Alain Brunelle

Impact of slow gold clusters on various solids: nonlinear effects in secondary ion emission

Abstract A liquid metal ion source (LMIS) has been installed on a pulsed ion gun built at the IPN. The time of flight (TOF) spectra of the pulsed beam were recorded. With the gold source several cluster ions (up to 10 atoms in the cluster) and doubly charged ions were identified in the ion beam TOF spectra. With a second pulsation, single cluster ions can be selected as projectiles for secondary ion TOF mass spectrometry. We have studied the secondary ion emission (SIE) induced by cluster impact from a variety of targets: organic, CsI, metallic. A large enhancement of yield is observed by comparison to single atomic ion impact (e.g. factor of 30 between Au 3 + and Au + ). The secondary ion yields increase strongly with the number of constituents in the cluster. This effect is not linear. A comparison with other types of clusters and also fission fragments of 252 Cf has been performed. The rate of secondary emission stimulated by cluster is similar to SI yield induced by fission fragments.

In Situ Lipidomic Analysis of Nonalcoholic Fatty Liver by Cluster TOF-SIMS Imaging

Mass spectrometry imaging has been used to map liver biopsies of several patients suffering from nonalcoholic fatty liver disease. This steatosis is characterized by an accumulation of triacylglycerols and diacylglycerols in the liver. Using time-of-flight-secondary ion mass spectrometry (TOF-SIMS) with a bismuth cluster ion source, it has been possible to map lipids in situ at the micrometer scale and to simultaneously characterize their molecular distribution on liver sections. Accumulation of triacylglycerols, diacylglycerols, monoacylglycerols, fatty acids, with the apparition of myristic acid, together with a dramatic depletion of vitamin E and a selective macrovacuolar localization of cholesterol are observed in steatosis areas of fatty livers compared to control livers. These ion species are concentrated in small vesicles having a size of a few micrometers. Moreover, very fine differences in lipid localizations, depending on alkyl acid chain lengths of diacylglycerols and fatty acids, have been found after careful scrutiny of the ion images. Finally, TOF-SIMS has revealed lipid zonation in the normal human liver and accumulation of very similar lipids to those detected in areas of the fatty livers, which are not characterized as steatotic ones by the histological control performed on serial tissue sections.

Mass spectrometry imaging of rat brain sections: nanomolar sensitivity with MALDI versus nanometer resolution by TOF–SIMS

Mass spectrometry imaging is becoming a more and more widely used method for chemical mapping of organic and inorganic compounds from various surfaces, especially tissue sections. Two main different techniques are now available: matrix-assisted laser desorption/ionizaton, where the sample, preliminary coated by an organic matrix, is analyzed by a UV laser beam; and secondary ion mass spectrometry, for which the target is directly submitted to a focused ion beam. Both techniques revealed excellent performances for lipid mapping of tissue surfaces. This article will discuss similarities, differences, and specificities of ion images generated by these two techniques in terms of sample preparation, sensitivity, ultimate spatial resolution, and structural analysis.

Changes of phospholipid composition within the dystrophic muscle by matrix-assisted laser desorption/ionization mass spectrometry and mass spectrometry imaging.

Duchenne muscular dystrophy (DMD) is a neuromuscular disease linked to the lack of dystrophin, a submembrane protein, leading to muscle weakness and associated with a defect of the lipid metabolism. A study of the fatty acid composition of glycerophos-phatidylcholines by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS) and tandem mass spectrometry (MS/MS) enabled us to characterize a change in the lipid composition of dystrophic cells at the time of the differentiation. This modification has been used as a marker to identify with profiling and imaging MALDI-ToF MS regenerating areas in sections of an mdx mouse leg muscle. It is the first time that such a slight change in fatty acid composition has been observed directly on tissue slices using mass spectrometry. This approach will be useful in monitoring the treatment of muscular regeneration.

MALDI Imaging and Structural Analysis of Rat Brain Lipid Negative Ions with 9-Aminoacridine Matrix

Mass spectrometry imaging is of growing interest for chemical mapping of lipids at the surface of tissue sections. Many efforts have been devoted to optimize matrix choice and deposition technique for positive ion mode analyses. The identification of lipid species desorbed from tissue sections in the negative mode can be significantly improved by using 9-aminoacridine together with a robust deposition method, yielding a superior signal-to-noise ratio and thus a better contrast for the ion images in comparison to classical matrices such as α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxybenzoic acid, or 2,4,6-trihydroxyacetophenone. Twenty-eight different lipid species (phosphatidic acids, phosphatidylethanolamines, phosphatidylserines, phosphatidylglycerols, phosphatidylinositols, phosphatidylinositol-phosphates, and sulfatides) were scrutinized on rat brain tissue sections, and systematic MS/MS studies were conducted. It was possible to identify isobaric species differing by their fatty acid chains thanks to the improved sensitivity.

