Towards reconfigurable lab-on-chip using virtual electrowetting channels

Lab-on-a-chip systems rely on several microfluidic paradigms. The first uses a fixed layout of continuous microfluidic channels. Such lab-on-a-chip systems are almost always application specific and far from a true "laboratory." The second involves electrowetting droplet movement (digital microfluidics), and allows two-dimensional computer control of fluidic transport and mixing. Integrating the two paradigms in the form of programmable electrowetting channels would take advantage of both the "continuous" functionality of rigid channels, which are used in numerous applications, and the "programmable" functionality of digital microfluidics which permits electrical control of on-chip functions. In this dissertation, for the first time, such programmable virtual microfluidic channels were demonstrated using an electrowetting platform. These "wall-less" virtual channels can be formed reliably and rapidly, with propagation rates of 3.5-3.8 mm/s. Pressure driven transport in these virtual channels at flow rates up to 100 microL/min can be achieved without distortion of the channel shape. Further, these channels can be split into segments or droplets of precise volumes, with accuracies exceeding 99%. Critical parameters for such deterministic splitting of liquid samples have been identified with the aid of numerical models and confirmed experimentally. A number of reconfigurable operations were demonstrated, including interactions between continuously-flowing channels and programmed droplet motion. This approach was used to develop a programmable heterogeneous immunoassay protocol, showing a significant improvement in performance by using continuous flow washing as compared to the droplet-based washing in conventional digital microfluidics. The limit of detection obtained with this technique for a streptavidin - biotin binding assay was 10 nM, illustrating potential for improved performance with other heterogeneous immunoassays. The first demonstration of reconfigurable electrowetting channels in this dissertation and their seamless integration with digital microfluidics makes this approach applicable to a wide range of clinical or pharmaceutical applications.