Biomedical Engineering Reference
In-Depth Information
their magnetic separation and movement; it is generally assumed that
magnetosomes (organelles containing individual magnetic nanoparticles
covered with a lipid bilayer) are involved in magnetoreception.
5
Also mag-
netotactic algae of the genus Anisonema (Euglenophyceae) have been isolated
from a coastal mangrove swamp in northeastern Brazil; the magnetic re-
sponse of the cells was caused by many magnetite particles organized in
chains.
6
Paramagnetic behavior of erythrocytes (red blood cells) is caused by
the presence of methaemoglobin containing iron atoms in the cell haemo-
globin in the ferric state.
7
As already stated, an absolute majority of prokaryotic and eukaryotic cells
is diamagnetic. In those cases, when an ability to respond to external mag-
netic field should be added, several basic procedures can be used for the
modification of the cells surface, such as the nonspecific attachment of
magnetic nanoparticles (e.g., by the magnetic fluid treatment),
8
by binding
of maghemite particles
9
or magnetite particles
10-14
on the cell surface, by
covalent immobilization of magnetic particles on cell surface or vice
versa,
15,16
by specific interactions with immunomagnetic nano- and micro-
particles,
17-19
magnetic quantum dots
20
or magnetoliposomes,
21
by the
biologically driven precipitation of paramagnetic compounds on the cell
surface,
22
by crosslinking of the cells or isolated cell walls with a bifunc-
tional reagent in the presence of magnetic particles
23
or by entrapment
(together with magnetic particles) into biocompatible polymers.
24,25
As can
be seen, in most cases the magnetic properties of the modifiers are caused
by the presence of nano- or microparticles of magnetite (Fe
3
O
4
) or maghe-
mite (g-Fe
2
O
3
); in some cases also ferrite particles
26
or chromium dioxide
particles have been used.
27
Alternatively, the modification can be performed
by binding paramagnetic cations on acid groups on the cell surface
28
or by
the binding of ferritin
29
or magnetoferritin
30
on the cell surface. In most
cases the attached magnetic particles or ions do not have a negative effect on
the viability and phenotype alternation of modified cells. It should be taken
into account that in specific cases the surface-bound particles can be in-
ternalized by the treated cells and will appear in protoplasm.
The individual modification procedures will be described in more detail
below.
d
n
8
y
4
n
g
|
5
.
10.2.1 Interaction of Target Cells with Magnetic Nano- and
Microparticles
Different types of magnetic microparticles as well as ionically and sterically
stabilized magnetic nanoparticles have been used for magnetic cell modi-
fication. Magnetic modification of microbial cells can be performed using
appropriate magnetic fluid. In the simplest way, perchloric acid stabilized
magnetic fluid was mixed with baker's or brewer's yeast cells washed with
and suspended in acetate buffer, pH 4.6 or in glycine-HCl buffer, pH 2.2;
alternatively tetramethylammonium hydroxide stabilized magnetic fluid
was used for baker's yeast cells modification in 0.1 M glycin-NaOH buffer,
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