S. Della-Negra

Analysis of Native Biological Surfaces Using a 100 kV Massive Gold Cluster Source

In the present work, the advantages of a new, 100 kV platform equipped with a massive gold cluster source for the analysis of native biological surfaces are shown. Inspection of the molecular ion emission as a function of projectile size demonstrates a secondary ion yield increase of ~100× for 520 keV Au(400)(4+) as compared to 130 keV Au(3)(1+) and 43 keV C(60). In particular, yields of tens of percent of molecular ions per projectile impact for the most abundant components can be observed with the 520 keV Au(400)(4+) probe. A comparison between 520 keV Au(400)(4+) time-of-flight-secondary ion mass spectrometry (TOF-SIMS) and matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) data showed a similar pattern and similar relative intensities of lipid components across a rat brain sagittal section. The abundant secondary ion yield of analyte-specific ions makes 520 keV Au(400)(4+) projectiles an attractive probe for submicrometer molecular mapping of native surfaces.

Time-of-flight secondary ion mass spectrometry imaging of biological samples with delayed extraction for high mass and high spatial resolutions

Rationale In Time‐of‐Flight Secondary Ion Mass Spectrometry (TOF‐SIMS), pulsed and focused primary ion beams enable mass spectrometry imaging, a method which is particularly useful to map various small molecules such as lipids at the surface of biological samples. When using TOF‐SIMS instruments, the focusing modes of the primary ion beam delivered by liquid metal ion guns can provide either a mass resolution of several thousand or a sub‐µm lateral resolution, but the combination of both is generally not possible. Methods With a TOF‐SIMS setup, a delayed extraction applied to secondary ions has been studied extensively on rat cerebellum sections in order to compensate for the effect of long primary ion bunches. Results The use of a delayed extraction has been proven to be an efficient solution leading to unique features, i.e. a mass resolution up to 10000 at m/z 385.4 combined with a lateral resolution of about 400 nm. Simulations of ion trajectories confirm the experimental determination of optimal delayed extraction and allow understanding of the behavior of ions as a function of their mass‐to‐charge ratio. Conclusions Although the use of a delayed extraction has been well known for many years and is very popular in MALDI, it is much less used in TOF‐SIMS. Its full characterization now enables secondary ion images to be recorded in a single run with a submicron spatial resolution and with a mass resolution of several thousand. This improvement is very useful when analyzing lipids on tissue sections, or rare, precious, or very small size samples.

Hypervelocity nanoparticle impacts on free-standing graphene: A sui generis mode of sputtering

The study of the interaction of hypervelocity nano-particles with a 2D material and ultra-thin targets (single layer graphene, multi-layer graphene, and amorphous carbon foils) has been performed using mass selected gold nano-particles produced from a liquid metal ion source. During these impacts, a large number of atoms are ejected from the graphene, corresponding to a hole of ∼60 nm(2). Additionally, for the first time, secondary ions have been observed simultaneously in both the transmission and reflection direction (with respect to the path of the projectile) from a 2D target. The ejected area is much larger than that predicted by molecular dynamic simulations and a large ionization rate is observed. The mass distribution and characteristics of the emitted secondary ions are presented and offer an insight into the process to produce the large hole observed in the graphene.

SIMS instrumentation and methodology for mapping of co-localized molecules.

We describe an innovative mode for localizing surface molecules. In this methodology, individual C60 impacts at 50 keV are localized using an electron emission microscope, EEM, synchronized with a time-of-flight mass spectrometer for the detection of the concurrently emitted secondary ions. The instrumentation and methodologies for generating ion maps are presented. The performance of the localization scheme depends on the characteristics of the electron emission, those of the EEM and of the software solutions for image analysis. Using 50 keV C60 projectiles, analyte specific maps and maps of co-emitted species have been obtained. The individual impact sites were localized within 1-2 μm. A distinctive feature of recording individual impacts is the ability to identify co-emitted ions which originate from molecules co-located within ~10 nm.

