Interlaboratory comparison of nanoparticle size measurements between NMIJ and NIST using two different types of dynamic light scattering instruments.

The question of how to relate particle sizes measured using a fixed-angle dynamic light scattering (DLS) instrument with those measured using a multi-angle DLS instrument is addressed. A series of nearly monodisperse polystyrene latex (PSL) particles with nominal diameters of 100 nm, 70 nm, 50 nm, and 30 nm were measured using two different types of DLS instruments: one owned by the National Metrology Institute of Japan (NMIJ) of the multi-angle type and the other owned by the National Institute of Standards and Technology (NIST) of the fixed-angle type. The mean particle size of the PSL particles was measured using the multi-angle-type instrument at various scattering angles and at various concentrations of particle suspension. These data were used to establish the functional dependence of the measured particle size on the scattering angle and particle concentration through the least-squares fitting method. The established function was then used to predict the mean particle sizes that would have been obtained if the same scattering angle and particle concentrations as those used at NIST had been selected at NMIJ. The mean particle sizes obtained at NIST and at NMIJ agreed quite well for all four PSL particle samples after compensating for the angle and concentration differences. The result of this study clearly demonstrates that consideration for the dependence of measured particle sizes on the scattering angle and particle concentration is crucial in intra-method comparisons of mean particle sizes obtained using DLS.

Nanoscale reference materials for environmental, health and safety measurements: needs, gaps and opportunities.

The authors critically reviewed published lists of nano-objects and their physico-chemical properties deemed important for risk assessment and discussed metrological challenges associated with the development of nanoscale reference materials (RMs). Five lists were identified that contained 25 (classes of) nano-objects; only four (gold, silicon dioxide, silver, titanium dioxide) appeared on all lists. Twenty-three properties were identified for characterisation; only (specific) surface area appeared on all lists. The key themes that emerged from this review were: 1) various groups have prioritised nano-objects for development as "candidate RMs" with limited consensus; 2) a lack of harmonised terminology hinders accurate description of many nano-object properties; 3) many properties identified for characterisation are ill-defined or qualitative and hence are not metrologically traceable; 4) standardised protocols are critically needed for characterisation of nano-objects as delivered in relevant media and as administered to toxicological models; 5) the measurement processes being used to characterise a nano-object must be understood because instruments may measure a given sample in a different way; 6) appropriate RMs should be used for both accurate instrument calibration and for more general testing purposes (e.g., protocol validation); 7) there is a need to clarify that where RMs are not available, if "(representative) test materials" that lack reference or certified values may be useful for toxicology testing and 8) there is a need for consensus building within the nanotechnology and environmental, health and safety communities to prioritise RM needs and better define the required properties and (physical or chemical) forms of the candidate materials.

Development and evaluation of an aerosol generation and supplying system for inhalation experiments of manufactured nanoparticles.

Risk assessment of nanoparticles by inhalation experiments is of great importance since inhalation is considered the most significant route of exposure to nanoparticles suspended in air. However, there have been few inhalation experiments using manufactured nanoparticles, mainly because of the difficulty in stably dispersing the nanoparticles in air for a long period of time. In this study, we report for the first time the development of a rational system for stably and continuously dispersing and supplying manufactured nanoparticles for inhalation experiments. The system was developed using a spray-drying technique, in which a nebulizer was used to atomize nickel oxide (NiO) and fullerene (C60) nanoparticle suspensions, and the resulting droplets were dried to generate aerosol nanoparticles. The size, concentration and morphology of the aerosol particles were evaluated by in-line measurements using an aerosol measuring device and off-line measurements based on the collection of the aerosol particles. After examining the effects of the conditions for the suspensions and the aerosol generation, we were able to obtain NiO and C60 aerosol nanoparticles with average diameters of 53-64 and 88-98 nm, respectively. By feeding these aerosols into a whole-body exposure chamber for rats, a stable supply of the aerosol nanoparticles could be achieved for long hourly durations (6 h per day) as well as for long terms (5 days per week for 4 weeks).