BIOMEDICAL MICROFLUIDICS AND ELECTROKINETICS - Complex Systems Science in Biomedicine - page 635

Figure 3 . Active microelectronic DNA chip device and DNA transport. ( a ) Basic structure of
an active microelectronic array that contains 100 microlocation test sites. ( b ) Basic scheme for
electrophoretic transport of charged molecules (DNA, RNA) on the active microelectronic
array test sites. Reprinted with permission from Gurtner et al. (8).

3.1. Dielectrophoresis (DEP)

Dielectrophoresis, or DEP, is a force on particles in a nonuniform electric
field arising from differences in dielectric properties between the particles and
the suspending fluid. The time-averaged force on a homogeneous sphere of ra-
dius r p can be approximated as

G

F = QF r

3

K E

2

2 e( ) . [9]

DEP mp rms

Here Re( K ) is called the dielectrophoretic mobility and is the real part of K , the
Clausius-Mosotti factor,

FF
F F

p m

. [10]

K =

+ 2

p m

The Clausius-Mosotti factor depends on the complex permittivity of particle and
medium. Complex permittivity is

, [11]

FFTX * = j /