Combined scanning transmission X-ray and electron microscopy for the characterization of bacterial endospores

Endospores (also referred to as bacterial spores) are bacterial structures formed by several bacterial species of the phylum Firmicutes. Spores form as a response to environmental stress. These structures exhibit remarkable resistance to harsh environmental conditions such as exposure to heat, desiccation, and chemical oxidants. The spores include several layers of protein and peptidoglycan that surround a core harboring DNA as well as high concentrations of calcium and dipicolinic acid (DPA). A combination of scanning transmission X-ray microscopy, scanning transmission electron microscopy, and energy dispersive spectroscopy was used for the direct quantitative characterization of bacterial spores. The concentration and localization of DPA, Ca2+, and other elements were determined and compared for the core and cortex of spores from two distinct genera: Bacillus subtilis and Desulfotomaculum reducens. This micro-spectroscopic approach is uniquely suited for the direct study of individual bacterial spores, while classical molecular and biochemical methods access only bulk characteristics.

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Imrich Barak, Rizlan Bernier-Latmani, Jan Jamroskovic, Paul Pao-Yun Shao, Elena Suvorova Buffat
Wiley-Blackwell, 2014
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https://infoscience.epfl.ch/record/200134?ln=en

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Self-Cleaning cotton textiles surfaces modified by photoactive SiO2/TiO2 coating

Danièle Laub

The photocatalytic activity of TiO2–SiO2-coated cotton textiles was investigated through the self-cleaning of red wine stains. It was shown that a TiO2–SiO2 species could be produced at temperatures of 100 °C with acceptable photo-activity on non-heat resistant materials. The most suitable Ti-content of the coating was found to be 5.8% and for SiO2, the content was 3.9% (w/w). The discoloration of red wine led to CO2 evolution that was more efficient for TiO2–SiO2-coated cotton for samples than of TiO2-coated ones. The reasons for these results are discussed. The textile surface did not show any change after several consecutive light-induced discoloration cycles of a red wine stain. By high-resolution transmission electron microscopy (HRTEM), the TiO2–SiO2 layer thickness on the cotton fibers was detected to 20–30 nm. The TiO2 and SiO2 were both observed to have particle sizes between 4 and 8 nm. Further electron microscopy work coupled with energy dispersive spectroscopy (EDS) showed that the Ti-particles were always surrounded by amorphous SiO2 and never alone by themselves. Infrared spectroscopy revealed that no modification of the cotton could be detected after photo-discoloration processes with TiO2–SiO2, taking a wine stain as model compound. The mixed TiO2 and SiO2 colloids lead during the dip-coating and subsequent thermal treatment on cotton to an organized structure of highly dispersed TiO2 particles always surrounded by amorphous silica.

2006

Scanning and transmission electron microscopy for evaluation of order/disorder in bone structure

Philippe Buffat, Elena Suvorova Buffat

A comparative characterization of the structure of normal and abnormal (osteoporotic) human lumbar and thoracic vertebrae samples was carried out to reveal the type of possible disorder. Samples from the bone fragments extracted during the surgery due to vertebra fractures were examined by scanning electron microscopy (SEM), conventional and high resolution transmission electron microscopy (TEM and HRTEM), and X-ray energy dispersive spectroscopy (EDS). Contrary to what might be expected in accordance with possible processes of dissolution, formation and remineralization of hard tissues, no changes in phase composition of mineral part, crystal sizes (length, width, and thickness), and arrangement of crystals on collagen fibers were detected in abnormal bones compared to the normal ones. The following sizes were determined by HRTEM for all bone samples: <= 20 nm in length, 3-15 nm in width, and 0.8 nm in thickness (the height of hexagonal HAP unit cell along the [2 (11) over bar0] direction. Significant overgrowth of organic fibers filled up the former paths for blood vessels and nerves together with organic films covering the mineral part was revealed by SEM only in osteoporotic bones. EDS showed that this organic tissue was not mineralized. Penetration of such organic fibers inside bones can result in bone dilatation and lower the mineral density, deteriorating the mechanical properties and finally terminating in fracture.

2007

Investigation of the microstructure, properties and biocompatibility of the Ti-6Al-4V alloy nitrided under glow discharge was performed. The microstructural analyses were carried out using light microscopy, X-ray diffraction, analytical scanning and transmission electron microscopy. Phase identifications and chemical composition of the layer and bulk material (substrate) were determined by electron diffraction and energy dispersive X-ray spectrometry. Atomic force microscopy was applied for layer surface topography measurements. Microhardness and Young's modulus measurements as well as frictional wear resistance and corrosion resistance tests were performed. The investigation revealed a clear correlation between the micro/nano structure and surface topography of the layer with its micromechanical, tribological and corrosion properties. In-vitro examinations of biofilm and cell behaviour show that the nitrided Ti-6Al-4V alloy exhibits good biocompatibility.

2006