumes and with an accuracy of over 99%. An electrohydrodynamic technique is developed for rapid mixing inside the stationary droplets, enhancing the mixing time and eliminating the need for frequent and cyclic transport of the droplet on the chip. A dielectrophoretic-gravity driven technique is developed for concentrating and focusing the particles and cells inside the sample droplet. Also, a systematic study has been performed on the surface properties and geometry of the biosensors to optimize their geometry and configuration on DMF devices for complete sample removal after biosensing. Finally, the application of the developed techniques for enhanced on-chip biosensing is shown for detection of Cryptosporidium as a proof of concept.

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