Elemental or molecular imaging of a surface corresponds to the direct visualization of the distribution of elements, their isotopes or molecules (endogenous or exogenous). Several techniques (bi- and tridimensional) allow the determination of the elemental or molecular composition of samples, such as X-ray fluorescence spectrometry, immunohistochemistry, tomography (PET, CT), autoradiography, magnetic resonance imaging (MRI), etc. However, with some of these techniques the number of elements or molecules that can be mapped simultaneously remains limited. Moreover, these techniques require the prior presence of a label or a contrast agent. Mass spectrometry imaging or MSI presents itself as an attractive alternative that does not require prior labeling to access the distribution, composition, chemical structure and quantity of a large number of elements or molecular species in a mixture, whether organic or inorganic, on a surface or in a volume, in a targeted manner or without a priori.

Its principle is as follows: irradiate a focused beam (laser for MALDI (Matrix-Assisted Laser Desorption/Ionization) or LA-ICP (Laser Ablation Inductively-Coupled Plasma), ions for SIMS (Secondary Ion Mass Spectrometry), or solvent for DESI (Desorption/Electrospray Ionization)) on the surface of a sample, inducing a phenomenon of desorption/ionization in the gas phase of the analytes. The ionized analytes are then transferred and separated according to their mass to charge ratio m/z in the analyzer. The beam scans a delimited area in which a mass spectrum will be generated for each pixel forming the acquired image. Finally, for a given m/z value, a density map of the detected ions can be constructed on which the signal intensity is represented by a color scale.

Mass spectrometry imaging has the potential to revolutionize our understanding of matter in many fields of application (biology, biomedical, lipidomics, metabolomics, proteomics, geology, astrophysics, heritage, surface analysis, etc.).

Even if the current trend is interdisciplinarity, there are currently two main communities at the national level: mainly physicists and geochemists for surface or deep analysis (SIMS), and mainly chemists / biologists for analysis in MALDI, LA-ICP and DESI. The objective of the GDR MSI is to federate these communities by creating the first national network in MSI, in order to learn to know each other by sharing expertise and experience, and to strengthen the visibility of the French community in the field of MSI at the European level.