Karina Bley

Using the Polymeric Ouzo Effect for the Preparation of Polysaccharide-Based Nanoparticles

The polymeric ouzo effect, a nanoprecipitation process, is used for the preparation of polysaccharide-based nanoparticles. Dextran, pullulan, and starch were esterified with hydrophobic carboxylic acid anhydrides to obtain hydrophobic polysaccharides, which are insoluble in water. The additional introduction of methacroyl residues offers the possibility to cross-link the generated nanostructures, which become insoluble in organic solvents. To make use of the ouzo effect for the formation of nanoparticles, the polymer has to be soluble in an organic solvent, which is miscible with water. Here, acetone and THF were used. Immediately after the organic polymer solution is added to water, nanoparticles are generated. The size of the nanoparticles can be adjusted between 50 and 200 nm by changing the concentration of the initial polysaccharide solution. The degree of hydrophobic substitution was shown to have a very minor effect on the particle size. Dispersions with solids contents of up to 2% were obtained. Furthermore, the mechanical properties of the nanoparticles were investigated with force microscopy, and it was shown by fluorescence correlation spectroscopy that a fluorescent dye could be encapsulated in the nanoparticles by the applied nanoprecipitation procedure.

Kelvin Probe Force Microscopy in Nonpolar Liquids

Work function changes of Au were measured by Kelvin probe force microscopy (KPFM) in the nonpolar liquid decane. As a proof of principle for the measurement in liquids, we investigated the work function change of an Au substrate upon hexadecanethiol chemisorption. To relate the measured contact potential difference (CPD) during the chemisorption of alkanethiols to a change of the work function, the influence of physisorbed decane must be taken into account. It is crucial that either the work function of the scanning probe microscope (SPM) tip or the sample surface remains constant throughout the reaction, since both contribute to the CPD. We describe two routes for determining the work function shift of Au coated with a monolayer of alkanethiols: In the first route, the SPM tips were taken as reference surfaces (constant tip work function). For this approach, we used Au(111) surfaces and kept the SPM tip ex situ during the adsorption process. In the second route, structured surfaces with reactive and inert parts were studied by KPFM (constant reference work function). For this route, we prepared nanometer sized Au structures by nanosphere lithography on SiO(x) substrates. Now, the SiO(x) served as the inert reference surface. The shifts in the work function after exposure to the hexadecanethiol (HDT) solution were determined to be ΔΦ(Au+HDT,decane-Au,air) = -1.33 eV ± 0.07 eV (route I) and ΔΦ(Au+HDT,decane-Au,air) = -1.46 eV ± 0.04 eV (route II). Both values are in excellent agreement with the work function shifts determined by ultraviolet photoemission spectroscopy (UPS) reported in literature. The presented procedures of measuring work function changes in decane open new ways to study local reactions at solid-liquid interfaces.

Direct visualization of the interfacial position of colloidal particles and their assemblies

A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply this method to investigate the formation of complex, binary assembly structures directly at the interface, to visualize soft, nanoscale hydrogel colloids in the swollen state, and to visualize and quantify the equilibrium position of individual micro- and nanoscale colloids at the air-water interface depending of the amount of charge present on the particle surface. We find that the degree of deprotonation of the carboxyl group shifts the air-water contact angle, which is further confirmed by colloidal probe atomic force microscopy. Remarkably, the contact angles determined for individual colloidal particles feature a significant distribution that greatly exceeds errors attributable to the size distribution of the colloids. This finding underlines the importance of accessing soft matter on an individual particle level.

Functional superhydrophobic surfaces made of Janus micropillars.

Particle coated micropillar arrays having hydrophobic sidewalls and hydrophilic silica tops are fabricated, enabling the top sides to be selectively post-functionalized. The so termed Janus pillars remain in the Cassie state even after chemical modification of the top faces.

Nanoprobing the acidification process during intracellular uptake and trafficking

UNLABELLED Many nanoparticular drug delivery approaches rely on a detailed knowledge of the acidification process during intracellular trafficking of endocytosed nanoparticles (NPs). Therefore we produced a nanoparticular pH sensor composed of the fluorescent pH-sensitive dual wavelength dye carboxy seminaphthorhodafluor-1 (carboxy SNARF-1) coupled to the surface of amino-functionalized polystyrene NPs (SNARF-1-NP). By applying a calibration fit function to confocal laser scanning microscopy (CLSM) images, local pH values were determined. The acidification and ripening process of endo/lysosomal compartments containing nanoparticles was followed over time and was found to progress up to 6h to reach an equilibrium pH distribution (maximum pH5.2 [±0.2]). The SNARF-1-NP localization in endo/lysosomal compartments was confirmed by transmission electron microscopy (TEM) and quantitative co-localization analysis with fluorescent endolysosomal marker Rab-proteins by confocal laser scanning microscopy (CLSM). The herein described nanoparticular pH-sensor is a versatile tool to monitor dynamic pH processes inside the endolysosomal compartments. FROM THE CLINICAL EDITOR In this interesting article, the authors elegantly designed a nanoparticular pH sensor with fluorescence probe with the capability to measure intracellular and intravesicular pH changes. The application of this method would enable the further understanding of nanoparticle uptake and intracellular physiology.

