Figure 1.

(a)–(d) Schematics of the microchip (not to scale). (a) Channel top view with shaded area indicating the post region. (b) Zoom-in of the post region. (c) Channel side cross section with PDMS reservoir holder and integrated electrodes. (d) SEM image of the post region. (e) and (f) show numerical simulations of $\nabla |\overrightarrow{E}{|}^2$ for a post pair based on a DC experiment where 3000 V is applied across a 1 cm long channel. Under DC conditions (e), small arrows indicate the nDEP force direction and large arrows indicate the electrokinetic forces resulting from electroosmosis and electrophoresis. Under AC conditions (f), only nDEP forces are prevalent. Note that arrow size does not represent the magnitude of the forces. For all experiments, the electric field is applied along the y axis.