Higher sensitivity secondary ion mass spectrometry of biological molecules for high resolution, chemically specific imaging

Abstract

To expand the role of high spatial resolution secondary ion mass spectrometry (SIMS) in biological studies, numerous developments have been reported in recent years for enhancing the molecular ion yield of high mass molecules. These include both surface modification, including matrix-enhanced SIMS and metal-assisted SIMS, and polyatomic primary ions. Using rat brain tissue sections and a bismuth primary ion gun able to produce atomic and polyatomic primary ions, we report here how the sensitivity enhancements provided by these developments are additive. Combined surface modification and polyatomic primary ions provided Ϸ15.8 times more signal than using atomic primary ions on the raw sample, whereas surface modification and polyatomic primary ions yield Ϸ3.8 and Ϸ8.4 times more signal. This higher sensitivity is used to generate chemically specific images of higher mass biomolecules using a single molecular ion

Surface analysis of lipids by mass spectrometry: More than just imaging

“…Met-SIMS involves the coating of the sample with a thin layer of metal (~1 nm) such as gold or silver [172,173]. As no solvents are used, Met-SIMS provides enhanced biomolecular ion yields without delocalization.…”

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

“…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].…”