Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids
ReviewLipid imaging with time-of-flight secondary ion mass spectrometry (ToF-SIMS)☆
Highlights
► Recent instrumental and sample preparation methodologicaladvances achieved in ToF- SIMS, as well as the successful applications of these advances in the detection of lipid from biological material are described in this review. ► The performance of ToF-SIMS in the analysis of lipids is compared to similar imaging techniques, including MALDI, DESI and dynamic SIMS. ► Various lipid species detected and identified using ToF-SIMS are compiled in tables and organized using the lipid classification system established by the Lipid MAPS consortium. ► State-of-the-art ToF-SIMS instruments, the J105 3D Chemical Imager and C60+-QSTAR, are described and their potential application in the field of lipidomics is discussed.
Introduction
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a surface analysis technique capable of producing high resolution chemical images and is a well-suited platform for the analysis of lipids directly from the surface of biological materials. With this technique the sample surface is bombarded with a focused high energy primary ion beam (1–40 keV), causing desorption of secondary ions. A mass spectrometry-based image is then produced by rastering the ion beam across the sample surface. The high lateral resolution and sensitivity attributed to SIMS allows for the detection of lipid molecules at the nanometer scale and at attomolar concentrations [1], [2]. The ToF detection scheme also offers parallel detection of multiple lipid species, ideal for the analysis of complex biological samples.
In addition to ToF-SIMS, matrix-assisted laser desorption ionization (MALDI) and desorption electrospray ionization (DESI) are imaging mass spectrometry (IMS) techniques utilized in the analysis of biological materials. Like ToF-SIMS, MALDI [3], [4], [5], [6] and DESI [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18] have proven to be particularly successful in the detection and analysis of lipids. The pitfalls, advantages and successful applications of each technique are reviewed in detail elsewhere and are only briefly discussed in this review [19], [20], [21], [22], [23], [24]. In terms of spatial resolution, MALDI and DESI are capable of resolving features as small as 20 μm and 100 μm, respectively. In many cases for tissue imaging, ToF-SIMS offers a complementary perspective to these alternative IMS techniques since the lateral resolution of ToF-SIMS can be below 1 micron (Fig. 1). Various efforts have been made to improve the spatial resolution of MALDI imaging, including oversampling [25], laser modulation [26] (i.e. smart beam technology) and solvent-free sublimation matrix application techniques [27]. Despite these efforts, the technique has not achieved the spatial resolution of ToF-SIMS.
In terms of chemical specificity, however, MALDI and DESI techniques cover a broader range of biomolecules—including proteins, peptides and nucleotides. The ability to detect proteins and peptides directly correlates to the techniques’ success in bio-analytical chemistry and biomedicine. Currently, MALDI is the prominent IMS method utilized in medical and bioanalytical research with applications in clinical diagnostics [28], [29], [30], [31], [32], pharmaceutical research [33] and biomarker discovery [34]. Although proteins represent only 20 % (by weight) of a cell, proteomics has traditionally been at the heart of biomedical investigations. However, a recent trend among system biologists from proteomics to lipidomics [35] raises the question: Will SIMS, with its higher spatial resolution and equivalent sensitivity to lipids, be more readily accepted into the biochemical and biomedical community?
