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

Singlet oxygen (1Δg) is a very efficient oxidizing agent that targets numerous molecules in living cells. We report a comprehensive in vitro study of 1Δg-generation in the presence of two fullerene-based water-soluble sensitizers, fullerol C60(OH)n and fullerene-core star-like polymer, C60 [>N-CH2CH2(OCH2CH2)2OCH3]6. Efficiencies of the photodynamic generation of 1Δg in the presence of C60-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 1Δg. Remarkably, the Youngʹs modulus values obtained for four different cell lines revealed a pronounced drop as a function of exposure to 1Δg. Thus, our ESR and AFM results bring the evidence that the multi-functionalized fullerene-based compounds are efficient 1Δg-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.