Fullerene derivatives have appealing properties that can potentially be used in materials science and medical applications. In particular, fullerenes are known to produce reactive oxygen species upon their excitation with light. This makes them particularly attractive as photosensitizers for photodynamic therapy (PDT). Photodynamic therapy is a new modality of treatment of cancer as well as some non-cancerous conditions. It involves the combined actions of a drug (photosensitizer) and light to produce a cytotoxic effect. Water-soluble hexa(sulfo-n-butyl)fullerenes (FC4S) was reported recently to generate singlet oxygen (1O2) and superoxide radical (O2-·) upon its excitation with light, making it a promising candidate for PDT treatments. Recently, we synthesized new amphiphilic fullerene derivatives, namely, fullerene-diphenylaminofluorene-oligo(ethylene glycol) conjugates, C60(>DPAF-PEG600) and C60(>DPAF-PEG2000), as potential photosensitizers. In this paper we compare FC4S to PEG-based fullerenes in terms of their singlet oxygen photosensitization ability. We measured time-resolved kinetics of singlet oxygen luminescence photosensitized by excitation of fullerenes via a 10 ns pulsed laser at 523 nm. For FC4S we observed "normal" kinetics with a monoexponential decay profile giving a time constant 3.8 us in water. In contrast, for the case of C60(>DPAF-PEG600) and C60(>DPAF-PEG2000), a non-monoexponential decay profile with a long tail (~ 102 μs) in water was observed. We hypothesize that this is due to formation of vesicles by PEG fullerenes in aqueous solution. To investigate photodynamic activity of these fullerene derivatives in vitro, we used HeLa human adenocarcinoma and B16 mouse melanoma cell lines. FC4S showed clear photodynamic effects in both cell lines. The total fluence required to kill 50% of the cells at the drug concentration of 20 μM was 36 Jcm-2 for HeLa cells and 72 Jcm-2 for B16 cells. Neither PEG-based fullerene derivatives showed any appreciable photodynamic activity, possibly, due to low efficiency of singlet oxygen generation.
The novel mechanical and electrical properties of carbon nanotubes have potential applications in a variety of fields, and their size makes them appealing for use in biosensors. However, in order to exploit their potential, carbon nanotubes must be functionalized for biologic compatibility. Sulfonated and polyanilinated multi-walled and single-walled carbon nanotubes were investigated by several spectroscopic and microscopic methods to asses their feasibility in characterization of functionalized carbon nanotubes (CNT). Transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and energy-dispersive X-ray analysis (EDX) were applied to confirm the presence of heteroatoms that were not present in the parent CNTs. EELS ratio mapping, used in conjunction with bright-field TEM imaging, is an extremely powerful tool for examining functionalized nanotubes and other composites because it provides a means of showing the spatial arrangement of individual elements in a sample. This characterization approach provides clear evidence of functional group incorporation onto the CNT. Subsequent atom mapping along the vicinity of the tube structure also allowed us to illustrate the three dimensional distribution of the heteroatoms along the CNT surface. Other elemental analysis techniques can confirm and possibly quantify the presence of a particular element, but fail to illustrate its spatial distribution in a material. In this study, the presence of nitrogen and sulfur atoms along the surface of a nanotube have been confirmed and shown to be uniform by means of TEM and EELS. EDX plots have been investigated as an additional measure of functionalization.