A method for preparation of silica nanocapsules is described, by interfacial polymerisation of nanoemulsions which are prepared by the phase inversion temperature (PIT) method. This is a low-energy emulsification technique which does not require any special equipment, such as high-pressure homogenisers. The nanoemulsions were prepared with decane as the oil phase, in which tetraethoxysilane (TEOS) was dissolved with an ethoxylated alcohol as the surfactant. The hydrolysis and polymerisation of the TEOS was performed under acidic and basic conditions using HCl and ammonia, respectively. The obtained nanocapsules with an average size between 100 and 300 nm, which were comprised of an oil core (decane) and silica shell, were characterised using dynamic light scattering, fourier transform infrared spectroscopy (FTIR), high-resolution scanning electron microscopy (HR-SEM) and by fluorescence of an encapsulated solvatochromic dye. The capsules could be positively or negatively charged by adsorption of ionic surfactants after they were formed.
Polyelectrolyte protected beta-carotene nanoparticles (nanosuspensions) with average diameter of <100 nm were achieved by turbulent mixing and flash nanoprecipitation (FNP). Three types of multi-amine functional polyelectrolytes, epsilon-polylysine (epsilon-PL), poly(ethylene imine) (PEI), and chitosan, were investigated to electrosterically protect the nanoparticles. Particle size and distribution were measured by dynamic light scattering (DLS); particles were imaged via scanning electron microscopy (SEM) and cryogenic transmission electron microscopy (cryo-TEM). Low pH and high polyelectrolyte molecular weight gave the smallest and most stable particles. High drug loading capacity, >80 wt%, was achieved by using either PEI or chitosan. X-ray diffraction (XRD) patterns showed that beta-carotene nanoparticles were amorphous. These findings open the way for utilization of FNP for preparation of nanoparticles with enhanced bioavailability for highly water insoluble drugs. (C) 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4295-4306, 2010
A new approach to achieve coalescence and sintering of metallic nanoparticles at room temperature is presented. It was discovered that silver nanoparticles behave as soft particles when they come into contact with oppositely charged polyelectrolytes and undergo a spontaneous coalescence process, even without heating. Utilizing this finding in printing conductive patterns, which are composed of silver nanoparticles, enables achieving high conductivities even at room temperature. Due to the sintering of nanoparticles at room temperature, the formation of conductive patterns on plastic substrates and even on paper is made possible. The resulting high conductivity, 20% of that for bulk silver, enabled fabrication of various devices as demonstrated by inkjet printing of a plastic electroluminescent device.
It was found that during the evapn. of water from a droplet of a silver nanoparticles dispersion a self-assembly process leads to the coalescence of the nanoparticles at room temp. and eventually results in a 3D, micrometer-sized dendrite. Direct in situ HR-TEM observation of coalescence events of individual nanoparticles revealed that during this process a transformation of the nanoparticles' crystal structure takes place, from the common fcc silver structure to the unusual hcp structure. It was found that even-though a majority of the nanoparticles in the dispersion have the fcc structure the obtained dendrites are characterized by the hcp structure, reflecting the crystal structure transformation due to the coalescence process. [on SciFinder(R)]
How do intricate multi-residue features such as protein-protein interfaces evolve. To address this question, we evolved a new colicin-immunity binding interaction. We started with Im9, which inhibits its cognate DNase ColE9 at 10-14 M affinity, and evolved it toward ColE7, which it inhibits promiscuously (Kd > 10-8 M). Iterative rounds of random mutagenesis and selection toward higher affinity for ColE7, and selectivity (against ColE9 inhibition), led to an ∼105-fold increase in affinity and a 108-fold increase in selectivity. Anal. of intermediates along the evolved variants revealed that changes in the binding configuration of the Im protein uncovered a latent set of interactions, thus providing the key to the rapid divergence of new Im7 variants. Overall, protein-protein interfaces seem to share the evolvability features of enzymes, i.e., the exploitation of promiscuous interactions and alternative binding configurations via 'generalist' intermediates, and the key role of compensatory stabilizing mutations in facilitating the divergence of new functions. [on SciFinder(R)]
