272.4.5 Gold Nanoparticles
Gold nanoparticles (Fig. 2.7) have several properties that make them a promising
agent for stem cell labeling and tracking. They have a strong “surface plasmon reso-
nance” i.e. resonant oscillation of conduction electrons at an interface stimulated by
light; this means that they can easily scatter and adsorb visible light. They have a
high spatial and temporal sensitivity compared to MRI, positron emission tomogra-
phy (PET) and computer tomography (CT) [ 78 ]. It is also relatively easy to manu-
facture gold nanoparticles and conjugate them to a variety of biomolecular targets
[ 16 ]. Gold nanoparticles can also be induced by infrared light, which causes vibra-
tional energy and heat that can for example kill select cancer cells [ 79 ]. In particular,
gold nanoparticles and their hybrids with different shapes, including GNSs, GNRs,
and GNTs that were tuned to desired NIR spectral ranges, have shown their poten-
tial for biomedical photoacoustic imaging and photothermal therapy. The optical
tunability and responsiveness in the NIR range (i.e., 650 to 1400 nm) offer promis-
ing potential for minimally invasive theranostics of diseases because of the relative
transparency of biological tissues to NIR [ 27 , 28 , 30 – 33 , 35 , 80 ]. Most biological
components are relatively transparent to NIR. Also NIR responsive nanoparticles
allow selective and sensitive sensing of targets in the presence of biological back-
ground materials, minimizing the sample preparation and purification time.
Furthermore, as discussed above with, coating the gold nanoparticles with a silica
layer facilitates the uptake to cell and increases their photoacoustic signal [ 25 ].
For stem cell tracking, most studies have utilized GNRs [ 81 ]. Studies have dem-
onstrated their successful mesenchymal cell labeling and photoacoustic longitudi-
nal in vivo tracking in mice and rats, with results validated by histology and mass
Fig. 2.6 Scanning Electron Microscopy images of polymeric nanoparticles of poly(carbonate)
(PC), poly(styrene-co-acrylic acid) (PS-co-AA), poly(vinyl acetate) (PVAc) and poly(vinyl carba-
zole) (PVK) prepared by dialysis of the polymers. Reprinted with permission from Hornig et al. [ 77 ]
2 Nanotechnology-Based Stem Cell Applications and Imaging