Understanding the transport, orientation, and deformation of biological macromolecules in microfluidic systems is critical to the development of a host of lab on a chip applications. Since the interaction of flowing macromolecules with any immobilized enzymes or antigens will be affected by the conformation of the macromolecule, the dynamic effects of flow on the orientation and conformation of the macromolecule and the interactions of the macromolecules with the device walls must be quantified. Here we discuss experiments aimed at both identifying new fluid physics as the characteristic dimensions of the geometry approach those of the macromolecules and at identifying design issues for microfluidic systems. Epifluorescence microscopy has been used for direct visualization of DNA flowing through silicon-fabricated microfluidic devices and for high resolution particle image velocimetry measurements. Preliminary experiments have focused on a contraction/expansion flow consisting of two large reservoirs connected by a long rectangular channel. Measurements of both velocity and conformation fields suggest the relative importance of shear and extensional flows in stretching macromolecules and the potential of using flow to manipulate macromolecules in microfluidic devices.
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