Work with dc electrokinetics has demonstrated that is works well for bulk transport of fluid an particles. However, it is difficult to achieve control of individual or groups of particles. This paper investigate the use of induced-charge electroosmosis (ICEO) as a means of providing control over particles within bulk dc electroosmotic flow. ICEO flow develops when an electric double layer is induced by an applied electric field at the surface of a conducting object. Here conducting posts are positioned in a microfluidic channel and ICEO flow develops around them due to an applied ac electric field. A dc electric field is applied across the length of the channel to induce electroosmotic flow past the ICEO region. Around one arrangement of posts the ac and dc flow fields combine to produce a region of recirculation which could be useful for holding a particle or particles within a fixed region of the channel. An alternative arrangement of posts functions to focus the flow into the center of the channel. A numerical model of the system is developed and used to explore means of adapting the ICEO flows to many situations. A method for fabricating a microfluidic system for ICEO flows is presented.

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