The contributions of metal impurities and tube structure to the toxicity of carbon nanotube materials

Carbon nanotubes (CNTs) are a class of materials that have stimulated a great deal of interest among researchers due to their unique chemical and electronic properties. However, the apparent toxicity of CNTs has raised concerns about their use in research and applications. Chunying Chen and Yuliang Zhao at the Chinese Academy of Sciences in Beijing and their co-workers have re-examined the safety profile of CNTs, highlighting the role that metallic impurities left over from nanotube synthesis play in their toxicity. The researchers found that these metallic particles readily leach out of the nanotubes, including into simulated biological fluids mimicking those found in the lung, stomach and intestines. Iron particles leached into acidic fluids caused particular safety concerns—electron-spin resonance analysis showed that leached iron particles were generating cytotoxic free radical species at levels much higher than the nanotubes themselves. Cell viability studies demonstrated a clear negative correlation between the amount of metal residue in the nanotube sample and the health of the cultured cells.

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