Switching light with light – advanced functional colloidal monolayers

Colloidal monolayers comprising of highly ordered two dimensional crystals are of high interest to generate surface patterns for a variety of different applications. Mostly, unfunctionalized polymer or silica colloids are assembled into monolayers. However, the incorporation of functional molecules into such colloids offers a convenient possibility of implementing additional properties to the two-dimensional crystal. Here, we present the formation of novel functional colloidal monolayers with photoswitchable fluorescence. The miniemulsion polymerization technique was used to incorporate an appropriate dye system of a perylene-based fluorophore and a bis-arylethene as a photochrome in polymeric colloids in defined ratios. Upon irradiation with UV or visible light the photochrome reversibly isomerizes from the ring-closed form, which is able to absorb light of the emission wavelength of the fluorescent dye and the ring-open form, which is not. The fluorescence emission of the dye can thus be reversibly switched on and off with light even when embedded in colloids. The colloids were self-assembled at the air-water interface to produce hexagonally ordered functional monolayers and more complex binary crystals. We investigate in detail the influence of the polymeric matrix on the switching properties of the fluorophore/photochrome system and find that the rate constants for the photoswitching, which all lie in the same range, are less influenced by the polymeric environment than expected. We demonstrate the reversible switching of the fluorescence emission in self-assembled colloidal monolayers. The arrangement of broadly distributed functional colloids into ordered monolayers with high addressability was obtained by the formation of binary colloidal monolayers.

Large area conductive nanoaperture arrays with strong optical resonances and spectrally flat terahertz transmission

Using simple and inexpensive nanosphere lithography, we produce large, centimeter-squared sized thin golden films patterned with a hexagonal array of nanoapertures with controllable dimensions on the order of 100–300 nm, spaced by a 350–375 nm pitch distance. The optical transmission spectra of our samples are dominated by the resonant plasmonic features in the spectral range 500–700 nm, caused by the nanostructure in the film. At the same time, the transmission at terahertz (THz) radiation is as high as ∼10% and is spectrally flat. Our measurements are in agreement with finite difference time domain simulations. Such thin metal hole array films allow for very efficient injection of optical energy, while at the same time maintaining reasonably high transparency of THz waves. These structures can be used in any application combining strong optical sensitivity and THz transparency, in optical biomolecular sensing, or as optically transparent electrodes.

Nano-holes vs nano-cracks in thin gold films: What causes anomalous THz transmission?

Nano-structuring materials can change their properties extraordinarily, but so can defects caused by manufacturing. We study the effect of capacitive defects on terahertz transmission in golden nanomeshes, and find their influence crucial.

Balancing ballistic and hopping light transport by purposive arraying of colloidal particles

Ordered and disordered monolayers of spheres were assembled on dielectric and metallized substrate using the Langmuir-Blodgett style technique. The coexistence of Mie and diffraction resonances was investigated. Experiments showed the weak dependence of diffraction resonances on the distance between spheres, but their gradual destruction with increasing disorder. In turn, Mie resonances appear along the increased light localization in the monolayer, but experience strong blue shift and gradual reduction of the magnitude along the increased isolation in the lattice. Calculation proved that hybridization of Mie resonances rapidly vanishes along the increase of the spacing between spheres and the hopping of excitations between spheres can be expected only in tightly packed arrays.

Geometrical control of the resonances and mode composition in hybrid plasmonic photonic crystals

Hybrid optical materials combining metallic plasmonic and dielectric photonic crystals in one hetero-structure possess several resonance mechanisms which critically influence light transport. In particular, a hybrid consisting of a monolayer of dielectric spheres assembled on a metal film-coated substrate simultaneously supports dielectric and surface plasmon polaritons (SPPs), Fabry-Perot resonances of the effective dielectric slab and Mie resonances of individual spheres. A seemingly powerful method to control the optical behavior of such hybrids is to play with the package density of spheres in the monolayer. But up to now this approach achieved only incremental variations. However, in this report we demonstrate that reduction of the sphere size by preserving the lattice constant brings dramatic changes to the optical response of the structure, if a semitransparent metal substrate is used.