Page 141 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

6.2 Photothermal therapy 139

Among all the carbon nanostructures, single-walled carbon nanotubes (SWCNTs)
were the first ones introduced for PTT application. Delivering SWCNTs to the desired
region is facilitated by intravenous or intratumoral injection. Choi et al. investigated
the effect of intravenously injection of PEG-conjugated SWCNTs on human epider-
mal mouth tumor in mouse [34]. Their results demonstrated that compared to nonirra-
diated laser group NIR irradiation significantly decreased tumor volume. To increase
cellular uptake, Robinson et al. functionalized SWCNTs using PL-PEG and C18-
PMH-PEG which were intravenously injected into mice with xenograft tumors. Their
nanoparticle provided the opportunity of both imaging and therapy in a single plat-
form [35]. Exploiting lower power density led to produced clear fluorescence image
while administrating higher power density led to destroy tumor cells. The author
claimed that by using their introduced nanoparticles, the power densities needed
to kill abnormal cells successfully was much lower than the corresponding amount
that was necessary by using nanorods. To improve PTT application of SWCNTs,
carbon nanotube sorting technique was utilized to separate particular chirality with
the best performance in NIR region by density gradient ultracentrifugation. Antaris
et al. found that density gradient ultracentrifugation could separate carbon nanotubes
with 80% purity [36]. After high-purity separation, SWCNTs surfaces were modified
using PL-PEG polymers. Low dose SWNTs, 0.254 mg/kg, was sufficiently enough
for tumor shrinkage during exposure of ultralow irradiation power density of 0.6 W/
2
cm which has to do with not only removing all SWCNTs with no absorbance in NIR
region but improving cellular uptake of separated-SWCNTs by surface modification
as well [36]. The authors claimed that around 4 µg of SWCNTs per mouse were
enough for both imaging and therapy which was the lowest amount of PTT agent
being reported for both therapy and diagnostic purpose in a mouse model [36].

6.2.6 Graphene
Graphene is a two-dimensional allotrope of carbons bonding together hexagonally.
Having strong absorption cross-section in NIR window, graphene has been success-
fully utilized for PTT application. In 2010, Liu et al. studied the effect of PEGylated
nanographene sheets injected intravenously as a PTT agent [37]. PEG was covalently
attached to six-armed amine groups and then attached to the surface of nanographene
oxide (GO). This modification not only improved water solubility of graphene but
provided the opportunity for further surface modifications with fluorescent dyes as
well. An account of high modified-graphene accumulation in the tumorogenic region
in one hand and strong NIR absorption in the other hand, the introduced nanopar-
ticles destroyed cancer cells in an efficient manner during laser irradiation. Histologi-
cal analysis indicated no cellular toxicity [37]. Although the amounts of graphene
needed for PTT have been higher than SWNTs, the cellular uptakes of SWCNTs
have been lower than graphene motivating to consider graphene as a good candidate
for PTT application. To decrease the amount of graphene needed for PTT therapy,
several approaches have been accomplished. In 2010, Robinson et al. reduced gra-
2
phene oxide to graphene to restore sp carbon nanostructures leading to an increase