Confocal Raman microscopy in life sciences.

Microscopy techniques are widely used in life sciences to study cells and tissues. Fluorescence microscopy, for example, is a very common method in many laboratories. While reliable and strong fluorescence signals are a clear advantage of this method, the labelling procedure with fluorescent dyes, the availability of required antibodies or the potentially necessary genetic modifications of the studied organism all introduce potential complications. By contrast, confocal Raman microscopy is a label-free and non-destructive imaging technique. In contrast to infrared microscopy, it is easily applicable in aqueous environments. Different microscope setups and combinations allow for the examination of various solid and liquid samples, even in their typical environments. The article demonstrates the analyzing capability of confocal Raman microscopy and correlative techniques through application examples of eukaryotic and prokaryotic cells, and cancerous and normal tissues and shows how confocal Raman microscopy provides valuable information for a more comprehensive understanding of the investigated sample.

Piezoelectrical shear-force distance control in near-field optical microscopy for biological applications.

We present a piezoelectrical shear-force distance control setup for scanning near-field optical microscopy. The setup is compact and tip exchange is easy. The topographical sensitivity is comparable to optical feedback systems. With an acceptable vibration amplitude of 5-10 nm we obtained a topographical resolution of 5 pm/square root of Hz. Because there is no laser necessary for tip position feedback, there is no extraneous light to interfere with spectroscopic and other low-light level experiments. Our technique permits measurements of soft biological samples in aqueous solution, which opens up many possible applications of near-field optical microscopy in biology and medicine.

Hierarchical self-organization of perylene bisimide--melamine assemblies to fluorescent mesoscopic superstructures.

A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were synthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energies for the hydrogen bonds between the imide and the complementary melamine moiety have been determined in several solvents by NMR and UV/Vis titration experiments with monotopic model compounds 5 and 9. The effects of the solvent polarity and specific solvent-solute interactions on the degree of polymerization of (3 x 8)n are discussed, and a general formula to estimate the chain length of [AA-BB]n nylon-type supramolecular polymers is derived. In addition to the formation of a hydrogen-bonded supramolecular chain. pi-pi interactions were observed for perylene bisimide-melamine assemblies 3b x 8b and 3b x 8c in aliphatic solvents. The orthogonal nature of hydrogen bonding and pi-pi interactions leads to three-dimensional growth yielding large-sized aggregates already in dilute solution. On suitable substrates, densely intertwined networks of nano- to mesoscopic strands are formed which have been investigated by electron microscopy, confocal fluorescence microscopy and optical polarization microscopy. The high fluorescence and excellent photostability of these superstructures is promising for future studies on energy migration and artificial light harvesting at the nano- and mesoscopic length scale.

Near-field luminescence measurements on GaInAsP/InP double heterostructures at room temperature.

Spatially resolved near-field luminescence spectroscopy was carried out on locally grown InP ridges, overgrown by a GaInAsP layer in metal organic molecular beam epitaxy. For free access to the quaternary layer the cleaved surface was investigated. Two different reflection scanning near-field microscopy setups were used. In the illumination mode we were able to estimate the charge-carrier diffusion in the InP. For improving the spatial resolution, measurements were also carried out in the collection mode. Here a shift of the center wavelength toward lower energy occurs near the side facets. This can be a result of a material composition gradient or of strained growth near the side facets. A second recombination channel at 1115 nm occurs at the growth-nongrowth transition. With the simultaneous recorded topography this recombination channel can be localized in the quaternary layer grown on the side of the InP ridge.

Raman microscopic investigations of BaTiO(3) precursors with core-shell structure.

Due to their outstanding dielectric and ferroelectric properties, barium titanate (BaTiO(3))-based ceramics have found many applications in electronic devices. To optimise the final quality of such ceramics, a detailed knowledge of the complex processes involved in the formation of BaTiO(3) is required. The phase formation process in ordered structures of the BaCO(3)/TiO(2) system was analysed by X-ray diffraction and by Raman spectral imaging (RSI) as a function of the annealing temperature. RSI was used for the first time as a locally resolving method for phase analysis, and proved to be a useful tool in examining the formation process of BaTiO(3) starting from spherical, core-shell structured precursors of the type TiO(2) core/BaCO(3) shell. The Raman spectra of different BaO-TiO(2) phases appearing as intermediate phases during the formation of BaTiO(3) were recorded for separately-prepared pure substances. Using these spectra as fingerprints, and choosing phase filters by setting wave number windows, "phase landscape pictures" of the samples at different temperatures during the genesis of BaTiO(3) could be created with a lateral resolution of up to 200 nm. These pictures confirm shell-like formation of the different barium titanate phases according to the diffusion of barium and oxygen ions from the Ba-rich shell into the TiO(2) core. At an intermediate state of the phase formation process, the phase sequence Ba(2)TiO(4), BaTiO(3), BaTi(2)O(5), BaTi(4)O(9) and BaTi(5)O(11) to TiO(2) was detected from the outer to the inner parts of the core-shell structures.