FIG. 2.

Schematic illustrating the mechanism of continuous-flow sheath-free electrokinetic particle separation in a bifurcating microchannel. Particles undergo a lateral migration, U_w, due to the wall-induced electrical lift force (see inset I), which competes with the axial electrokinetic motion, U_EK, resulting in a three-dimensional particle focusing along the centerline of the main-branch (see inset II). At the bifurcation, the focused two types of particles enter into either side-branch from near the inner wall, and are then continuously separated based on the difference in the particle velocity ratio, i.e., U_w/U_EK in Eq. (3). The background color and lines in the two insets represent the electric field contour (the darker the larger magnitude) and electric field lines (similar to fluid streamlines⁵⁷), respectively.