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<p>Digital microfluidics as implemented in electrowetting-on-dielectric (EWD) technology has been widely used as a platform for miniaturizing the biomedical or biochemical laboratory on a chip in recent years. DNA pyrosequencing, one of the DNA sequencing-by-synthesis methods, has been successfully integrated on EWD devices. However, this platform requires microliters of reagents and 200~300V of applied voltages, which contributes to higher costs and limits the feasibility of a portable system. This dissertation proposes a low voltage EWD device using multi-layer insulators that can manipulate picoliter droplets on chip. A 300pl droplet was dispensed and actuated at voltages as low as 11.4Vrms and 7.2Vrms respectively on a 95um electrode a EWD device with a 20um SU8 gasket. The stacked insulators in the actuator consisted of 135nm tantalum pentoxide (Ta2O5) and 180nm parylene C films deposited and coated with 70 nm of CYTOP. The physical scaling of electrodes was further demonstrated for 33um and 21um electrode devices, resulting in droplets of 12pl and 5pl respectively in conjunction with 3um gaskets. Manipulation of magnetic beads during dispensing, droplet splitting and merging, and droplet transport were also demonstrated on the scaled EWD devices. The chemiluminescent light produced by the on-chip reaction of 100pl ATP-luciferin and luciferase could be detected with an external cooled CCD camera, but detecting this reaction with smaller-scale droplet reactions was limited by the external detector's sensitivity. Based on fundamental theories and experiments, the actuation voltage and dimensional scaling of EWD devices have been demonstrated, but the use of picoliter droplets in biochemical applications will required improved sensing methods.</p> / Dissertation

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Microfluidic based miniature lab-on-a-chip devices integrate different laboratory functionality in microscale. Microarray technology is evolving as a powerful tool for biomedical and pharmaceutical applications to identify gene sequences or to determine gene expression levels. Preparation of samples and spotting the arrays are the two major steps required for making microarrays. The microfluidic components developed in this research would facilitate performing the above-mentioned steps by a single lab-on-a-chip. Three microfluidic modules were developed: a non-contact microdispenser, an interface connecting the microdispenser with planar Electrowetting on Dielectric (EWOD) sample manipulator and a microvalve that controls the flow at the interface. An electrostatically actuated non-contact type drop-on-demand based microdispenser was developed. The dispenser was designed using finite element modeling technique that solved electrostatically actuated dispensing process. Prototypes were fabricated and tested verifying stable droplet dispensing with error in subsequent droplet generation was less than 15% between each droplet. The frequency of stable generation was 20 Hz and the average volume of dispensed droplet was 1 nL. A closed-channel EWOD actuated interface was developed that allowed a series of droplets to merge inside at the interface converting droplet flow to a continuous flow. An innovative design modification allowed series of droplet merging inside closed-channel. The interface allows integration of pressure driven devices such as: pumps, dispensers, and valves with droplet based planar EWOD devices. A novel EWOD based microvalve was developed that utilizes a thermo-responsive polymer to block and unblock a pressurized continuous flow. EWOD actuation was used to control the positioning of the valving polymer at location of interest. The valve also isolated a pressurized flow from an integrated planar EWOD device. Valves with zero leak rates were demonstrated. Such a valve will be useful in controlling microflows in EWOD to pressure driven flows such as dispensers.

Microfluidic based miniature lab-on-a-chip devices integrate different laboratory functionality in microscale. Microarray technology is evolving as a powerful tool for biomedical and pharmaceutical applications to identify gene sequences or to determine gene expression levels. Preparation of samples and spotting the arrays are the two major steps required for making microarrays. The microfluidic components developed in this research would facilitate performing the above-mentioned steps by a single lab-on-a-chip. Three microfluidic modules were developed: a non-contact microdispenser, an interface connecting the microdispenser with planar Electrowetting on Dielectric (EWOD) sample manipulator and a microvalve that controls the flow at the interface. An electrostatically actuated non-contact type drop-on-demand based microdispenser was developed. The dispenser was designed using finite element modeling technique that solved electrostatically actuated dispensing process. Prototypes were fabricated and tested verifying stable droplet dispensing with error in subsequent droplet generation was less than 15% between each droplet. The frequency of stable generation was 20 Hz and the average volume of dispensed droplet was 1 nL. A closed-channel EWOD actuated interface was developed that allowed a series of droplets to merge inside at the interface converting droplet flow to a continuous flow. An innovative design modification allowed series of droplet merging inside closed-channel. The interface allows integration of pressure driven devices such as: pumps, dispensers, and valves with droplet based planar EWOD devices. A novel EWOD based microvalve was developed that utilizes a thermo-responsive polymer to block and unblock a pressurized continuous flow. EWOD actuation was used to control the positioning of the valving polymer at location of interest. The valve also isolated a pressurized flow from an integrated planar EWOD device. Valves with zero leak rates were demonstrated. Such a valve will be useful in controlling microflows in EWOD to pressure driven flows such as dispensers.

