(316e) 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),^[1] the probably most prominent form of
hollow carbon, has been used to enclose various atoms and even molecules.^[2] 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.^[3] Selective covalent chemical
derivatization of the outside carbon shells with a negatively charged polymer permits
highly stable dispersion in water while the inside’s 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.^[4] 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 (10’000 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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[3]          Accepted for
publication in Angewandte Chemie (10.1002/anie.201602745R1)

[4]          R. N. Grass, E. K.
Athanassiou, W. J. Stark, Angew. Chem.
Int. Ed. 2007, 46, 4909.

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