Clusters of Carbon Nanospheres Derived from Graphene Oxide

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(2)-hybridized carbon atoms together with COOH, C═O, 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.