Environmental Engineering Reference
In-Depth Information
Fig. 14.2 Schematic of the DEP patterning chamber with interdigitated bar electrode array at the
bottom surface (nonconducting substrate). The geometric parameters of the device include cham-
ber height (
h
), electrode spacing (
l
), electrode width (
d
), and electrode height (
w
). The electrodes
are connected in different phase sequences to apply the DEP effect
Fig. 14.3 Random distribution of particles contained within the fluidic trench of a lab-on-a-chip
system (a), Particles arranged by dielectrophoresis into a periodic grating pattern (b)
An increasingly important application of DEP is the selective separation of
nanoparticles in lab-on-a-chip systems, where all of the components are built in a
single device [
16
]. One of the common strategies for dielectrophoretic separation in
lab-on-chip systems is flow separation: flow is used to carry two kinds of different
particles in a microchannel. One kind of particles is trapped on the electrode arrays
located at the bottom of the channel, and the other would be brought out of channel
by the flow [
17
]. The scheme of a dielectrophoresis-based lab on a chip designed to
manipulate and detect nanometer scale particles is presented in Fig.
14.3
, where the
central components are the microfluidic trench and the dielectrophoresis electrode
array.
We do note here that one prominent difference between fluid motion in micro
channels and that in nanochannels is the strong fluid-wall interactions observed in
the latter. As the channel size decreases, the surface-to-volume ratio increases and
various properties of the walls, such as surface roughness, greatly affect the fluid
motion in nanochannels. In the case of the nanoparticle flow above a surface
covered with electrodes, some parts of the surface are more accessible to diffusing
particles than others [
18
]. Hence, the current density across the surface may
strongly vary from one place to another, and the boundaries or interfaces can be
microscopically wavy-rough. If one considers uncharged electrodes (their volume
