Encapsulation, release and applications of LbL polyelectrolyte multilayer capsules

Ever since their invention in 1998, polyelectrolyte multilayer micro- and nano-capsules have impacted various areas of biology, chemistry and physics. Here we highlight progress achieved since the millennium in the areas of encapsulation in and release from microcapsules, describe various structures including multicompartment and anisotropic constructs, and provide examples of several applications in biology. We also describe application areas such as drug delivery, intracellular trafficking, enzyme-catalyzed reactions, mechano-biology which benefited from recent developments in the area of polyelectrolyte multilayer capsules.     

Effect of charge order on the plasmon dispersion in transition-metal dichalcogenides

We investigate the dispersion of the charge carrier plasmon in the three prototypical charge-density wave bearing transition-metal dichalcogenides 2H-TaSe(2), 2H-TaS(2), and 2H-NbSe(2) employing electron energy-loss spectroscopy. For all three compounds the plasmon dispersion is found to be negative for small momentum transfers. This is in contrast with the generic behavior observed in simple metals as well as the related system 2H-NbS(2), which does not exhibit charge order. We present a semiclassical Ginzburg-Landau model which accounts for these observations, and argue that the vicinity to a charge ordered state is thus reflected in the properties of the collective excitations.     

Nanoparticle modification by weak polyelectrolytes for pH-sensitive pickering emulsions

The affinity of weak polyelectrolyte coated oxide particles to the oil-water interface can be controlled by the degree of dissociation and the thickness of the weak polyelectrolyte layer. Thereby the oil in water (o/w) emulsification ability of the particles can be enabled. We selected the weak polyacid poly(methacrylic acid sodium salt) and the weak polybase poly(allylamine hydrochloride) for the surface modification of oppositely charged alumina and silica colloids, respectively. The isoelectric point and the pH range of colloidal stability of both particle-polyelectrolyte composites depend on the thickness of the weak polyelectrolyte layer. The pH-dependent wettability of a weak polyelectrolyte-coated oxide surface is characterized by contact angle measurements. The o/w emulsification properties of both particles for the nonpolar oil dodecane and the more polar oil diethylphthalate are investigated by measurements of the droplet size distributions. Highly stable emulsions can be obtained when the degree of dissociation of the weak polyelectrolyte is below 80%. Here the average droplet size depends on the degree of dissociation, and a minimum can be found when 15 to 45% of the monomer units are dissociated. The thickness of the adsorbed polyelectrolyte layer strongly influences the droplet size of dodecane/water emulsion droplets but has a less pronounced impact on the diethylphthalate/water droplets. We explain the dependency of the droplet size on the emulsion pH value and the polyelectrolyte coating thickness with arguments based on the particle-wetting properties, the particle aggregation state, and the oil phase polarity. Cryo-SEM visualization shows that the regularity of the densely packed particles on the oil-water interface correlates with the degree of dissociation of the corresponding polyelectrolyte.     

Electroactive multilayer assemblies of bilirubin oxidase and human cytochrome C mutants: insight in formation and kinetic behavior

Here, we report on cytochrome c/bilirubin oxidase multilayer electrodes with different cytochrome c (cyt c) forms including mutant forms of human cyt c, which exhibit different reaction rates with bilirubin oxidase (BOD) in solution. The multilayer formation via the layer-by-layer technique and the kinetic behavior of the mono (only cyt c) and biprotein (cyt c and BOD) multilayer systems are studied by SPR and cyclic voltammetry. For the layer construction, sulfonated polyaniline is used. The only cyt c containing multilayer electrodes show that the quantity of deposited protein and the kinetic behavior depend on the cyt c form incorporated. In the case of the biprotein multilayer with BOD, it is demonstrated that the catalytic signal chain from the electrode via cyt c to BOD and oxygen can be established with all chosen cyt c forms. However, the magnitude of the catalytic current as well as the kinetic behavior differ significantly. We conclude that the different cytochrome c forms affect three parameters, identified here, to be important for the functionality of the multilayer system: the amount of molecules per layer, which can be immobilized on the electrodes, the cyt c self-exchange rate, and the rate constant for the reaction with BOD.     

