Design and Development of Theranostic Nanomedicines - Nanotechnology for Biomedical Imaging and Diagnostics - page 428

15.2.3 carbon nanomaterials

With rapid development in nanotechnology, carbon nanomaterials have become an
attractive class of theranostic agents, owing to their unique physical and chemical
properties. several types of carbon nanomaterials have been applied in theranostic
studies, including fullerene, carbon nanotubes (CnTs), graphene, carbon dots, and
nanodiamonds. among all theranostic carbon nanomaterials, CnTs are the most
extensively studied. The large surface area of CnTs is available for efficient drug
loading and bioconjugation with targeting and signaling molecules [56]. Moreover,
CnTs can be developed with strong absorbance in the nir region for photoacoustic
and raman imaging, as well as pTT of tumor.
CnTs can be categorized as single-walled carbon nanotubes (sWCnTs) and mul-
tiwalled carbon nanotubes (MWCnTs). sWCnTs are made up of a single rolled-up
layer of a graphene sheet, and MWCnTs consist of multiple rolled-up layers of
graphene [57]. Typical sWCnTs have diameters of less than 5 nm, whereas MWCnTs
can have diameters as large as 100 nm. The lengths of CnTs can range from hundreds
of nanometers to tens of micrometers.
similar to gnps, many CnTs have strong optical absorption in the nir region,
therefore suitable for photoacoustic or raman imaging. Multimodal imaging
approach is also readily achievable, as the surface of CnTs can be easily function-
alized [57]. For example, sWCnTs can be treated to have a large number of car-
boxyl groups on the surface, which can be applied to conjugate various types of
imaging moieties, such as nir fluorescent dyes, radioisotopes, and magnetic
nanoparticles [14].
The intense nir absorption of CnTs has made them a promising pTT tool for
cancer treatment. it has been shown that upon irradiation by nir light, CnTs were
internalized in cells and triggered endosomal rupture and cell death [58].
anticancer drugs can also be attached to the functional surface of CnTs through
covalent bonds. For instance, pastorin et al . attached MTX to the amino functional-
ized surface of CnTs via amide coupling [59]. however, it was found that covalent
amide bond was unfavorable to elicit intracellular drug release. To overcome this
issue, Kam et al . coupled sirna to CnTs via a disulfide bond, which can be cleaved
by enzymes in the endolysosome [60]. in another study, cleavable ester bond was
used to connect pTX and CnTs and conjugates showed higher efficiency in suppress-
ing tumor growth than pTX alone [61]. The higher efficiency is largely due to the
increased accumulation of conjugates in the tumor region, which was attributed to the
prolonged circulation time [14].
other than bioconjugation through covalent bonds, anticancer drugs can also be
loaded to CnTs through aromatic stacking mechanism. For example, DoX could
be efficiently loaded onto sWCnTs via supramolecular π-π stacking [62, 63]. The
resulting sWnT-DoX complex demonstrated enhanced therapeutic efficacy and
reduced toxicity compared to free DoX.
although many types of nanoparticles without targeting molecules can
be delivered to tumor through passive targeting, few have been reported to be