No abstract

No abstract

Layer-by-layer polyelectrolyte adsorption at colloid particle surfaces as well as the removal of the core latex to obtain multilayer microcapsules is conducted by means of membrane filtration. As target particles for adsorption we use nonsoluble polystyrene sulfate latex, soluble melamine formaldehyde resin latex, and decomposable glutaraldehyde fixed human red blood cells. The materials adsorbed are poly(allylamine hydrochloride), poly(styrenesulfonate), poly(diallyldimethylammonium chloride), chitosan, and chitosansulfate. The coating process is carried out under different membrane filtration conditions with respect to the pressure regime, the filter materials, and the stirring conditions. We characterize the prepared multilayers at the particle surface or in the microcapsule (shell) form by atomic force microscopy, confocal laser scanning microscopy, transmission electron microscopy, single-particle light scattering, and electrophoresis. The quality, performance, and yield of the presented method are compared with the results obtained by centrifugation and sequential adsorption as alternative preparation strategies. Membrane filtration surpasses all other methods, so far established, with respect to the above criteria.

Electron tomography is a well-established technique for three-dimensional structure determination of (almost) amorphous specimens in life sciences applications. With the recent advances in nanotechnology and the semiconductor industry, there is also an increasing need for high-resolution three-dimensional (3D) structural information in physical sciences. In this article, we evaluate the capabilities and limitations of transmission electron microscopy (TEM) and high-angle-annular-dark-field scanning transmission electron microscopy (HAADF-STEM) tomography for the 3D structural characterization of partially crystalline to highly crystalline materials. Our analysis of catalysts, a hydrogen storage material, and different semiconductor devices shows that features with a diameter as small as 1-2 nm can be resolved in three dimensions by electron tomography. For partially crystalline materials with small single crystalline domains, bright-field TEM tomography provides reliable 3D structural information. HAADF-STEM tomography is more versatile and can also be used for high-resolution 3D imaging of highly crystalline materials such as semiconductor devices.

Ultrathin polymer capsules prepared by stepwise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde latex particles and biological cells with subsequent dissolution of the core have been examined by scanning force microscopy (SFM) in the dried state. Folds generated during the dryinginduced collapse of the shells are observed. The thickness of a single polyelectrolyte layer in the dried state was determined as 1.3 ( 0.3 nm. Imaging at high resolution revealed the existence of domains and invaginations. This typical lateral pattern has been quantified by means of an autocorrelation analysis of the SFM images. A characteristic domain size of 50-100 nm is found. If the polyelectrolytes have been cross-linked prior to the core decomposition, a surface separation into defined domains is not observed. The nature and size of the domains are discussed in relation to the drying and the molecular parameters of the layer constituents.

Heating-induced morphological changes of micrometer size capsules prepared by step-wise deposition of oppositely charged polyelectrolytes onto melamine formaldehyde (MF) latex particles and biological cells with subsequent dissolution of the core have been investigated by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). For poly(styrenesulfonate-Na salt)/poly(allylamine hydrochloride) polyelectrolyte capsules a remarkable heating-induced shrinking is observed. An increase of the wall thickness corresponding to the capsule diameter decrease is found. The morphology of these microcapsules after temperature treatment is characterized. The thickening of the polyelectrolyte multilayer is interpreted in terms of a configurational entropy increase via polyanionpolycation bond rearrangement.

Unravelling principles underlying neurotransmitter release are key to understand neural signaling. Here, we describe how surface mobility of voltage-dependent calcium channels (VDCCs) modulates release probabilities (P(r)) of synaptic vesicles (SVs). Coupling distances of <10 to >100 nm have been reported for SVs and VDCCs in different synapses. Tracking individual VDCCs revealed that within hippocampal synapses, ∼60% of VDCCs are mobile while confined to presynaptic membrane compartments. Intracellular Ca(2+) chelation decreased VDCC mobility. Increasing VDCC surface populations by co-expression of the α2δ1 subunit did not alter channel mobility but led to enlarged active zones (AZs) rather than higher channel densities. VDCCs thus scale presynaptic scaffolds to maintain local mobility. We propose that dynamic coupling based on mobile VDCCs supports calcium domain cooperativity and tunes neurotransmitter release by equalizing Pr for docked SVs within AZs.

Rhodamin 6G were precipitated within the capsules.