Abstract
The increasing use of nanoparticles (NP) in commercial products requires elaborated techniques to detect NP in the tissue of exposed organisms. However, due to the low amount of material, the detection and exact localization of NP within tissue sections is demanding. In this respect, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Ion Beam Microscopy (IBM) are promising techniques, because they both offer sub-micron lateral resolutions along with high sensitivities. Here, we compare the performance of the non-material-consumptive IBM and material-consumptive ToF-SIMS for the detection of ZrO2 NP (primary size 9–10 nm) in rat lung tissue. Unfixed or methanol-fixed air-dried cryo-sections were subjected to IBM using proton beam scanning or to three-dimensional ToF-SIMS (3D ToF-SIMS) using either oxygen or argon gas cluster ion beams for complete sample sputtering. Some sample sites were analyzed first by IBM and subsequently by 3D ToF-SIMS, to compare results from exactly the same site. Both techniques revealed that ZrO2 NP particles occurred mostly agglomerated in phagocytic cells with only small quantities being associated to the lung epithelium, with Zr, S, and P colocalized within the same biological structures. However, while IBM provided quantitative information on element distribution, 3D ToF-SIMS delivered a higher lateral resolution and a lower limit of detection under these conditions. We, therefore, conclude that 3D ToF-SIMS, although not yet a quantitative technique, is a highly valuable tool for the detection of NP in biological tissue.
Highlights
The detection of nanoparticles (NP) in tissue sections is an important prerequisite to determine potential risks for human health upon nanoparticle exposition
particle-induced X-ray emission (PIXE) images of a ZrO2 containing tissue section three days post-instillation are shown in Figure 1a where the signal distribution of phosphorus, sulfur, and zirconium is presented
It is of toxicological relevance that with both techniques, ZrO2 NP occurred in the lung as agglomerates, most probably in phagocytic cells, whereas no or negligible small quantities were associated with the lung epithelium
Summary
The detection of nanoparticles (NP) in tissue sections is an important prerequisite to determine potential risks for human health upon nanoparticle exposition. Due to their small sizes and low quantities the unambiguous detection and localization of NP is a demanding task. Secondary Ion Mass Spectrometry (ToF-SIMS) shows a high potential to detect a great variety of NP composed of inorganic materials along with the organic and inorganic composition of tissue thin sections. Due to small masses of NP signal intensities are low and an unambiguous identification is challenging. A second high resolution technique validating the identification and signal distribution of the ToF-SIMS results is desirable to prove the correct interpretation of the ToF-SIMS results at this stage of ToF-SIMS method development
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