Publication
The application of engineered nanoparticles (ENP) increased almost exponentially during the last decade. Next to carbon based ENP, metal based ENP are the next most commonly employed. Utilization of such particles for medical applications, remediation of toxic substances, consumer products, new materials, and numerous other fields has been reported already. Despite their extraordinary success and implementation, concerns have been raised about possible negative effects in humans and the environment. Once released, ENP are easily distributed via the atmosphere and the aquatic environment where an exposure to organisms can occur. To understand ENP release, life cycle (fate), and exposure as well as to evaluate their toxicological mechanisms, appropriate, media-specific (aerosols and dispersions) analytical methods are required. First, the development of a new set-up to determine ENP in aerosols is presented. For this purpose online (SMPS) and offline (electrostatic sampling on TEM grids) aerosol particle measurement techniques were combined. The aim was to study the release and fate of metallic ENP from commercial available spray products. Method development and verification was performed employing a well characterized aqueous Ag-NP spray product. The investigations have shown that the method offers the possibility to determine size, and element -specific nanoparticle release. Furthermore information about particle morphology and quantity could be obtained. It was revealed, that the release of nanoparticles strongly depends on the type of spray. Pump sprays did not show to produce airborne ENP in the aerosol, whereas propellant gas sprays released nanoparticles in substantial quantities. The release of nanoparticles was correlated with the droplet size distributions generated from the different spray types. Following method development, the setup was applied to determine ENP release of commercial available sprays, indicated to contain ENP. The obtained data was useful to model the consumer exposure of ENP from such products. Second, a set-up to determine ENP in dispersions was developed. For this purpose an asymmetric flow field flow fractionation (A4F) apparatus was coupled to an UV/Vis, light scattering- and inductively coupled plasma mass spectrometric (ICPMS) detector, simultaneously. In the beginning, method development and systematic investigations of prospects and limitations was performed employing well-characterized Au nanoparticles (Au-NP). The investigation revealed that A4F is a versatile separation technique for metallic ENP. In contrast, size determination with the A4F system, derived from the retention times of nanoparticles in the chromatogram, was erroneous. Unspecific interaction of ENP with the A4F channel membrane led to retention time shifts resulting in biased size information. For this reason, online dynamic light scattering (DLS) was employed and it offered a reliable determination of nanoparticle dimensions. Determination of nanoparticle concentration also proved to be to be problematic. Unspecific loss of nanoparticles in the A4F separation channel led to insufficient recovery prevented direct quantification of nanoparticles. To overcome this problem an alternative method was employed. With ICPMS after ultracentrifugation, quantification of the ionic and particulate -fraction of metallic ENP dispersions was possible. Validation of the set-up was performed with certified Au-NP reference materials obtained from NIST and results showed excellent agreement. Combining both of these new methods provided a comprehensive understanding of the metallic ENP systems. After method development with well defined nanoparticle systems, the set-up was tested for its applicability to "real world" samples. First, the characterization of commercial available, polydisperse, commercial Ag nanoparticle (Ag-NP) products was performed. The new developed set-up allowed obtaining an element specific, mass, and number size distribution. Furthermore, Ag-NP concentrations as well as the toxicological relevant ionic Ag concentration could be determined. Figures of merit compared to transmission electron microscopy (TEM) and batch-DLS results were in good agreement and the new method was advantageous in terms of analysis time and reliability. Furthermore the possibility to characterize SiO2 coated Au nanoparticles (Au@SiO2) was investigated. These particles are employed for Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS). It was shown that in terms of particle size characterization, the method provided excellent data. However, determination of Si concentrations to calculate the shell thickness of such particles was impeded by the poor A4F peak shape as well as the high Si background in ICPMS. In conclusion, both setups show great potential for the characterization of metallic ENP either in aerosols or dispersions, respectively.
Francesco Stellacci, Zekiye Pelin Güven, Giulia Rossi