Nanoparticles for Photodynamic Therapy Applications - Intracellular Delivery: Fundamentals and Applications - page 539

particle, combining MRI, phosphorescence and PDT properties. The main drawback
of this approach is the 366 nm irradiation, which is not really compatible with a
good penetration of light in the tissue.
Lo and collaborators have achieved the tri-functionalization of mesoporous silica
nanoparticles. They have incorporated a near-infra-red fluorescent contrast agent
into the silica framework of MSN to obtain traceable imaging of nanoparticles.
A palladium-porphyrin photosensitizer (PdTPP, Fig. 26 ) was incorporated in the
pores of the nanoparticles to enable PDT. Targeting the over-expressed a v b 3 integ-
rins of cancer cells was achieved by grafting the surface of the particle with
cRGDyK peptides. These particles were shown to exhibit strong affinity for, and
uptake by U87-MG glioblastoma cells (which over-express a v b 3 integrins) com-
pared to MCF-7 human breast cancer cells (which are a v b 3 integrins deficient).
In vitro evaluation of the theranostic platform demonstrated targeting specificity and
minimal collateral damages as well as an important cell death after irradiation.

4 Semi-conductors Nanoparticles (Quantum Dots

and Silica Nanoparticles)

4.1 Quantum Dots (QDs)

QDs have already been explored as potential agent for PDT and numerous papers
have been published. In this part, we will just give few examples of recent studies.
A review of Biju et al. ( 2010 ) described the different quantum dots that have been
used so far for PDT applications. Indeed, exceptional photostability of QDs in addi-
tion with their broad absorption, their surface coating that can be functionalized to
make them water soluble and biocompatible and their large two-photon absorption
cross-section make them ideal candidates for PDT under the condition that they
have good efficiency to produce ROS by direct irradiation or energy transfer to
acceptor molecules. The combination of QDs and photosensitizers enabled the use
of an excitation wavelength where the photosensitizer alone does not absorb.
Thanks to the broad absorption spectrum of QDs, it is easy to find an excitation
wavelength to activate the photosensitizer.
The first demonstration of a combination of QD with PDT photosensitizer with
FRET (Förster Resonance Energy Tranfer) to facilitate the excitation of a phthalo-
cyanine was described in 2003 by Samia et al. ( 2003 ) Indeed, QDs can be consid-
ered as energy donors and the possibility for energy transfer between QD and cell
molecules has a potential to induce generation of ROS although results in the litera-
ture have been contradictory (Juzenas et al. 2008 ). Some studies find significant
ROS production from QDs and others none (Ipe et al. 2005 ). It appears that QDs
with CdSe (Chan et al. 2006 ) and CdTe (Choi et al. 2007 ) are very efficient at ROS
generation while core/shell CdSe/ZnS does not produce significant ROS by itself
(Ipe et al. 2005 ).