Clusters of Carbon Nanospheres
Derived from Graphene
Oxide
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Abstract
Stable and water-dispersible cluster of carbon nanospheres
(CCNs)
can be synthesized from graphite or graphene nanoplatelets via sonication
assisted chemical exfoliation/oxidation. Separation of CCNs with a
diameter of ∼130 nm from other products in the reaction including
the graphene oxide sheets (GOShs) and other smaller carbon-based particles,
could be done by centrifugation. Structural analysis of these CCNs
by UV–vis absorption, fluorescent, IR, Raman, and X-ray photoelectron
spectroscopic, combustion elemental, and electron diffraction analyses,
indicates an extended π–π conjugation network of
sp<sup>2</sup>-hybridized carbon atoms together with COOH, CO,
and OH functionalities. The spherical morphology of the CCNs is established
by scanning electron microscopic analysis, while transmission electron
microscopy indicates that the obtained CCNs are an aggregate of 5
nm carbon spheres (giant fullerenes) and GOShs. Dispersing the CCNs
in curcumin solution results in curcumin adsorption onto the CCNs
at 18.5 ± 1.4% (wt curcumin/wt loaded CCNs). The curcumin-loaded
CCNs are taken up into human embryonic kidney (HEK293T) cells with
detachment of the curcumin from the CCNs once inside the cells, such
that curcumin is detected in the nucleus while the CCN carriers are
only found outside the nucleus. The use of CCNs as the carrier gives
a significantly better transportation of curcumin into the nucleus
of the cells compared to curcumin alone. CCNs show no significant
in vitro cytotoxicity to the HEK293T and human epidermoid cervical
carcinoma cell lines at up to 3 μg/mL