4SIMS Secondary Ion Mass Spectrometry probing analytical technique for measuring the surface or near surface chemical or isotopic composition of solidsuses probe ions to sputter target ions in laterally microscale or smaller regions (ion microprobe)analytical characteristics:nm depth resolutionlateral resolution 10’s nm to mmmost sensitive of the probing analytical techniques, ppb-ppmentire periodic table, H to Usimple sample preparationAlthough the instrument is new, the analytical technique has been widely utilized for decadesThis of course is SIMS or secondary ion mass spectrometry.The NanoSIMS is a specialized form of ion microprobe.
5SIMS Data Basic Dimensions: 1 dimension 2 dimensions 3 dimensions ratios1816O/O24Mg/28SiMass spectrumcps,ppm SeBasicfrom tiny mass consumedDimensions:1 dimension‘depth profile’: composition along a line normal to the surface‘line scan’: composition along a line parallel to the surface2 dimensions‘image’ (map) of the surface distribution of secondary ion species3 dimensionsa stacked series of secondary ion images collected at discrete depths into the targetImageDepth profileLine scan
6SIMS analytical Energy Analyzer Mass Analyzer Ion source Secondary ion Collection OpticsDetectorPrimary ion columnThe typical layout of a SIMS instrument is shown here. There are two basic components: the ion probe and the analyzer.The ion probe comprises a source of ions ( O,Cs,Ar,Ga), a column to accelerate and focus the primary ions to a fine spot, and the sample under vacuum.As a consequence of bombarding the sample with primary ions, secondary ions of the target (which must be a solid) are produced, and these are subsequently analyzed within the second major component, the mass analyzer, or more technically, the secondary ion mass spectrometer. The analytical technique is thus commonly referred to as SIMS..Sampleundervacuum
8Features of NanoSIMS dynamic SIMS probe lateral resolution for bulk sample ion chemical/isotopic characterizationnot for molecular identification or oxidation stateprobe lateral resolution50 nm for 133Cs+200 nm for 16O-ability to scan the primary beam and record secondary ion images at ultra-fine-scale lateral resolutionvery low eroson rate, ~nm/hr (sample preservation)simultaneous multicollection of up to 5 isotope speciesroutine high mass resolutionresolve isobaric interferences
9Ion imaging of TiCN alloy demonstrating sub-50 nm edge resolution with Cs+ 3 x 3 um, 26CN10 x 10 um, 24C2
11NanoSIMS labs bio-SIMS program 0. Harvard Medical School/ MIT, Boston USA National Resource for Mass Spectrometry Imaging, NIH NCRR1. Washington University, Saint Louis, MO2. Max Planck Institute, Mainz, Germany3. Institut Curie, Paris, France4. Oxford University, U.K5. Lawrence Livermore National Lab, Livermore, CA, USA University of California, Davis6. National Institute for Materials Science, Tsukuba, Japan7. LAM, Centre de Recherche Public-GL, Luxembourg8. ExxonMobil, New Jersey, USA9. University of Tokyo10. The UWA11. Rouen Univ, Francebio-SIMS programbio-SIMS programbio-SIMS program
12Non-metallic elements used in SIMS biological analysis Naturally-occurring isotopes12C – all cell organelles14N – DNA, RNA, proteins31P – DNA, RNA (nucleic acids)32S – proteinsArtificial isotopes (stable or radioactive)14C – turnover/pathways of C15N – turnover/pathways of labelled amino acids (proteins), nucleic acids17F – Fluoracil, cancer drug targetting chromosomes81Br – in Bromodeoxyuridine (BrdU), specifically incorporated into DNA during DNA synthesis123, 125, 127I – in Iododeoxyuridine
13Examples of metallic elements used in SIMS biological analysis Li, Na, K, Rb, CsBe, Mg, Ca, Sr, BaTi, Cr, Mn, Fe, Ni, Pb, Al, InAu, AgSc, lanthanides, actinidesto date, few studies, poor sensitivity and spatial resolution
14O- primary ion bombardment, positive secondary ions, and a silicon matrix
15Cs+ primary ion bombardment, negative secondary ions, and a silicon matrix Compared to other probe techniques, SIMS has the highest sensitivity.
16Sample preparationmust be dehydrated, +/- fast freezing, chemical fixation (glutaraldehyde, Os tetroxide), epoxy embedding, cryo-sectioning (0.3 – 1 µm)will feature of interest be preserved?other documentation techniques to map features (confocal, VPSEM, TEM, etc.)Example of human hair cross-section deposited on Si (Hallegot and Corcuff, 1993)Scanning electron microscopy imagescortexcuticleImportant to emphasize that the N50 should not be used for mapping internal structures of cells, which can be done by other methods (confocal microscopy, TEM, SEM, etc). The idea is to use the instrument for process tracing, particularly using tagged molecules in experimental conditions.
17nanoSIMS samples Sample holder for 1 cm samples Thin membranes on Si wafer
18Imaging of resin embedded biological tissues 12C14N32SA mucous-producing cell in coral tissueScale = 3umPrimary ions: Cs+150 mm12C14N31PA symbiotic algae in coral tissueScale = 2umPrimary ions: Cs+
19Imaging isotopic tracers in resin embedded biological tissues 150 mm44Ca / 40Ca44Ca used as a tracer of calcium (40Ca) to determine pathways of movement & uptake1.2.3.Region44Ca/40CaNatural abundance0.021. Mucous cell0.052. Spiked Seawater0.73. Epithelial cells0.374. Stinging cell4.Coral epithelium44Ca 1 minScale = 5umFOV = 35umPrimary ions: O-Significant44Cauptake
21Imaging of As within human hair Audinot et al. (2003)Heavy metal exposureAn example of where the NanoSIMS is capable, but can be done with other instrumentation, and therefore not particularly cost effective
22Analytical Issues: will the metal ions be detectable? are there non-metallic ion labels that can be used as proxies for the metals?quantitation: how important?sample preparation to avoid element migration or loss
23nanoSIMS & ARC Metals in Medicine is capable of playing a vital rolethe analytical capabilities and experience with metals in biological media needs to be developedR. Stern and P. Clode are here to enter into research partnerships with you