Dispersion stability of nanoparticles in ecotoxicological investigations: the need for adequate measurement tools |
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Authors: | Ratna Tantra Shingheng Jing Sivaraman K Pichaimuthu Nicholas Walker James Noble Vincent A Hackley |
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Institution: | (1) National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK;(2) School of Biosciences, University of Exeter, Geoffrey Pope Building, Exeter, EX4 4QD, UK;(3) National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899-8520, USA |
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Abstract: | One of the main challenges in nanoecotoxicological investigations is in the selection of the most suitable measurement methods
and protocols for nanoparticle characterisation. Several parameters have been identified as being important as they govern
nanotoxicological activity, with some parameters being better defined than others. For example, as a parameter, there is some
ambiguity as to how to measure dispersion stability in the context of ecotoxicological investigations; indeed, there is disagreement
over which are the best methods to measure nanoparticle dispersion stability. The purpose of this article is to use various
commercially available tools to measure dispersion stability and to understand the information given by each tool. In this
study, CeO2 was dispersed in two different types of media: de-ionised water and electrolyte-containing fish medium. The DLS mean particle
size of freshly dispersed sample in DI water was ~200 nm in diameter. A visual sedimentation experiment showed that nanoparticle
dispersion made in the fish medium was less stable compared to corresponding dispersion in de-ionised water. Stability of
these dispersions was monitored using various techniques, for a period of 3 days. Our findings have shown that dispersion
stability can be suitably assessed by monitoring: (a) surface charge, (b) sedimentation events and (c) presence of agglomerates,
through time. The majority of techniques employed here (zeta potential, particle size via DLS, fluorescence and UV–Vis spectroscopy
and SEM) were shown to provide useful, complementary information on dispersion stability. Nanoparticle Tracking Analysis (NTA)
provides useful, quantitative information on the concentration of nanoparticles in suspension, but is limited by its inability
to accurately track the motion of large agglomerates found in the fish medium. |
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