Ms. Grace So Profile

Grace So

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Proceedings Article | 12 October 2005 Paper

Singlet oxygen production by amphiphilic C60 derivatives and its correlation to cell cytotoxicity in vitro

Grace So, Aliaksandr Karotki, Sarika Verma, Tanya Hauck, Brian Wilson, Kenneth Pritzker, Long Chiang

Proceedings Volume 5969, 59690D (2005) https://doi.org/10.1117/12.629268

KEYWORDS: Oxygen, Fullerenes, Photodynamic therapy, Luminescence, In vitro testing, Melanoma, Absorption, Cancer, Materials science, Molecules

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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)[60]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, [60]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.

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