(560h) Addressing of Small Droplets in Systems of Two Aqueous Phases Mediated By Electric Field

Systems of two aqueous phases provide mild conditions in extraction of proteins and other biomolecules. These systems are typically formed either by two incompatible polymers dissolved in water (polyethylene glycol and dextran) or by a mixture of polymer molecules (e.g. polyethylene glycol), inorganic salt and water. Droplets of one phase can serve as containers of reactants in microfludic devices. One possibility how to address a droplet is to use an external electric field of proper orientation. We have found that electric charge is spontaneously formed at the interface of two aqueous phases. The interaction of the imposed electric field and electric double layer around a droplet leads to the electroosmotic slide and oriented movement of the droplet.

We have tested addressing of droplets in several systems of two aqueous phases in open and closed microfluidic devices. Polyethylene glycol (PEG), different inorganic salts and water were used to prepare aqueous two phase systems. Top and bottom phases were formed. The top phase is rich of PEG (PEG phase) and the bottom phase is rich of a dissolved inorganic salt (salty phase). We obtained the dependences of droplet velocity on the applied strength of electric field, droplet size, and droplet composition. It was found that droplets of the salty phase placed on PEG phase move much faster than droplets of PEG phase placed on the salty phase. The salty droplets moved always to the negatively charged electrode. The effective electrophoretic mobilities were determined for all studied two aqueous phase systems. Finally, the addressing of salty droplets at microchannel bifurcation and complex microfluidic structures will be presented. The way of efficient separation of electrode chambers and the main fluidic structure will be also shown.