Probing Nanoparticles with Laboratory-Based Grazing Incidence X-Ray Fluorescence Spectroscopy

Nanoparticles are materials where at least one dimension is below 100 nanometers. Increasing attention is also being given to environmental micro- and nanoplastics (MNPs), which are plastic particles smaller than five millimeters and one micrometer, respectively. Accurate characterization of these particles is important because their size, shape, and composition strongly influence their properties and functionality. However, their small size makes them challenging to analyse, while the carbon-based nature of MNPs limits the use of some techniques commonly applied to engineered nanomaterials. Since no single analytical technique can provide a complete characterization, complementary microscopic and spectroscopic techniques are often required. This PhD thesis investigated total reflection X-ray fluorescence (TXRF) and grazing incidence X-ray fluorescence (GIXRF) as non-destructive techniques for ultra-trace elemental analysis and the characterization of nanomaterials. A central part of the research was the development of GIMOXS (Grazing Incidence Modular Optics X-ray Spectrometer), a modular X-ray fluorescence spectrometer that enables both TXRF and GIXRF measurements. The instrument can analyse a wide range of nanomaterials, from metals to carbon-based systems. Its modular design allows different excitation energies and measurement geometries to be selected depending on the analytical requirements. An optimized detector, combined with a vacuum chamber and electron trap, enables the detection of low-energy characteristic X-rays. Very good detection limits were achieved for both low- and high-Z elements, demonstrating the potential of GIMOXS for ultra-trace analysis. The instrument was also able to characterize gold nanoparticles based on their particle size. The research further focused on improving sample preparation for combining TXRF and GIXRF with correlative microspectroscopic techniques. By modifying the reflector surface, hydrophobic and hydrophilic regions were created, which helped to control the location of the nanoparticles. Marangoni drying further improved the homogeneity of the nanoparticle distribution. The target elements carbon, scandium, and titanium were localized within the same spot, while titanium could be quantitatively determined under all experimental conditions. Finally, TXRF was evaluated for the analysis of metal-labelled nanoplastics with low metal loadings. The results showed that TXRF can quantify the metal loading in these particles and support their sensitive detection in exposure and toxicological studies. Such labelled nanoplastics can be used as more realistic test materials for investigating the behaviour and potential risks of nanoplastics. Overall, the research demonstrates that TXRF and GIXRF are valuable tools for nanomaterial characterization. Their low detection limits, flexible instrumentation, improved sample preparation, and broad elemental applicability create opportunities for future applications in the study of, among others, ultra-trace analysis, nanomaterials, micro- and nanoplastics, and nanoparticle exposure.