Nanoparticles for Photodynamic Therapy Applications - Intracellular Delivery: Fundamentals and Applications - page 532

can be loaded with different types of cargo and can mediate cytosolic release of
cell-impermeable molecules in P-gp-expressing cells via light mediated endosomal
breakage. Indeed, the exposure to light of the MSN at the dye's excitation wave-
length leads to ROS-mediated membrane damage and therefore to the specific
delivery of the cargo.

3.2 Covalent Encapsulation of PS in Silica Nanoparticles

When physically entrapped inside the silica network, the PS can be prematurely
released from the carrier which can lead to a reduced efficiency of treatment and to
side-effects. Covalent coupling of the PS inside or at the surface of the nanoparti-
cles is expected to overcome these drawbacks.
Davydenko et al. ( 2006 ) studied the sensibilization of C 60 fullerene anchored
through covalently bonded spacers to hydrophilic non porous pyrogenic silica
nanoparticles of 10 nm diameter modified by g-aminopropyl groups. The ability of
fullerene to generate active forms of oxygen was demonstrated using photosensitive
organic molecules. No in vitro or in vivo studies have been done, but these first
results suggested that these systems might be useful as fluorescent probes and
active species for PDT.
Rose Bengal (RB, Fig. 21 ) decorated nanoparticles were used for inactivation of
gram-positive bacteria by Zhang and collaborators (Guo et al. 2010b ). Rose Bengal
(4,5,6,7-tetrachloro-2¢,4¢,5¢,7¢-tetraiodofluorosceine in disodium salt), a well-
known anionic photosensitizing molecule was covalently conjugated to the amine
functionalized surface of silica nanoparticles prepared by hydrolysis of TEOS in
reverse microemulsion. The grafted particles were characterized using TEM, showing
particles in the range of 50-80 nm and FTIR, showing the presence of RB on the
particles. The characterization of RB, free or decorated on SiO 2 particles, as a
source of singlet oxygen under illumination, was performed through the photo-
bleaching of ADPA in solution. The quantum yield of generating singlet oxygen of
the particles was found to be 0.60 in D 2 O (0.75 for the free RB). The in vitro pho-
todynamic inactivation of the RM-modified nanoparticles were investigated in
gram-positive bacteria, using methicillin-resistant Staphylococcus aureus (MRSA)

Cl

Cl Cl

OOC Cl

I I

O O OH

I I

Fig. 21 Rose Bengal (RB)