low-frequency dispersion of surface conducting particles as measured by means of electrorotation

High-magnetic-field electromagnetophoresis of micro-particles in a capillary flow system

The electromagnetophoretic migration of micro-particles in a capillary flow system was demonstrated using a homogeneous magnetic field applied at right angles to an electric current. We utilized a high-magnetic-field of 10 T for observing this phenomenon. When the direction of the electric current was alternatively changed, polystyrene latex particles in a flowing aqueous medium migrated zigzag affected by a Lorentz force exerted on the medium. Carbon particles also migrated in the same manner with polystyrene particles. Further, we tried the electromagnetophoretic migration of biological particles, such as yeasts and human red blood cells. The migration velocity component perpendicular to the flow was proportional to both the electric current and the magnetic flux density. These results proved that the dominant force of the zigzag migration was an electromagnetophoretic buoyancy generated in the flowing medium. Moreover, it was found that the force exerted on the particles in the magnetic field of 10 T was sufficient for the desorption of particles adsorbed on the capillary wall.

Coupled electrorotation of polymer microspheres for microfluidic sensing and mixing

We show that coupled electrorotation (CER) of microscopic particles using microfabricated electrodes can be used for localized sensing and mixing. The effective use of microelectromechanical systems and micro total analysis systems requires many types of control. These include the abilityto (1) manipulate objects within microchannels by noncontact means, (2) mix fluids, and (3) sense local chemical parameters. Coupled electrorotation, in which the interactions between induced electric dipoles of adjacent particles lead to particle rotation, addresses aspects of all three challenges simultaneously. CER is a simple means of controlling the rotation of dielectric objects using homogeneous external radio frequency electric fields. CER is sensitive to several chemical and physical parameters such as the solution conductivity, pH, and viscosity. As a step toward integrating CER devices into microfluidic systems, a simple chip was designed to induce local mixing and to detect local changes in salt concentration, pH, and viscosity.