Introduction
© 2006 IOP
There are mixed reports on the toxic and non-toxic effects of carbon nanotubes in living systems. In a departure from most other findings, researchers at the Chinese Academy of Sciences now show that a solution of multiwalled carbon nanotubes (MWNT) can stimulate the growth of a single-celled organism (Tetrahymena pyriformis). This freshwater protozoan is commonly used in laboratory toxicological research and health-risk assessments.
Ying Zhu and colleagues1 incubated the protozoan with MWNT solutions of different concentrations for up to 48 hours. In a yeast-extract culture medium, the MWNTs stimulated growth of the protozoan by threefold in a concentration-dependent manner. When the yeast medium was replaced with filtered pond water, MWNTs inhibited the growth of the protozoans. Atomic force microsope images and thermogravimetric analysis revealed the formation of conjugates between the nanotubes and peptone — a major food component in the yeast extract. Based on imaging of peptone labelled with a fluorescent tag, Zhu and colleagues suggest that the MWNTs serve as an efficient carrier of this foodstuff into the protozoans, and thereby stimulate their growth.
This work provides new insights into the importance of culture-media components in understanding how carbon nanotubes may affect living systems.