Julian S. Taurozzi

Ultrasonic dispersion of nanoparticles for environmental, health and safety assessment – issues and recommendations

Abstract Studies designed to investigate the environmental or biological interactions of nanoscale materials frequently rely on the use of ultrasound (sonication) to prepare test suspensions. However, the inconsistent application of ultrasonic treatment across laboratories, and the lack of process standardization can lead to significant variability in suspension characteristics. At present, there is widespread recognition that sonication must be applied judiciously and reported in a consistent manner that is quantifiable and reproducible; current reporting practices generally lack these attributes. The objectives of the present work were to: (i) Survey potential sonication effects that can alter the physicochemical or biological properties of dispersed nanomaterials (within the context of toxicity testing) and discuss methods to mitigate these effects, (ii) propose a method for standardizing the measurement of sonication power, and (iii) offer a set of reporting guidelines to facilitate the reproducibility of studies involving engineered nanoparticle suspensions obtained via sonication.

A standardised approach for the dispersion of titanium dioxide nanoparticles in biological media

Abstract We describe a comprehensive optimisation study culminating in a standardised and validated approach for the preparation of titanium dioxide (TiO2) nanoparticle dispersions in relevant biological media. This study utilises a TiO2 reference nanomaterial based on a commercially available powder that has been widely examined in both acute and chronic toxicity studies. The dispersion approach as presented here satisfies four key harmonisation requirements not previously addressed: (1) method transferability, based in part on the use of a sonication energy calibration method that allows for power measurement and reporting in a device-independent manner; (2) optimisation of sonication parameters and thorough method validation in terms of particle size distribution, pH, isoelectric point, concentration range and batch variability; (3) minimisation of sonolysis side effects by elimination of organics during sonication and (4) characterisation of nanoparticle agglomeration under various dispersion conditions by use of laser diffraction spectrometry, an in situ size characterisation technique that provides advantages over other techniques more commonly employed within the context of nanotoxicology (e.g. dynamic light scattering). The described procedure yields monomodal, nanoscale, protein-stabilised nanoparticle dispersions in biological media that remain stable for at least 48 h (acute testing timeframe) under typical incubation conditions.

Hydrodynamic fractionation of finite size gold nanoparticle clusters.

We demonstrate a high-resolution in situ experimental method for performing simultaneous size classification and characterization of functional gold nanoparticle clusters (GNCs) based on asymmetric-flow field flow fractionation (AFFF). Field emission scanning electron microscopy, atomic force microscopy, multi-angle light scattering (MALS), and in situ ultraviolet-visible optical spectroscopy provide complementary data and imagery confirming the cluster state (e.g., dimer, trimer, tetramer), packing structure, and purity of fractionated populations. An orthogonal analysis of GNC size distributions is obtained using electrospray-differential mobility analysis (ES-DMA). We find a linear correlation between the normalized MALS intensity (measured during AFFF elution) and the corresponding number concentration (measured by ES-DMA), establishing the capacity for AFFF to quantify the absolute number concentration of GNCs. The results and corresponding methodology summarized here provide the proof of concept for general applications involving the formation, isolation, and in situ analysis of both functional and adventitious nanoparticle clusters of finite size.