A sequential injection microfluidic mixing strategy

A novel micromixing strategy is presented, which exploits the axial diffusion of a continuous sequence of discrete samples in a microchannel expansion. Mixing of a continuous sequence in an electroosmotic flow through a sudden expansion region is first modeled assuming an ideal, square-wave injection. The effect of expansion geometry and injection frequency is investigated. To facilitate sequential injection on-chip, two new sequential sample injection schemes are developed and coupled with an expansion region. The first of these designs produces two sample pairs that flow out of separate channels into a common expansion region. This design results in high axial mixing rates but an inherent bias in the injector produces significant cross-stream concentration gradients in the output. These results indicate that the effectiveness of this micromixing strategy is critically dependant on the injection method. A second injector design effectively eliminates the effect of the injection bias using a symmetric microchannel configuration with three solution inlets. The resulting symmetrical injection micromixer produces a continuous uniform stream, 99% mixed, in only 2.3 mm.