SNAP · Smart Nanomaterials with Applications in Photodynamic Therapy

Smart Nanomaterials with Applications in Photodynamic Therapy

During his two years at Trinity College Dublin Kevin Flavin acquired extensive and interdisciplinary expertise in the design, synthesis and characterization of nanomaterials. In particular, he focused on the functionalization of single-walled carbon nanotubes and carbon nano-onions, which is extremely important as it increases their solubility and processability, and couples the unique properties of these carbon based nanomaterials with other types of materials. This research take advantage of the unique structures and physical properties of in particular single-walled nanotubes (SWNTs) and during the course of this effort many fundamental problems associated with the production of suitable carbon nanotubes, such as purification, solubilization, debundling and assembly, are addressed in a systematic manner. The first two objectives presented in the original proposal have been reached. -Transformation of CNTs into soluble materials that can be easily manipulated in solution developing synthetic schemes for the production of monodisperse and individual nanotubes. -Synthesis and characterisation of a number of photosensitizers (PSs) that respond to an optical input. Incorporating a suitable receptor into the PS structure will allow not only control singlet oxygen production by manipulating the optical input but also switch it on or off based on the presence of a specific substrate or environmental conditions, such as for example pH or Na+ concentration. This will allow differentiation between healthy and tumoral cells which represent a major problem when using traditional PSs. A full characterization is necessary for the understanding and developing of new materials that contain CNTs. Many publications tend to provide only FT-IR and Raman spectra but this does not offer the necessary quantitative information. Only the combination of different analytical methods can provide a full picture of functionalised CNTs. In addition to FTIR and Raman, he routinely uses UV/vis-NIR absorption spectroscopy to get useful information about electronic transitions of nanotubes and thermal gravimetric analysis (TGA) to get information on the purity and also on the functionalization of tubes. In addition, he was trained to use microscopy techniques such as TEM (transmission electron microscopy), SEM (scanning electron microscopy), and AFM (atomic force microscopy), that offer much insight into the presence of CNTs in solution. While developing the procedure for SWNT functionalisation a new chemical treatment for preparing high purity selectively oxidized SWNTs while preserving optical/electronic properties of the material has been developed. Efficient removal of both metal and carbonaceous impurities was demonstrated by AFM, TEM, Raman and absorption spectroscopy, while XPS confirmed quantitative conversion of oxidized defects to functionalizable carboxylic acid groups. Furthermore persistence of the characteristic optical properties was confirmed using absorption and NIR photoluminescent spectroscopy, thus indicating preservation of the electronic structure. This chemical treatment thus paves the way for the preparation of high purity, covalently functionalized SWNTs enhancing their potential for use in high-performance optical/electronic applications. New objectives established during the course of the work and new lines of research The ERG fellow covalently functionalized the SWNTs with photosensitisers made by collaborator Prof. Donal O'Shea, UCD, Dublin. After functionalisation a complete quenching of the photosensitiser was observed, which means that this new material could no longer be used for photodynamic therapy. This however paves the way for potential use as a donor-acceptor material in photovoltaic applications i.e. solar energy conversion. In collaboration with Prof. Dirk M. Guldi, Friedrich-Alexander-University, Germany, the donor-acceptor properties of the material ware characterized by means of various spectroscopic techniques.

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