Biomedical Engineering Reference
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on the surface of the particles. The HB incorporating particles were incubated
in vitro
with human breast carcinoma MCF-7 cells. CLSM observation showed that
the particles were indeed internalized into the cells. The phototoxicity of HB in the
lipid-covered MSN were investigated for PDT
in vitro
. The cell activity decreased
to 44.6% after light exposure (15 min, 480 nm), showing the potential of these
particles for PDT applications.
3.1.2
Multifunctional Silica Nanoparticles for PDT and Diagnosis
A marked advantage of using nanoparticles is that they can be used as multi-tasks
platforms. Indeed, their chemical composition can be modulated to, (i) couple or
encapsulate photoactivable units for PDT treatment, (ii) target the nanoparticles to
tumor cells or neovascularization by coupling vector units as well as, (iii) use them
as a diagnostic agent by incorporating a contrast enhancer, (iv) use them for other
therapies such as hyperthermia. Moreover, as with biodegradable nanoparticles it is
possible to play with the hydrophilic/hydrophobic balance to increase their plas-
matic lifetime. For biomedical applications, multifunctional nano-objects combine
two or more functions, such as fluorescent markers or photothermal therapy agents
with MRI contrast agents or hyperthermia therapy agents.
An example of a single particle platform that combines two functions has been
described by Rossi and collaborators (Tada et al.
2007
) in 2007. Silica-coated mag-
netic nanoparticles containing methylene blue (Fig.
11
) as PS have been prepared
and therefore combine therapy (PDT) and diagnostic (MRI contrast agent) possibili-
ties. The particles were composed of silica spheres of about 30 nm diameter contain-
ing 11 nm-diameter magnetic particles. The PS, methylene blue, was added to the
silica precursor tetraorthosilicate during the growth of the silica layer and was there-
fore entrapped in the silica matrix. The magnetic cores were prepared by coprecipi-
tation of Fe
2+
/Fe
3+
ions under alkaline conditions followed by stabilization with
tetraethylammonium oxide. The immobilized drug could generate
1
O
2
, detected by
its characteristic phosphorescence decay curve in the near infra-red and by a chemi-
cal method using DPBF to trap
1
O
2
. The encapsulation of the PS in the silica led to
a
1
O
2
quantum yield of 3 ± 2%, while the quantum yield of methylene blue free in
acetonitrile was 50%. This difference in
1
O
2
quantum yield values was also reported
by Tang et al. (
2005a
). This can be due to scattering of nanoparticles, local seques-
tration of
1
O
2
and/or intrinsic lower encapsulated methylene blue
1
O
2
quantum yield.
The magnetization curve confirmed the superparamagnetic behavior of the particle.
Another example of potentially interesting magnetic nanocarriers for PDT was
reported by Zhou and collaborators (Liu et al.
2008a
). Fe
3
O
4
nanoparticles were
coated with a silica layer using tetraethoxysilane in a cottonseed oil using reverse
microemulsion method in presence of purpurin-18 (Fig.
15
) as PS.
Nanoparticles with a 20-30 nm diameter were obtained. The characterization of
the PS in particle was achieved by UV-visible spectroscopy. The generation of
1
O
2
was followed by
N, N
-dimethyl-4-nitrosoaniline (RNO) bleaching assay and was
found to be less effective for the encapsulated purpurin than for the free PS.
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