In vitro assay of singlet oxygen generation in the presence of water-soluble derivatives of C60

Singlet oxygen ((1)Delta(g)) is a very efficient oxidizing agent that targets numerous molecules in living cells. We report a comprehensive in vitro study of (1)Delta(g)-generation in the presence of two fullerene-based water-soluble sensitizers, fullerol C-60(OH)(n) and fullerene-core star-like polymer, C-60 [>N-CH2CH2(OCH2CH2)(2)OCH3](6). Efficiencies of the photodynamic generation of (1)Delta(g) in the presence Of C-60-derivatives and a reference sensitizer, the amino acid protoporphyrin IX-derivative, PP(Ala)(2)(Arg)(2), were measured using electron spin resonance (ESR). Subsequently, atomic force microscopy (AFM) experiments were performed to measure the local elastic properties of living and glutaraldehyde-fixed cells exposed to the toxic action of (1)Delta(G). Remarkably, the Young's modulus values obtained for four different cell lines revealed a pronounced drop as a function of exposure to (1)Delta(G) Thus, our ESR and AFM results bring the evidence that the multi-functionalized fullerene-based compounds are efficient (1)Delta(g)-generators in aqueous media and might be implemented as oxidizing agents in biological systems. Moreover, we also show that AFM can be used as a sensitive tool for detecting early changes occurring to the subcellular structures under exposure to the oxidative stress. (C) 2004 Elsevier Ltd. All rights reserved.