Electrospun Amphiphilic Nanofibers as Templates for In Situ Preparation of Chloramphenicol-Loaded Liposomes.

The hydration of phospholipids, electrospun into polymeric nanofibers and used as templates for liposome formation, offers pharmaceutical advantages as it avoids the storage of liposomes as aqueous dispersions. The objective of the present study was to electrospin and characterize amphiphilic nanofibers as templates for the preparation of antibiotic-loaded liposomes and compare this method with the conventional film-hydration method followed by extrusion. The comparison was based on particle size, encapsulation efficiency and drug-release behavior. Chloramphenicol (CAM) was used at different concentrations as a model antibacterial drug. Phosphatidylcoline (PC) with polyvinylpyrrolidone (PVP), using ethanol as a solvent, was found to be successful in fabricating the amphiphilic composite drug-loaded nanofibers as well as liposomes with both methods. The characterization of the nanofiber templates revealed that fiber diameter did not affect the liposome size. According to the optical microscopy results, the immediate hydration of phospholipids deposited on the amphiphilic nanofibers occurred within a few seconds, resulting in the formation of liposomes in water dispersions. The liposomes appeared to aggregate more readily in the concentrated than in the diluted solutions. The drug encapsulation efficiency for the fiber-hydrated liposomes varied between 14.9 and 28.1% and, for film-hydrated liposomes, between 22.0 and 77.1%, depending on the CAM concentrations and additional extrusion steps. The nanofiber hydration method was faster, as less steps were required for the in-situ liposome preparation than in the film-hydration method. The liposomes obtained using nanofiber hydration were smaller and more homogeneous than the conventional liposomes, but less drug was encapsulated.

Strong, Rapid, and Reversible Photochromic Response of Nb Doped TiO2 Nanocrystal Colloids in Hole Scavenging Media.

Understanding photochromicity is essential for developing new means of modulating the optical properties and optical response of materials. Here, we report on the synthesis and exciting new photochromic behavior of Nb5+ doped TiO2 nanoparticle colloids (NCs). We find that, in hole scavenging media, Nb5+ doping significantly improves the photochromic response time of TiO2 nanoparticles. In the infrared regime, Nb-doped TiO2 NCs exhibit 1 order of magnitude faster photoresponse kinetics than the pristine TiO2. Enhanced photochromic response is observed in the visible light regime as well. The transmittance of Nb-doped TiO2 NCs drops to 10% in less than 2 min when irradiated by UV-light in the 500 nm range. The photochromic reaction is fully reversible. The physical origin of the high reaction rate is the high Nb5+ concentration. As a donor dopant, Nb5+ builds up a significant positive charge in the material, which leads to highly efficient electron accumulation during the UV irradiation and results in a rapid photoresponse. EPR experiments identify a new defect type from Nb5+ doping, which alters the physical mechanisms available for transmittance modulation. Our new NCs are economic to synthesize and highly suitable for switchable photochromic applications, e.g., smart windows for modulating visible light and infrared transmittance in built-environments.

Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate.

Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO2 nanoparticles (NPs) on Si substrates. The NPs are bound into the film by p-toluenesulfonic acid (PTSA) and the film is made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon substrate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.

Bacterial polysaccharide levan as stabilizing, non-toxic and functional coating material for microelement-nanoparticles.

Levan, fructose-composed biopolymer of bacterial origin, has potential in biotechnology due to its prebiotic and immunostimulatory properties. In this study levan synthesized by levansucrase from Pseudomonas syringae was thoroughly characterized and used as multifunctional biocompatible coating material for microelement-nanoparticles (NPs) of selenium, iron and cobalt. Transmission electron microscopy (TEM), hydrodynamic size measurements (DLS) and X-ray photoelectron spectroscopy (XPS) showed the interaction of levan with NPs. Levan stabilized the dispersions of NPs, decreased their toxicity and had protective effect on human intestinal cells Caco-2. In addition, levan attached to cobalt NPs remained accessible as a substrate for the colon bacteria Bacteroides thetaiotaomicron. We suggest that the combination of levan and nutritionally important microelements in the form of NPs serves as a first step towards a novel "2 in 1" approach for food supplements to provide safe and efficient delivery of microelements for humans and support beneficial gut microbiota with nutritional oligosaccharides.

Photocatalytic antibacterial activity of nano-TiO2 (anatase)-based thin films: effects on Escherichia coli cells and fatty acids.

