Dielectrophoresis negative

Figure 1. Real part of the Clausius-Mossotti factor for a solid spherical dielectric particle at various medium conductivities (for Sp = 2.55, o, = 0.01 S/m, and = 78.5). Switch of the sign of Re. K indicates switch between positive and negative dielectrophoresis.

Figure 3. Diagram showing the principle of dielectrophoresis (DEP), which only occurs in a non-homogeneous electric field, (a) Particle more polarizable than the medium positive dielectrophoresis (pDEP) (b) particle less polarizable than the medium negative dielectrophoresis (nDEP).

DEP force. The frequency dependence and the direction of the DEP force are governed by the real part of the Clausius-Mossotti factor. If the particle is more polarisable than the medium, (Re[/cm] > 0). the particle is attracted to high intensity electric field regions. This is termed as positive dielectrophoresis (pDEP). Conversely, if the particle is less polarisable than the medium, (Re[/cm] < 0), the particle is repelled from high intensity field regions and negative dielectrophoresis (nDEP) occurs. Therefore the real part of the Clausius-Mossotti factor characterizes the frequency dependence of the DEP force, as demonstrated in Fig. 1. 

M. P. Hughes and H. Morgan, Measurement of bacterial flagellar thmst by negative dielectrophoresis, Biotechnol. Prog., 15, 245-249 (1999). 

Y. Huang and R. Pethig, Electrode design for negative dielectrophoresis, Meas. Sci. TechnoL, 2, 1142-1146 (1991). 

Negative dielectrophoresis causes particles and cells to be repelled from regions of high electric field strength. This effect can be used to levitate particles over, for example, a planar array of electrodes. A common geometry is a four-electrode field trap with electrodes forming the sides or comers of a square and with the particle levitated over the center of the square. The viscous forces from the medium will damp the motion of the particle. 

Hamada, R., Takayama, H., Shonishi, Y, Mao, L., Nakano, M., Suehiro, J., 2013. A rapid bacteria detection technique utilizing impedance measurement combined with positive and negative dielectrophoresis. Sens. Actuators B Chem. 181, 439—445. 

Church C, Zhu J, Xuan X (2011) Negative dielectrophoresis-based particle separation by size in a serpentine microchannel. Electrophoresis 32 527-531... 

Fig. 4 Plot of the Clausius-Mossotti factor against frequency for two different solid particles. In the shaded area, one particle experiences positive dielectrophoresis and the other negative dielectrophoresis, enabling separation in this frequency window...

Huang Y, Pethig R (1991) Electrode design for negative dielectrophoresis applications. Meas Sci Technol 2 1142-1146... 

Dielectrophoretic Motion of Particles and Cells, Fig. 5 A particle trapped by a negative dielectrophoresis quadrupole trap... 

A lab-on-a-chip device, Envirostat 2.0, was developed to allow for contactless cultivation of a single bacterial cell by negative dielectrophoresis (nDEP) in a precisely controllable microenvironment [18]. Stable trapping in perfusing growth medium was achieved by a miniaturization of an octupole electrode, which matched the dimensions of bacteria. 

At conductivities greater than 1 S/m living cells show negative dielectrophoresis, independent of the frequency That means, they were repelled from the electrodes From a purely physical point of view this means that the real and imaginary part of the effective complex permittivity (s =8 + jx/So27cf) of cells is smaller than that of the surrounding solution In the case of most plant and animal cells the conductivity of the cytoplasm ranges between 0 3 and 0 6 S/m and permittivity between 50 and 70 For frequencies up to 200 MHz the conductivity is the dominant quantity... 

One reason for the lower conductivity of the cytoplasm is the decreased mobility of ions compared to the outside medium Another reason is the pumping of ions across cell membranes We investigated algae yeast cells isolated plant protoplasts, animal cells like erythrocytes fibroblasts and hybndoma cells All cells exhibit exclusively negative dielectrophoresis This effect can be used to develop various cell manipulation principles... 

To measure characteristic parameters of single cells requires exact positioning (pm-range) However, most cells show physiological reactions after mechanical contact with artificial surfaces The occurrence of negative dielectrophoresis allows the development of field cages since cells are focused toward the central part of three-dimensional octupole-electrode configurations (for more details see [2, 7])... 

Note that the dielectric force F is directed along the gradient of the electric field intensity V . For the metallic particle, the force direction is always toward the direction of the largest field. On the other hand, the force on a nonmetallic particle will be toward the direction of the largest field only if Ep > e (positive dielectrophoresis) it will be toward the lowest field if e > p (negative dielectrophoresis). If Ep E or Ea Ep, the magnitude of the force is not influenced, but the direction is. Obviously if there are two particles with Ep [Pg.81]

The sign of the quantity cp-Ed) is important If Cp is greater than Ed, then the direction of the force is toward the region of high electrical field strength it is called positive dielectrophoresis. On the other hand, if Ep is smaller than Ed, the direction of the force is reversed, and one has what is called negative dielectrophoresis the particle is forced in the direction of lower field strength (Pohl and Kaler, 1979). (Of course, the particle may experience zero force as weU.) Note further that the dielectrophoretic force... 

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