Biomedical Engineering Reference
In-Depth Information
their
in vivo
toxicity, and improve their pharmacokinetic properties [71, 72]. CNTs
can be radiolabeled by surface modification and subsequent labeling or by encapsu-
lation of the radionuclide within their inner walls [73-76]. CNTs have also been
reported to localize on cells via different routes based on their layering and size.
Small CNTs with lengths less than 400 nm can be taken up into cells by diffusion,
while larger CNTs enter cells by endocytosis [77]. based on the number of layers,
mWNTs are often localized on the cell surface, while the SWNTs are internalized
into the nucleus (short SWNTs) or cytoplasm (long SWNTs) [78, 79].
One of the first studies that used CNTs for
in vivo
imaging was done by surface
modification of SWNT and mWNT to create a free -NH
3
+
group. This amine group
was then covalently conjugated to DTpA and subsequently chelated to
111
In with
greater than 80% radiolabeling yield [76]. The
111
In-DTpA-mWNT showed good
stability in serum at 24 h p.i. at 37°C. The distribution study using microSpeCT/CT
showed that within 1 min of injection, the
111
In-DTpA-mWNT began accumulating
in the kidney and bladder with maximal accumulation seen in these organs after
30 min. At 24 h p.i., there was minimal radioactivity left in the kidney, indicating high
renal clearance of
111
In-DTpA-mWNT. Interestingly, the nonfunctionalized mWNT
accumulated mostly in the liver and lungs [75]. A recent approach filled the interior
of SWNTs with radiohalogens such as
125
I, while modifying the surface with the
sugar
N
-acetylglucosamine (glcNAc
D
). This formed a high radionuclide payload
conjugate of glcNAc
D
-Na
125
I-SWNTs. In contrast to the injected free Na
125
I control,
which accumulated mainly in the high-affinity organs such as thyroid and stomach,
the Na
125
I-SWNTs were localized predominantly in the lungs with no uptake in the
thyroid, stomach, or bladder. This preferential and persistent uptake in the lungs at 4
and 24 h and 7 days p.i. indicated interactions of the sugar group with lung-localized
proteins. An
in vitro
cytotoxicity assay of Na
125
I-SWNTs on human lung epithelial
cells revealed no toxicity at concentrations up to 125 µg/ml. This study shows that
encapsulated high-density radionuclides in SWNT can be safely directed to the site
of action without leakage for organ-specific diagnostic imaging [74].
7.3.6
Radiolabeled gold Nanoparticles for spect imaging
gold nanoparticles (AuNps), owing to their optical, conductive, and electronic prop-
erties, have been widely used in biomedical applications. because they can absorb
light in the visible/near-infrared (NIR) region to produce surface plasmons or waves
of excitation in the atoms making up a conductive material, they can be used for
photothermal therapy as well as other photosensing applications. The absorption
wavelength is dependent upon the size and shape of the AuNp with larger gold parti-
cles absorbing more in the red region. A typical example is observed in gold nanorods
(gNRs), which have two characteristic absorption wavelengths corresponding to the
transverse (480-520 nm) and longitudinal (700-900 nm) sections of the rods [80]. In
general, AuNps with surface plasmon absorption in the far visible/NIR wavelength
allow for the application of light irradiation that will penetrate further into tissues
with less damage as compared to UV-Vis irradiation [80-82]. The ability to design
not only the nanorods but other AuNps with different surface plasmon wavelengths
has greatly expanded their practical applications in nanomedicine [83].
Search WWH ::
Custom Search