Stable Colloidal Dispersions of C60 Fullerenes in Water: Evidence for Genotoxicity

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Abstract
Stable aqueous suspensions of colloidal C60 fullerenes free of toxic organic solvents were prepared by two methods: ethanol to water solvent exchange (EthOH/nC60 suspensions) and extended mixing in water (aqu/nC60 suspensions). The extended mixing method resulted in the formation of larger (d̄p ≈ 178 nm) and less negatively charged (ζ ≈ −13.5 mV) nC60 colloids than nC60 prepared by ethanol to water solvent exchange (d̄p ≈ 122 nm, ζ ≈ −31.6 mV). Genotoxicity of these suspensions was evaluated with respect to human lymphocytes using single-cell gel electrophoresis assay (Comet assay). The assay demonstrated genotoxicity for both types of suspensions with a strong correlation between the genotoxic response and nC60 concentration, and with genotoxicity observed at concentrations as low as 2.2 μg/L for aqu/nC60 and 4.2 μg/L for EtOH/nC60. The Olive tail moments (OTM) for these two concentrations were 1.54 ± 0.24 and 1.34 ± 0.07, respectively, which in comparison to the negative control OTM of 0.98 ± 0.17 is statistically different with a p value of at least 0.05. Aqu/nC60 suspensions elicited higher genotoxic response than EthOH/nC60 for the same nC60 concentration. The results represent the first genotoxicity data for colloidal fullerenes produced by simple mixing in water.