Fabrication and Analysis of Spatially Uniform Field Electrokinetic Flow Devices:  Theory and Experiment

Abstract

A uniform-field design approach can improve the performance of microanalytical, chip-based devices for a number of applications, including separations and sample preparation. The faceted prism paradigm allows the design of microfluidic devices possessing spatially uniform fields in electrokinetically driven flows. We present the first quantitative study of the velocity fields obtained using faceted interfaces between deep and shallow channel sections. Electrokinetic flows were generated in a series of wet-etch fabricated microfluidic channels. The resulting velocity fields were analyzed by particle image velocimetry and compared with simulations of the two-dimensional Laplace equation using both the designed channel geometry and the as-fabricated channel geometry. This analysis found localized differences between the designed and observed flow fields that were directly attributable to the limitations of isotropic substrate etching. Simulations using the as-fabricated channel geometry reproduced the experimental electrokinetic velocity field, quantitatively accounting for speed field variations due to the limits of the fabrication method. The electrokinetic speed fields were also compared to corresponding pressure-driven speed fields.

Dielectrophoretic Manipulation of Particles and Cells Using Insulating Ridges in Faceted Prism Microchannels

“…This type of ridge represents the most trivial form of faceted prism, taken from a larger family of uniform-field designs. , The simulation was performed under conditions for which DEP is negligible (Figure a) and also when DEP is significant (Figure b). As can be observed in the simulation results, when DEP is insignificant (at low applied electric fields), the particles flow unhindered over the ridge …”

“…A schematic representation of the insulating ridge geometry used in this work is shown in Figure . Simulation results for a straight channel with a ridge oriented perpendicular to the flow direction are shown in Figure . This type of ridge represents the most trivial form of faceted prism, taken from a larger family of uniform-field designs. , The simulation was performed under conditions for which DEP is negligible (Figure a) and also when DEP is significant (Figure b).…”

“…Figure c and d show simulation results for a single-particle type migrating through the pitchfork geometry at applied field strengths below (c) and above (d) the inhibition threshold. In this case, the simulation includes effects such as etch-back that cause deviation from exact mathematical designs …”

“…To this end, we employ faceted prisms to fabricate insulating ridges. , The technique was introduced by Fiechtner and Cummings, who derived the design rules theoretically that are necessary for the design of ideal prismatic sections. In a companion paper, we present the first experimental demonstration of faceted prism microchannels, in which fields are applied at low levels, and images of the resulting velocity fields are obtained using particle image velocimetry. In the present paper, we present the first demonstration of the faceted prism methodology for particle filtration and concentration by dielectrophoresis at comparatively large applied fields.…”

Microscale Field-Flow Fractionation: Theory and Practice

“…, efficiency of a system and indicates the number of times a certain separation level is accomplished in a channel. H can be closely approximated by the ratio of variance to the length of the channel, L, [26] according to (10) The plate height generally represents the length of the separation column required to generate a defined level of separation between two particles. Ideally, H should be as small as possible to maximize the level of separation between two samples generated in a given instrument.…”