Subcellular imaging mass spectrometry of brain tissue

Abstract

Imaging mass spectrometry provides both chemical information and the spatial distribution of each analyte detected. Here it is demonstrated how imaging mass spectrometry of tissue at subcellular resolution can be achieved by combining the high spatial resolution of secondary ion mass spectrometry (SIMS) with the sample preparation protocols of matrix-assisted laser desorption/ionization (MALDI). Despite mechanistic differences and sampling 10(5) times less material, matrix-enhanced (ME)-SIMS of tissue samples yields similar results to MALDI (up to m/z 2500), in agreement with previous studies on standard compounds. In this regard ME-SIMS represents an attractive alternative to polyatomic primary ions for increasing the molecular ion yield. ME-SIMS of whole organs and thin sections of the cerebral ganglia of Lymnaea stagnalis demonstrate the advantages of ME-SIMS for chemical imaging mass spectrometry. Subcellular distributions of cellular analytes are clearly obtained, and the matrix provides an in situ height map of the tissue, allowing the user to identify rapidly regions prone to topographical artifacts and to deconvolute topographical losses in mass resolution and signal-to-noise ratio.

Imaging of peptides in the rat brain using MALDI-FTICR mass spectrometry

“…Very high spatial resolution is obtained using SIMS (pixel size Ͻ1 m) [19], however its sensitivity rapidly decreases with increasing mass, making the technique less suited for protein analysis. Surface modification techniques such as metal assisted SIMS or matrix enhanced SIMS can be used to extend the useable mass range to small peptides and proteins [14,[21][22][23][24][25][26][27][28][29][30].…”

Automated, feature-based image alignment for high-resolution imaging mass spectrometry of large biological samples

“…Any such variation (including a localized protrusion) can be readily identified by calculating the variation of an ion's mass with position (a so-called height map) [4,15]. This height map can be used to correct the mass measurements but cannot remove any ionization artifacts.…”

“…This is accomplished by rastering the sample, followed by a high-resolution scan of selected areas. This approach of combining ionization beam and sample stage rastering has been developed further to provide high-resolution imaging of large areas: in mosaic mode imaging the sample is divided into a mosaic of small areas (termed tiles) with the sample stage raster; each tile is then analyzed with high spatial resolution using ion beam rastering and the results are combined to provide the final, complete (mosaic) dataset [2][3][4]10].Mosaic mode image (high-resolution imaging of large areas) has been limited by the user-intensive nature of data analysis. The accuracy of sample stages capable of moving through large areas (e.g., 5 ϫ 5 cm) are often significantly less than the resolution of the SIMS imaging mass spectrometry experiment, for example, 5 and 0.2 m, respectively.…”

“…Recent advances in both ionization efficiency (polyatomic primary ions) and sample preparation have significantly improved the sensitivity for detecting intact, medium-sized molecular ions (Ͻ1000 Da) from tissues and cells [1][2][3][4][5][6]. High-resolution images of small peptides, lipids, cholesterol, vitamins, and pharmaceuticals have all been reported, and through the use of large polyatomic primary ions three-dimensional (3D) molecular imaging results are beginning to appear [7][8][9].…”

“…This is accomplished by rastering the sample, followed by a high-resolution scan of selected areas. This approach of combining ionization beam and sample stage rastering has been developed further to provide high-resolution imaging of large areas: in mosaic mode imaging the sample is divided into a mosaic of small areas (termed tiles) with the sample stage raster; each tile is then analyzed with high spatial resolution using ion beam rastering and the results are combined to provide the final, complete (mosaic) dataset [2][3][4]10].…”