Biomedical Engineering Reference
In-Depth Information
conjugated with antibody proteins that are specifi c to the cell membrane protein
of interest; the magnetic particle-bound cells are attracted by the highly enhanced
magnetic force such that, fi nally, the cells change their pathway. Non-bound cells,
however, have no infl uence on the magnetic fi eld and maintain their pathways.
Recently, Pamme
et al.
reported the details of an immunomagnetic cell sorting
technique using microfl uidic devices for separating mouse macrophages and
human ovarian cancer (HeLa) cells [26]. Likewise, Xia
et al.
reported an integrated
microfl uidic device for removing
Escherichia coli
bound to magnetic nanoparticles
from fl owing solutions [101]. For this, the authors used ferromagnetic microstruc-
tures integrated into the microfl uidic device, which was similar to the scheme of
the device reported by Kang
et al
. [41, 42] Subsequently, Inglis
et al.
reported the
details of a microfl uidic device for the immunomagnetic separation of blood cells,
by exploited ferromagnetic wires embedded in the bottom glass substrate [102].
The use of magnetic microparticles is preferred in conventional macroscale cell
separations, because they offer a high magnetic mobility when bound to the cell
surfaces, whereas the magnetic nanoparticles provide much less magnetic mobil-
ity than do microparticles. However, within the microfl uidic environment, the
microparticles used for immunomagnetic cell sorting may be inadequate due to
their high magnetic susceptibility, which consequently results in a high magnetic
force acting on the cells. This leads to the cell-magnetic particle complexes becom-
ing trapped in the microfl uidic channels, and causes microchannel clogging. In
addition, the fast drag velocity of the magnetic microparticle-bound cells restricts
the magnetophoretic analysis for the cell- surface protein - binding capacities [97] .
3.5.2
Separation of Nanomaterials
Magnetophoresis assisted by microfl uidic techniques can be applied to the separa-
tion of magnetic nanoparticles suspended in aqueous solution. Recently, the mag-
netophoretic continuous separation of nanoparticles attracted interest and was
demonstrated in a microfl uidic device (Figure 3.18) [41]. These authors had previ-
ously reported a microfl uidic purifi cation method using single-walled carbon
nanotubes (SWCNTs), which attracted much attention and promised a wide range
of applications [103, 104]. Unfortunately, SWCNTs are synthesized using metal
catalysts such as Fe, Ni, and Co, and these must be removed from the pure
SWCNTs in order for the latter to achieve many potential applications. Despite
various successful reports regarding SWCNT purifi cation, including gas-phase
oxidation, wet-chemical and thermal treatments, microwave-assisted methods, and
combined multistep purifi cation platforms [105, 106], the current purifi cation
methods, mainly using chemical, thermal, and ultrasonic treatments, have resulted
in structural defects or the surface modifi cation of the SWCNTs [106]. Because
most metal catalysts used in SWCNT synthesis are superparamagnetic [107],
several approaches for the magnetic purifi cation of SWCNTs have been demon-
strated, using magnetic- trapping methods [108 - 110] . Unfortunately, however,
these (largely macroscale) purifi cation schemes have been limited to obtaining
