The same properties that make engineered nanoparticles attractive for numerous applications -- small as a virus, biologically and environmentally stabile, and water-soluble -- also cause concern about their long-term impacts on environmental health and safety (EHS)
One particular characteristic, the tendency for nanoparticles to clump together in solution, is of great interest because the size of these clusters may be key to whether or not they are toxic to human cells. Researchers at the National Institute of Standards and Technology (NIST) have demonstrated for the first time a method for producing nanoparticle clusters in a variety of controlled sizes that are stable over time so that their effects on cells can be studied properly.
In their tests, the NIST team made samples of gold, silver, cerium oxide and positively-charged polystyrene nanoparticles and suspended them separately in cell culture medium, allowing clumping to occur in each. They stopped the clumping by adding a protein, bovine serum albumin (BSA), to the mixtures. The longer the nanoparticles were allowed to clump together, the larger the size of the resulting cluster. For example, a range of clustering times using 23 nanometer silver nanoparticles produced a distribution of masses between 43 and 1,400 nanometers in diameter. Similar size distributions for the other three nanoparticle types were produced using this method.
The researchers learned that using the same "freezing times" -- the points at which BSA was added to halt the process -- yielded consistent size distributions for all four nanoparticle types. Additionally, all of the BSA-controlled dispersions remained stable for 2-3 days, which is sufficient for many toxicity studies.
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