The capability to easily and inexpensively fabricate microfluidic devices with negligible dependence on specialized laboratory equipment continues to be one of the primary forces driving the widespread use of plastic-based devices. These devices are typically produced as replicas of a rigid mold or master incorporating a negative image of the desired structures. The negative image is typically constructed from either thick photoresists or etched silicon substrates using conventional photolithographic fabrication processes. While these micromachining techniques are effective in constructing masters with micron-sized features, the need to produce masters rapidly in order to design, fabricate, and test microfluidic devices, is a major challenge in microfluidic technology. In this research, we use inexpensive photosensitized copper clad circuit board substrates to produce master molds using conventional printed circuit technology. The techniques provide the benefits of parallel fabrication associated with photolithography without the need for cleanroom facilities, thereby offering a degree of speed and simplicity that allows microfluidic master molds to be constructed in approximately 30 minutes in any laboratory. These techniques are used to produce a variety of microfluidic channel networks using PDMS (polydimethylsiloxane) and melt-processable plastic materials.

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Directed immune cell migration plays important roles in immunosurveillance and immune responses. Understanding the mechanisms of immune cell migration is important for the biology of immune cells with high relevance to immune cell trafficking mediated physiological processes and diseases. Immune cell migration can be directed by various guiding cues such as chemical concentration gradients (a process termed chemotaxis) and direct current electric fields (dcEF)(a process termed electrotaxis). Microfluidic devices that consist of small channels with micrometer dimensions have been increasingly developed for cell migration studies. These devices can precisely configure and flexibly manipulate chemical concentration gradients and electric fields, and thus provide powerful quantitative test beds for studying the complex guiding mechanisms for cell migration. In the research of this thesis, a PDMS-based and a glass-based microfluidic devices were developed for producing controlled dcEF and these devices were used to analyze electrotaxis of activated human blood T cells. Using both devices, we have successfully demonstrated that activated human blood T cells migrate toward the cathode of the applied dcEF. Furthermore, a novel microfluidic device was developed to configure better controlled single or co-existing chemical gradients and dcEF to mimic the complex guiding environments in tissues and this device was used to investigate the competition of chemical gradients and dcEF in directing activated human blood T cell migration.

A microfluidic-based inductance sensor operating at 1.5 GHz is presented that can detect single 4.5 μm superparamagnetic particles flowing in a microfluidic channel. The particles are detected as they pass over a micron-sized planar gold loop electrode, with a maximum signal-to-noise ratio of 26.3 dB for an 80 μm/s flow rate; the magnetic beads are simultaneously observed with microscope images. The sensor consists of a coupled-line resonator and microwave interferometric system coupled to the loop electrode that is integrated within a polydimethylsiloxane-on-glass microfluidic chip assembly. A time-averaged inductance change caused by a single particle is related to the real part of its magnetic Clausius-Mossotti factor. The effective real part of the magnetic permeability for a particular particle is estimated to be 1.13 at 1.5 GHz. The sensor detects magnetic particles in flow and does not require an external biasing magnetic field, which distinguishes it from other magnetic microparticle sensors.

Directed immune cell migration plays important roles in immunosurveillance and immune responses. Understanding the mechanisms of immune cell migration is important for the biology of immune cells with high relevance to immune cell trafficking mediated physiological processes and diseases. Immune cell migration can be directed by various guiding cues such as chemical concentration gradients (a process termed chemotaxis) and direct current electric fields (dcEF)(a process termed electrotaxis). Microfluidic devices that consist of small channels with micrometer dimensions have been increasingly developed for cell migration studies. These devices can precisely configure and flexibly manipulate chemical concentration gradients and electric fields, and thus provide powerful quantitative test beds for studying the complex guiding mechanisms for cell migration. In the research of this thesis, a PDMS-based and a glass-based microfluidic devices were developed for producing controlled dcEF and these devices were used to analyze electrotaxis of activated human blood T cells. Using both devices, we have successfully demonstrated that activated human blood T cells migrate toward the cathode of the applied dcEF. Furthermore, a novel microfluidic device was developed to configure better controlled single or co-existing chemical gradients and dcEF to mimic the complex guiding environments in tissues and this device was used to investigate the competition of chemical gradients and dcEF in directing activated human blood T cell migration.

