Photoacoustic and Ultrasound Imaging with Nanosized Contrast Agents - Nanotechnology for Biomedical Imaging and Diagnostics - page 297

Octanethiol-functionzalized
AuNPs

(a) (b)

Homing ligands
(e.g. biotin)

Au

Phospholipid
coating

SCH 2 (CH 2 ) 6 CH 3 H

H

O

2-4 nm

S NH

H

Caproyl spacer

O

x

ca. 150 nm

O N

5 mm

H

After

Before

O O
O O O

O

(c) (d)

O
O

O

O

N

N
N

x=2H
or
for example Zn, Cu, Pd

N

100 nm 100 nm 5 nm

BV

SLN

15 min post. i.d.

figure 10.8 In vivo photoacoustic (PA) imaging of potentially biodegradable contrast
agents in small animals in vivo . (a) gold nanobeacons (gnBs) synthesized from octanethiol-
functionalized gold nanoparticles (AunPs) with phospholipid coating. (b) In vivo PA images
acquired before and after intravenous injection of gnBs (reprinted with permission from
ref. [117]. © John Wiley & Sons. (c) Schematic and TEM images of a pyropheophorbide-lipid
porphysome. (d) In vivo PA images acquired after intradermal injection of porphysomes.
(reprinted with permission from ref. [126]. © Macmillan Publishers Ltd.)

10.5.3 dye-enhanced single-walled carbon nanotubes

As one of the explored nanosized contrast agents, single-walled carbon nanotubes
(SWCnTs) have been considerably examined as a theranostic agent in preclinical
studies [130-137]. The advantages of SWCnTs include the large surface area, easy
fabrication and bioconjugation, strong mechanical properties, and strong optical
absorption. In addition, unlike other plasmonic gold nanoparticles, SWCnTs have
the broader optical absorption spectrum. Thus, any optical wavelength can be
possibly chosen according to specific applications. Based on these desirable optical
characteristics, SWCnT has been successfully used as a PA contrast agent. However,
there is still an ongoing debate on the toxicity of carbon nanotubes for biomedical
applications. Thus, increasing PA sensitivity is the key issue for developing new
carbon nanotube-based agents, and then the injection dose can be greatly reduced.
Consequently, its ongoing concern on toxicity can be relatively relieved. recently, de
la Zerda et al . demonstrated SWCnTs conjugated to ICg (SWCnT-ICg) for
molecular PA imaging of brain tumors in living mice [137]. Figure 10.9a shows the
schematic of SWCnT-ICg conjugate, and the corresponding optical spectra are