Microfluidic tools for high content cell assay formats

Microfluidics offers a simple, cost-effective, 'conceive-design-build' experimental platform for performing both high throughput and high content cell assays. Such assays will have potential applications in screening and diagnostics, both in clinical and research settings. Reduced time for 'Targets-to-Hits' in pharmaceutical drug discovery and portable, 'on-the-fly' cell diagnostic systems, possible through such microfluidics-enabled assay approaches, will have huge commercial impact. In this work, two parallel microfluidic formats---continuous flow and droplet-based, for performing cell assays were conceptualized and tools that fit into such formats were developed.; Two dielectrophoresis (DEP)-based cell/particle handling methods, together offering a wide range of possibilities for the continuous flow microfluidic cell assay format were developed in this thesis. The DC-DEP method uses one or two pairs of insulating oil menisci and the AC-DEP method uses Cr/Au electrodes to create focusing or trapping of particles against cross flows. While the AC-DEP method is more amenable for trapping cells, the DC-DEP method is easy to prototype, tunable with respect to the dimensions of the potential well, easily reconfigurable and works well for handling particles. Mathematical correlations that can assist the design of DC-DEP geometry for a specific dimensional requirement of potential well were developed through simulations. For applications in droplet-based microfluidic format, I developed a scaling relation with 2 adjustable parameters following a dimensional analysis approach for predicting the size of droplets generated in a two-phase system from the flow rate or pressure ratio used to drive the two flows. I also developed a vacuum-assisted method for generating and manipulating droplets that addresses some of the limitations associated with droplet generation using pressure-driven methods. This method is scalable for any number of multiplexed droplet generations and offers a good degree of control in droplet size and droplet generation rates. These two contributions will greatly enhance the usability of droplet-based formats for cell assays.; Often mathematical analysis tools are needed to dissect useful information from raw experimental cell perfusion data. A model system of amphetamine-induced dopamine efflux was investigated and a simple transporter trafficking model was developed from simple kinetic equations to illustrate this. While adding a significant contribution to the understanding of drug abuse, this study also offered useful insights to the design of microfluidic format for cell perfusion assays.