Sebastiaan Van Nuffel oral presentation (OB1-Thu1-1-5)
Understanding MALDI through 3D ToF-SIMS Imaging
1 CNRS - ICSN, 1 avenue de la Terrasse, 91190 Gif-sur-Yvette, France
2 Université Paris-Sud, Rue du Belvédère, 91400 Orsay, France
3 Université de Montréal, Boulevard Edouard-Montpetit, H3T 1J4 Montreal, Canada
Imaging mass spectrometry (IMS) has become a powerful tool to characterise the spatial distribution of biomolecules in thin tissue sections. In the case of matrix-assisted laser desorption ionisation (MALDI) IMS, homogeneous matrix deposition is critical to produce high quality ion images and sublimation in particular has shown to be an excellent matrix deposition method for the imaging of phospholipids. Matrix deposition by sublimation is however a completely solvent-free system as opposed to more conventional spray methods . The analytes within the tissue section are therefore never resolubilised, which prevents the formation of matrix/analyte co-crystals presumed to be necessary for laser desorption ionisation. To understand the desorption-ionisation process after matrix deposition by sublimation, it is necessary to study the matrix-tissue interface prepared for MALDI IMS.
Here, liver tissue sections were first mounted on conductive indium tin oxide coated microscope slides and then 2,5-dihydroxybenzoic acid matrix was applied to the tissue by either spray or sublimation. Combined with atomic force microscopy measurements and advanced multivariate image analysis using principal component analysis , 3D Time-of-Flight (ToF) SIMS measurements in dual-beam mode allowed the spatial distribution of biomolecules in the matrix and tissue layers to be visualised with nanometric depth resolution .
Aside from major differences in surface morphology between the matrix layers generated by either sublimation or spray deposition, different 3D spatial distributions were observed for different biomolecules such as cholesterol, glycerides and phosphatidylcholines, suggesting analyte migration from the section to the matrix. These spatial distributions were also corroborated by successive MALDI MS laser ablation measurements.
Our conclusions are that after matrix deposition by sublimation, there is a privileged molecular migration from the tissue section to the matrix layer. Desorption is then induced by laser ablation and ionisation occurs by proton or cation exchange presumably in the gas phase.
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