Small 10.1002/smll.201000989 (2010)

Several studies in cells and different organisms have shown that size, shape, surface chemistry and surface area of nanomaterials can affect the way they interact with biological and environmental systems. However, the results from these studies remain inconclusive and, in some cases, difficult to interpret because the toxic effects may not be related to the nanoparticles themselves. Using well-defined gold nanoparticles that do not aggregate or dissociate into ions, Vincent Rotello and co-workers at the University of Massachusetts now show that surface properties can affect the way fish take up and remove nanoparticles from their systems.

Rotello and colleagues synthesized positively charged, neutral, negatively charged and hydrophobic gold nanoparticles and exposed them to the freshwater Japanese medaka fish for 24, 72 and 120 hrs. Positively charged particles were taken up by the fish more readily than the neutral or negatively charged ones, and the three types of particle were found to accumulate mainly in the intestines. It is thought that the negatively charged mucus layer on the surfaces of the gills and intestines attracts the positively charged particles, whereas the accumulation of neutral and negatively charged particles may be mediated by positive ions such as calcium, magnesium and sodium. Hydrophobic particles killed the fish within 24 hrs and substantial amounts were found in the brain, gills, heart, liver and dorsal fin, suggesting entry into the circulatory system.

The study suggests that hydrophilic nanoparticle surfaces can prevent accumulation and facilitate their removal from the fish, whereas hydrophobic particles can distribute throughout the organs and cause mortality.