We present the design, fabrication, and characterization of a micromixer that uses an electrokinetic instability (EKI) as the stirring mechanism. We have observed that microchannel liquid flows subjected to sinusoidally alternating electric fields exhibit, under certain electric field strengths and geometries, a flow instability capable of rapidly stirring micro- and nanoliter volume solutions [1]. We have performed a fluorescein dilution experiment to observe the rapid dispersion of dyed and undyed buffers within the mixing chamber as a result of EKI stirring. The flow field was imaged using an inverted, epifluorescent microscope fitted with a 12 bit, cooled CCD camera. We have initially characterized the mixer performance by computing ensemble-averaged probability density functions (PDF's) and power spectra of the instantaneous, spatial fluorescence intensity fields. This novel stirring mechanism has the potential for significantly improving the functionality of microfluidic, bioanalytical devices.
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