Obviously size matters for nanoparticles, or the world wouldn’t be making such a big deal of them. Size also matters when it comes to toxicity of nanoparticles. A recent study published in Advanced Materials (Length-Dependent Uptake of DNA-Wrapped Single-Walled Carbon Nanotubes) by Matthew Becker and others, emphasizes that size (such as length and diameter of particles) matters particularly when deciphering toxicity studies. One source of size variation suggests the authors is dispersion of single-walled carbon nanotubes (SWNT) used in toxicity testing.
According to the article:
“Given a constant dosage, differences in dispersion ranging from macroscopic aggregates to micrometer-scale clusters bundles of multiple nanotubes or individually dispersed nanotubes will dramatically affect the absolute size and amount of nanotube surface area to which the cells will be exposed.”
Surfactants are materials used to increase water solubility and in some cases dispersion of a material, and are commonly used in studies of nanoparticle toxcity. Becker’s group used DNA as a surfactant, because they noted,
“These dispersions, in the case of DNA, are even stable enough to allow for the separation of the dispersed material into well-defined subpopulations of the SWNTs.”
Using this method to test the toxicity of SWNTs of varying length to muscle cells, the authors concluded that, “The assays determined an approximate uptake threshold of approximately (189+17) nm. Indicating that nanotubes shorter than this are consumed and likely induce more toxicity.”
Though they note that identifying an upper threshold for toxicity of nanoparticles is nothing earth-shattering or new, they do suggest that such behavior is likely to be a “general phenomenon,” though the actual size threshold is likely to vary depending on the type of cell.
For more information check out: Length-Dependent Uptake of DNA-Wrapped Single-Walled Carbon Nanotubes, by Becker et al, Vol 19:939-945.