Trapping DNA with a high throughput microfluidic device.

Long strands of DNA can be trapped and concentrated near the inlet of a microfluidic channel by applying a pressure gradient and an opposing electric field. The mechanism for trapping involves a migration of DNA perpendicular to both the fluid flow and the electric field. Migration leads to a highly nonuniform distribution of DNA within a cross section of the channel, with the bulk of the DNA concentrated in a thin (10 μm) layer next to the walls of the channel. This highly concentrated layer generates an electrophoretic flux toward the inlet to the device, despite the much larger fluid flow in the opposite direction. In this paper, the extent to which DNA can be trapped and concentrated by this means has been characterized by fluorescence measurements. At short times (<2 hours) nearly all the incoming DNA remains trapped within the device until the electric field is turned off. The DNA largely accumulates near the inlet, but after 30-60 minutes additional DNA starts to accumulate deeper into the channel. Eventually DNA leaks from the device itself, but ≈80% of the incoming DNA can be retained for up to 5 hours. Optimizing the electric field strength can increase the amount of DNA that can be trapped, but the efficiency is not affected by the channel cross-section.