Section snippets
Sample preparation
Well-developed sample preparation techniques are crucial for successful ToF-SIMS investigations. The major challenge in proper sample preparation is interfacing the biological samples with biologically unfavorable vacuum conditions while preserving chemical and spatial integrity. A variety of protocols for both tissue and cellular samples have been established; the most frequently employed procedures are reviewed below. In general these techniques contain steps in which the tissue samples are
Modes of operation and instrumentation
In the field of SIMS there are two fundamental modes of operation based on the primary ion fluence termed static and dynamic. Static SIMS represents acquisitions with primary ion fluencies below 1012 ions/cm2. In this mode, less than 1 % of surface molecules are perturbed, as a result, the probability of impacting the same area twice is extremely low. Intact molecular ion species are typically observed under static conditions; as a result this mode of operation is often used in lipid
Tissue imaging experiments
Rat brain sections, a well-established model system for tissue-based IMS studies, have been employed to illustrate the potential of ToF-SIMS imaging for lipid-based investigations. Sjovall and co-workers were the first to report a number of sulfoglycosphingolipids (sulfatides) and cholesterol in the white matter of a rat brain as well as glycerophospholipids molecules, specifically glycerphosphocholines (GPCho) and glycerophosphoinositols (GPIns), in the gray matter of a rat brain section using
Single cell imaging experiments
Currently, ToF-SIMS is the only mass spectrometry imaging technique capable of characterizing the lateral distribution of lipids on a cellular and subcellular level [82], [83]. The first ToF-SIMS images of cells were obtained using atomic projectile sources. These high resolution images of isolated cells provided useful elemental distributions and isotopic information. However, the extensive molecular fragmentation from the energetic impact and the resulting chemical damage accumulation
Sensitivity issues
At the cellular level, instrument performance is greatly limited by sensitivity. The trade-off between high resolution and secondary ion yields has often limited the detection of intact phospholipids at the cellular level. As smaller and smaller regions are probed for high lateral resolution, the number of molecules available to be desorbed, ionized and detected is reduced. The production of secondary ions is often the limiting factor in sensitivity. The search for methods to enhance ionization
Dynamic SIMS
Although this review mainly focuses on studies employing static SIMS, dynamic SIMS has also been successfully employed in lipid studies. As previously mentioned, this method employs a continuous primary ion beams that produces mostly atomic and diatomic species. Despite the highly destructive secondary ion generation process, this method is capable of achieving spatial resolution of at least 50 nm. In order to investigate lipid processes, halogen-based or stable isotopic tracers (13C, 14N or
Challenges associated with the SIMS analysis of lipids
The increased sensitivity to intact lipid species afforded by the technical and methodological advances described above brings about new challenges in the analyses of lipids. For instance, the ability to properly identify lipid molecules from a complex mixture is crucial for in situ lipidomics-based investigation. In SIMS-based investigations, lipid assignments are typically based on standard reference spectra, mass accuracy of the molecular-ion peaks and previous knowledge of the sample's
Recent developments in instrumentation
Although many traditional ToF-SIMS instruments have been updated with cluster ion sources, their overall design and capabilities are still generally underdeveloped for the complex nature of biological-based applications. Currently, technical design flaws associated with traditional static ToF-SIMS instruments hinder the technique's ability to effectively and efficiently analyze lipids and other bio-molecules. For example, traditional ToF-SIMS instruments employ pulsed primary ion beams and
Conclusions
Since lipids play a significant role in basic cellular processes, it is important to study and understand these molecules. As illustrated here, ToF-SIMS is an emerging platform for lipid-based imaging studies. The technique been successfully applied to elucidating a number of biological quandaries and complex biological processes. Several recent achievements in both technology and methodology promise to further expand the impact of these studies.
Although these are important qualities associated
Acknowledgments
The authors would like to acknowledge the LipidMAPS Consortium (GM069338-07) for financial support. Also additional financial support from the National Institutes of Health (2R01 EB002016-18) and the National Science Foundation (# CHE-0908226) is appreciated.
References (111)
Cluster primary ion bombardment of organic materials
Appl. Surf. Sci.
(2004)- et al.
An update of MALDI-TOF mass spectrometry in lipid research
Prog. Lipid Res.
(2010) - et al.
Imaging of lipid species by MALDI mass spectrometry
J. Lipid Res.
(2009) - et al.
Mass spectrometric imaging of lipids using desorption electrospray ionization
Journal of Chromatography B-Analytical Technologies in the Biomedical and Life Sciences
(2009) - et al.
Desorption electrospray ionization imaging mass spectrometry of lipids in rat spinal cord
J. Am. Soc. Mass Spectrom.
(2010) - et al.
Development of capabilities for imaging mass spectrometry under ambient conditions with desorption electrospray ionization
Int. J. Mass Spectrom.
(2007) - et al.
Direct quantification of organic acids in aerosols by desorption electrospray ionization mass spectrometry
Atmos. Environ.
(2009) - et al.
Desorption electrospray ionization (DESI) mass spectrometry and tandem mass spectrometry (MS/MS) of phospholipids and sphingolipids: ionization, adduct formation, and fragmentation
J. Am. Soc. Mass Spectrom.
(2008) - et al.
Why don't biologists use SIMS? A critical evaluation of imaging MS
Appl. Surf. Sci.
(2006) - et al.
MALDI-MS imaging of features smaller than the size of the laser beam
J. Am. Soc. Mass Spectrom.
(2005)
Sublimation as a method of matrix application for mass spectrometric imaging
J. Am. Soc. Mass Spectrom.
MALDI MS imaging of amyloid
Amyloid, Prions, and Other Protein Aggregates, Pt B
Localization of cholesterol in rat cerebellum with imaging TOF-SIMS—effect of tissue preparation
Appl. Surf. Sci.
