Our research team at Oregon State University, led by Robert Tanguay, investigated size- and surface coating-dependent toxicity of AgNPs while also controlling particle agglomeration. We exposed embryonic zebrafish to AgNPs that were 20 and 110 nm in size coated with either polypyrrolidone (PVP) or citrate surface coatings. The zebrafish were placed in media of varying ionic strength: standard zebrafish embryo medium (EM, high ionic strength), 62.5 µM calcium chloride solution (CaCl2, low ionic strength) and ultrapure water (UP). The AgNPs were synthesized by nanoComposix (San Diego, CA) and have been selected by the Nanotechnology Health Implications Research (NCNHIR) Consortium to address the increasing health and safety concerns of AgNPs via an interdisciplinary programme.

Zebrafish embryos can develop quite normally in a broad range of ionic strength media ranging from high (EM) to low (CaCl2 and UP). To our surprise, we found that AgNPs suspended in UP and CaCl2 were more toxic to the zebrafish embryos than were the AgNP suspensions prepared in EM. The AgNPs suspended in lower ionic strength media remained stable and well dispersed and were more readily taken up the embryos. In contrast, the AgNPs suspended in higher ionic strength solutions rapidly agglomerated, which meant that they were less readily taken up. Our team also found that 20 nm sized AgNPs were more toxic than the 110 nm sized ones, and that the PVP coated AgNPs were more toxic than the citrate coated material for the same particle core size.

The amount of silver we found in the embryonic tissue correlated well with observed toxicity, but only for those solutions in which the AgNPs were well dispersed.

Our group's results provide a novel in vivo whole animal approach to evaluate the toxicity of engineered nanoparticles and we conclude that attempts to accurately identify nanoparticle hazard must take into consideration how the environment alters particle properties.

More details of the work can be found in the journal Nanotechnology.