Structural and analytical studies of silica accumulations in <Emphasis Type="Italic">Equisetum hyemale</Emphasis>

Horsetail (Equisetum spp.) is known as one of the strongest accumulators of silicon among higher terrestrial plants. We use the combination of position-resolved analytical techniques, namely microtomography, energy-dispersive X-Ray elemental mapping, Raman microscopy, as well as small-angle and wide-angle scattering of X-rays, to study the type, distribution and nanostructure of silica in the internodes of Equisetum hyemale. The predominant silicification pattern is a thin continuous layer on the entire outer epidermis with the highest density in particular knob regions of the long epidermal cells. The knob tips contain up to 33 wt% silicon in the form of pure hydrated amorphous silica, while the silica content is lower in the inner part of the knobs and on the continuous layer. In contrast to the knob tips, the silica in these regions lacks silanol groups and is proposed to be in close association with polysaccharides. No mentionable amount of crystalline silica is detected by wide-angle X-ray scattering. The small-angle X-ray scattering data are consistent with the presence of colloidal, sheet-like silica agglomerates with a thickness of about 2 nm. From these results we conclude that there are at least two distinct forms of silica in E. hyemale which may have different functions. The close association of silica with cell wall polymers suggests that they may act as a polymeric template that controls the shape and size of the colloidal silica particles similar to many other biominerals and mineralised tissues. We propose that owing to its specific distribution in E. hyemale, a protective role and possibly also an important biomechanical role are among the most likely functions of silica in these plants. Figure 3D rendering of X-ray microtomography data from a dry Equisetum hyemale stalk. The red colour indicates high X-ray absorption values due to local silica accumulations     

Mapping the intracellular distribution of carbon nanotubes after targeted delivery to carcinoma cells using confocal Raman imaging as a label-free technique

The uptake of carbon nanotubes (CNTs) by mammalian cells and their distribution within cells is being widely studied in recent years due to their increasing use for biomedical purposes. The two main imaging techniques used are confocal fluorescence microscopy and transmission electron microscopy (TEM). The former, however, requires labeling of the CNTs with fluorescent dyes, while the latter is a work-intensive technique that is unsuitable for in situ bio-imaging. Raman spectroscopy, on the other hand, presents a direct, straightforward and label-free alternative. Confocal Raman microscopy can be used to image the CNTs inside cells, exploiting the strong Raman signal connected to different vibrational modes of the nanotubes. In addition, cellular components, such as the endoplasmic reticulum and the nucleus, can be mapped. We first validate our method by showing that only when using the CNTs' G band for intracellular mapping accurate results can be obtained, as mapping of the radial breathing mode (RBM) only shows a small fraction of CNTs. We then take a closer look at the exact localization of the nanotubes inside cells after folate receptor-mediated endocytosis and show that, after 8-10 h incubation, the majority of CNTs are localized around the nucleus. In summary, Raman imaging has enormous potential for imaging CNTs inside cells, which is yet to be fully realized.     

Beitrag zur kolorimetrischen bestimmung von sulfid-ionen

Zusammenfassung Nach einer kurzen Diskussion der Molybdänblau- und Methylenblaumethode sowie der überprüften Farbreaktion mit Ammoniummolybdat und Kaliumrhodanid werden weitere Versuche zur Kolorimetrie von Sulfidionen bzw. von Schwefelwasserstoff mitgeteilt. Das in einer früheren Mitteilung empfohlene Wismutreagens wurde nach eingehenden Versuchen geringfügig abgeändert. Es ist nunmehr etwa 3 Wochen haltbar. Die Analysenergebnisse sind befriedigend.Aus der nun vorliegenden vollständigen Literaturübersicht und der abgeschlossenen Überprüfung aller bekannten Verfahren unter Verwendung des Spektrophotometers von Beckman kann geschlossen werden, daß keine der gegenwärtig bekannten kolorimetrischen Methoden restlos befriedigt, wenngleich die im einzelnen erreichten Nachweisempfindlichkeiten für Zwecke der Mikroanalyse als sehr gut bezeichnet werden dürfen.

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Summary After a short discussion of the molybdenum blue- and the methylene blue method and also the color reaction with ammonium molybdate and potassium thiocyanate, further studies are reported of the colorimetry of sulfide ions and hydrogen sulfide. After extensive investigation, the bismuth reagent recommended in an earlier paper is modified slightly. It is now stable for about three weeks. The analytical findings are satisfactory.It may be concluded from the now available complete literature survey and the completed trial of all known procedures with use of the Beckman spectrophotometer, that none of the present colorimetric methods is entirely satisfactory, even though the detection sensitivities obtained in isolated instances can be regarded as very good for microanalytical purposes.

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Résumé Après une courte discussion sur la méthode au bleu de molybdène et au bleu de méthylène ainsi que de la réaction colorée bien établie au molybdate d'ammonium et au thiocyanate de potassium, on présente d'autres expériences sur la colorimétrie de l'ion sulfhydrique et de l'hydrogène sulfuré. Le réactif au bismuth recommandé dans une précédente communication a été modifié d'une façon insignifiante après des essais précis. Il se conserve au moins pendant trois semaines. Les résultats d'analyse sont satisfaisants.A partir de la revue bibliographique actuellement complète et du contrôle achevé pour tous les procédés connus à l'aide du spectrophotomètre de Beckman, on peut conclure qu'aucune des méthodes colorimétriques actuellement connues n'est absolument satisfaisante même quand les sensibilités particulières atteintes en vue de la micro-analyse se recommandent comme excellentes.

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Derzeit in Fa. Doz. Dr. Slevogt, Wessobrunn b. Weilheim, Obb.     

New insights into plant cell walls by vibrational microspectroscopy

Vibrational spectroscopy provides non-destructively the molecular fingerprint of plant cells in the native state. In combination with microscopy, the chemical composition can be followed in context with the microstructure, and due to the non-destructive application, in-situ studies of changes during, e.g., degradation or mechanical load are possible. The two complementary vibrational microspectroscopic approaches, Fourier-Transform Infrared (FT-IR) Microspectroscopy and Confocal Raman spectroscopy, are based on different physical principles and the resulting different drawbacks and advantages in plant applications are reviewed. Examples for FT-IR and Raman microscopy applications on plant cell walls, including imaging as well as in-situ studies, are shown to have high potential to get a deeper understanding of structure–function relationships as well as biological processes and technical treatments. Both probe numerous different molecular vibrations of all components at once and thus result in spectra with many overlapping bands, a challenge for assignment and interpretation. With the help of multivariate unmixing methods (e.g., vertex components analysis), the most pure components can be revealed and their distribution mapped, even tiny layers and structures (250 nm). Instrumental as well as data analysis progresses make both microspectroscopic methods more and more promising tools in plant cell wall research.