Wissenschaftliche Artikel der BAM
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Currently established and projected regulatory frameworks require the classification of materials (whether nano or non-nano) as specified by respective definitions, most of which are based on the size of the constituent particles. This brings up the question if currently available techniques for particle size determination are capable of reliably classifying materials that potentially fall under these definitions.
In this study, a wide variety of characterisation techniques, including counting, fractionating, and spectroscopic techniques, has been applied to the same set of materials under harmonised conditions.
The selected materials comprised well-defined Quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity. As a result, each technique could be evaluated with respect to the determination of the number-weighted median size. Recommendations on the most appropriate and efficient use of techniques for different types of material are given.
Titanium dioxide (TiO₂) nanoparticles (NPs) are one of the main sources of the nanoparticulate matter to which humans are directly exposed and several studies have demonstrated their potential toxic effects. The in vivo detailed spatial distribution of TiO₂ NPs is investigated herein for the first time, using a 2D chemical imaging analysis based on confocal Raman spectroscopy. The invertebrate nematode C. elegans was employed as a prototypical model of living organisms. Rod, bipyramidal and quasispherical engineered TiO₂ NPs with different primary particle sizes and agglomeration states were prepared, characterized and then administered to nematodes. Exploiting the typical fingerprint of TiO₂ in the Raman spectrum, we monitored the biodistribution of NPs inside the worm using a non-invasive, label-free method. The high spatial resolution chemical imaging and the specificity of the Raman technique in the localization of TiO₂ NPs helped in the design of behavioral C. elegans studies aimed at elucidating the relationship among the size, shape, and agglomeration state of NPs and their ability to induce specific toxic effects. Rod-shaped NPs were the most toxic, greatly impairing pharyngeal function, reproduction and larval growth; this indicates that the rod shape, more than the bipyramidal and spherical shapes, enables NPs to interact with biological systems. These findings indicate that this Raman-nematode combined approach represents a step forward in the field of detection of NPs in living organisms, and being rapid and inexpensive enough, it can be applied as the first screening for the ability of NPs to biodistribute and exert toxicological properties in vivo.
Advances in scanning electron microscopy (SEM) enable the high-resolution imaging of single nanoparticles (NPs) with sizes well below 10 nm. The SEM analysis in transmission mode (T-SEM) of NPs on thin film supports has many benefits when compared to the analysis of NPs on bulk substrates. The enhanced material (mass – thickness) contrast of the T-SEM imaging mode is well suited for in-depth and, particularly valuable, to very accurate, traceable, lateral dimensional measurements of NPs. Compared to samples prepared on bulk substrates, T-SEM with energy dispersive X-ray spectroscopy (EDS) achieves a drastically improved spatial resolution of the emitted X-rays. The poor signal-to-noise ratio of the X-ray spectra emitted by a single nanoparticle (NP) can be improved by the use of high-sensitivity (high collection solid angle) silicon drift (SDD), energy-dispersive X-ray spectrometers (EDS). The EDS spectral imaging of a single NP with a spatial resolution below 10 nm has become possible. This is demonstrated by means of various examples of nanostructures. Advanced data processing of T-SEM/EDS results sets the stage for the automated classification of NPs by feature analysis. This method combines the detection of morphological structures of interest by image processing of T-SEM micrographs with the chemical classification by EDS.