Patent DE-19860118-C1 (DE)
Title: System for dielectrophoretical manipulation of particles suspended in a liquid
Inventor: FUHR GUENTER
IPC: B01F13/00
Filed: 1998-12-23
Granted: 2000-09-28
Abstract: The electrodes for use in a micro-system, for dielectrophoretical manipulation of particles suspended in a liquid, are deployed with at least one micro-electrode on a side wall of the channel to generate a field barrier along a reference surface, which passes through the channel at least partially.  The micro-electrode has a given curvature or angle in relation to the channel flow direction, so that the reference surface has a determined curvature in relation to the flow direction. At least two micro-electrodes are at facing channel walls, of the same design and orientation, each as a curved strip. The micro-electrodes have a curvature so that, according to the flow profile, the force applied to the particles in each zone of the field barrier is directed upstream in relation to the micro-electrode. The two electrodes form a downstream closed angle section. Four micro-electrodes can be used as focus electrodes to form a particle funnel. They are curved so that the force acting on a particle moves it from one end of the electrode to the other end, in a direction change between the upstream and downstream zones flanking the electrode. The electrodes can have a sorting action with the field barrier acting with the flow profile of the suspension through the channel, so that particles with different passive electrical characteristics are directed into different paths by the electrodes. Trap electrodes can be deployed as a group across the channel. The micro-electrodes can be positioned in pairs at the bottom and top surfaces of the channel, and the electrodes at facing channel walls can have different geometric shapes. The channel has a rectangular cross section, with the electrodes at the narrower walls, with a flat electrode at one wall and a strip electrode at the facing wall. The flat electrodes are not earthed. The channel can be divided by a wall into two part-channels. An opening in the dividing wall is at the facing micro-electrodes. Two micro-electrodes can be at the bottom and top surfaces of the channel as focus electrodes, and a third auxiliary electrode is at the center of the channel at a gap from the top and bottom surfaces. The opening in the dividing wall is upstream of the auxiliary electrode. A cube-shaped gathering electrode can be in one channel wall, with a number of reservoirs, working with a deflection electrode at the facing channel wall to deflect the particles in the reservoirs. A number of cube-shaped electrodes can be at one channel wall, with facing deflection electrodes at the opposite wall to deflect the particles in the gaps between the cube electrodes. Independent claims are also included for  (1) a technique to manipulate particles in a liquid suspension in a fluid micro-system (24). The micro-system (24) is closed at the end in the reference direction. The particles are moved at a given speed by centrifugal and/or gravity forces on a parallel line to the reference direction. Deflection forces are applied to divert the particles from the reference direction.  (2) an appts. with a micro-system (24) to be fitted to the rotor of a centrifuge. The centrifugal forces act on the particles in the channel (21), in parallel to the channel alignment. The ends of the channel are closed or can be closed when subjected to centrifugal forces.  Preferred Features:The micro-system (24) is fitted to a swing rotor centrifuge appts. so that the particles settle as a sediment by gravity when the rotor is at rest, and a moved by the centrifugal forces when the rotor is operating. The deflection forces are applied by electrical polarizing forces, optical forces, magnetic forces or ultrasonic forces. The centrifugal forces acting on the particles are equal to or weaker than the deflection forces. The centrifugal force moves the particles sufficiently slowly that they can be deflected out of the reference direction. The centrifuge is controlled by an electrical or optic sensor which registers the particle movement speeds. The centrifugal forces move the particles in a number of movements through separate centrifugal steps, with adjustments to the micro-system between the steps to alter the alignment in relation to the centrifugal forces. The rotary speed of the centrifuge is set according to the dimensions or density of the particles. Rising forces are applied to the particles, against the direction of the centrifugal and/or gravity forces. The micro-electrodes (10-12) are structured to generate field barriers in the micro-system, at facing longitudinal sides of the channel. The electrodes are supplied with a high frequency alternating voltage. The micro-electrodes are strip electrodes, at an angle to the channel alignment, to generate field barriers in the channel. The micro-system is in a swing mounting at the centrifuge rotor. An electronic control is at the centrifuge rotor for the micro-system.