Improvement of biological time-of-flight-secondary ion mass spectrometry imaging with a bismuth cluster ion source

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

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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

McDonnell

Heeren

Lange

et al. 2006

“…Moreover, erosion of the material occurs without significant interlayer mixing and/or the formation of topographical features, allowing depth resolution of 10 to 30 nm to be achieved [8 -10]. These attributes have compelled a majority of SIMS workers to quickly adopt this new technology.Although many different cluster projectiles have been examined, practical considerations have led to wide adaptation of liquid metal ion sources consisting of Au or Bi projectiles (Au 3 ϩ and Bi 3 ϩ , respectively) [13][14][15][16], and gas ion sources consisting of SF 5 ϩ or C 60 ϩ projectiles [6,17,18]. The physics of the ion/solid interaction is likely to be quite different between the carbon and metal-type sources since at 20 keV incident energy, each carbon atom carries 333 eV of kinetic energy while each metal atom in a trimer carries 6667 eV of kinetic energy.…”

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confidence: 99%

Direct comparison of Au₃⁺ and C₆₀⁺ cluster projectiles in SIMS molecular depth profiling

Cheng

Kozole

Hengstebeck

et al. 2007

The sputtering properties of two representative cluster ion beams in secondary ion mass spectrometry (SIMS), C 60 ϩ and Au 3 ϩ , have been directly compared. Organic thin films consisting of trehalose and dipalmitoylphosphatidylcholine (DPPC) are employed as prototypical targets. The strategy is to make direct comparison of the response of a molecular solid to each type of the bombarding cluster by overlapping the two ion beams onto the same area of the sample surface. The ion beams alternately erode the sample while keeping the same projectile for spectral acquisition. The results from these experiments are important to further optimize the use of cluster projectiles for SIMS molecular depth profiling experiments. For example, Au 3 ϩ bombardment is found to induce more chemical damage as well as Au implantation when compared with C 60 ϩ . Moreover, C 60 ϩ is found to be able to remove the damage and the implanted Au effectively. Discussions are also presented on strategies of enhancing sensitivity for imaging applications with cluster SIMS. (J Am Soc Mass Spectrom 2007, 18, 406 -412) © 2007 American Society for Mass Spectrometry E nergetic cluster ion bombardment and secondary ion mass spectrometry (SIMS) experiments have opened new applications in molecular depth profiling and 3D chemical imaging [1][2][3]. With this approach, it has been reported for many systems, that cluster projectiles remove large amounts of material from molecular solids without the damage accumulation associated with atomic projectiles [4 -12]. Moreover, erosion of the material occurs without significant interlayer mixing and/or the formation of topographical features, allowing depth resolution of 10 to 30 nm to be achieved [8 -10]. These attributes have compelled a majority of SIMS workers to quickly adopt this new technology.Although many different cluster projectiles have been examined, practical considerations have led to wide adaptation of liquid metal ion sources consisting of Au or Bi projectiles (Au 3 ϩ and Bi 3 ϩ , respectively) [13][14][15][16], and gas ion sources consisting of SF 5 ϩ or C 60 ϩ projectiles [6,17,18]. The physics of the ion/solid interaction is likely to be quite different between the carbon and metal-type sources since at 20 keV incident energy, each carbon atom carries 333 eV of kinetic energy while each metal atom in a trimer carries 6667 eV of kinetic energy. Moreover, there is a large mass variation between the atoms comprising these cluster species.The imaging capability of the two types of sources is quite different. The liquid metal ion gun (LMIG) technology yields very bright ion beams with a probe size of less than 100 nm in diameter [19]. The gas ion source requires apertures to define the beam size, sacrificing beam current. Recently, a C 60 source has been introduced [20] that achieves a submicron probe size with enough current to acquire images in a reasonable amount of time. In general, however, higher lateral resolution is achieved with the LMIG design if there is enough sensitivity in the mass...

“…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].…”

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confidence: 99%

“…This is much smaller than many of the biological samples of interest; for example, a tissue section of an adult rat brain is approximately 2 ϫ 1 cm. Reports [5,6] on SIMS imaging mass spectrometry analysis of large samples first mention a low-resolution scan. This is accomplished by rastering the sample, followed by a high-resolution scan of selected areas.…”

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confidence: 99%

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

Broersen

Liere

Altelaar

et al. 2008

High-resolution imaging mass spectrometry of large biological samples is the goal of several research groups. In mosaic imaging, the most common method, the large sample is divided into a mosaic of small areas that are then analyzed with high resolution. Here we present an automated alignment routine that uses principal component analysis to reduce the uncorrelated noise in the imaging datasets, which previously obstructed automated image alignment. An additional signal quality metric ensures that only those regions with sufficient signal quality are considered. We demonstrate that this algorithm provides superior alignment performance than manual stitching and can be used to automatically align large imaging mass spectrometry datasets comprising many individual mosaic tiles. (J Am Soc Mass Spectrom 2008, 19, 823-832) © 2008 American Society for Mass Spectrometry I maging mass spectrometry is a rapidly developing analytical tool because it provides the ability to map the profiles of specific biomolecules, in which the intrinsic mass of the molecule differentiates between any modified forms; to record the distributions of multiple analytes in parallel; and to perform these analyses without a label and with clinical samples [1]. This combination of specificity, parallel detection, and non-targeted analysis has led to great excitement for its potential as a discovery tool.It is the goal of many research groups to be able to perform high-resolution analysis of large samples, thus combining the ability to examine distributions between organs/tumors and their surroundings as well as to investigate the subcellular/intracellular locations of the biomolecules. The central premise of this approach is that the subcellular locations will provide some of the information required to explain differences in the more global patterns.High spatial resolution measurements are a wellestablished ability of secondary ion mass spectrometry (SIMS). 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].The images are normally created by moving the ionization beam in a set pattern across the sample and performing mass analysis at each point of the raster (spatially correlated mass spectrometry). The raster pattern typically uses 8-or 10-bit encoding; as a result the maximum analysis field contains 256 ϫ 256 (or 1024 ϫ 1024) pixels. In a typical high spatial resolution SIMS measurement the pixel size is about 200 nm, meaning maximum analysis areas of approximately 50 or 200 m, respectively. This is much smaller than many of the biological samples of interest; for example, a tissue section of an adult rat ...