Imaging of lipids in cultured mammalian neurons by matrix assisted laser/desorption ionization and secondary ion mass spectrometry

Imaging mass spectrometry (IMS) provides a novel opportunity for visualization of molecular ion distribution. Currently, there are two major ionization techniques, matrix-assisted laser desorption/ionization (MALDI) and secondary ion mass spectrometry (SIMS) are widely used for imaging of biomolecules in tissue samples. MALDI and SIMS-based IMS have the following features; measurable mass ranges are wide and small, and the spatial resolutions are low and high, respectively. To the best of our knowledge, this is a first report to identify the lipids in cultured mammalian neurons by MALDI-IMS. Further, those neurons were analyzed with SIMS-IMS in order to compare the distribution pattern of lipids and other derived fragments. The parameters which influence the identification of lipids in cultured neurons were optimized in order to get an optimum detection of lipid molecules. The combined spatial data of MALDI and SIMS supported the idea that the signals of small molecules such as phosphatidylcholine head groups and fatty acids (detected in SIMS) are derived from the intact lipids (detected in MALDI-IMS).