Surface characterization of biological nanodomains using NP-ToF-SIMS

This paper describes the application of nanoparticle bombardment with time-of-flight secondary ion mass spectrometry (NP-ToF-SIMS) for the analysis of native biological surfaces for the case of sagittal sections of mammalian brain tissue. The use of high energy, single nanoparticle impacts (e.g. 520 keV Au400) permits desorption of intact lipid molecular ions, with enhanced molecular ion yield and reduced fragmentation. When coupled with complementary molecular ion fragmentation and exact mass measurement analysis, high energy nanoparticle probes (e.g. 520 keV Au400 NP) provide a powerful tool for the analysis of the lipid components from native brain sections without the need for surface preparation and with ultimate spatial resolution limited to the desorption volume per impact (~103 nm3).

The collision of a hypervelocity massive projectile with free-standing graphene: Investigation of secondary ion emission and projectile fragmentation

We present here the study of the individual hypervelocity massive projectiles (440-540 keV, 33-36 km/s Au4004+ cluster) impact on 1-layer free-standing graphene. The secondary ions were detected and recorded separately from each individual impact in the transmission direction using a time-of-flight mass spectrometer. We observed C1-10± ions emitted from graphene, the projectiles which penetrated the graphene, and the Au1-3± fragment ions in mass spectra. During the projectile-graphene interaction, the projectile loses ∼15% of its initial kinetic energy (∼0.18 keV/atom, 72 keV/projectile). The Au projectiles are neutralized when approaching the graphene and then partially ionized again via electron tunneling from the hot rims of the holes on graphene, obtaining positive and negative charges. The projectile reaches an internal energy of ∼450-500 eV (∼4400-4900 K) after the impact and then undergoes a ∼90-100 step fragmentation with the ejection of Au1 atoms in the experimental time range of ∼0.1 μs.

Mapping Dicorynia guianensis Amsh. wood constituents by submicron resolution cluster‐TOF‐SIMS imaging

The preparation of tropical wood surface sections for time-of-flight secondary ion mass spectrometry imaging is described, and the use of delayed extraction of secondary ions and its interest for the analysis of vegetal surface are shown. The method has been applied to the study by time-of-flight secondary ion mass spectrometry imaging with a resolution of less than one micron of a tropical wood species, Dicorynia guianensis, which is one of the most exploited wood in French Guiana for its durable heartwood. The heartwood of this species exhibits an economical importance, but its production is not controlled in forestry. Results show an increase of tryptamine from the transition zone and a concomitant decrease of inorganic ions and starch fragment ions. These experiments lead to a better understanding of the heartwood formation and the origin of the natural durability of D. guianensis. Copyright

An Integrative Approach to Decipher the Chemical Antagonism between the Competing Endophytes Paraconiothyrium variabile and Bacillus subtilis

An integrative approach combining traditional natural products chemistry, molecular networking, and mass spectrometry imaging has been undertaken to decipher the molecular dialogue between the fungus Paraconiothyrium variabile and the bacterium Bacillus subtilis, which were isolated as endophytes from the conifer Cephalotaxus harringtonia and are characterized by a strong and mutual antibiosis. From this study, we highlight that bacterial surfactins and a fungal tetronic acid are involved in such competition and that the fungus is able to hydrolyze surfactins to fight against the bacterial partner.

Mapping #Dicorynia guianensis# Amsh. wood constituents by submicron resolution cluster-TOF-SIMS imaging

The preparation of tropical wood surface sections for time-of-flight secondary ion mass spectrometry imaging is described, and the use of delayed extraction of secondary ions and its interest for the analysis of vegetal surface are shown. The method has been applied to the study by time-of-flight secondary ion mass spectrometry imaging with a resolution of less than one micron of a tropical wood species, Dicorynia guianensis, which is one of the most exploited wood in French Guiana for its durable heartwood. The heartwood of this species exhibits an economical importance, but its production is not controlled in forestry. Results show an increase of tryptamine from the transition zone and a concomitant decrease of inorganic ions and starch fragment ions. These experiments lead to a better understanding of the heartwood formation and the origin of the natural durability of D. guianensis. Copyright

Simultaneous detection and localization of secondary ions and electrons from single large cluster impacts

The use of large cluster primary ions (e.g. C60, Au400) in secondary ion mass spectrometry has become prevalent in recent years due to their enhanced emission of secondary ions, in particular, molecular ions (MW ≤ 1500 Da). The co-emission of electrons with SIs was investigated per projectile impact. It has been found that SI and electrons yields increased with increasing projectile energy and size. The use of the emitted electrons from impacts of C60 for localization has been demonstrated for cholesterol deposited on a copper grid. The instrumentation, methodologies, and results from these experiments are presented.