Gold-Enhanced Biomolecular Surface Imaging of Cells and Tissue by SIMS and MALDI Mass Spectrometry

Abstract

Surface metallization by plasma coating enhances desorption/ionization of membrane components such as lipids and sterols in imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) of tissues and cells. High-resolution images of cholesterol and other membrane components were obtained for neuroblastoma cells and revealed subcellular details (resolving power 1.5 µm). Alternatively, in matrix-enhanced SIMS, 2,5-dihydroxybenzoic acid electrosprayed on neuroblastoma cells allowed intact molecular ion imaging of phosphatidylcholine and sphingomyelin at the cellular level. Gold deposition on top of matrix-coated rat brain tissue sections strongly enhanced image quality and signal intensity in stigmatic matrixassisted laser desorption/ionization imaging mass spectrometry. High-quality total ion count images were acquired, and the neuropeptide vasopressin was localized in the rat brain tissue section at the hypothalamic area around the third ventricle. Although the mechanism of signal enhancement by gold deposition is under debate, the results we have obtained for cells and tissue sections illustrate the potential of this sample preparation technique for biomolecular surface imaging by mass spectrometry.Unraveling the spatial distribution of cellular membrane components is an important research topic in current molecular cell biology. Understanding the behavior and function of the major constituents of these membranes, i.e., lipids and sterols, has been hampered by methodological limitations, despite their relatively simple structures. Most of the current knowledge on lipid localization has been obtained using fluorescence imaging techniques.

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

“…Recently, imaging mass spectrometry (IMS) has been recognized as a proteomic tool for in situ spatial analysis of (diseased) tissue [9,10]. Matrixassisted laser desorption/ionization (MALDI) MS has been shown to be able to determine the localization of native biomolecular components like proteins and peptides in tissue [11][12][13][14][15]. Often, the data includes several unknown species with a spatial distribution that indicates it is associated with a disease or biochemicallyaltered region of the tissue.…”

“…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].…”

In situ temperature-time effect on MetA-S-SIMS

“…The recent MetA-S-SIMS methodology is based on the deposition of a nm-thick gold or silver layer on the sample via evaporation or sputtering [8 -10]; a variant uses metal nanoparticle deposition [11]. The method has been successfully applied in several fields ranging from biological and polymer samples to paper research [12][13][14][15][16].In contrast to the use of MALDI-matrices or monolayers on noble metal substrates, MetA-S-SIMS does not require dissolution of the sample. Moreover, the metal layer facilitates charge compensation for thick insulating samples, and often electron flooding and the associated risk of sample damage [17] can be avoided completely [8].…”

“…Problems arise with the detection of components with molecular weight ϾkDa [8]. Expectedly, the ion yield enhancement not only depends on the analyte under study [16] and the applied metal [10,18] but also on the specific sample in which it occurs. Examples hereof include the suppression of the Ca ϩ detection in paper fibers [13], different ion yield enhancement factors for positive and negative ions from the same analyte [10].…”

“…The recent MetA-S-SIMS methodology is based on the deposition of a nm-thick gold or silver layer on the sample via evaporation or sputtering [8 -10]; a variant uses metal nanoparticle deposition [11]. The method has been successfully applied in several fields ranging from biological and polymer samples to paper research [12][13][14][15][16].…”