Robust microfluidic platform for single molecule rapid buffer exchange, mixing and quality control schemes

The introduction of microfluidic devices into the burgeoning biochip market, projected to reach 4 billion dollars by 2010, will play a significant role in the shaping of this market. However, to reach potential, microfluidics will have to become a robust and reliable technology. Hence, our laboratory has been exploring a particular platform to study PDMS based microfluidic chips, sub-components, quality control schemes and buffer exchange capabilities to perform single molecule studies. After developing a stable, rugged and easy to use PDMS based microfluidic platform to manipulate DNA molecules with optical tweezers, we have used that same platform to hold an exponential mixer, investigated the electromechanical properties of PDMS valves in biochips, and ultimately constructed a rapid buffer exchange prototype as a tool to more accurately study single molecules. The topological mixing scheme exploits flow laminarity by repeatedly splitting, rotating, recombining and folding the flows and exponentially increase the concentration gradients. We recorded PDMS valve opening times in the order of a hundred microseconds that are suitable for rapid buffer exchange applications, found typical resistances of 5x10 9 O that are suitable for patch clamping, recorded valve hysterisis, and studied its valve impedance spectra at different conditions to define quality control parameters. Finally, we successfully developed a rapid buffer exchange tool to analyze tethered single molecules in the order of 10 ms by employing EOF, rather than PDF, to decrease the thickness of the diffusive layer and reach shorter buffer exchange time constants.