Arnoud Prop oral presentation (OB1-Thu1-1-4)
A multimodal approach to depth profiling MALDI matrix layers applied by wet and dry application methods
M4I division of Mass Spectrometry Imaging, Maastricht University, Universiteitssingel 50, 6229ER Maastricht, Netherlands
Matrix- Assisted laser desorption Ionization (MALDI) as the most widely used MSI technique has gained popularity over the years in biomedical research. In order to ionize the molecules tissue sections or analytes of interest must be covered with laser-absorbing organic compound or as now referred to as MALDI matrix. A wide range of MALDI matrix application techniques are available, with a huge disparity in the results. Fundamentals on the extraction mechanisms of analytes into the matrix are not yet fully understood. With the use of depth profiling TOF-SIMS analysis we introduce a novel method to study the distribution of analytes in the matrix crystals and the extraction efficiency of different matrix application methods.
Silicon wafers were sprayed with a mix of lipid standards (cholesterol, a PC and a ceramide). For on-tissue analysis, mouse brain tissue was flash frozen and 12 µm section were cut and thaw mounted on ITO slides. CHCA was applied to by spraying (TM-sprayer, HTX technologies) and by sublimation using a homebuilt sublimation device (IDEE, Maastricht University). The samples were analyzed using a PHI (Physical Electronics, MO, USA) NanoTOF II TOF-SIMS fitted with a 30 kV Bi LMIG for pulsed analysis and both a 20 kV Ar1500+ GCIB and a 20 kV C60+ for DC sputtering.
Different components in the layer could be distinguished and visualized in a 3D model of the depth profile from the matrix covered standards. Lipids were distributed homogenously through the sprayed CHCA layer. Sublimation experiments show a selective extraction of lipids into the matrix layer; cholesterol was fully extracted while the PC and ceramide show limited extraction.
Secondly, CHCA applied to tissue was analyzed. Depth profiles of the sublimed matrix layer show an enhanced extraction from tissue of certain lipids concentrated to the upper layer of crystal coating. Depth profiles of the sprayed CHCA stack show an increased number of analytes extracted in a homogeneous fashion.