Titanium dioxide is a photocatalyst with well-known ability to oxidise a wide range of organic contaminants as well as to destroy microbial cells. In the present work TiO2 nanoparticles with high specific surface area (150m(2)/g) were used to prepare nanostructured films. The TiO2 nanoparticle-based film in combination with UV-A illumination with intensity (22W/m(2)) comparable to that of the sunlight in the UV-A region was used to demonstrate light-induced antibacterial effects. Fast and effective inactivation of Escherichia coli cells on the prepared thin films was observed. Visualization of bacterial cells under scanning electron microscopy (SEM) showed enlargement of the cells, distortion of cellular membrane and possible leakage of cytoplasm after 10min of exposure to photoactivated TiO2. According to the plate counts there were no viable cells as early as after 20min of exposure to UV-A activated TiO2. In parallel to effects on bacterial cell viability and morphology, changes in saturated and unsaturated fatty acids - important components of bacterial cell membrane-were studied. Fast decomposition of saturated fatty acids and changes in chemical structure of unsaturated fatty acids were detected. Thus, we suggest that peroxidation and decomposition of membrane fatty acids could be one of the factors contributing to the morphological changes of bacteria observed under SEM, and ultimately, cell death.

An energy transfer kinetic probe for OH-quenchers in the Nd(3+):YPO4 nanocrystals suitable for imaging in the biological tissue transparency window.

Tetragonal xenotime-type yttrium orthophosphate (YPO4) Nd(3+) doped nanoparticles suitable for biomedical applications were prepared by microwave-hydrothermal treatment. We applied the energy transfer probing based on the analysis of kinetics of impurity quenching to determine the presence and spatial position of -OH fluorescence quenching acceptors in the impurity-containing nanoparticles. We show that the impurity quenching kinetics of the 0.1 at% Nd(3+) doped YPO4 nanoparticles is a two stage (ordered and disordered) static kinetics, determined by a direct energy transfer to the -OH acceptors. Analyzing the ordered stage, we assume that the origin of the -OH groups is the protonation of the phosphate groups, while analyzing the disordered stage, we assume the presence of water molecules in the mesopores. We determine the dimension of the space of the -OH acceptors as d = 3 and quantify their absolute concentration using the disordered Förster stage of kinetics. We use the late stage of kinetics of fluorescence hopping (CDD ≫ CDA) quenching (the fluctuation asymptotics) at 1 at% Nd(3+) concentration as an energy transfer probe to quantify the relative concentration of -OH molecular groups compared to an optically active rare-earth dopant in the volume of NPs, when energy migration over Nd(3+) donors to the -OH acceptors accelerates fluorescence quenching. In doing so we use just one parameter α = γ(A)/γ(D) = n(A)√[C(DA)]/n(D)√[C(DD)], defined by the relation of concentration of the -OH acceptors to the concentration of an optically active dopant. The higher is the α, the higher is the relative concentration of -OH acceptors in the volume of nanoparticles. We find α = 2.95 for the 1 at% Nd(3+):YPO4 NPs that, according to the equation for α, and the results obtained for the values of the microparameters CDD(Nd-Nd) = 24.6 nm(6) ms(-1) and CDA(Nd-OH) = 0.6 nm(6) ms(-1), suggests twenty times higher concentration for acceptors other than donors. As the main result we have established that the majority of -OH acceptors is located not on the surface of the Nd(3+):YPO4 nanoparticles, as many researchers assumed, but in their volume, and can be either associated with crystal structure defects or located in the mesopores.

TiO2 nanowire dispersions in viscous polymer matrix: electrophoretic alignment and optical properties.

The changes in optical properties during TiO2 nanowire orientation in polydimethylsiloxane (PDMS) matrix under the influence of an electric field are strongly influenced by nanowire (NW) diameter. It was demonstrated for the first time that either positive or negative change in transmittance can be induced by NW alignment parallel to the electric field depending on the NW diameter. These effects can be explained by the interplay between scattering and reflectance. Experimental findings reported could be important for smart window applications for the regulation of visible or even infrared transparency, thus reducing the energy consumption by air conditioning systems in buildings and automobiles in the future.

Dissolution of silver nanowires and nanospheres dictates their toxicity to Escherichia coli.

Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of 100 × 6100 nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag(+) ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ~80-100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles.