Intrinsic biological property of colloidal fullerene nanoparticles (nC60): Lack of lethality after high dose exposure to human epidermal and bacterial cells

Colloidal fullerene nanoparticles (nC60) were reported to be toxic to fish brains, human cells and microorganisms, while new observations suggest that the observed toxicity may be due to tetrahydrofuran (THF) solvent or its oxidative by-products in nC60 preparations. Here, we report a novel method for preparing nC60 nanoparticles that does not use THF solvent, but provides nC60 with an average particle size of 43.8 nm and a yield approximately 100 times higher than the THF method. The prepared nC60 showed a similar antioxidant capacity compared to a water-soluble vitamin E analog. No mortality to human epidermal keratinocytes was observed at a concentration 170 times higher than the reported LC50 values for other human cell lines. No toxicity was observed to E. coli or B. subtilis at up to 342 μg/mL nC60 for 16 h, which was hundred times higher than the reported minimum inhibitory concentrations of nC60 prepared using THF method for these two bacteria. When E. coli was exposed to 85.5 μg/mL nC60 with daily passage for 4 days, the stationary phase populations at different passages were not statistically different (p = 0.05) from the control without nC60 nanoparticles. These results reveal that the intrinsic biological property of nC60 is non-toxic, confirming the prior non-toxic reports when using nC60 prepared with non-THF methods.