Copper nanoparticles can be utilized as a low-cost replacement for silver and gold nanoparticles which are currently used in ink-jet printing of conductive patterns. However, the main obstacle for using copper nanoparticles is their spontaneous oxidn. at ambient conditions. Here the authors describe the synthesis of nonoxidizable copper nanoparticles by coating them with a silver shell, and ink-jet printing of these particles. The formation of these core-shell nanoparticles is driven by a transmetalation reaction on the surface of copper nanoparticles, where the copper atoms present on the particles' surface are used as the reducing agent for the silver. This process results in formation of solely copper-silver core-shell nanoparticles, with no individual silver particles. It was found that coating 40 nm copper nanoparticles with a 2 nm layer of silver prevents oxidn. of the copper core and preserves its metallic characteristic. Characterization of these nanoparticles by HR-TEM, SEM, EDS, XRD, spectrophotometry and XPS confirm the core-shell structure and their stability to oxidn. Ink-jet printing of concd. aq. dispersions of these copper-silver nanoparticles was done on various substrates, and it was found that conductive and decorative patterns with metallic appearance, stable to oxidn. (up to 150°) are formed. [on SciFinder(R)]
Highly luminescent org. nanoparticles were formed by embedding hydrophobic and hydrophilic (CdSe)ZnS quantum dots with core/shell structure into Et cellulose nanoparticles. The nanoparticles were prepd. from oil-in-water nanoemulsions by a phase inversion process at const. temp., followed by a solvent evapn. The obtained fluorescent Et cellulose nanoparticles were functionalized by immobilization of a specific antibody, and applied in rapid agglutination test for detection of Yersinia pestis F1-antigen. [on SciFinder(R)]
The formation of nanoparticles by interaction of an anionic polyelectrolyte, sodium polyacrylate (NaPA), was studied with a series of oppositely charged surfactants with different chain lengths, alkyltrimethylammonium bromide (CnTAB). The binding and formation of nanoparticles was characterized by dynamic light scattering, ζ-potential, and self-diffusion NMR. The inner nanostructure of the particles was obsd. by direct-imaging cryogenic-temp. transmission electron microscopy (cryo-TEM), indicating aggregates of hexagonal liq. crystal with nanometric size. [on SciFinder(R)]
Phase changes during the prepn. of nano-emulsions contg. polymerizable monomer as the oil phase, by the phase inversion temp. technique (PIT), were investigated using light microscopy, cryo-TEM and viscosity measurements. The nano-emulsions were prepd. using a poly(oxyethylene) nonionic surfactant and a polymerizable acrylic monomer (lauryl acrylate) as the oil phase. Inversion of the emulsion, followed by rapid cooling, resulted in emulsions having an av. droplet size as low as 25 nm. Cryo-TEM was used to observe the structures that are present above and below the phase transition temp., and gave, for the first time, visual indication of the presence of a microemulsion and a locally ordered structure in the process. At high surfactant concns., the inversion-cooling process yields emulsions with unique structures, in which the oil phase is present as worm-like structures. [on SciFinder(R)]
Synthesis of well dispersed copper nanoparticles was achieved by redn. of copper nitrate in aq. soln. using hydrazine monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addn. of silver nanoparticles to the reaction mixt. leads to formation of aq. dispersion of copper nanoparticles and also results in a drastic redn. in reaction time compared to procedures reported in the literature. The absorption spectrum of the dispersions, HR-TEM, and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size in the range of 5-50 nm. [on SciFinder(R)]
We report here a concept for utilization of the "coffee ring effect" and inkjet printing to obtain transparent conductive patterns, which can replace the widely used transparent conductive oxides, such as ITO. The transparent conductive coating is achieved by forming a 2-D array of interconnected metallic rings. The rim of the individual rings is less than 10 μm in width and less than 300 nm in height, surrounding a "hole" with a diam. of about 150 μm; therefore the whole array of the interconnected rings is almost invisible to the naked eye. The rims of the rings are composed of self-assembled, closely packed silver nanoparticles, which make the individual rings and the resulting array elec. conductive. The resulting arrays of rings have a transparency of 95%; resistivity of 0.5 cm2 was 4 ± 0.5 Ω/☐, which is better than conventional ITO transparent thin films. The silver rings and arrays are fabricated by a very simple, low cost process, based on inkjet printing of a dispersion of 0.5 wt % silver nanoparticles (∼20 nm diam.) on plastic substrates. The performance of this transparent conductive coating was demonstrated by using it as an electrode for a plastic electroluminescent device, demonstrating the applicability of this concept in plastics electronics. It is expected that such transparent conductive coatings can be used in a wide range of applications such as displays (LCD, plasma, touch screens, e-paper), lighting devices (electroluminescence, OLED), and solar cells. [on SciFinder(R)]
The binding mechanism of poly(diallyldimethylammonium chloride), PDAC, and sodium dodecyl sulfate, SDS, has been comprehensively studied by combining binding isotherms data with microcalorimetry, zeta potential, and cond. measurements, as well as ab initio quantum mech. calcns. The obtained results demonstrate that surfactant-polymer interaction is governed by both electrostatic and hydrophobic interactions, and is cooperative in the presence of salt. This binding results in the formation of nanoparticles, which are pos. or neg. charged depending on the molar ratio of surfactant to PDAC monomeric units. From microcalorimetry data it was concluded that the exothermic character of the interaction diminishes with the increase in the surfactant/polymer ratio as well as with an increase in electrolyte concn. [on SciFinder(R)]
Alginate-gelatin beads with dispersed droplets of a model pheromone, dodecyl acetate, were prepd. as a vehicle for slow release of pheromones into the atm. over a prolonged period of time. The beads are prepd. in two steps, the first being prepn. of an oil-in-water emulsion composed of dodecyl acetate as the oil phase and gelatin as the emulsifier, which provides steric stabilization. After mixing with alginate soln., this emulsion is embedded within beads by simple electrostatic crosslinking. Bead porosity at micrometric and nanometric scales plays an important role in controlling the release of dodecyl acetate. [on SciFinder(R)]
A new method for the prepn. of nanoparticles from nano-emulsions using a low-energy emulsification method based on phase inversion at const. temp. (catastrophic inversion) is described. This method does not require any special equipment such as high-pressure homogenizers. The method is demonstrated for the prepn. of Et cellulose nanoparticles contg. pyrene (a microviscosity and micropolarity probe) as a hydrophobic model mol. The nano-emulsions were prepd. using a combination of non-ionic surfactants: Polyglycerol fatty acid ester (decaglycerol mono laurate) and sorbitan ester (Span 20), volatile org. solvent (toluene) and Et cellulose. Toluene was evapd. from the nano-emulsions, resulting in Et cellulose nanoparticles 50-120 nm in size. The emission colors of the pyrene-embedded nano-emulsions changed from blue to violet after the evapn. of the toluene because of the absence of excimers. This method may be applied for the prepn. of a variety of polymeric nanoparticles in which functional mols. are embedded within the particles. [on SciFinder(R)]
We describe a new method for the prepn. of org. nanoparticles from nanoemulsions which were prepd. by the phase inversion temp. (PIT) method. This is a low-energy technique which does not require any special equipment such as high pressure homogenizers. In this work, the method is demonstrated for prepn. of nanoparticles of poly-lauryl acrylate contg., in some cases, a crosslinker (trimethylolpropane triacrylate-TMPTA) and pyrene as microviscosity and micropolarity probes, resp. The nanoemulsions were prepd. by using a poly(oxyethylene) nonionic surfactant, Brij 96V (POE (10) oleyl alc.), and combinations of Brij 96V and Brij 92V (POE (2) oleyl alc.), with acrylate monomers which form the oil phase in the oil-in-water (O/W) emulsions. The nanodroplets were polymd., yielding nanoparticles having an av. diam. between 50 and 120 nm with a narrow size distribution, using a water-sol. thermal initiator (ammonium persulfate) and activated by ferrous ions, Fe+2. The emission colors of the pyrene-embedded nanoemulsions changed from blue to violet after polymn., due to the absence of excimers. This method may be applied for the prepn. of a variety of polymeric nanoparticles, in which functional mols. are embedded within the particles. [on SciFinder(R)]
The efficient amplification of genomic libraries, cDNA libraries and other complex mixts. of genes by PCR is impeded by two phenomena: firstly, short fragments tend to be amplified in preference to larger ones; and, secondly, artifactual fragments are generated by recombination between homologous regions of DNA. Recombination in this case occurs when a primer is partially extended on one template during one cycle of PCR and further extended on another template during a later cycle. Thus, chimeric mols. are generated, the short ones of which are then preferentially amplified. A variety of PCR protocols have been proposed to minimize these problems, most of which rely on high template concns. and low nos. of PCR cycles. Clearly, however, such an approach is not viable if little template DNA is available. Here we describe a protocol for amplifying complex DNA mixts., based on the compartmentalization of genes in a water-in-oil (w/o) emulsion. Template fragments are segregated in the minute aq. droplets of the emulsion and amplified by PCR in isolation. This approach alleviates the problems described above while enabling the use of small amts. of template DNA and high nos. of PCR cycles. Box 1 described an alternative method for generating very stable emulsions for emulsion PCR using the surfactant ABIL EM 90. [on SciFinder(R)]