Guided Electrokinetic Assembly of Polystyrene Microbeads onto Photopatterned Carbon Electrode Arrays.

Assembly of microdevices from constituent parts currently relies on slow serial steps via direct assembly processes such as pick-and-place operations. Template Electrokinetic Assembly (TEA), a guided, noncontact assembly process, is presented in this work as a promising alternative to serial assembly processes. To characterize the process and its implementation of electrokinetic, dielectrophoretic, and electro-osmotic phenomena, we conducted studies to examine the assembly of polymer microparticles at specific locations on glassy carbon interdigitated electrode arrays (IDEAs). The IDEAs are coated with a layer of lithographically patterned resist, so that when an AC electric field is applied to the IDEA, microparticles suspended in the aqueous solution are attracted to the open regions of the electrodes not covered by photoresist. Interplay between AC electro-osmosis and dielectrophoretic forces guides 1 and 5 µm diameter polystyrene beads to assemble in regions, or "wells", uncovered by photoresist atop the electrodes. It was discovered that AC electro-osmosis under an applied frequency of 1 kHz is sufficient to effectively agglomerate 1 µm beads in the wells, whereas a stepwise process involving the application of a 1 MHz signal, followed by a 1 kHz signal, is required for the positioning of 5 µm beads, which are mainly affected by dielectrophoretic forces. Permanent entrapment of the microparticles is then demonstrated via the electropolymerization process of the conducting polymer polypyrrole.