Biomedical Engineering Reference
In-Depth Information
absorption dyes to selectively strengthen tumor thermal damage (Chen et al.
1995
).
Recent researches find that quite a few nanoparticles including GNPs have the ability
to absorb mightily the NIR irradiation to generate sufficient heat to cause cell death.
Compared to traditional dyes, their metal surfaces are less sensitive to chemical
corrosion and photobleaching, and have much higher heat absorption intensity.
GNPs received most attention as photosensitizers used in PTT because of their
good absorption property, which offer lots of opportunities to make them suitable
for use in tumor hyperthermia. Above all, such material has a strong optical extinc-
tion peak known as surface plasma resonance (SPR) that can be varied by control
of particle morphology and light in the resonance band can be efficiently absorbed
by them. Therefore they can enhance the photothermal effect under irradiation of
NIR light. Besides, GNPs are easily synthesized to precisely control the morphology,
size, structure and chemical composition, which determines that GNPs would be
connected to its target molecule such as antibodies or coated with PEG on the
surface. GNPs are easily modified and its IR absorption peaks will not change after
that. Bits immunogenicity and clearance rate will be reduced. GNPs connected
targeting molecules can specifically kill the tumor cells without affecting normal
cells. In addition, GNP is safe for treating human cancer because of its little toxicity,
good biocompatibility and small side effects. GNPs have much morphology include
nanospheres, nanoshells, nanocages, and nanorods. Laser with longer wavelength
would obtain deeper penetration and cause less harm to human body. Different shapes
of GNPs would produce different and adjustable optical extinction peaks, which
can be seen by the color of different morphology and size of GNP suspensions.
Controlling the morphology and size of nanoparticle tailors them to achieve
maximum absorption under the irradiation of light with different frequencies.
The nanoparticles are conjugated to special antibodies as targeted labels which
will combine with receptors over pressed by types of cancer cells. Table
3
shows
various antibodies conjugated with gold nanostructures and CNTs used in PTT.
Various gold structures are believed to be nontoxic (Villiers et al.
2010
) even at
high concentration because gold is a kind of inert metal in the body (Sabadell et al.
1999
). In fact, gold colloids have been used to treat arthritis (Tarsy
1941
) for over
100 years.
In addition to gold nanostructures, CNTs, owing to its good absorption charac-
teristics, have also been utilized as photothermal enhancers under irradiation of NIR
light (Kam et al.
2005
). The toxicity of CNTs has been a major concern for the
researchers. In the studies of CNTs used in biomedical applications, they are
considered to be safe for the body. Gold-plated CNTs can enhance NIR contrast
(~102-fold) and preliminary in vitro viability tests show that golden carbon nanotubes
have minimal toxicity (Kim et al.
2009
). The CNTs can be produced (Karthikeyan
et al.
2009
) by techniques like arc discharge (Sun et al.
2007
), laser ablation (Scott
et al.
2002
), CVD (Tao et al.
2007
) and super-growth CVD (Hata et al.
2004
), etc.
In order to prevent proteins from depositing on the nanoparticles, which would
result in their being captured by the immune system and dragged out of the blood-
stream into the liver or spleen, scientists have made efforts on coating them with a
layer of nontoxic PEG. This impedes the adsorption of proteins, in effect disguising
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