458426 Hollow Carbon Nanobubbles: Graphene Related Nanocapsules That Form Stable Dispersions in Water and Can Incorporate a Cargo
Graphene related structures, such as carbon nanotubes and fullerenes attracted tremendous attention in various fields. The central cavity of buckminsterfullerene (C60), the probably most prominent form of hollow carbon, has been used to enclose various atoms and even molecules. The limited space (few atoms per C60) and the difficult fill/release processes, however, do not permit a real container/cargo function. Capsule systems have attracted tremendous attention in catalysis, biomaterials, as electrode material and for the encapsulation of sensitive materials (therapeutics, fluorescent markers and others). For most container-type applications, however, a hollow nanosphere should carry a hydrophobic cargo through an aqueous environment, i.e. the nanocapsule is chemically different at its inner- and outer surface.
We developed multi-walled carbon nanotube related nanocapsules consisting of a few layers graphene-like carbon. Selective covalent chemical derivatization of the outside carbon shells with a negatively charged polymer permits highly stable dispersion in water while the insides hydrophobicity provides room to accommodate cargo. The synthesis starts from carbon coated cobalt metal nanoparticles (C/Co) with a shell of the above mentioned 3 - 4 layers of sp2-hybridized carbon. After surface modification the templating metal core can be selectively removed by acidic dissolution at elevated temperature.
The accessibility of the bubble interior was shown with rhodamine B. An unusual intense rhodamine B accumulation in the interior of the nanobubbles (10000 times more rhodamine B in the bubble interior than in the outside solution) and an unexpected hysteresis in filling and release were found. It was further shown that doxorubicin, one of the most widely used commercial anti-breast-cancer drugs, can be loaded to the hollow carbon nanobubbles.
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 Accepted for publication in Angewandte Chemie (10.1002/anie.201602745R1)
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