Environmental Engineering Reference
In-Depth Information
charge density is zero), or the amplitude of surface roughness in micro channel
is with some orders of magnitude lower than the height of micro channel, the
roughness effect inside the micro channel geometry can be neglected.
Another specific effect that can occur at the microscale level between the
particles and the electrodes is the Casimir-Lifshitz effect [
8
,
19
]. Specifically,
this effect states that one can observe an attraction between bulk material bodies,
due to the modification of the zero-point energy associated with the electromagnetic
modes in the space between them. The Casimir-Lifshitz can be strongly influenced
by the surface roughness of the particles therefore when neglect the roughness
effect, the Casimir effect can be neglected too.
Due to the advances in microfabrication techniques that allowed progressively
smaller microstructures to be constructed, DEP can be used for the manipulation of
nanobioparticles, such as macromolecules, viruses, and spores. DEP of viral parti-
cles is becoming an important technique for the separation, concentration, and
identification of viruses; in addition, it allows for fast detection and concentration
of microorganisms in a single step. Microdevices based on DEP could be employed
as online detectors of the viral particles for clinical, analytical, and environmental
applications [
20
].
The manipulation, concentration, and separation of DNA molecules are impor-
tant in different fields such as genetics, microbiology, medicine, and biochemistry;
therefore, methods that allow to concentrate, trap, and separate DNA have impor-
tant analytical applications [
21
-
23
]. Traditional methods for sample concentration
as filtration, liquid-liquid extraction, centrifugation, and adsorption are useful in
some situations, but processing times are long and they are not suitable for single
molecule manipulation. Because DNA is a uniformly charged molecule, with the
mass/charge ratio constant at all lengths, means that in a DEP separation, all the
molecules and fragments of DNA would move at the same speed, resulting in no
size fractionation, DEP being an ideal technique for trapping, concentration, and
stretching of DNA molecules achieved in microdevices [
20
].
On the other hand, DEP seems highly suited for protein separation methods as it
has the potential to provide a concentration tool and to improve current separation
approaches especially in combination with other techniques [
24
]. The analysis of
proteins often requires powerful separation, fractionation, and preconcentration
techniques, in many cases achieved only through the combination of different
techniques. Sensitive protein detection as well as purification is also an important
aspect in diagnosis as well as techniques to identify and manipulate proteins with
label free methods. Although the studies with DEP manipulation of proteins are not
as numerous as the studies focused on DNA, many research groups have obtained
important results in this field, since DEP is a nondestructive technique without
modification of proteins
biological functionality [
20
-
23
]. In this sense, protein
dielectrophoresis has the potential to play an important role in manipulation,
fractionation, preconcentration, and separation method in bioanalysis or as a
manipulation tool for nanotechnological applications. As a novel technique used
to the protein manipulation, dielectrophoresis has therefore a great potential for
protein concentration, and it could be employed as a separation and concentration
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