Biomedical Engineering Reference
In-Depth Information
NIR-to-visible up-conversion nanomaterials emit higher energy photons after
absorbing lower energy photons. Up-conversion, in which excitation light at a
longer wavelength produces emission at a shorter wavelength is very promising
since it becomes possible to excite the photosensitizers in the near IR. Qian et al.
(
2009a
) described the synthesis of mesoporous-silica-coated NaYF
4
@silica nano-
particles with a core-shell structure containing ZnPc (Fig.
17
) molecules as pho-
tosensitizer in the mesoporous silica matrix. The absorption peak of ZnPc located
at 670 nm overlaps with the red emission peak of the up-conversion of the NaYF
4
nanocrystals, what is a suitable situation for the activation of ZnPc and the further
production of
1
O
2
. NaYF
4
:Yb/Er nanocrystals (35 nm width × 60 nm length) were
coated by an amorphous silica shell (10 ± 1.5 nm)
via
a microemulsion method,
and then by a mesoporous silica layer (11 ± 1.5 nm) onto the NaYF
4
:Yb/Er@silica
nanoparticles. N
2
-absorption/desorption isotherm confirmed the mesoporous
nature of the outer silica shell and the surface area was found to be 770 m
2
g
−1
.
Pore size distribution has a mean size of 2 nm. After the incubation of the nano-
particles with MB49 bladder cancer cells for 24 h, the subsequent intracellular
localization of the nanoparticles could be realized using a confocal microscope
equipped with a 980 nm near IR laser. Fluorescence of the nanoparticles was
mainly observed in the cytoplasm. The introduction of a PS such as ZnPc into the
mesoporous silica shell was realized by soaking the nanoparticles in a concen-
trated solution of ZnPc in pyridine. Then, the release of ZnPc in different solvent
was studied. It appeared that ZnPc was released within 1 h in ethanol, but no
release was observed in deionized water, Phosphate Buffered Saline (PBS) or cell
culture media. The production of
1
O
2
for further PDT applications was shown by
exposing the NaYF
4
/ZnPc nanoparticles to near IR laser irradiation in the presence
of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA).
1
O
2
formation
could be observed with the NaYF
4
/ZnPc nanoparticles whereas no production was
detected the NaYF
4
nanoparticles without ZnPc.
In vitro
experiments showed that
the viability of cells incubated with the NaYF
4
ZnPc nanoparticles and exposed to
NIR irradiation for 5 min was significantly lower than those incubated with ZnPc-
free NaYF
4
nanoparticles. Further work (Guo et al.
2010a
) demonstrated the effi-
cacy of these particles for inducing cytotoxicity and its mechanism by
1
O
2
-induced
apoptosis. The intracellular uptake and photodynamic effect of these upconversion
nanoparticles were studied on MB49 murine bladder cancer cells, revealing a
time- and concentration-dependent accumulation. A maximum of particles were
found in the cells after a 6 h incubation time. There is an increased accumulation
of nanoparticles in the cells when they are incubated with increasing concentra-
tions (between 200 and 600 mg/mL). Their photodynamic efficiency in activating
the loaded ZnPc upon irradiation with 980 nm NIR light was confirmed in living
cells. The cytotoxic effect of the released oxygen was demonstrated. Indeed, the
cell viability for MB49-PSA cells treated with ZnPc loaded NaYF
4
nanoparticles
was found to be around 60% without irradiation and around 20% with a 5 min
irradiation (500 mW).
Another approach has been published by Zhang et al. (
2007
). NaYF
4
/Yb
3+
, Er
3+
nanoparticles have been used as photon up-converting nanoparticles and coated
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