Transverse Migration and Concentration of DNA in Microfluidic Channels

The migration and subsequent concentration of long strands of DNA due to a pressure driven flow and parallel electric field within a microfluidic channel were measured.  The concentration rate and efficiency of trapping the DNA were quantified as functions of the channel size and the ionic and polymeric concentrations of the buffer solution.  Buffers with large ionic concentrations hinder the ability to concentrate the DNA at the entry of the microcapillary and reduce the short-time efficiency of the trapping from nearly 100% under optimum conditions to zero.  The results also demonstrate that flexible strands of DNA migrate transverse to an applied shear flow and opposing electrophoretic flow, even when the buffer solution lacks any measurable viscoelastic response.  Optimizing the electric field strength can increase the amount of DNA that can be trapped, and the efficiency is not affected by the size of the channel cross-section.  The results are qualitatively consistent with a model for DNA migration that incorporates velocity disturbances induced by the electric field acting on the polyelectrolyte.