Recent publication highlights

Abstract: Paper-supported solvent-responsive elastomeric opal films based on hard-soft core-interlayer-shell spheres featuring remarkably distinct iridescent reflection colors were investigated. By using extrusion and compression molding, elastomeric opal films could be obtained, which were incorporated into a porous paper sheet to build robust composites. Swelling of the opal paper composites caused by various solvents was accompanied with a tremendous photonic band gap shift of the reflection colors. The combination of the extraordinary optical properties of the elastomeric opal films used with the remarkable features of highly porous paper can be the basis for a whole family of polymer-based soft sensors featuring a fascinating optical, fast and reversible response.

Abstract: Hydrophilic paper was rendered with hydrophobic and superhydrophobic property after the treatment with solutions and nanoparticles of cellulose stearoyl ester (CSE), respectively. Cellulose stearoyl ester with a degree of substitution of 2.99 was synthesized from cellulose using stearoyl chloride. By dip-coating paper in CSE solution of at least 3 mg/ml in toluene, paper became hydrophobic with stable water contact angles of more than 120°. After further spray-coating using CSE nanoparticles that were prepared from CSE solution via nanoprecipitation, paper surface became superhydrophobic with water contact angles of larger than 150°. These superhydrophobic surfaces also exhibited self-cleaning character. Furthermore, the superhydrophobic paper surfaces showed a temperature-responsive character and could be turned hydrophobic after a heat-treatment at 70 °C for 5 min.

Abstract: Controlling structure and function to switch ionic transport through synthetic membranes is a major challenge in the fabrication of functional nanodevices. Here we describe the combination of mesoporous silica thin films as structural unit, functionalized with two different redox-responsive ferrocene-containing polymers, polyvinylferrocene (PVFc) and poly(2-(methacryloyloxy)ethyl ferrocenecarboxylate) (PFcMA), by using either a grafting to, or a grafting from approach. Both mesoporous film functionalization strategies are investigated in terms of polymer effect on ionic permselectivity. A significantly different ionic permselective behavior can be observed. This is attributed to different polymer location within the mesoporous film, depending on the functionalization strategies used. Additionally, the influence of chemical oxidation on the ionic permselective behavior is studied by cyclic voltammetry showing a redox-controlled membrane gating as function of polymer location and the pH value. This study is a first step of combining redox-responsive ferrocene-containing polymers and mesoporous membranes, and thus towards redox-controlled ionic transport through nanopores.

Abstract: In the present study, we introduce a novel approach to control and modulate fluid transport inside microfluidic papers using lab-engineered paper sheets. Lab-sheets consisting of different fiber sources (eucalyptus sulfate and cotton linters pulp) and varying porosities were designed and further modified with small millimeter-scaled channels using hydrophobic barriers consisting of fiber-attached, hydrophobic polymers. The capillary-driven transport of an aqueous solution was monitored visually, and the influence of parameters such as fiber source, paper grammage, and channel width on the flow rates through the channel was investigated. The experimental results were compared with those obtained with commercially available filter papers. Our findings suggest that accurate control of fluid transport processes with standard filter papers is complex. Additionally, if the channel width is smaller than the mean fiber length, flow rates become dependent on the geometric parameters of the channel because of the formation of dead-end pores at the hydrophobic barriers. Finally, control of the paper sheets porosity, by varying the fiber density of the lab-made paper, affords the fabrication of chemically identical sheets whereby capillary flow is largely influenced and can be modulated accordingly by simple papermaking processes.

Abstract: Microparticle manipulation: The photoisomerization of surfactants adsorbed at a gas–liquid interface drives a Marangoni flow that can be used for the trapping and manipulation of small particles. By switching the laser wavelength, a flow either into or away from the focal spot can be induced. The picture shows a microparticle trapped in the focal region by the inflow.

Abstract: The viral channel KcvNTS belongs to the smallest K+ channels known so far. A monomer of a functional homotetramer contains only 82 amino acids. As a consequence of the small size the protein is almost fully submerged into the membrane. This suggests that the channel is presumably sensitive to its lipid environment. Here we perform a comparative analysis for the function of the channel protein embedded in three different membrane environments. 1. Single-channel currents of KcvNTS were recorded with the patch clamp method on the plasma membrane of HEK293 cells. 2. They were also measured after reconstitution of recombinant channel protein into classical planar lipid bilayers and 3. into horizontal bilayers derived from giant unilamellar vesicles (GUVs). The recombinant channel protein was either expressed and purified from Pichia pastoris or from a cell-free expression system; for the latter a new approach with nanolipoprotein particles was used. The data show that single-channel activity can be recorded under all experimental conditions. The main functional features of the channel like a large single-channel conductance (80 pS), high open-probability (> 50%) and the approximate duration of open and closed dwell times are maintained in all experimental systems. An apparent difference between the approaches was only observed with respect to the unitary conductance, which was ca. 35% lower in HEK293 cells than in the other systems. The reason for this might be explained by the fact that the channel is tagged by GFP when expressed in HEK293 cells. Collectively the data demonstrate that the small viral channel exhibits a robust function in different experimental systems. This justifies an extrapolation of functional data from these systems to the potential performance of the channel in the virus/host interaction. This article is part of a Special Issue entitled: Viral Membrane Proteins—Channels for Cellular Networking.