Radio-labeled Nanoparticles for Biomedical Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 204

as nanodiamond has been explored for biomedical applications due to its biocompat-
ibility, ability to cross the cell membrane, and capability to be functionalized [134].
In a study by Rojas et al ., 18 f was radiolabeled on nanodiamonds via the reaction
of 18 f-Sfb ω-aminopropyl [135]. The radiolabeled nanodiamonds were further
functionalized to study their in vivo biodistribution. Initial pharmacokinetics and
peT imaging showed high retention in the lung, liver, and spleen, and significant
excretion through the urinary tract. In further studies, the addition of surfactants to
the nanodiamonds did not affect the biodistribution result, whereas the removal of
larger nanodiamonds by filtration led to lower liver uptake with no retention in the
lung or spleen. This suggests that the high pulmonary retention is most likely due to
size exclusion and phagocytosis [135]. In clinical applications, 68 ga-labeled carbon
nanoparticles have also been used for pulmonary embolism peT/CT ventilation/
perfusion (V/Q) imaging and have demonstrated superiority to conventional V/Q
lung scintigraphy [136].

7.4.6 Radiolabeled auNps for pet imaging

gold nanostructures have been explored for theranostic application via peT imaging in
various disease models [137, 138]. gold nanoshells (NS) have been used for multimo-
dality theranostics with 64 Cu radiolabeling and RgDfK peptide conjugation. peT/CT
images of these 64 Cu-NS-RgDfK nanoprobes were compared with the nontargeted
64 Cu-NS in nude rat models bearing head and neck squamous cell carcinoma xenografts.
The images showed significant tumor uptake and tumor vascular specificity, indicating
active targeting and promising improved efficacy of photothermal ablation [139]. A
chelator-free [ 64 Cu]CuS nanoparticle with controlled specific activity was prepared for
tumor theranostic application. The pegylated [ 64 Cu]CuS nanoparticles showed about
15% ID/g blood retention at 4 h p.i. in biodistribution studies and high tumor-to-
muscle ratio (T/m = 6.55) at 24 h p.i. Interestingly, this peg-[ 64 Cu]CuS nanoparticle
also displayed photothermal properties [140].
Recently, a novel class of nanomaterials, gold nanocages (AuNCs), have been
radiolabeled with 64 Cu with high specific activity for peT imaging applications. In
contrast to 55 nm AuNCs, the smaller 30 nm AuNCs showed superior blood reten-
tion and lower hepatic and splenic uptake. In a murine emT-6 tumor model, the
smaller cages also showed a significantly higher level of tumor uptake and a greater
tumor-to-muscle ratio than the large AuNCs. Quantitative peT imaging confirmed
rapid accumulation and retention of AuNCs inside the tumors (fig. 7.4). The ability
to directly and quickly image the distribution of AuNCs in vivo provided a direction
to further optimize their physicochemical properties for a range of theranostic
applications [141].

7.4.7 Radiolabeled silica Nanoparticles for pet imaging

Silica nanoparticles, due to their biocompatibility and non-toxicity, have been radiola-
beled for various biomedical applications [142, 143]. Labeled with 18 f, the thermally
hydrocarbonized porous silicon nanoparticles passed intact through the gastrointestinal