A microfluidic-based inductance sensor operating at 1.5 GHz is presented that can detect single 4.5 μm superparamagnetic particles flowing in a microfluidic channel. The particles are detected as they pass over a micron-sized planar gold loop electrode, with a maximum signal-to-noise ratio of 26.3 dB for an 80 μm/s flow rate; the magnetic beads are simultaneously observed with microscope images. The sensor consists of a coupled-line resonator and microwave interferometric system coupled to the loop electrode that is integrated within a polydimethylsiloxane-on-glass microfluidic chip assembly. A time-averaged inductance change caused by a single particle is related to the real part of its magnetic Clausius-Mossotti factor. The effective real part of the magnetic permeability for a particular particle is estimated to be 1.13 at 1.5 GHz. The sensor detects magnetic particles in flow and does not require an external biasing magnetic field, which distinguishes it from other magnetic microparticle sensors.

Magnetic micro-robots are small robots under 1mm in size, made of magnetic materials, with relatively simple structures and functionalities. Such micro-robots can be actuated and controlled remotely by externally applied magnetic fields, and hence have the potential to access small and enclosed spaces. Most of the existing magnetic micro-robots can operate in wet environments. When the robots are actuated by the applied magnetic field to move inside a viscous liquid, they invoke flow motions around them inside the liquid. The induced flows are relatively local as the velocity of these flows decays rapidly with the distance from a moving robot, and the flow patterns are highly correlated with the motions of the micro-robots which are controllable by the applied magnetic field. Therefore, it is possible to generate local flow patterns that cannot be easily done using other microfluidic techniques. In this work we propose to use rotational motion of the magnetic micro-robots for local manipulation of flows. We employ electromagnetic techniques to successfully deliver actuation and motion control onto the micro-robots. Rotational magnetic field is applied to induce rotational motion of micro-robots both when they stay near a surface and are suspended in the liquid. Rotational flows are locally generated in the vicinity of micro-robots inside the viscous liquid. Implementation of three major applications using the flows generated by the rotating micro-robots are demonstrated in this work: 1) Two-dimensional (2D) non-contact manipulation of micro-objects. 2) Three-dimensional (3D) propulsion for the micro-robot to swim in a liquid. 3) Size-based sorting of micro-particles in microfluidic channels under continuous flow. The first two applications occur in otherwise quiescent liquid, while the third requires the presence of non-zero background flow. For the first application, we propose two methods to achieve precise positioning of the microrobots on a surface: 1) Using visual-feedback-control to adjust the rotation for one single microrobot. Micro-robot can be precisely positioned at any location on a surface using this method. 2) Using a specially prepared surface with magnetic micro-docks embedded in it, which act as local magnetic traps for multiple micro-robots to hold their positions and operate in parallel. Physical models are established for both the micro-robot and the micro-objects present in the induced rotational flow. The rotational flows induced by rotating micro-robots are studied with numerical simulations. Experimental demonstrations are first given at sub-millimeter scale to verify the proposed method. Micro-manipulation of polymer beads is performed with both positioncontrol methods. Automated micro-manipulation is also achieved using visual-feedback. Micromanipulation at micron-scale is then performed to demonstrate the scalability and versatility of the proposed method. Non-contact manipulation is achieved for various micro-objects, including biological samples, using a single spherical micro-robot. Inspired by flagellated microorganisms in nature, we explore the hydrodynamics of an elastic rod-like structure - the artificial flagellum, and verify by both simulation and experiments that rotation and deformation of such structure can result in a propulsive force on a micro-robot it is attached to. Optimization of flagellum geometry is achieved for a single flagellum. A swimming micro-robot design with multiple flexible flagella is proposed and fabricated via an inexpensive micro-fabrication process involving photolithography, micro-molding and manual assembly. Experiments are perform to characterize the propulsive force generation and the resulting swimming performance of the fabricated micro-robots. It is demonstrated that the swimming speed can be improved by increasing the number of attached flagella. For the size-based sorting application, we integrate the micro-robots into microfluidic channels by using the substrate embedded with magnetic micro-docks, which are capable of holding the robots under continuous flow inside the channels while the robots spin. Numerical analysis is carried out of the flows inside the microfluidic channel in the presence of rotating micro-robots, and a physical model is established and discussed for size-based lateral migration of spherical micro-objects inside the induced rotational flows. Experimental demonstrations are performed for using the induced rotational flows to divert the trajectories of micro-particles based on their sizes under continuous flow. In addition, we propose the method of using the two photon polymerization (TPP) technique to fabricate magnetic micro-robots with complex shapes. The method could also achieve fabrication of arrays of micro-robots for more sophisticated applications. However, experimental results prove that the TPP is insufficient to achieve magnetic micro-robots that meet our needs for size-based sorting application due to physical limitations of the materials. Despite that, it is potentially powerful and suitable for fabrication of micro-robots with complex structures at small scales.

