Microencapsulation by means of step-wise adsorption of polyelectrolytes

Step-wise adsorption of polyelectrolytes is used for the fabrication of micro- and nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed.

Amyloid-beta-sheet formation at the air-water interface

An amyloid(1-40) solution rich in coil, turn, and alpha-helix, but poor in beta-sheet, develops monolayers with a high beta-sheet content when spread at the air-water interface. These monolayers are resistant to repeated compression-dilatation cycles and interaction with trifluoroethanol. The secondary structure motifs were detected by circular dichroism (CD) in solution and with infrared reflection-absorption spectroscopy (IRRAS) at the interface. Hydrophobic influences are discussed for the structure conversion in an effort to understand the completely unknown reason for the natural change of the normal prion protein cellular (PrP(C)) into the abnormal prion protein scrapie (PrP(Sc)).

Selective staining by the fluorochrome, 5,5-diphenyl-9-ethyl-DiOC2(3). I. Physicochemical studies of dye-dye and dye-tissue interactions

The 5,5'-diphenyl-9-ethyl-oxacarbocyanine (5,5'-diphenyl-9-ethyl-DiOC2(3); CD) has properties suitable for histological investigations including the spectral range for absorption and fluorescence emission, the values of the corresponding molar coefficients and fluorescence quantum yield. Furthermore, CD remains relatively unchanged over the entire pH range and interacts with protein beta-sheets. The latter fact is detectable spectroscopically as a bathochromic shift. In water-containing media such as the histological stain and washes, CD exists as a monomer, a dimer and in two aggregated states. These differ in their binding affinity to tissue sections, in their solubility in water, alcohol and water/alcohol mixtures, and in their UV/VIS absorption and fluorescence emission. The ratio of the various CD states and the contrast of selectively stained tissue areas can be controlled via the staining conditions and the sequence of the washes. Furthermore, mounting in a xylene-based medium produces a solvatochromic spectral shift of the CD monomer, which leads to a marked elevation in phase contrast.

Selective staining by the fluorochrome 5,5-diphenyl-9-ethyl-oxacarbocyanine. II. Application to paraffin embedded nervous tissue

We present a simple and rapid method to label specific structures of neural tissue in paraffin sections. After incubation of deparaffinized sections in the cyanine dye 5,5'-diphenyl-9-ethyl-oxacarbocyanine (DEOC), three different washing and mounting procedures were performed. Incubation in DEOC followed by washes in ethanol and water and mounting in glycerol-gelatin resulted in selective labeling of myelin in the central and peripheral nervous systems. Weak labeling of myelin and axons and staining of nuclei of neurons was seen after incubation in DEOC followed by washes in ethanol and xylene, and mounting in Eukitt. Nuclear proteins, the endoplasmic reticulum and the Golgi apparatus were stained strongly and exclusively after incubation in DEOC, washes in water, ethanol and xylene, and mounting in Eukitt. Thus the absorption pattern of DEOC is changed significantly by solvents applied after the fluorochrome. In any case, fluorescence did not fade even after repeated and intense fluorescence microscopy over a period of 6 months.

Microencapsulation of Organic Solvents in Polyelectrolyte Multilayer Micrometer-Sized Shells

Hollow-shell micrometer-sized particles were fabricated in aqueous media by stepwise deposition of oppositely charged polyelectrolytes onto melamine latex particles and biological cells with a dissolution of the core afterward. It is demonstrated that these shells can be suspended in various organic media, such as methanol, ethanol, pentanol, hexanol, octanol, octane, and decane, by a gradual solvent exchange. At this stage of the procedure the shells contain the respective organic solvent. Oil suspensions in water are then formed by transferring the particles from the organic media into water, without the use of any further surfactant addition. By an additional adsorption step employing phospholipids, it is possible to obtain a dispersion of shells in organic solvents containing an aqueous solution inside. AFM measurements are provided which show that the shells preserve their integrity in the different solvents. Confocal microscopy is employed to demonstrate encapsulation of solvents and the presence of lipids. Copyright 1999 Academic Press.