C60-Fullerenes: detection of intracellular photoluminescence and lack of cytotoxic effects

Recent advances in materials science have fueled tremendous interest in numerous potential biomedical applications of various nanomaterials. For example, fullerene C60 molecules are unique for their multi-functional uses in materials science and optics [1-4], and are considered for a variety of biological applications (reviewed in [5]), such as imaging probes [6], antioxidants [7-9] and drug carriers (taxol) [10]. Our laboratory is interested in exploring whether novel multifunctional nanoparticles can be designed for cancer therapy and diagnosis. Realization of such a goal requires a better understanding of the interactions between nanoparticles and cells and it is important to determine whether or not the particles by themselves impact cell growth and differentiation. We have chosen C60 for initial studies because the established chemistries afford us the flexibility to couple various biologically interesting and relevant molecules.However, some undesirable properties of C60 present specific challenges. For example, due to its inherent hydrophobicity, C60 is poorly soluble and naturally forms large micron-sized clusters in aqueous media. Therefore, organic solvents are routinely used for solubilization of C60 [11] Consequently, cell biological studies with pristine C60 have been limited.Whereas chemical conjugation of C60 to various water soluble molecules improves the overall aqueous compatibility, pristine C60 is routinely dissolved in toluene [12,13], tetrahydrofuran (THF) [14] or other organic solvents, and then exchanged into water by extracting the organic phase with water. The resultant preparation is often referred to 'water soluble C60' which is typically of light yellow color and is estimated to contain a few hundred micrograms of C60/ml [15]. It has been suggested that the aqueous C60 is toxic to cultured cells and the toxic effects are due to peroxidation of lipids in cell membranes [16-19]. Various groups have reported that C60 (prepared using differe