(403e) Tilted Post Arrays: DNA Electrophoresis in Anisotropic Media

Microfabricated post arrays are one microfluidic method for separating long DNA. The vast majority of experiments focus on ordered hexagonal arrays, although there are some data for square arrays, quasi-hexagonal arrays, and disordered arrays. Hexagonal arrays are anisotropic media. This anisotropy contrasts sharply with gel electrophoresis, where the random fibers of the gel are normally modeled as an isotropic medium. We will present Brownian dynamics simulation data that show that the electrophoretic mobility and dispersivity undergo a qualitative shift when the electric field vector is no longer coincident with the lattice vectors of the post array. Moreover DNA electrophoresis in such “tilted” post arrays features electrophoretic mobilities that are relatively insensitive to the electric field. As a result, operating a tilted post array at a high electric field can lead to exponential reductions in the time required to achieve a desired resolution when compared to typical post arrays. Our simulations results predict that these “tilted” post arrays provide superior separations. Although the DNA dynamics in a post array are complicated, the electrophoretic mobility results indicate that the “free path”, i.e., the average distance of ballistic trajectories of point sized particles launched from random positions in the unit cell until they intersect the next post, is a useful proxy for the detailed DNA trajectories. The analysis of the free path reveals a fundamental connection between anisotropy of the medium and DNA transport therein that goes beyond simply improving the separation device.