Sub-Micrometer-Scale Mapping of Magnetite Crystals and Sulfur Globules in Magnetotactic Bacteria Using Confocal Raman Micro-Spectrometry

The ferrimagnetic mineral magnetite Fe3O4 is biomineralized by magnetotactic microorganisms and a diverse range of animals. Here we demonstrate that confocal Raman microscopy can be used to visualize chains of magnetite crystals in magnetotactic bacteria, even though magnetite is a poor Raman scatterer and in bacteria occurs in typical grain sizes of only 35-120 nm, well below the diffraction-limited optical resolution. When using long integration times together with low laser power (<0.25 mW) to prevent laser induced damage of magnetite, we can identify and map magnetite by its characteristic Raman spectrum (303, 535, 665 cm(-1)) against a large autofluorescence background in our natural magnetotactic bacteria samples. While greigite (cubic Fe3S4; Raman lines of 253 and 351 cm(-1)) is often found in the Deltaproteobacteria class, it is not present in our samples. In intracellular sulfur globules of Candidatus Magnetobacterium bavaricum (Nitrospirae), we identified the sole presence of cyclo-octasulfur (S-8: 151, 219, 467 cm(-1)), using green (532 nm), red (638 nm) and near-infrared excitation (785 nm). The Raman-spectra of phosphorous-rich intracellular accumulations point to orthophosphate in magnetic vibrios and to polyphosphate in magnetic cocci. Under green excitation, the cell envelopes are dominated by the resonant Raman lines of the heme cofactor of the b or c-type cytochrome, which can be used as a strong marker for label-free live-cell imaging of bacterial cytoplasmic membranes, as well as an indicator for the redox state

Nanostructure and mechanics of mummified type I collagen from the 5300-year-old Tyrolean Iceman

Skin protects the body from pathogens and degradation. Mummified skin in particular is extremely resistant to decomposition. External influences or the action of micro-organisms, however, can degrade the connective tissue and lay the subjacent tissue open. To determine the degree of tissue preservation in mummified human skin and, in particular, the reason for its durability, we investigated the structural integrity of its main protein, type I collagen. We extracted samples from the Neolithic glacier mummy known as ‘the Iceman’. Atomic force microscopy (AFM) revealed collagen fibrils that had characteristic banding patterns of 69 ± 5 nm periodicity. Both the microstructure and the ultrastructure of dermal collagen bundles and fibrils were largely unaltered and extremely well preserved by the natural conservation process. Raman spectra of the ancient collagen indicated that there were no significant modifications in the molecular structure. However, AFM nanoindentation measurements showed slight changes in the mechanical behaviour of the fibrils. Young's modulus of single mummified fibrils was 4.1 ± 1.1 GPa, whereas the elasticity of recent collagen averages 3.2 ± 1.0 GPa. The excellent preservation of the collagen indicates that dehydration owing to freeze-drying of the collagen is the main process in mummification and that the influence of the degradation processes can be addressed, even after 5300 years

Repulsive bimodal atomic force microscopy on polymers

Bimodal atomic force microscopy can provide high-resolution images of polymers. In the bimodal operation mode, two eigenmodes of the cantilever are driven simultaneously. When examining polymers, an effective mechanical contact is often required between the tip and the sample to obtain compositional contrast, so particular emphasis was placed on the repulsive regime of dynamic force microscopy. We thus investigated bimodal imaging on a polystyrene-block-polybutadiene diblock copolymer surface and on polystyrene. The attractive operation regime was only stable when the amplitude of the second eigenmode was kept small compared to the amplitude of the fundamental mode. To clarify the influence of the higher eigenmode oscillation on the image quality, the amplitude ratio of both modes was systematically varied. Fourier analysis of the time series recorded during imaging showed frequency mixing. However, these spurious signals were at least two orders of magnitude smaller than the first two fundamental eigenmodes. Thus, repulsive bimodal imaging of polymer surfaces yields a good signal quality for amplitude ratios smaller than A 01/A 02 = 10:1 without affecting the topography feedback. © 2012 Gigler et al; licensee Beilstein-Institut.This work was financially supported by the European Commission (FORCETOOL, NMP4-CT-2004-013684) and the Excellence Cluster “Nanosystems Initiative Munich> (NIM).Peer Reviewe

