Nanoparticles as Contrast Agents for Optoacoustic Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 118

OA imaging using a contrast agent composed of a plant virus protein shell that encap-
sulates Icg has been recently demonstrated [66]. This nanoconstruct is comprised of
a protein shell, purified from the plant-infecting brome mosaic virus (BmV) and
encapsulated dye. These viruse-based nanoconstructs as optical viral ghosts (OVgs)
since the genomic content of the wild-type BmV is eliminated and replaced with Icg,
while the capsid protein (cP) subunits remain as the encapsulating shell [66]. These
nanoconstructs were shown to provide higher PA signals than blood in tissue phan-
toms and display superior photostability compared to the nonencapsulated dye.
Besides Icg-based nanoparticles, other NIR-active compounds such quantum
dots and dyes have been investigated. Quantum dots can convert the absorbed energy
(up to 60%) into heat and then at certain condition into sound [74], which is sufficient
for detection of quantum dots using thermal or ultrasound transducers. gao et al . [75]
summarized recent developments in the field of stem cell tracking with optically
active nanoparticles including quantum dots for the OA and fluorescence imaging.
coregistration of the OAT and fluorescence images enabled simultaneous visualiza-
tion of the tumor location, angiogenesis, and brain structure. The fluorescent prop-
erties of quantum dots-based contrast agents were used for OA imaging [74, 76].
Recently, Prussian blue nanoparticles have been described as a novel contrast agent
for enhancing OAT in vitro and in vivo [77]. These Prussian blue nanoparticles of
approximately 40 nm are composed of iron-based pigment fe III 4 [fe II (cN) 6 ] 3 · n H 2 O
capped with citric acid and feature strong absorption NIR photons.

5.3.2 carbon Nanotubes

Noninvasive detection of various molecular markers of diseases can allow for much
earlier diagnosis, control for treatment, and better prognosis that will eventually lead
to personalized medicine [78-80]. Numerous biomedical applications of single-
walled and multiwalled carbon nanotubes (sWNTs and mWNTs, respectively, or
cNTs in general) have been demonstrated over the years in this regard [26, 79,
81-83]. many modifications of sWNTs have raised significant interest over the past
decades for their unique physical and optical properties for OAT and imaging. Owing
to their ability to absorb light at a wide range of wavelengths spanning the ultraviolet,
visible, and NIR spectral ranges, cNTs are natural contrast agents for OA and pho-
tothermal (PT) technique. When compared with blood in phantom studies, sWNTs
were found to show significant signal enhancement for OAT at 1064 nm excitation
[26]. Recently, noninvasive sWNT-enhanced OA identification of sentinel lymph
nodes (sLNs) in a rat model was reported [84]. In this study, sLNs were successfully
imaged in vivo with high contrast-to-noise ratio (>80) and good resolution (~500 µm).
Because sWNTs have optical absorption over a wide excitation wavelength range,
the imaging depth could be maximized by varying the incident light wavelength to
the NIR, where biological tissues (e.g., hemoglobin, tissue pigments, lipids, and
water) have low light absorption. Targeted sWNTs have frequently been used for
molecular OA imaging. Integrin αvβ3 and arginine-glycine-aspartic acid (or RgD
peptide), a potent integrin αvβ3 antagonist, are among the most extensively studied
and validated receptor-ligand pairs used in conjunctions with sWNTs [39, 85].