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are observed in the emission spectra, the research team asserts that an interfacial barrier preventing complete transfer of the electron to the lowest energy conduction band exists. The researchers conclude that uniformity of morphology is directly related to the uniformity of quantum confinement in the particles, and affects electronic delocalization across the heterojunction. Band misalignment is more prevalent in morphologically uniform particles,
and there appears to be a barrier to electron transfer between CdS and CdSe in these cases. The researchers suggest that nanostructures with uniform morphologies are desirable for light-emitting devices while those with some structural variation are more suited for light-harvesting applications because the barrier to electron transfer across the junction is less prevalent. Alia P. Schoen
ed layer-by-layer coating for genetically engineered yeast cells, which offers high permeability and biocompatibility. The research, published in the 2011 odifying the surface of cells is online edition of Soft Matter (DOI: a useful way of altering their 10.1039/c0sm01070g), looks at yeast functionality or protecting them from cells (S. cerevisiae) engineered to exhostile environments. As living cells press green fluorescent protein (GFP) become increasingly exploited for uses (see Figure). These cells can be used in biomedicine and biosensing, the abilas biosensors, as the production of the ity to tailor their external properties is of fluorescent protein is triggered by cergrowing importance. In order to avoid tain inducer molecules. By dispersing the cytotoxicity of ionic polymer coatthem in aqueous solutions, the cells ings, the groups of V. Tsukruk from the are coated in successive layers of poly Georgia Institute of Technology and M. (N-vinylpyrrolidone) and tannic acid, in Stone from the Air Force Research Labowhich the hydroxyl groups of the acid ratory have developed a hydrogen-bondform a hydrogen bond to the carbonyl groups of the polymer. The properties of the polymer membrane are assessed with respect to the number of bilayers applied and also compared with the commonly used polyelectrolyte cell coating poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/PSS). Using the resazurin assay to test cell viability shows that while three of the hydrogenbonded bilayers cause only 20% cell death, the same number of A confocal microscopy image of green fluorescing yeast cells traditional polyelec(~5 μm) that have been coated with polymer shells (labeled for red trolyte layers results fluorescence). Reproduced with permission from Soft Matter (2011) in over 80%. The toDOI: 10.1039/c0sm01070g. © 2011 Royal Society of Chemistry. pography and perme-
ability of the coatings are studied on hollow polymer shells formed by coating silica particles and then removing the interior. The surface of the tannic-acid/ polymer structures appears grainy and porous in atomic force microscopy imaging, and correspondingly they have a much higher (up to five times) diffusion coefficient than PA
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