Nanoparticles as Contrast Agents for Optoacoustic Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 128

AuCl 4 - Ag + Cl -

(a)

Au

3Ag + AuCl 4 - → 3Ag + + 4Cl - + Au

Ag

Ag

Au

(b)

Thin triangular
plate

Thick triangular
plate

Cube

Sphere

Rod

Wire

figure 5.14 schematic illustration of the experimental procedure that generates hollow
gold nanoparticles by templating against silver templates (a); Tem images of silver nanopar-
ticles with different typical morphologies and their corresponding gold hollow nanostructures
(b). (Adapted with permission from Ref. [143]. © Wiley-VcH Verlag gmbH & co. KgaA.)

well-defined surface chemistry, as well as their strong and highly wavelength-tunable
optical absorption in the NIR optical window. The review [148] discussed synthesis,
optical properties, and applications of gold nanocages in the context of cancer diag-
nostics. A recent in vivo study showed that gold nanocages can effectively enhance
OA images when injected into the blood stream during the imaging of a rat's cerebral
cortex [149]. By adjusting the amount of HAucl 4 added, the sPR peaks of the resul-
tant nanocages can be precisely tuned throughout the visible and NIR regions [145].
In addition, the sPR peaks of nanocages can be tuned to any wavelength in the NIR
region by controlling the size and/or wall thickness [148].
A significant feature of gold nanocages as contrast agents resides in their much
larger absorption cross sections (almost five orders of magnitude) than those of con-
ventional organic dyes, relatively low cytotoxicity of gold, and the ease of bioconju-
gation with tumor-specific ligands [147, 150]. figure 5.15 shows the OA images of a