This thesis presents optofluidic nanostructures for analyte transport, concentration and sensing. This work was part of a larger collaborative project between the BC Cancer Agency and the departments of Chemistry, Electrical and Mechanical Engineering at the University of Victoria. In this work, arrays of nanoholes are used as optofluidic platforms for sensing, combining the characteristics of these nanostructures for both fluidic transport and plasmonic (optical) sensing. Two different modes are considered: flow-over mode, where the sample solution containing the analyte flows on top of the nanohole arrays, and a novel flow-through mode, where the nanoholes are used as nanochannels, enabling solution transport and analyte sieving. Flow-through nanohole array operation and sensing is first demonstrated, offering a six-fold improvement in sensor response compared to established flow-over sensing formats. Through a subsequent theoretical scaling analysis and computational analyses, the benefits of the flow-through nanohole sensing format are further quantified. A first analysis is dedicated to study the enhancement offered by the flow-through operation mode using a mass transport approach. A second analysis offers an ample study of benefits and limitations of the flow-through nanostructure operation using the combination of mass transport and binding kinetic parameters for different analytes with characteristics of clinical relevance. The mass transport analysis indicates much higher analyte collection efficiency (~ 99%) offered by the flow-through mode, compared to the flow-over platform (~ 2%). The analysis including both mass transport and binding kinetics demonstrate up to 20-fold improvement in response time for typical biomarkers. This thesis also presents the use of the flow-through optofluidic platform as an active analyte concentrator. In combination with a pressure bias, an electric field is used to concentrate electrically charged analyte for subsequent sensing. Fluorescein enrichment of 180-fold in 60 s was achieved, and 100-fold enrichment and simultaneous surface plasmon resonance (SPR) sensing of a protein (bovine serum albumin, BSA) was demonstrated. These experiments represent the first active utilization of a nanohole metallic layer as an electrode, and the first demonstration of a photonic nanostructure achieving both concentration and sensing of analytes. Towards the integration of optofluidic nanostructures into microfluidic environments for portable lab-on-chip diagnostic systems, this dissertation also includes the development of two nanohole array based sensing systems with simple flow-over operation. The first system consisted of a hand-held device with a dual-wavelength light source to increase the spectral diversity. The second system consisted of nanohole arrays integrated with a microfluidic concentration gradient generator for the detection and quantification of ovarian cancer antibody and antigen. Additionally, this dissertation includes a novel technique to actuate liquids in microchannels through ground-directed electric discharges. Experiments demonstrate average fluid velocities on the order of 5cm/s and applicability of the technique in serpentine channels, for on-demand fluid routing, to initiate a mixing process, and through an on-chip integrated microelectrode. / Graduate

The ability to rapidly, sensitively, and accurately detect the presence of a pathogen is a vital capability for first responders in the assessment and treatment of scenarios such as disease outbreak and bioterrorism. Nucleic acid tests such as the polymerase chain reaction (PCR) are supplanting traditional techniques due to the improved speed, specificity, sensitivity, and simplicity. Still, amplification by PCR is often the bottleneck when processing genetic samples. Conventional PCR machines are bulky, slow, and consume large reagent volumes and an affordable, compact, efficient, easy-to-use alternative has yet to emerge. In this work, a microfluidic PCR platform was developed consisting of a low-cost, multi-chamber polymer microchip and a laser-mediated thermocycler capable of independent thermal control of each reaction chamber. Innovations in polymer microchip modeling, fabrication, and characterization yielded a low-cost solution for sample handling. A simple optical system featuring an infrared laser diode and solenoid-driven optical shutter was combined with a microfluidic temperature measurement system utilizing embedded thermocouples to achieve rapid thermocycling capable of multiplexed temperature control. We validated the instrument with sensitive amplifications of multiple viral targets simultaneously. This technology is a breakthrough in practical microfluidic PCR instrumentation, providing the foundation for a paradigm shift in low-cost, high-throughput genetic diagnostics.