Vaterite Stability in the Presence of Chromate

Vaterite aggregates grown in Cr(VI)-bearing silica gel were studied by combining scanning electron microscopy and Raman spectroscopy. All the vaterite samples were spherical aggregates consisting of lens-shaped individuals, and their morphology was distinctive for vaterite. Raman spectra corresponding to the aggregates grown in gels containing high Cr(VI) concentrations showed the typical bands of vaterite. However, in contrast to their morphology, the Raman spectra of the aggregates grown in the presence of lower Cr(VI) concentrations exclusively showed bands characteristic of calcite. These aggregates are interpreted as calcite pseudomorphs formed after vaterite through a replacement process. The replacement involves the interface coupling of the dissolution of vaterite and the precipitation of the stable polymorph calcite. The fact that only those vaterite aggregates formed in the presence of low Cr(VI) concentrations transformed into calcite indicates the presence of high Cr(VI) concentrations in the growth medium contributes to stabilize vaterite and prevents its transformation into calcite in the short term

Raman Study of Synthetic Witherite–Strontianite Solid Solutions

Characterization of zoned crystals of a synthetic witherite–strontianite solid solution (BaxSr1-xCO3) was carried out using electron microprobe analysis and Raman spectroscopy. The sample was obtained by coprecipitation using the silica gel method. As each carbonate crystal from this preparation showed the whole range of intermediate compositions BaxSr1-xCO3, 0.1≤x≤0.9, the solid solution could be studied for single crystals. Peak-shape analysis of the Raman bands showed that the peak shifts depend on the replacement of the Ba and Sr cations introducing different radii and masses. We observed a shift to higher wave numbers for an increase of the SrCO3 content

Growth of Calcium Carbonate in the Presence of Cr(VI)

The extended use of hexavalent chromium Cr(VI) compounds in industrial processes caused a significant increase of the concentration of this highly toxic heavy metal in natural environments. In order to investigate the influence of Cr(VI) in the formation of CaCO3, crystallization experiments were carried out in a double diffusion system, using silica hydrogel with different Cr(VI) contents as the growth medium. Crystalline products were examined by scanning electron microscopy, Raman spectroscopy, electron microprobe analysis, and single crystal X-ray diffraction. Increasing Cr(VI) concentration caused inhibition of the nucleation and growth of calcite and promoted the formation of the metastable polymorphs aragonite and vaterite. This effect correlated with a decrease of crystal size. Furthermore, the habit of calcite crystals changed with increasing Cr(VI) concentrations from {104} to forms increasingly elongated parallel to the c-axis. Raman spectroscopy, single crystal X-ray diffraction (XRD), and electron microprobe analysis (EMPA) gave strong indications of an isomorphic anion substitution of trigonal planar carbonate by the tetrahedral chromate within the calcite lattice. The apparent partitioning coefficients of Cr(VI) into calcite determined in this work suggest that the fate of this pollutant in natural environments can be significantly influenced by CaCO3 precipitation processes

Hyperspectral Image Analysis for Automatic Detection and Discrimination of Residual Manufacturing Contaminants

In modern manufacturing, divergent market dynamics impel companies to move toward a zero-defect production by reducing the risk of errors and defects down to zero. Paint-coating of metal surfaces is one of such process steps and most prominent as consumers will be animated to buy based on their first impression. Despite significant advances in automation and precision engineering of paint-coating, the presence of process contaminants as residual of different stages of production may compromise the process. In this contribution, we focus on the paint-coating of washing machine cabinets as a representative. Within the last decade, hyperspectral imaging technology has shown promising potentials in a variety of applications that aim at detecting objects and discriminating materials. In this work, we present a hyperspectral acquisition and analysis system that verifies the feasibility of detection and discrimination of process contaminants smeared on the washing machine cabinet based on spectral information. The acquisition system, aided by a robot arm, collects hyperspectral images based on two scenarios: contaminants on flat steel sheets and contaminants on washing machine chassis. This dataset, which is published publicly, is calibrated, analysed, and segmented through the proposed analysis models. The results for both flat base and structured washing machine surfaces indicate the great capacity of this technology for being integrated into the pre-treatment stage before painting metal parts

Cristalización de CaCO3 en presencia de Cr(VI)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEEspaña. Ministerio de Ciencias e InnovaciónMadrid (Comunidad Autónoma)pu

Raman study of synthetic BaCO3 - SrCO3 solid solutions

Program and Abstract Volume. Compiled in 2011 by Lunar and Planetary Institute (Houston). LPI Contribution No. 1616. Sponsors: Spanish National Research Council; Lunar and Planetary Institute.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu