Isomotive electrode

FIG. 22-33 A practical isomotive field geometry, showing eo, the critical radius characterizing the isomotive electrodes. Electrode 3 is at ground potential, while electrodes 1 and 2 are at Vj = V. and V2 = V = —V. respectively. The inner faces of electrodes 1 and 2 follow = o [sin (36/2)]" , while electrode 3 forms an angle of 120 about the midline. 

Another hmitation to be considered is the volume that the DEP force can affect. This factor can be controlled by the design of electrodes. As an example, consider electrodes of cylindrical geometry. A practical example of this would be a cylinder with a wire running down the middle to provide the two electrodes. The field in such a system is proportional to 1/r. The DEP force is then Fdep VIE I < 1/r, so that any differences in particle polarization might well be masked merely by positional differences in the force. At the outer cyhnder the DEP force may even be too small to affect the particles appreciably. The most desirable electrode shape is one in which the force is independent of position within the nonuniform field. This isomotive electrode system is shown in Fig. 22-33. 

There are a number of experimental aspects which affect biological DEP. One wants and indeed needs a nonuniform electric field to cause DEP. A variety of electrode shapes can be used, including pin-pin, wire-wire, pin-plate, and isomotive geometries. These are sketched in Figure 5. The isomotive electrode system is one designed to produce a constant DEP force over a finite region of a DEP chamber. It is particularly useful for analytical and in delicately comparative experiments. The pin-pin and wire-wire electrodes are relatively easy to construct and handle. 

DEP chambers can be very simple and still yield significant answers to the experimenter. The isomotive electrode geometry is useful in analytical and comparative experiments because it produces a DEP force independent of position over the working area of the chamber. - There are many other useful electrode shapes that can be used depending on the application desired. 

Typical deflections experienced by cells in such a device amount to several millimeters for axial flow path lengths of 100 mm far an applied potential field of 4-8 volts rms (root mean square) in a medium of appropriate conductivity (Pohl, 1977). The particular electrode configuration employed is called the isomotive electrode configuration it creates a constant dielectrophoretic force on a particle or cell over a wide region, i.e. over a large range of radial locations (Pohl and Kaler, 1979). The magnitude of this farce is... 

FIGURE 5. Various electrode shapes Isomotive for producing dielectropheretic fields. 

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