Biomedical Engineering Reference
In-Depth Information
Fig. 18
Merocyanine 540
(Reproduced by permission
of The Royal Society of
Chemistry)
SO
3
Na
N
O
O
N
S
N
O
with a PS (Merocyanine 540, Fig.
18
)-encapsulating porous thin layer of silica.
A mouse monoclonal antibody, anti-MUC1/episialin which is highly specific towards
MCF-7/AZ cancer cells was covalently attached to the silica surface. The genera-
tion of
1
O
2
was detected chemically using ADPA.
In vitro
PDT tests were per-
formed to confirm the PDT cytotoxicity of the particles towards MCF-7/AZ breast
cancer cells, thus demonstrating the potential of these IR-region excitable
nanoparticles.
Two-photon absorption (TPA)-induced excitation of photosensitizers is another
promising approach to increase light penetration. Indeed, the photosensitizers can
absorb simultaneously two less-energetic photons, the excitation in the NIR region
avoids tissue absorbing or scattering and induce a deeper light penetration in the
tissue.
Velusamy et al. (
2009
) synthesized new quadrupolar chromophores for two-
photon absorption (Fig.
19
) with a very high two-photon absorption cross-section of
7080 GM at 800 nm in toluene and a fluorescence quantum yield of 0.25. The com-
pound was insoluble in water and was thus encapsulated in SiO
2
nanoparticles fol-
lowing the reverse microemulsion method. The nanoparticles were of a 60 nm
diameter. The fluorescence quantum yield dropped to 0.08 with a red shift of l
em
.
Quantum yield of
1
O
2
generation of the nanoparticles was determined to be 0.51 in
D
2
O. Those nanoparticles were incubated with macrophages and shown to be tightly
bound to the membrane with no toxicity as determined by MTT assay. Macrophage
cells were then irradiated with a two-photon laser at 2.6 W/cm
−2
(800 nm) for 3 min.
The results indicated a significant and NP-dose responsive cell death, thus demon-
strating the suitability of the nanoparticles for two-photon PDT.
The Prasad group described the synthesis (Kim et al.
2007
) of organically modi-
fied silica nanoparticles co-encapsulating HPPH (Fig.
13
) and an excess amount of
BDSA (9,10-bis (4¢-(4″-aminostyryl)styryl)anthracene, Fig.
20
), a highly two-
photon active molecule (TPA cross section in the aggregated state at 750 nm = 217
GM) as a donor. The size of nanoparticles entrapping 1.1 wt.% HPPH and 1.1 wt.%
HPPH / 20 wt.% BDSA was 25 ± 7 nm and 30 ± 6 nm respectively. HPPH absorp-
tion in nanoparticles had significant overlap with the fluorescence of BDSA aggre-
gates which enabled an efficient energy transfer through FRET mechanisms. After
indirect two-photon excitation (850 nm) the authors proved that the energy of the
NIR light is efficiently up-converted by BDSA aggregates to excite HPPH. After
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