Modeling complex interactions in microfluidic systems

A microfluidic system is a minute chemical processing plant consisting of interconnected networks of microchannels and reservoirs operating with small volumes of reagents. In many microfluidic systems, it is necessary to propel fluids from one part of the device to another, control fluid motion, stir and interact various reagents, and detect the presence of target analytes. In microfluidic systems, these tasks are far from trivial. The thesis focuses on fluid manipulation including fluid propulsion and mixing under the action of electric and/or magnetic fields, and on the modeling of biological interactions that occur in various microfluidic bio-detector systems. Magneto-hydrodynamic (MHD) based microfluidic networks and MHD chaotic stirrers, in which the flow is directed by judicious interplay between electric and magnetic fields, have been designed, modeled, constructed, and tested. The MHD networks allow one to move reagents along any desired path, stir liquids, and facilitate chemical and biological interactions without the use of any mechanical pumps, valves or moving parts. Since MHD forces, being volumetric, do not scale well with size reduction, the possibility of using electro-osmosis for liquid propulsion and stirring is also discussed. In particular, novel chaotic stirrers that are driven by spatial and temporal modulation of the zeta potentials along the conduit\u27s walls are proposed. After sequential fluid manipulation, the sample will be delivered to the detection zone where biological interactions take place. Biological interactions between analytes in solution and ligands immobilized on a surface were modeled, and the theoretical predictions were compared with experimental measurements of the interaction between the Human Interleukin 5 (IL5) and its IL5 receptor. The thesis concludes by developing mathematical models and simulation tools to model the biological interactions that occur in lateral flow and sedimentation bio-detectors operating with sandwich and competitive assays. The theoretical predictions favorably agree with the experimental results available in the literature. The models can be used to test various operating conditions and assist in the microfluidic devices\u27 design and optimization