Ultrafast active mixer using polyelectrolytic ion extractor.

We report on a low voltage, straight/smooth surface, and efficient active micromixer. The mixing principle is based on alternative ion depletion-enrichment using a pair of positively charged polyelectrolytic gel electrodes (pPGEs), which face each other joined by a microchannel. This system has an external AC signal source electrically connected to the pPGEs via the respective 1 M KCl solutions and Ag/AgCl electrodes. When an electric bias is applied between the two pPGEs, anions are extracted through one of the pPGEs to create a local ion-deficient region. Simultaneously, an ion-rich area appears near the other pPGE due to an inward anionic flux. As the direction of the charge flow is periodically reversed by the AC signal source, the ion depletion-enrichment regions are alternately swapped with each other on the 'push-pull' basis. The turmoil between the pPGEs quickly mixes the solutions in the microchannel without any mechanical moving part or specially machined structures. In the proposed system, both AC frequency and current density can be easily and finely controlled so that one can quickly find the optimal conditions for a given sample. The micromixer as made showed a mixing efficiency higher than 90% for sample solutions of 1 mM Rhodamine 6G and PBS at pH 7.4 when the flow rate was under 6 mm s(-1). In addition to the solution-solution mixing, the micromixer can effectively mix suspended microparticles with solution. As a representative example, rapid and efficient lysis of human red blood cells was demonstrated allowing minimal damage of the white blood cells.