A Picoliter-Volume Mixer for Microfluidic Analytical Systems

Mixing confluent liquid streams is an important, but difficult operation in microfluidic systems. This paper reports the construction and characterization of a 100-pL mixer for liquids transported by electroosmotic flow. Mixing was achieved in a microfabricated device with multiple intersecting channels of varying lengths and a bimodal width distribution. All channels running parallel to the direction of flow were 5 μm in width whereas larger 27-μm-width channels ran back and forth through the parallel channel network at a 45° angle. The channel network composing the mixer was ∼10 μm deep. It was observed that little mixing of the confluent solvent streams occurred in the 100-μm-wide, 300-μm-long mixer inlet channel where mixing would be achieved almost exclusively by diffusion. In contrast, after passage through the channel network in the ∼200-μm-length static mixer bed, mixing was complete as determined by confocal microscopy and CCD detection. Theoretical simulations were also performed in an attempt to describe the extent of mixing in microfabricated systems.