Biomedical Engineering Reference
In-Depth Information
(4)
Purify the resulting suspension by centrifugation at 4000 rpm (1467
g
) for
10 min and by dialysis for 24 h against deionized water using a 14 kDa
membrane.
(5)
Determine the size distribution with dynamic light scattering (DLS). DLS
is also used to establish the zeta potential.
(6)
Establish the silver concentration at 450 µg/mL by inductively coupled
plasma optical emission spectrometry.
(7)
Like QDs, the particle size and shape is established by TEM by putting a
drop of a diluted solution on a Formvar-coated copper grid.
2.2.6 Magnetic Nanoparticles
Inorganic magnetic nanoparticles (MNPs) are rapidly emerging as important
NMs in medicine.
89-94
These NMs include nanowires, nanospheres, nanotubes,
and magnetic thin films. Medical applications of MNPs include diagnosis (such
as detection of malignant tissues in magnetic resonance imaging (MRI) and cell
tracking) and therapy (such as guided drug and gene delivery, cancer therapy,
tissue engineering, and bioseparation). The diagnostic and therapeutic applica-
tions of MNPs can be combined such as in MNP-mediated drug delivery and
MRI imaging (i.e., theranostics).
83,89-92,95
MNPs (5-60 nm) can be coated with dextran, phospholipids, or other com-
pounds to inhibit aggregation and passive or active targeting agents.
96
After sur-
face functionalization and attachment of DNA fragments, proteins, peptides, or
drugs, MNPs can be used for drug delivery, magnetic separation, diagnostics,
or MRI contrast enhancement.
89-93,96-105
A nonspecific labeling method based
on anionic MNPs can be used to predict uptake efficiency in various cell types
including tumor cells and at the same time provides sufficient magnetization for
MRI detection and distal manipulation.
106,107
MNPs represent an important class of NMs. Their magnetic properties
drastically change with size as magnetic anisotropic energy (
KV
, where
K
is
the magnetic anisotropic constant and
V
is the particle volume) becomes com-
parable to the thermal energy (
kT
) resulting in moment randomization and
superparamagnetism.
108,109
Their magnetic signal stands out in the presence of
biomolecules making them readily identified even in vivo.
92,110,111
The MNPs
do not show net magnetic moment in the absence of external magnetic field
allowing for their long-term stability in various dispersion media.
112
Their sus-
ceptibility to functionalization and manipulation under an external magnetic
field provide controllable magnetic tagging of biomolecules, leading to highly
efficient bioseparation-biodelivery
111
and highly sensitive biolabeling and MRI
contrast enhancement.
92,97,111
To be applicable for biomedical applications, the NMs need to be mono-
disperse to have uniform physical and chemical properties that are important
for controlled biodistribution, bioelimination, and contrast effects.
112
The
MNPs need to be water soluble and can be modified, so that they are capable
of binding specifically to a biological entity. They have to be able to withstand
