Biomedical Engineering Reference
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absorb over a larger fraction of UV zone. ZnO is a direct band gap semiconductor
with a band gap of 3.4 eV. ZnO nanostructures typically have a near-band-edge
emission in the UV region and a defect-related visible emission in the blue to green
region (Lin et al.
2005
; Liu et al.
2008b
; Cheng et al.
2005
). With UV illumination,
ZnO photocatalyst in aqueous solution can generate ROS such as hydroxyl radical,
hydrogen peroxide and superoxide, which makes it possible and high efficient for
the application of ZnO nanoparticles in the decomposition of some organic com-
pounds and induced cytotoxicity against some mutated cells (Brunner et al.
2006
;
Wang et al.
2007
; Xu et al.
2007a
). Considering the possibility of combined appli-
cation of nano-sized ZnO particles with anticancer drugs in PDT, Guo et al. (
2008
)
studied the synergistic potency of the high reactivity of ZnO nanoparticles with
daunorubicin, one of the most important anticancer drugs in the clinic treatment of
acute leukemia and solid tumors (Beguin et al.
1997
; Lowis et al.
2006
), to inhibit
multidrug resistance of drug-resistant leukemia K562/A02 cells and facilitate the
relevant drug delivery efficiency. They explored the cytotoxic effect of anticancer
drug daunorubicin on leukemia cancer cells in the absence and presence of ZnO
nanoparticles
via
fluorescence microscopy, UV-Vis absorption spectroscopy and
electrochemical analysis. Their observations demonstrate the apparently enhanced
cellular uptake of daunorubicin for both leukemia cell lines in the presence of the
different sized ZnO nanoparticles. They demonstrated (Li et al.
2010a
) that differ-
ent-sized ZnO nanoparticles exposed to SMMC-7721 cancer cells could exert dose-
dependent cytotoxicity suppression
in vitro
, and this cytotoxicity of nanoparticles
was time- and dose- dependant, while the size-depended effect was not clear in the
scope from 20 to 100 nm. UV irradiation could readily enhance the proliferation
suppression ability of ZnO nanoparticles on cancer cells. More importantly, these
effects were size dependent, while the smaller the nanoparticle size, the higher the
cytotoxicity of cancer cell proliferation caused by ZnO nanoparticle. Meanwhile, if
ZnO nanoparticles combined with daunorubicin, cytotoxicity of daunorubicin for
SMMC-7721 cancer cells was especially enhanced. These observations suggest
that ZnO nanoparticles could play an important role in the PDT and have the great
potential and promising applications in clinical and biomedical engineering.
Liu et al. reported synthesis of ZnO-porphyrin conjugates and their potential
applications in PDT of cancer (Liu et al.
2008b
). ZnO nanoparticles were synthe-
sized and conjugated to the porphyrin derivative,
meso
-tetra (o-amino phenyl)
porphyrin (MTAP, Fig.
42
). The key step of the synthesis is the ligation of MTAP
to Zn
via
a cysteine. The surface of ZnO nanoparticles was first modified to contain
−COOH group. The isoelectric point of ZnO is 9 and Zn
2+
is dominant on the sur-
face of the ZnO nanoparticles. The −SH group of L-cysteine can react with Zn
2+
to
form Zn(II) complex ZnO-(L-cysteine), since Zn-S bond is stronger than Zn-O
bond. ZnO-(L-cysteine) contains −COO− group which can conjugate with the
primary amine group of MTAP, when appropriately activated (Wang et al.
2002
).
They investigated the fluorescence resonance energy transfer following UV
irradiation and the energy transfer rate was measured to be as high as 83%. Their
observations indicate that ZnO-(L-cysteine)-MTAP nanoparticle conjugates are
efficient photodynamic agents that can be induced by 365 nm UV light.
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