Page 137 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

6.2 Photothermal therapy 135

FIGURE 6.1
(A) The schematic of destroying the abnormal cells intravenously injected and
accumulated in tumors via EPR effect. (B) Most commonly used nanoparticles for PTT.

to the enhanced permeability and retention effect (EPR). Then, the desired area is
exposed to NIR irradiation. There is a claim that AuroShell can be able to selectively
destroy cancer cells with minimum damage to the normal surrounded tissues.

6.2.2 Gold nanorods

Elongating to resemble rods, GNRs exhibit two plasmon resonance in transverse and
longitudinal aspect. The transverse SPR mode is located at around 520 nm while the
longitudinal SPR mode appears in a wide range of visible to NIR wavelength depend-
ing on the length-to-width aspect ratio. By increasing the aspect ratio, the SPR longi-
tudinal peak shifted from blue to red. The optical properties of GNR is explained by
Gans theory—an extended version of Mie theory with geometric parameters consid-
eration [16]. Well-designed GNR with maximum absorption spectra in NIR region
is absorbed great attention for PTT. Table 6.1 is summarized some of the significant
studies in this field of interest. The main drawback of utilizing GNR is related to
the presence of cytotoxic cetyltrimethylammonium bromide (CTAB) used in syn-
thesis process. To tackle the problem, thiolated molecules have been introduced to
replace CTAB. In 2009, Akiyama et al. showed that replacing thiolated molecules