Electrokinetic fluid control in two-dimensional planar microfluidic devices.

We present microfluidic device designs with a two-dimensional planar format and methods to facilitate efficient sample transport along both dimensions. The basic device design consisted of a single channel for the first dimension which orthogonally intersected a high-aspect ratio second-dimension channel. To minimize dispersion of sample moving into and through the sample transfer region, control channels were placed on both sides of the first-dimension channel, and the electrokinetic flow from these control channels was used to confine the sample stream. We used SIMION and COMSOL simulations of the electric fields and fluid flow to guide device design. First, devices with one, two, and four control channels were fabricated and tested, and four control channels provided the most effective sample confinement. The designs were evaluated by measuring the sample stream widths and concentration to width ratios as a function of the electric field strength ratio in the control channels and first-dimension (1D) channel (EC/E1D). Next, both a single open channel and an array of parallel channels were tested for the second dimension, and improved performance was observed for the parallel channel design, with stream widths as narrow as 120 microm. The ease with which fluids could be introduced into both the first and second dimensions was also illustrated. Sample plugs injected into the planar region were confined as effectively as sample streams and were easily routed into the planar region by reconfiguring the applied potentials.