Carbon nanotubes (CNTs) have remarkable properties with applications in a wide range of fields. Moreover, the presence of an inner cavity expands their versatility, allowing their endohedral modification. Among the large variety of materials that can be filled in their interior, the encapsulation of biomedically relevant payloads inside CNTs has taken a great deal of attention. CNTs not only offer protection to the encapsulated cargo from the biological milieu, but also can be externally modified by the attachment of selected biomolecules that can provide an increase in the biocompatibility and selectivity of the material.
Filling of CNTs is typically performed using an excess of the guest material and a large amount of the filler remains external to the walls after synthesis. The non-encapsulated compounds can induce negative side effects when employed in the biomedical field. For this reason, a subsequent washing protocol for the selective elimination of the external material, while preserving the inner compound, must be performed. In this context, we have reported a fast and simple method that allows the formation of a wide variety of multiwalled carbon nanocapsules (closed-ended filled CNTs), clean from external, non-encapsulated material. The proposed methodology consists in thermally annealing open-ended MWCNTs in the presence of a chosen payload at temperatures ranged between 1000 °C and 1200 °C, which leads to their simultaneous filling and end-closing. Once the MWCNTs are filled, the non-encapsulated compounds can be easily removed in a fast manner. This approach has demonstrated to be highly versatile, since several biomedically relevant compounds have been sealed in the cavities of CNTs. In vitro studies of both empty and filled MWCNTs showed that nanocapsules did not induce cellular death after being internalized by cells.
Non-cytotoxic carbon nanocapsules synthesized via one-pot filling and end closing of multi-walled carbon nanotubes
Markus Martincic, Sandra Vranic, Elzbieta Pach, Stefania Sandoval, Belén Ballesteros, Kostas Kostarelos, Gerard Tobias
Carbon 141, 782-793, 2019
Figure: (a) Schematic representation of the synthesis of multiwalled carbon nanocapsules (closed-ended filled carbon nanotubes), (b) BET surface area of empty MWCNTs annealed at different temperatures and (c) flow cytometry using PI/Annexin V staining (alive cells are represented in P18 region, early apoptotic in P19, late apoptotic and/or necrotic cells in P17 and necrotic cells in P16.)