Resumen de Development of carbon nanocapsules for biomedical applications /
The high surface area and hollow core of carbon nanotubes (CNTs) makes them ideal candidates for the development of smart nanovectors in nanomedicine. Their inner cavity can be employed to host selected payloads for either diagnosis or therapeutic purposes while the external walls can be modified to increase their biocompatibility and even for targeting purposes. A major challenge to turn the potential of CNT based devices into customer applications is to reduce or eliminate their toxicity. Taking into account health and safety concerns, intensified research efforts are conducted to improve the biocompatibility of CNTs, including the development of new shortening and purification strategies.
The first part of this thesis focused on the influence of steam on the length, purity, and sidewall integrity of chemical vapor deposition (CVD) and arc discharge single-walled carbon nanotubes (SWCNTs). In order to obtain individualized carbon nanotubes we developed a protocol that consisted of dispersing the samples in ortho-dichlorobenzene and employed scanning electron microscopy (SEM) to acquire the images. Short CVD CNTs with median length of ca. 200 nm can be obtained after 10 h of steam treatment, whereas arc discharged CNTs show low reactivity towards steam. The efficiency of other commonly employed shortening methods, namely ball milling, sulfuric/nitric acids, and piranha was also investigated for both SWCNT and multi-walled CNTs (MWCNTs) CNTs grown by CVD. A combination of piranha and steam turned out to be the most efficient for SWCNTs, and a combined sulfuric/nitric acids and steam for MWCNTs. These protocols provide a good balance between length distribution, sidewall integrity and purity of samples with a high yield of production.
In the second part, we report on the encapsulation of selected metal halides, of interest for both imaging and therapy, inside CVD and arc discharge SWCNTs. The role of temperature on the degree of end-closing has been investigated and which has allowed the preparation of closed-ended metal halide filled CNTs. Bulk filling of carbon nanotubes results in samples that contain a large amount of non-encapsulated material, external to the carbon nanotubes, which can affect and even dominate the properties of filled carbon nanotubes. Therefore, we developed a straight forward approach that allows the removal of non-encapsulated compounds in a time efficient and environmentally friendly manner, using water as a “green” solvent in a Soxhlet setup, while minimizing the residual waste.
The last part of the thesis describes the external modifications of previously filled CNTs. SWCNTs have been covalently functionalized via Tour and Prato reactions, the former resulting in a higher degree of functionalization. To complete the study, lutetium chloride filled MWCNTs were externally decorated with gold nanoparticles. The developed hybrid nanocapsules hold potential to be employed as dual agents for diagnosis and therapy.
To summarize, this thesis brings new insights in the preparation of carbon nanocapsules, i. e. close-ended filled carbon nanotubes with chosen payloads, for the development of the next generation of theranostic agents.
