Spatially resolved determination of the structure and composition of diatom cell walls by Raman and FTIR imaging

Vibrational spectroscopic imaging has developed into a versatile tool to study the local composition of various materials. Here, we present for the first time that Raman mapping and Fourier transform infrared imaging are useful tools to study diatom cell walls as is demonstrated for the species Stephanopyxis turris. The unicellular diatoms exhibit intricately micro- and nano-patterned cell walls, which consist of amorphous silica as well as various organic and inorganic constituents, thus making up an extremely interesting inorganic/organic hybrid material. The structure and composition of this material as well as the biochemical and biophysical processes leading to its formation remain to be challenges for ongoing research. Whereas the lateral resolution of Fourier transform infrared imaging is limited to 5 μm by diffraction, Raman maps are shown to be capable of detecting the spatial distribution of the silica as well as an additional inorganic component and the organic material down to 330-nm resolution. Due to the spherical shape of the sample with a radius of 40 μm and the requirement to accurately focus the laser before each Raman measurement within the micrometer range, Raman maps of whole diatom cell walls were registered after an adjustment of the axial position. The results reveal local differences in the cell wall composition of the honeycomb-like structures and the bottom layer.     

Raman spectroscopic imaging for in vivo detection of cerebral brain metastases

We report for the first time a proof-of-concept experiment employing Raman spectroscopy to detect intracerebral tumors in vivo by brain surface mapping. Raman spectroscopy is a non-destructive biophotonic method which probes molecular vibrations. It provides a specific fingerprint of the biochemical composition and structure of tissue without using any labels. Here, the Raman system was coupled to a fiber-optic probe. Metastatic brain tumors were induced by injection of murine melanoma cells into the carotid artery of mice, which led to subcortical and cortical tumor growth within 14 days. Before data acquisition, the cortex was exposed by creating a bony window covered by a calcium fluoride window. Spectral contributions were assigned to proteins, lipids, blood, water, bone, and melanin. Based on the spectral information, Raman images enabled the localization of cortical and subcortical tumor cell aggregates with accuracy of roughly 250 μm. This study demonstrates the prospects of Raman spectroscopy as an intravital tool to detect cerebral pathologies and opens the field for biophotonic imaging of the living brain. Future investigations aim to reduce the exposure time from minutes to seconds and improve the lateral resolution.     

Silicone polycarbonates from new aryl-terminated siloxane precursors

Several synthetic routes to silicon polycarbonate copolymers utilizing aryl-terminated siloxanes have been examined. Anhydride capped siloxanes with varying polydimethylsiloxane units were prepared by the acid equilibration of 1,3-bis(4,4′-phthalicanhydride)tetramethyldisiloxane. These siloxanes were then imidized with aminophenol to the corresponding phenol capped siloxane. Reaction of these materials with 4,4′-isopropylidenediphenol (BPA) and phosgene (interfacially and non-interfacially) produced silicone polycarbonate copolymers. Similar copolymers were obtained by reaction with bis-chloroformate derivatives of 4,4′-isopropylidenediphenol (monomer and oligomers). The different synthetic routes significantly affect the thermal and mechanical properties as well as the composition of the new polymers. Materials synthesized by the bis-chloroformate route exhibit good hydrolytic and melt stabilities. Those made interfacially underwent phase separation in the melt.     

Interaction of a modulated electron beam with a magnetoactive plasma

Experimental results concerning the interaction of a modulated electron beam with a magnetoactive plasma in the whistler frequency range are reported. It was shown experimentally that when a beam is injected into the plasma, waves can be generated by two possible mechanisms: Cherenkov emission of whistlers by the modulated beam, and transition radiation from the beam injection point. In the case of weak beam currents (N _b/N ₀)≪⁻⁴) the Cherenkov resonance radiation is more than an order of magnitude stronger than the transition radiation; the Cherenkov emission efficiency decreases at high beam currents. The transformation of the distribution function of the beam is investigated for the case of weak beam currents. It is shown that in the case of the Cherenkov interaction with whistlers the beam is retarded and the beam distribution function becomes wider and acquires a plateau region. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 378–382 (25 March 1998)     

Optimale Tests und ungünstigste Verteilungen

Ohne Zusammenfassung     

Fluorous materials in microbubble engineering science and technology—Design and development of new bubble preparation and sizing technologies

Microbubbles are being used in ultrasound diagnosis imaging, could serve as contrast agents for multiple imaging modalities and for parenteral oxygen delivery, and have potential in materials science as new multi-scale materials for magnetic, optical and magneto-optical devices. We designed new procedures for the preparation of narrowly size-distributed, monomodal microbubble populations, as well as a new multifrequency acoustical device for microbubble sizing. Methods for microbubble stabilization using fluorinated gases and surfactants are also discussed. Prospects include further use of fluorinated amphiphiles for bubble stabilization and size control, and decoration of bubble surface with functional particles (e.g. magnetic iron oxide nanoparticles).     

Stacking of Self‐Assembled Surface Micelles in Ultrathin Films

Nonpolar fluorophilic/lipophilic tetrablock amphiphiles are investigated on the surface of water and on solid substrates using compression isotherms, Brewster angle microscopy, and atomic force microscopy. At low pressures, the tetrablocks form monolayers of closely packed surface hemimicelles. Further compression causes a 2D/3D transition. At the end of the plateau, half of the deposited material is expelled forming a second monolayer on top of the initially formed monolayer. Both layers of the films consist of surface micelles, thus providing the first example of spontaneous or compression‐driven stacking of self‐assembled nano‐objects.