Biomedical Engineering Reference
In-Depth Information
Fig. 40
Phenosafranine
N
N
NH
2
H
2
N
Cl
Fig. 41
Nile Blue
N
H
2
N
N
SO
4
N
2
6
ZnO/TiO
2
Nanoparticles
6.1
TiO
2
Nanoparticles
Inorganic nanoparticles are rapidly emerging in biomedical applications as drug
delivery carriers, biosensors, imaging diagnosis and disease therapeutics (Klostranec
and Chan
2006
). The inorganic nanoparticles that have been extensively explored
in the field of biomedicine cover a variety of materials and diverse shapes, such as
carbon nanotubes, silica nanospheres, metal nanoshells, and semiconductor quan-
tum dots.
The application of TiO
2
nanoparticles in life science is attracting more and more
attention since the first report of photocatalytic disinfection by Matsunaga et al.
(
1985
). In recent years, TiO
2
nanoparticles were applied in the field of photother-
apy of malignant cells, and have been regarded as the potential photosensitizing
agents for PDT due to their unique phototoxic effect upon the irradiation (Cai et al.
1991, 1992
; Fujishima et al.
2000
; Sakai et al.
1994
; Wamer et al.
1997
; Zhang and
Sun
2004
).
The TiO
2
nanoparticles are novel photo-effecting material with a band gap of
3.23 eV for anatase and 3.06 eV for rutile polymorph of TiO
2
, respectively. Under
the irradiation of UV light with the energy higher than that of the band gap of TiO
2
,
i.e. the light wavelength shorter than 385 and 400 nm for anatase and rutile poly-
morphs, respectively, the electrons in the valence band of TiO
2
can be excited to the
conduction band, creating the pairs of photo-induced electron and hole (Ashikaga
et al.
2000
). These photo-induced electrons and holes present strong reduction and
oxidation properties. In aqueous environment, the photo-induced holes can react
with hydroxyl ions or water to form powerful oxidizing radicals, such as hydroxyl
radicals OH·, perhydroxyl radicals HO
2
(Fujishima et al.
2000
) and superoxide
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