Nanoparticles as Contrast Agents for Optoacoustic Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 122

TomoWave Labs research group [14, 95]. This figure shows OA images of a mouse
before and after sWNT injection. A localized increase in OA image brightness gen-
erally implies an increase in the value at that location. OA signals from the organs
were correlated with the measured concentrations of sWNTs accumulated in these
organs as measured spectroscopically ex vivo in the harvested organs using the
intrinsic fluorescence of sWNTs. The methodology presented in this report can
further be extended to calibrate the sensitivity of an OA imaging system for a range
of changes in optical absorption coefficient values at specific locations in a mouse
body to enable noninvasive measurements of nanoparticle concentrations in vivo.
Recently, a novel class of hybrid cNTs (multicomponent nanoconstructs with
several types of nanoparticles, such as nanotubes and gold nanoparticles) was shown
to be more biocompatible and less toxic with better biodistribution and pharmacoki-
netic properties than individual nanocomponents. These hybrid constructs were
shown to permit more efficient and versatile bioconjugation with targeting agents
thus making these systems attractive for nanomedicine-related theranostics [81].

5.4 plasmoNic NaNoparticles as optoacoustic
coNtrast ageNts

5.4.1 types and properties of plasmonic Nanoparticles

surface plasmon nanoparticles (sPR), or plasmonic nanoparticles, with many dif-
ferent shapes have been designed, including nanospheres, gold nanorods, nanotu-
bule, bipyramids, ribbons, nanorice, nanocubes, triangular gold nanoplates, hollow
nanoshells, nanobowl multipods, gold nanostars, lumps, gold nanoshuttles, gold tet-
rahedra, octahedral, cubooctahedra, and polyhedral, branched, and hollow/porous
nanowires and nanodisks [96-98]. figure 5.10 presents typical examples of plas-
monic nanoparticles. Recently, in relation to OA imaging, different alloys, plasmonic
nanoparticles, and/or their compositions with other materials for manufacturing mul-
tilayered and multimaterial nanostructures, such as gold nanobeacons [29] and other
composites [99], have been applied.
Despite the large number of shapes of plasmonic nanoparticles, little is pub-
lished on the correlation of shapes and their utility in OA imaging. Plasmonic
nanoparticles for in vivo applications need to be engineered with absorption peaks
ranging from 600 to 900 nm [19]. As mentioned earlier, this spectral region is also
known as the “optical window,” where absorption is minimal and optical penetra-
tion is maximal [100]. The main plasmonic nanoparticles for OAT and imaging are
gold nanoshells, gold nanorods, gold nanocubes, and hollow gold nanoshells [19,
101-104]. In an interesting example, antibody-conjugated, epidermal growth factor
receptor (egfR)-targeted spherical gold nanoparticles undergo molecular-specific
aggregation when they bind to egfR on the cell surface, thereby leading to a red
shift in their plasmon resonance frequency leading to an enhanced PA imaging [80].
many of these gold nanoparticles are targeted and used mainly for molecular
imaging of cancer [105-108] due to high sensitivity of gold contrast in OA imaging.