Realization, characterization and functionalization of lipidic wrapped carbon nanotubes

Carbon nanotubes (CNTs) are cylindrical structures with diameter varying from a few nanometres to tens of nanometres and length ranging from less than a micron to centimetres. They have excellent mechanical strength, electrical conductivity and thermal stability, so that many potential applications have been proposed: CNTs based sensors, probes, actuators, nanoelectronic devices, and drug delivery systems within biomedical applications. In general, in large-scale production of CNTs, the as-prepared product exists as agglomerates with a size of up to hundreds of microns. In many applications it is important to use isolated CNTs or make CNT solutions or dispersions, especially in biomedical field where a strong interaction between the CNTs and the biological matter is required, but pristine CNTs are completely hydrophobic and thus cytotoxic. Many works in literature report the toxic effects of CNTs and their applicability in biomedical field, debating on different strategies of solubilization or dispersion to improve biocompatibility.

TEM imaging of L-CNT

Lipidic wrapping of CNTs (L-CNT) could be a valid alternative that comprises the advantage of non-covalent functionalization, good dispersion stability and good biocompatibility. Two kind of lipidic mixture will be employed, with cationic and anionic properties. Dispersion features will be investigated in terms of lipid concentration, CNTs concentration, size distribution, Z-potential and TEM imaging. Cytocompatibility of these sospensions was showed by specific test (WST-1 assay on COS-1 cells).

    
Viability assay: culture images and WST-1 test on different lipidic coating

Functionalization of lipidic wrapping around carbon nanotubes with a small peptide (H12 dodecapeptide) will demonstrate possibilities to combine CNTs with biological molecules without covalent functionalization of CNT themselves.

Light transmittance of platelet suspensions treated with ADP + ALM-CNT (green) and ADP + H12-CNT (red)

Realization of high concentrated and biocompatible CNT dispersions is one of the major challenges for applications of CNT in biological field. In this work high concentrated, biocompatible and stable CNT dispersions, realized through a lipidic wrapping, were realized (L-CNT). The lipidic wrapping, thanks to its hydrophobic and hydrophilic features, allows a good stabilization of CNTs in aqueous environments. Moreover, it was proved that functionalization of lipidic layer around CNT is very effective and allows a non-covalent binding of biological molecules (dodecapeptide was chosen as model) to CNTs, thus preserving their pristine mechanical and chemical properties but allowing, at the same time, their  “chemical recognition” by the cells. Future works will be addressed to the “indirect” functionalization of L-CNT with different biological moieties, with the aim of a “targeted” drug or gene delivery without any covalent CNTs chemical modification.

References

• L. Lacerda, V. Raffa, M. Prato, A. Bianco, K. Kostarelos, "Cell-Penetrating Carbon Nanotubes in the Delivery of Therapeutics", Nano Today (Elsevier), 2:6 (2007), pp. 38-43
• Raffa V., Menciassi A., Pensabene V., Ciofani G., Dario P. - Metodo di elettroporazione in vivo non invasiva mediata da nanotubi di carbonio e dispositivo per attuare tale metodo (Method and device for non-invasive in vivo electroporation mediated by carbon nanotubes) - Industrial Italian patent nr. FI2006A000295, November 24th, 2006