Graphite and graphene electrodes are used to study two electrochemical processes: the decoration of these electrodes with Au metallic nanoparticles through the use of electrodeposition, and electrowetting, the potential-dependent change in hydrophobicity of a surface. Electrodeposition provides a useful route to electrode functionalisation, in particular to combine the enhanced properties of metallic nanoparticles with the advantageous features of carbon materials. A combination of cyclic voltammetry, chronoamperometry, and both ex situ and in situ atomic force microscopy are used to deduce the mechanism of Au electrodeposition on graphite and graphene. Notably, the mechanism of Au nanoparticle formation cannot be deduced from simple voltammetry alone, and the spontaneous formation of Au within the timescale of the electrodeposition experiment is confirmed. Electrowetting is a uniquely responsive method to manipulate the wetting properties of an electrode. However, a dielectric coating is commonly required to protect the surface from electrolysis, which in turn further increases the potentials needed to perform electrowetting. In contrast to this, here it is shown that bare graphite and graphene electrodes support electrowetting without the disadvantages of a dielectric coating, allowing an unprecedented combination of performance and efficiency. Furthermore, the ideal behaviour this system demonstrates is implemented as a platform to study electrowetting itself. The influence of electrolyte composition, surface defects and electrode-blocking dielectric-like films are investigated to determine the factors that impede electrowetting, a key step to understanding the phenomenon that is normally hindered by the use of the dielectric.

Digital microfluidics is a new technology that permits manipulation of liquid droplets on an array of electrodes. Using this technology, nanoliter to microliter size droplets of different samples and reagents can be dispensed from reservoirs, moved, split, and merged together. Digital microfluidics is poised to become an important and useful tool for biomedical applications because of its capacity to precisely and automatically carry out sequential chemical reactions. In this thesis, a set of tools is presented to accelerate the integration of digital microfluidics into Lab-on-a-Chip platforms for a wide range of applications. An important contribution in this thesis is the development of three rapid prototyping techniques, including the use of laser printing to pattern flexible printed circuit board (PCB) substrates, to make the technology accessible and less expensive. Using these techniques, both digital and channel microfluidic devices can be produced in less than 30 minutes at a minimal cost. These rapid prototyping techniques led to a new method for manipulating liquid droplets on non-planar surfaces. The method, called All Terrain Droplet Actuation (ATDA), was used for several applications, including DNA enrichment by liquid-liquid extraction. ATDA has great potential for the integration of different physico-chemical environments on Lab-on-a-Chip devices. A second important contribution described herein is the development of a new microfluidic format, hybrid microfluidics, which combines digital and channel microfluidics on the same platform. The new hybrid device architecture was used to perform biological sample processing (e.g. enzymatic digestion and fluorescent labeling) followed by electrophoretic separation of the analytes. This new format will facilitate complete automation of Lab-on-a-Chip devices and will eliminate the need for extensive manual sample processing (e.g. pipetting) or expensive robotic stations. Finally, numerical modeling of droplet actuation on single-plate digital microfluidic devices, using electrodynamics, was used to evaluate the droplet actuation forces. Modeling results were verified experimentally using an innovative technique that estimates actuation forces based on resistive forces against droplet motion. The results suggested a list of design tips to produce better devices. It is hoped that the work presented in this thesis will help introduce digital microfluidics to many of the existing Lab-on-a-Chip applications and inspire the development of new ones.