In situ primary metabolites localization on a rat brain section by chemical mass spectrometry imaging.

We describe here the detection and identification of 13 primary metabolites (AMP, ADP, ATP, UDP-GlcNAc, ...) directly from rat brain sections by chemical mass spectrometry imaging. Matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) was combined with 9-aminoacridine as a powerful matrix. We also demonstrate that a new robotic sprayer allows us to homogeneously coat the surface with the matrix, enabling the acquisition of chemical images at a 50 microm resolution, leading us to precisely and simultaneously localize each metabolite over the tissue surface. These experiments open a new field of investigation for chemical mass spectrometry imaging and are of great interest for both chemists and biologists.

Energy loss by MeV carbon clusters and fullerene ions in solids

Abstract Energy losses by carbon clusters C p ( p ≤ 8) and fullerene ions C 60 in thin carbon foils have been measured in the energy range from 0.3 to 5.65 MeV/atom. A small enhancement in energy loss is obtained for carbon atoms in the clusters relative to single carbon ions at the same velocity. Very large pulse height defects have been observed in the energy response of a silicon detector bombarded by C 60 ions with energies ranging from 6 to 30 MeV.

Impact of rhizosphere factors on cyclic lipopeptide signature from the plant beneficial strain Bacillus amyloliquefaciens S499.

Cyclic lipopeptides (cLPs) of the surfactin, iturin and fengycin families synthesized by plant-associated Bacilli represent an important class of antibiotics as they may be tightly involved in the protective effect of selected strains against phytopathogens. However, their production by Bacillus cells developing on roots under rhizosphere conditions is still poorly understood. In this work, we combined electrospray and imaging mass spectrometry-based approaches to determine the detailed pattern of surfactins, iturins and fengycins produced in planta by Bacillus amyloliquefaciens S499. Very different production rates were observed for the three cLPs families. Whereas surfactin accumulated in significant amounts, much lower quantities of iturins and fengycins were detected in the environment of colonized roots in comparison with laboratory medium. In addition, the surfactin pattern produced by strain S499 evolving on roots is enriched in homologues with long fatty acid chains (C15) compared with the chains typically secreted under in vitro conditions. Additional experiments revealed that lipopeptide production by root-associated S499 cells is qualitatively and quantitatively dictated by the specific nutritional context of the rhizosphere (exudates enriched in organic acids, oxygen limitation) but also by the formation of biofilm-related structures around root hairs. As surfactins, iturins and fengycins retain specific functions and bioactivities, the biological relevance of their differential production observed in planta is discussed in the context of biocontrol of plant diseases.

Lipid mapping in human dystrophic muscle by cluster-time-of-flight secondary ion mass spectrometry imaging

Human striated muscle samples, from male control and Duchenne muscular dystrophy-affected children, were subjected to cluster-time-of-flight secondary ion mass spectrometry (cluster-ToF-SIMS) imaging using a 25 keV Bi3+ liquid metal ion gun under static SIMS conditions. Spectra and ion density maps, or secondary ion images, were acquired in both positive and negative ion mode over several areas of 500 × 500 μm2 (image resolution, 256 × 256 pixels). Characteristic distributions of various lipids were observed. Vitamin E and phosphatidylinositols were found to concentrate within the cells, whereas intact phosphocholines accumulated over the most damaged areas of the dystrophic muscles, together with cholesterol and sphingomyelin species. Fatty acyl chain composition varied depending on the region, allowing estimation of the local damage extent.

Lipid imaging with cluster time-of-flight secondary ion mass spectrometry

This brief article provides an overview of the current state of the art in biological imaging mass spectrometry using cluster time-of-flight secondary ion mass spectrometry (TOF–SIMS). Recent and spectacular improvements in terms of sensitivity of TOF–SIMS imaging methods have allowed many biological applications to recently be successfully tested, such as mapping of lipid disorders in human muscles of a patient suffering from dystrophy, localization of surfactins after the swarming of bacteria on a surface, or lipid mapping over whole-body animal sections.