5.3 Dielectrophoresis
Dielectrophoresis (DEP) is a phenomenon in which movement of dielectric parti-
cles occurs under the effect of force exerted due to non-uniform field. It was
demonstrated in 1950s by Herbert Pohl. DEP force depends on various parameters
like electrical properties of particle and its surrounding medium, shape and size of
dielectric particles and frequency and magnitude of applied field. DEP is helpful in
cell separation, cell concentration and nanoparticle/nanowire manipulation. DEP
process can be classified in two different types, positive DEP in which dielectro-
phoresis takes place in the direction of increasing electric field strength and
negative DEP in which dielectrophoresis takes place in the direction of reducing
field strength. Figure2.27shows the effect of non-uniform electric field on the
dielectric particles.
DEP force [ 82 ] is given by:
FDEP¼ 2 πr^3 ε 0 εmRe K½ðÞω ∇(^) Erms
(^2) ð 2 : 6 Þ
Where, r is the radius of the particle,εois permittivity of free space,εmis real
part of the permittivity of suspending medium, Ermsis root mean-square electric
field and K(ω) is Clausius-Mossotti factor (measure of effective polarizability of the
particle). Clausius-Mossotti factor is given by:
Fig. 2.27 Effect of non-uniform electric field on dielectric particle, positive and negative DEP
2 Microfluidics Overview 65