Stefan Seeger

Understanding protein adsorption phenomena at solid surfaces

Protein adsorption at solid surfaces plays a key role in many natural processes and has therefore promoted a widespread interest in many research areas. Despite considerable progress in this field there are still widely differing and even contradictive opinions on how to explain the frequently observed phenomena such as structural rearrangements, cooperative adsorption, overshooting adsorption kinetics, or protein aggregation. In this review recent achievements and new perspectives on protein adsorption processes are comprehensively discussed. The main focus is put on commonly postulated mechanistic aspects and their translation into mathematical concepts and model descriptions. Relevant experimental and computational strategies to practically approach the field of protein adsorption mechanisms and their impact on current successes are outlined.

Oil/Water Separation with Selective Superantiwetting/Superwetting Surface Materials

The separation of oil from oily water is an important pursuit because of increasing worldwide oil pollution. Separation by the use of materials with selective oil/water absorption is a relatively recent area of development, yet highly promising. Owing to their selective superantiwetting/superwetting properties towards water and oil, superhydrophobic/superoleophilic surfaces and underwater superoleophobic surfaces have been developed for the separation of oil/water-free mixtures and emulsions. In this Review, after a short introduction to oil/water separation, we describe the principles of materials with selective oil/water absorption and outline recent advances in oil/water separation with superwetting/superantiwetting materials, including their design, their fabrication, and models of experimental setups. Finally, we discuss the current state of this new field and point out the remaining problems and future challenges.

Superoleophobic Coatings with Ultralow Sliding Angles Based on Silicone Nanofilaments

Superoleophobic surfaces were fabricated by using organosilanes. The surfaces feature high contact angles and ultralow sliding angles for various nonpolar liquids, excellent transparency, and chemical and environmental stability. The microstructure and superoleophobicity of the surfaces can be regulated simply by the water concentration in toluene used during the coating procedure. Copyright

Mechanism of Membrane Interaction and Disruption by α-Synuclein

Parkinsons disease is a common progressive neurodegenerative condition, characterized by the deposition of amyloid fibrils as Lewy bodies in the substantia nigra of affected individuals. These insoluble aggregates predominantly consist of the protein α-synuclein. There is increasing evidence suggesting that the aggregation of α-synuclein is influenced by lipid membranes and, vice versa, the membrane integrity is severely affected by the presence of bound aggregates. Here, using the surface-sensitive imaging technique supercritical angle fluorescence microscopy and Förster resonance energy transfer, we report the direct observation of α-synuclein aggregation on supported lipid bilayers. Both the wild-type and the two mutant forms of α-synuclein studied, namely, the familiar variant A53T and the designed highly toxic variant E57K, were found to follow the same mechanism of polymerization and membrane damage. This mechanism involved the extraction of lipids from the bilayer and their clustering around growing α-synuclein aggregates. Despite all three isoforms following the same pathway, the extent of aggregation and their effect on the bilayers was seen to be variant and concentration dependent. Both A53T and E57K formed cross-β-sheet aggregates and damaged the membrane at submicromolar concentrations. The wild-type also formed aggregates in this range; however, the extent of membrane disruption was greatly reduced. The process of membrane damage could resemble part of the yet poorly understood cellular toxicity phenomenon in vivo.

Superwetting Double-Layer Polyester Materials for Effective Removal of Both Insoluble Oils and Soluble Dyes in Water

Inspired by the mussel adhesive protein and the lotus leaf, Ag-based double-layer polyester (DL-PET) textiles were fabricated for effective removal of organic pollutants in water. The DL-PET textiles are composed of a top superamphiphilic layer and a bottom superhydrophobic/superoleophilic layer. First, the PET textiles were modified with a layer of polydopamine (PDA) and deposited with Ag nanoparticles to form the PET@PDA@Ag textiles. The top superamphiphilic layer, formed by immobilizing Ag3PO4 nanoparticles on the PET@PDA@Ag textile, shows excellent visible-light photocatalytic activity. The bottom superhydrophobic/superoleophilic layer, formed by modifying the PET@PDA@Ag textile using dodecyl mercaptan, is mechanically, environmentally, and chemically very stable. The water-insoluble oils with low surface tension can penetrate both layers of the DL-PET textiles, while the water with soluble organic dyes can only selectively wet the top layer owing to their unique wettability. Consequently, the water-soluble organic contaminants in the collected water can be decomposed by the Ag3PO4 nanoparticles of the top layer under visible-light irradiation or even sunlight in room conditions. Thus, the DL-PET textiles can remove various kinds of organic pollutants in water including both insoluble oils and soluble dyes. The DL-PET textiles feature unique wettability, high oil/water separation efficiency, and visible-light photocatalytic activity.

