Nina Ogrinc Potocnik oral presentation (PB2-Mon4-1-4)
Tissue imaging of intact biomolecules: from lipids towards de-novo peptide sequencing with ME-SIMS
1 Maastricht MultiModal Molecular Imaging Institute, Universiteitssingle 50, 6229 HX Maastricht, Netherlands
2 Pacific Northwest National Laboratory, Battelle Boulevard, WA 99354 Richland, United States
3 Physical Electronics, Lake Drive East, MN 55317 Chanhassen, United States
Matrix Enhanced Secondary Ion Mass Spectrometry (ME-SIMS) overcame one of the biggest disadvantages of SIMS analysis, the capability of imaging large molecules at high spatial resolution. With increased ionization efficiency and minimized fragmentation caused by the primary ion beam the method is ideal for detection of intact bimolecular species (1). In the past, the use of ME-SIMS was limited to standards and extracts due to distortion of spatial resolution and delocalization of analytes caused by robustness of matrix application techniques. In addition, the desorbed species lacked proper identification and separation from isobaric compounds. Now, new enabling technologies such as parallel MS/MS capabilities on the PHI nano-TOF system (2), C60 primary ion source fused with the FT-ICR (3) and new sample preparation techniques give an opportunity to revisit the potential of ME-SIMS and apply it to a number of different biological settings.
First, we imaged mammalian tissue sections that were subjected to a variety of different matrices via supplication using a home-built sublimation chamber. Matrix sublimation produces small, homogenous crystal sizes, without the need for solvents that delocalize molecular species. Increased ionization efficiency of intact lipid and metabolite species were studied in comparison to Matrix-Assisted Laser Desorption Ionization (MALDI). The same or consecutive sections were subsequently analyzed by FTICR-SIMS, to accurately identify the enhanced molecular species of interest, and by the PHI nano-TOF II for high lateral resolution images and confident identification of said species with tandem MS.
Second, de-novo peptide sequencing was performed on endogenous neuropeptides directly from a pituitary gland. Careful sample preparation and the capability of using a 1 Da mass isolation window of the precursor ion followed by a collision-induced dissociation (CID) at 1.5 keV in an activation cell with argon gas enables the molecules to be fragmented in a specific pattern. Neuropeptides up to m/z 2000 were detected and sequenced from the posterior lobe. Further on, we applied it for the characterization of tryptically digested peptides from a variety of tissue sections investigating the applicability to bottom-up proteomics
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