Chemistry Reference
In-Depth Information
visualizing of this layer in the brain of Sprague-Dawley rats, also PEGylated gold
nanoshells were used by injection via the tail vein as well [
132
]. The nanoshells
were administrated three times successively, and after the final injection the rat
brain was imaged sequentially 10 times for more than about 6 h. The PA signal
enhancement after the injection as a function of time was quantified with a maximal
signal increase of about 63%.
In a recent report Bao et al. used PEGylated gold nanoprisms (AuNRs) with a
uniform thickness of ca. 10 nm, with three congruent edge lengths of ca. 120 nm in
in vivo settings [
158
]. The mice were treated with this AuNRs in order to visualize
tumor angiogenesis in gastrointestinal cancer cells. It is shown that the AuNRs have
the capacity to penetrate tumors and provide a high-resolution signal amplifier
for PAI.
5.2.3 AuNPs as Agents for Photothermal Therapy
As compared to the diagnostic approach followed by PAI during photothermal
experiments, a therapy approach is proposed by photothermia. Due to their SPR
properties AuNPs are able to absorb light from incident radiation with high
efficiency (extinction coefficient ~10
9
M
1
cm
1
)[
159
] in the near-infrared
(NIR) region of the electromagnetic spectrum and convert it into heat [
83
,
160
,
161
].
The generated heat is subsequently delivered to the immediate surroundings of the
AuNPs and allows a highly specific thermal ablation of diseased or infected tissue
[
162
-
165
]. The advantage of the use of light in the NIR region is that the tissue
damage and attenuation by biological fluids and tissues are minimal.
In 2003 Pitsillides et al. were the first who demonstrated that AuNPs can be used
for PTT [
166
]. Since that time, several other studies have examined the use of
AuNPs in PTT. Nam and coworkers designed AuNPs with a size of 10 nm with a
pH-dependent agglomeration behavior [
167
]. The incubation of HeLa and B16 F10
mouse melanoma cells with these AuNPs shows an aggregation of the AuNPs in a
typical tumor intercellular pH, leading to a shift of their absorption to the far- and
near-IR spectral regions and thus to a utilization in PTT.
Nevertheless, AuNRs [
168
], HAuNs [
105
], AuNCs [
104
,
144
,
169
-
171
], and
gold/silica nanoshells [
172
] with SPR frequencies in the NIR range are more
promising agents for PTT because the absorption of the NPs can be tuned by
synthetically varying the aspect ratio and shell thickness : core radius. The latter
were some of the first applied in PTT by Halas and West [
172
-
175
]. Based on
efficiently destroying breast carcinoma cells with PEGylated silica/gold nanoshells,
the particles were injected into the tumor interstitium of SCID mice bearing
sarcoma xenografts. A subsequent NIR light exposure demonstrated a 4-6 mm
depth of thermal damage [
172
]. Later on NIR PTT was demonstrated using
systemically administered PEGylated nanoshells in a colon cancer mouse model.
All tumors in nanoshell-treated mice were completely ablated after a single PTT
treatment and the animals appeared healthy and tumor free for more than 90 days
posttreatment. In contrast the tumors of the control animals and the additional
