Paramecium as a bioassay system for elucidation of cytotoxicity and biocompatibility of nanoparticles: effects of carbon nanofibers on proliferation and survival

Abstract

Carbon nanofibers (CNF), composed of carbon nanotubes, are a recent technological advance with wide applications in nano-engineering fields including biotechnology and biomedicine. However, little is known about the environmental effects of CNF, or their potential danger to human health. To elucidate the safety of CNF, we examined the cytotoxicity of CNF in Paramecium. In this study we considered the cytotoxicity effect of CNF in two categories of cellular properties, cell survival and cell proliferation. We show that CNF are ingested and concentrated as efficiently as nutritive bacteria by paramecia, revealing a means by which CNF could be introduced into the food webs of aquatic ecosystems. Clear cytotoxicity of CNF was detected in survival tests by extracellular application at extremely high concentration (up to 50 mg/ml) in culture medium containing nutritive bacteria. Contrary to this effect, no cytotoxicity was detected in survival tests using the modified Dryl's solution (K-DS) that is used as a buffered saline of culture medium. The cytotoxicity of CNF suggests an interaction between CNF and the components in culture medium or their metabolic products produced by digestion of components in culture medium. Another cytotoxicity effect was detected in proliferative activity test at lower concentrations of CNF (up to 500 µg/ml). The cytotoxicity on proliferative activity was reversible and recovery occurred within 24 hours after removal of CNF. Our results suggest that Paramecium is useful for a bioassay of nanoparticle cytotoxicity. For the elucidation of safety of CNF we have to examine both the optimum concentration of CNF and co-existing biomaterials in a test solution. In conclusion, CNF have a high potential for cytological and biomedical application under precise control of concentration.