Imaging technique Secondary Ion Mass Spectrometry: Basic Principles and Applications in Toxicology
Jean-Nicolas AUDINOT (Luxembourg Institute of Science and Technology - LIST)
Abstract:
Owing in particular to its excellent sensitivity, Secondary Ion Mass Spectrometry (SIMS) constitutes an extremely powerful technique of surfaces analysis. SIMS is based upon the sputtering of a few atomic layers from the surface of a sample, induced by a ’primary ion’ bombardment. An energetic primary ion impact triggers a cascade of atomic collisions resulting in an erosion of atoms and molecules. Some of the ejected particles can be spontaneously ionized and are representative of the target area composition. In a SIMS instrument, these “secondary ions” are accelerated and separated in function of their mass/charge ratio (m/z) before detection and counting. Its main fields of application lie in the semi-conductor, glass, organic and composite materials and metallurgical industries. But, thanks to the latest instrumentals development, the emerging fields of applications for SIMS are biology, medicine and cosmetics.
The last generation of dynamic SIMS instrument, the NanoSIMS50, allows to focalize the beam down to 50 nm that allows to perform mass spectrometry imaging at the subcellular structures with excellent limit of detection. The main advantage of this technology is the ability to make direct observation of the distribution of any element (and all isotopes) occurring at the surface of a sample, without any specific labelling with a fluorescent or radioactive probe.
Nanotoxicology has revolutionized and rejuvenated particle toxicology. In order to understand how nanoparticles interact with cellular systems and potentially cause adverse effects, it is important to be able to detect and localize them within cells or organisms. Due to their small size, transmission electron microscopy (TEM) is an appropriate technique often used for visualizing NPs inside cells, since light microscopy fails to resolve them at the single particle level. However, the presence of other cellular and non-cellular nano-sized structures in TEM cell sections, which may resemble NPs in size, morphology and electron density, can hinder the precise intracellular identification of NPs. Therefore, elemental analysis is recommended to confirm the presence of NPs inside the cell. During these last years, we have shown that the use of the nanoscale SIMS technique is of interest as a complementary tool to monitor the penetration of nanoparticles in tissues, thus helping to explain their toxicological effects.