Challenges of biological sample preparation for SIMS imaging of elements and molecules at subcellular resolution
Appl. Surf. Sci.
Which is more important in bioimaging SIMS experiments—the sample preparation or the nature of the projectile?
Appl. Surf. Sci.
Analysis of surface particles by time-of-flight secondary ion mass spectrometry
Mater. Chem. Phys.
FAB mass-spectrometry of lipids
Prog. Lipid Res.
ToF-SIMS imaging with cluster ion beams
Appl. Surf. Sci.
Localization of lipids in freeze-dried mouse brain sections by imaging TOF-SIMS
Appl. Surf. Sci.
Distribution of cholesterol and galactosylceramide in rat cerebellar white matter
Biochimica Et Biophysica Acta-Molecular and Cell Biology of Lipids
Localization of cholesterol, phosphocholine and galactosylceramide in rat cerebellar cortex with imaging TOF-SIMS equipped with a bismuth cluster ion source
Biochimica Et Biophysica Acta-Molecular and Cell Biology of Lipids
High resolution imaging by organic secondary ion mass spectrometry
Trends Biotechnol.
Sulfatide with different fatty acids has unique distributions in cerebellum as imaged by time-of-flight secondary ion mass spectrometry
Biochimica Et Biophysica Acta-Molecular and Cell Biology of Lipids
Lipid imaging in the zebra finch brain with secondary ion mass spectrometry
Int. J. Mass Spectrom.
Attempts for molecular depth profiling directly on a rat brain tissue section using fullerene and bismuth cluster ion beams
Int. J. Mass Spectrom.
Bioimaging TOF-SIMS: localization of cholesterol in rat kidney sections
FEBS Lett.
Lipid mapping in human dystrophic muscle by cluster-time-of-flight secondary ion mass spectrometry imaging
J. Lipid Res.
Localization of lipids in the aortic wall with imaging TOF-SIMS
Biochimica Et Biophysica Acta-Molecular and Cell Biology of Lipids
Time-of-flight secondary ion mass spectrometry of fatty acids in rat retina
Appl. Surf. Sci.
Lipid imaging by gold cluster time-of-flight secondary ion mass spectrometry: application to Duchenne muscular dystrophy
J. Lipid Res.
MALDI-TOF and cluster-TOF-SIMS imaging of Fabry disease biomarkers
Int. J. Mass Spectrom.
Lipid mapping of colonic mucosa by cluster TOF-SIMS imaging and multivariate analysis in cftr knockout mice
J. Lipid Res.
Biological tissue imaging with a hybrid cluster SIMS quadrupole time-of-flight mass spectrometer
Appl. Surf. Sci.
Transport of C-13-oleate in adipocytes measured using multi imaging mass Spectrometry
J. Am. Soc. Mass Spectrom.
Spatially resolved detection of attomole quantities of organic molecules localized in picoliter vials using time-of-flight secondary ion mass spectrometry
Anal. Chem.
Imaging of lipids directly from brain tissue via matrix assisted laser desorption ionization Time-of-Flight Mass Spectrometry (MALDI TOF MS)
J. Neurochem.
Brain tissue lipidomics: Direct probing using matrix-assisted laser desorption/ionization mass spectrometry
AAPS J.
Analysis of triglycerides in food items by desorption electrospray ionization mass spectrometry
Rapid Commun. Mass Spectrom.
Imaging of lipids in atheroma by desorption electrospray ionization mass spectrometry
Analytical Chemistry
Desorption electrospray ionization mass spectrometry analysis of lipids after two-dimensional high-performance thin-layer chromatography partial separation
Analytical Chemistry
Tissue imaging at atmospheric pressure using desorption electrospray ionization (DESI) mass spectrometry
Angew. Chem. Int. Ed.
Ambient molecular imaging by desorption electrospray ionization mass spectrometry
Nature Protocols
Study of latent fingermarks by matrix-assisted laser desorption/ionisation mass spectrometry imaging of endogenous lipids
Rapid Commun. Mass Spectrom.
Molecular imaging of adrenal gland by desorption electrospray ionization mass spectrometry
Analyst
Imaging mass spectrometry
Mass Spectrom. Rev.
Molecular mass spectrometry imaging in biomedical and life science research
Histochem. Cell Biol.
A concise review of mass spectrometry imaging
J. Chromatogr. A
Imaging mass spectrometry of natural products
Nat. Prod. Rep.
Optimizing UV laser focus profiles for improved MALDI performance
J. Mass Spectrom.
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This article is part of a Special Issue entitled Lipodomics and Imaging Mass Spectrometry.