Kevin Flavin

Functionalization of Carbon Nanoparticles Modulates Inflammatory Cell Recruitment and NLRP3 Inflammasome Activation

The inflammatory effects of carbon nanoparticles (NPs) are highly disputed. Here it is demonstrated that endotoxin-free preparations of raw carbon nanotubes (CNTs) are very limited in their capacity to promote inflammatory responses in vitro, as well as in vivo. Upon purification and selective oxidation of raw CNTs, a higher dispersibility is achieved in physiological solutions, but this process also enhances their inflammatory activity. In synergy with toll-like receptor (TLR) ligands, CNTs promote NLRP3 inflammasome activation and it is shown for the first time that this property extends to spherical carbon nano-onions (CNOs) of 6 nm in size. In contrast, the benzoic acid functionalization of purified CNTs and CNOs leads to significantly attenuated inflammatory properties. This is evidenced by a reduced secretion of the inflammatory cytokine IL-1β, and a pronounced decrease in the recruitment of neutrophils and monocytes following injection into mice. Collectively, these results reveal that the inflammatory properties of carbon NPs are highly dependent on their physicochemical characteristics and crucially, that chemical surface functionalization allows significant moderation of these properties.

Synthesis and Characterization of Boron Azadipyrromethene Single-Wall Carbon Nanotube Electron Donor-Acceptor Conjugates

The preparation of a novel donor-acceptor material, consisting of a red/near-infrared (NIR) absorbing boron azadipyrromethene donor covalently attached to a highly functionalized single-wall carbon nanotube (SWNT) acceptor, which bears great potential in the field of organic photovoltaics, has been demonstrated. Both purification and covalent functionalization of SWNTs have been demonstrated using a number of complementary characterization techniques, including atomic force microscopy, Raman, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared, and NIR-photoluminescence spectroscopy, and a functionalization density of approximately 1 donor molecule per 100 SWNT atoms has been estimated by XPS. The redox behavior of the fluorophore has been investigated by electrochemistry and spectroelectrochemistry as well as by pulse radiolysis. The donor-acceptor properties of the material have been characterized by means of various spectroscopic techniques, such as UV-vis NIR absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and time-resolved transient absorption spectroscopy. Charge transfer from the photoexcited donor to the SWNT acceptor has been confirmed with a radical ion pair state lifetime of about 1.2 ns.

Controlled carboxylic acid introduction: a route to highly purified oxidised single-walled carbon nanotubes

A chemical treatment for preparing high purity selectively oxidised SWNTs while preserving optical/electronic properties of the material has been developed. Efficient removal of both metal and carbonaceous impurities has been demonstrated by AFM, TEM, Raman and absorption spectroscopy, while XPS confirmed quantitative conversion of oxidised defects to functionalisable carboxylic acid groups. Furthermore persistence of the characteristic optical properties was confirmed using absorption and NIR photoluminescence spectroscopy, thus indicating preservation of the electronic structure. This chemical treatment thus paves the way for the preparation of high purity, covalently functionalised SWNTs enhancing their potential for use in high-performance optical/electronic applications. A comparison with commonly used purification protocols that utilize nitric acid and sodium hydroxide followed by piranha solution treatments or simple solvent washing is made, highlighting the advantages of the reported method for the production of SWNT starting materials ideal for efficient chemical modifications.

Multi-Functionalized Carbon Nano-onions as Imaging Probes for Cancer Cells

Carbon-based nanomaterials have attracted much interest during the last decade for biomedical applications. Multimodal imaging probes based on carbon nano-onions (CNOs) have emerged as a platform for bioimaging because of their cell-penetration properties and minimal systemic toxicity. Here, we describe the covalent functionalization of CNOs with fluorescein and folic acid moieties for both imaging and targeting cancer cells. The modified CNOs display high brightness and photostability in aqueous solutions and their selective and rapid uptake in two different cancer cell lines without significant cytotoxicity was demonstrated. The localization of the functionalized CNOs in late-endosomes cell compartments was revealed by a correlative approach with confocal and transmission electron microscopy. Understanding the biological response of functionalized CNOs with the capability to target cancer cells and localize the nanoparticles in the cellular environment, will pave the way for the development of a new generation of imaging probes for future biomedical studies.

Excited state on/off switching of a boron azadipyrromethene single-wall carbon nanotube conjugate

The synthesis and characterisation of an on/off fluorescence switchable boron difluoride azadipyrromethene single-wall carbon nanotube conjugate are presented and the ability to reversibly switch on and off the excited state by modulation of pH is illustrated.