Thanks to new microfabrication technology, labs-on-a-chip have developed large array parallel screening detection processes with very small analyte volume consumption. Cells, biomolecules, and micron-size particles can be manipulated and processed in micro biochemical reactors for diagnostical, drug screening, and drug detection purposes. The micro lab-on-a-chip can accomplish these tasks in a rapid, sensitive, and specific manner. Mixing in microreactors, however, stands out as one of the most time-consuming fluidic processes, even after all the advances made in lab-on-chip. Chaotic advection is an efficient mechanism that can enhance mixing in a usually diffusion dominated mixing in laminar flow. We found that a combination of fluid shear and large transverse force acting on the particles can form a set of stretches and folds which leads towards chaotic mixing. We identified a large electrokinetic force capable of moving particles into the saddle points region, where the stretches and folds can take place. With this force and the velocity shear generated in a micromixer, we have found a family of flow regimes among which efficient mixing can be obtained with specifically defined operating parameters. The microreactor has a large surface-to-volume ratio; hence, surface property is a very important parameter. A control scheme has been achieved, and has successfully prevented contamination. A reconfiguration scheme was demonstrated in a microfluidic device, where channels could be rendered selectively hydrophobic or hydrophilic, controlling the spontaneous wetting properties of water.
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