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We report on the effect of treating tissue sections by washing with volatile buffers at different pHs prior to negative ion mode lipid imaging.
The results show that washing with ammonium formate, pH 6. Major lipid species measured were glycerophosphoinositols, glycerophosphates, glycerolphosphoglycerols, glycerophosphoethanolamines, glycerophospho-serines, sulfatides, and gangliosides. Ion images from adult mouse brain sections that compare washed and unwashed sections are presented and show up to fivefold increases in ion intensity for washed tissue. The sample preparation protocol has been found to be applicable across numerous organ types and significantly expands the number of lipid species detectable by imaging mass spectrometry at high spatial resolution.
Lipids are essential components of all tissues as constituents of the cell membrane and participate in cellular functions ranging from modulation of membrane protein signaling, signal transduction, cell motility and adhesion, and apoptosis. In recent years, matrix-assisted laser desorption ionization MALDI imaging mass spectrometry IMS has emerged as a powerful tool for detecting the spatial localization of lipids in relation to disease states or developmental biology investigations.
Sample preparation is critical for achieving sensitive, reproducible and high spatial resolution images using IMS. Ionic matrices overcome this problem and the use of 2,5-DHA coupled with aniline has allowed improvements in peak detection for negative ion mode imaging. In this work we have investigated sample preparation protocols to enhance lipid detection in the negative ion mode. Washing the tissue with ammonium formate or ammonium acetate significantly improves sensitivity for negative ion mode lipid imaging.