Self‐Healing and Antifouling Multifunctional Coatings Based on pH and Sulfide Ion Sensitive Nanocontainers

Application of mesoporous silica nanoparticles (MSNs) as delivery tools for self‐healing coatings is limited by spontaneous leakage and specifically responsive release of small molecular inhibitors. In this work, a pH/sulfide ion responsive release system based on MSNs using a Cu‐BTA complex forms at the openings of the mesopores into which BTA (corrosion inhibitor) and benzalkonium chloride (biocide) are loaded. The spontaneous leakage of active species is completely avoided and premature release of the loaded composition was lowered to 0.02. The responsive release begins when the pH is lower than 5 or [S^2?] is higher than 0.02 mM (about 0.6 ppm). The hybrid coating containing the responsive release system exhibits feedback self‐healing property sensitive to lowering of pH and sulfide ion concentration and, at the same time, provides a high barrier level for a long time. Due to incorporation of biocide in the release system, the coating is also provided with antifouling properties.     

Supramolecular Templates for Nanoflake–Metal Surfaces

A sustainable method for the fabrication of metallic surfaces with flower‐like fractal morphology was developed by using a three‐dimensional supramolecular assembly as a template. Modifying Au nanoflakes with self‐assembled monolayers or polymers allows the surface wettability to be adjusted from superhydrophobic to superhydrophilic (see figure). Furthermore, Au nanoflakes present excellent substrates for surface‐enhanced Raman spectroscopy (SERS).

     

Complexes of poly(ethylene oxide)-block-poly(L-glutamate) and diminazene

Nanoparticles with a mean hydrodynamic radius of 16 nm and low polydispersity (P.I. = 0.1) were spontaneously formed by the complexation of poly(ethylene oxide)-block-poly(L-glutamate) (PEO-b-PLGlu) with diminazene. Only one of two possible binding sites of each diminazene molecule was involved in complexation. As determined by UV-vis difference spectra measurements, the complex binding constant is on the order of 1-2 x 10(4) M(-1). Circular dichroism measurements showed that the highly water-soluble diminazene can induce and stabilize the alpha-helical secondary structure of a PLGlu block.     

Maghemite nanoparticles protectively coated with poly(ethylene imine) and poly(ethylene oxide)-block-poly(glutamic acid)

Superparamagnetic iron oxide particles (SPIO) of maghemite were prepared in aqueous solution and subsequently stabilized with polymers in two layer-by-layer deposition steps. The first layer around the maghemite core is formed by poly(ethylene imine) (PEI), and the second one is formed by poly(ethylene oxide)-block-poly(glutamic acid) (PEO-PGA). The hydrodynamic diameter of the particles increases stepwise from D(h) = 25 nm (parent) via 35 nm (PEI) to 46 nm (PEI plus PEO-PGA) due to stabilization. This is accompanied by a switching of their zeta-potentials from moderately positive (+28 mV) to highly positive (+50 mV) and finally slightly negative (-3 mV). By contrast, the polydispersity indexes of the particles remain constant (ca. 0.15). M?ssbauer spectroscopy revealed that the iron oxide, which forms the core of the particles, is only present as Fe(III) in the form of superparamagnetic maghemite nanocrystals. The magnetic domains and the maghemite crystallites were found to be identical with a size of 12.0 +/- 0.5 nm. The coated maghemite nanoparticles were tested to be stable in water and in physiological salt solution for longer than 6 months. In contrast to novel methods for magnetic nanoparticle production, where organic solvents are necessary, the procedure proposed here can dispense with organic solvents. Magnetic resonance imaging (MRI) experiments on living rats indicate that the nanoparticles are useful as an MRI contrast agent.     

Spin-lattice interaction in the quasi-one-dimensional helimagnet LiCu2O2

The field dependence of the electron spin resonance in a helimagnet LiCu2O2 was investigated for the first time. In the paramagnetic state, a broad resonance line was observed corresponding to a g factor of 2.3. In the critical regime, around the paramagnetic to helimagnetic phase transition the resonance broadens and shifts to higher frequencies. A narrow signal is recovered at a low temperature, corresponding to a spin gap of 1.4 meV in zero field. A comprehensive model of the magnons is presented, using exchange parameters from neutron scattering [T. Masuda Phys. Rev. B 72, 014405 (2005)10.1103/PhysRevB.72.014405] and the spin anisotropy determined here. The role of the quantum fluctuations is discussed.