  An electrokinetically-driven deterministic lateral displacement (e-DLD)
device is proposed for the continuous, two-dimensional fractionation of
suspensions in microfluidic platforms. The suspended species are driven through
an array of regularly spaced cylindrical posts by applying an electric field
across the device. We explore the entire range of orientations of the driving
field with respect to the array of obstacles and show that, at specific
forcing-angles, particles of different size migrate in different directions,
thus enabling continuous, two-dimensional separation. We discuss a number of
features observed in the kinetics of the particles, including directional
locking and sharp transitions between migration angles upon variations in the
direction of the force, that are advantageous for high-resolution
two-dimensional separation. A simple model based on individual
particle-obstacle interactions accurately describes the migration angle of the
particles depending on the orientation of the driving field, and can be used to
re-configure driving field depending on the composition of the samples.
