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Measurement issues for evaluating and relating nanoparticles surface properties to bioaccessibility and health.

Stefaniak-AB; Day-GA; Hoover-MD
2nd International Symposium on Nanotechnology and Occupational Health, October 3-6, 2005, Minneapolis, Minnesota. Minneapolis, MN: University of Minnesota, 2005 Oct; :122
There is increasing evidence that particle surface area is better correlated with toxicity (e.g., inflammation) than particle mass for relatively insoluble ultrafine particles deposited in the lung. We are conducting an integrated evaluation of particle surface and bioaccessibility measurement methods for a range of ultrafine and fine particles of industrial and toxicological concern. Estimates of particle specific surface area (SSA) are made in two ways: 1) direct measurements such as by gas adsorption using the Brunauer, Emmett, and Teller (BET) method and 2) determinations from geometric relations with external particle dimensions. A smooth, compact spherical particle geometrical model for estimating particle surface area has also been used in conjunction with transmission or scanning electron microscopy (TEM or SEM) measurements of particle projected area diameter, x-ray diffraction (XRD) measurements of physical particle diameter, optical particle counter estimates of particle size distributions, and aerosol impactor measurements of particle aerodynamic size distributions. The accuracy of methods to estimate particle SSA using geometric relations has been found to depend upon the morphology regime of the material of interest. Particles with high surface roughness (e.g., attrited powders) will have higher SSA than predicted on the basis of their external dimensions. In addition, powders that are agglomerates of small primary particles can have SSA that is proportional to the dimensions of the primary particles rather than the dimensions of the agglomerate. In vitro measurements of the dissolution of well-characterized particles in simulated biological fluids (e.g., extracellular and phagolysosomal lung fluid) have shown that dissolution depends on both the SSA and the internal material structure of the particles. The following guidelines are provided for determining SSA of nanoparticles: if electron microscopy shows smooth spherical compact morphology, then a geometric model may give a reasonable estimate of SSA. If electron microscopy shows surface roughness, then attempts should be made to measure SSA directly. Direct measurement techniques should evaluate the influence of sample preparation (outgas temperature and method), instrument calibration (linearity of response over a range of SSAs), and sample analysis (choice of adsorbate gas) on determination of SSA.
Surface-properties; Toxins; Toxic-effects; Lung; Gas-adsorption; Microscopy; Aerosols; Particulates; In-vitro-studies; Sampling; Sampling-methods; Nanotechnology
Aleksandr B. Stefaniak, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA
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2nd International Symposium on Nanotechnology and Occupational Health, October 3-6, 2005, Minneapolis, Minnesota