A microfluidic thermocapillary pumping system for microfabricated analysis devices.

A non-mechanical pumping mechanism, thermocapillary pumping (TCP), is developed for moving nano-liter sized drops of liquid within integrated microfabricated analysis devices. In TCP, one end of a single drop is heated to create a surface tension difference between the ends of the drop, which causes a capillary pressure difference between the two drop ends and results in drop motion. TCP velocities of up to ~20 mm/min were measured with different liquids at temperature differences between approximately 10 and 70°C, in agreement with theoretical predictions within corresponding uncertainty limits. Several techniques are suggested for assisting TCP when contact angle hysteresis, a resistance opposing TCP, is too large. These techniques include using surface treatments to reduce the contact angle hysteresis, converging channels to offset hysteresis, or an applied pressure to assist in movement. Results are also presented from a finite difference, heat transfer analysis of TCP devices. The analysis incorporates both fluid flow and energy transport through multiple device layers. Factors examined include the choice of channel/substrate material and thickness, pumping velocity, and channel/substrate boundary conditions. Results from a base case design with single-sided heating (fused silica heater substrate, glass channel cap, and water) show that near uniform interface temperatures can be achieved with drop velocities below ~1 cm/s. Extending the analysis to thermal reaction channels heated from bottom side, it was shown that uniform reaction temperatures Were obtained when channel/reactor heights were maintained below ~50 mum. Lastly, an integrated Y-shaped device was designed and fabricated to integrate typical movement, mixing, and reaction operations within a single device. The above integral integrated reaction sequence was performed using a restriction digest reaction (RDR), which a common DNA analysis reaction. By integrating these operations into a single micro microfabricated device using TCP, the successful integration of a common DNA analysis reaction, a restriction digest reaction was demonstrated. Using repetitions of the Y-device case format, more complicated analysis systems, such as one for DNA sequencing, may be fabricated.Ph.D.Applied SciencesBiomedical engineeringChemical engineeringMechanicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131778/2/9929943.pd