XRF-analysis of fine and ultrafine particles emitted from laser printing devices.

In this work, the elemental composition of fine and ultrafine particles emitted by ten different laser printing devices (LPD) is examined. The particle number concentration time series was measured as well as the particle size distributions. In parallel, emitted particles were size-selectively sampled with a cascade impactor and subsequently analyzed by the means of XRF. In order to identify potential sources for the aerosols elemental composition, materials involved in the printing process such as toner, paper, and structural components of the printer were also analyzed. While the majority of particle emissions from laser printers are known to consist of recondensated semi volatile organic compounds, elemental analysis identifies Si, S, Cl, Ca, Ti, Cr, and Fe as well as traces of Ni and Zn in different size fractions of the aerosols. These elements can mainly be assigned to contributions from toner and paper. The detection of elements that are likely to be present in inorganic compounds is in good agreement with the measurement of nonvolatile particles. Quantitative measurements of solid particles at 400 °C resulted in residues of 1.6 × 10(9) and 1.5 × 10(10) particles per print job, representing fractions of 0.2% and 1.9% of the total number of emitted particles at room temperature. In combination with the XRF results it is concluded that solid inorganic particles contribute to LPD emissions in measurable quantities. Furthermore, for the first time Br was detected in significant concentrations in the aerosol emitted from two LPD. The analysis of several possible sources identified the plastic housings of the fuser units as main sources due to substantial Br concentrations related to brominated flame retardants.

On-Surface Aggregation of α-Synuclein at Nanomolar Concentrations Results in Two Distinct Growth Mechanisms

The aggregation of α-synuclein (α-Syn) is believed to be one of the key steps driving the pathology of Parkinsons disease and related neurodegenerative disorders. One of the present hypotheses is that the onset of such pathologies is related to the rise of α-Syn levels above a critical concentration at which toxic oligomers or mature fibrils are formed. In the present study, we find that α-Syn aggregation in vitro is a spontaneous process arising at bulk concentrations as low as 1 nM and below in the presence of both hydrophilic glass surfaces and cell membrane mimicking supported lipid bilayers (SLBs). Using three-dimensional supercritical angle fluorescence (3D-SAF) microscopy, we observed the process of α-Syn aggregation in situ. As soon as α-Syn monomers were exposed to the surface, they started to adsorb and aggregate along the surface plane without a prior lag phase. However, at a later stage of the aggregation process, a second type of aggregate was observed. In contrast to the first type, these aggregates showed an extended structure being tethered with one end to the surface and being mobile at the other end, which protruded into the solution. While both types of α-Syn aggregates were found to contain amyloid structures, their growing mechanisms turned out to be significantly different. Given the clear evidence that surface-induced α-Syn aggregation in vitro can be triggered at bulk concentrations far below physiological concentrations, the concept of a critical concentration initiating aggregation in vivo needs to be reconsidered.

Protein biomineralized nanoporous inorganic mesocrystals with tunable hierarchical nanostructures.

Mesocrystals with the symmetry defying morphologies and highly ordered superstructures composed of primary units are of particular interest, but the fabrication has proved extremely challenging. A novel strategy based on biomineralization approach for the synthesis of hematite mesocrystals is developed by using silk fibroin as a biotemplate. The resultant hematite mesocrystals are uniform, highly crystalline, and porous nanostructures with tunable size and morphologies by simply varying the concentration of the silk fibroin and iron(III) chloride in this biomineralization system. In particular, we demonstrate a complex mesoscale biomineralization process induced by the silk fibroin for the formation of hematite mesocrystals. This biomimetic strategy features precisely tunable, high efficiency, and low-cost and opens up an avenue to access new novel functional mesocrystals with hierarchical structures in various practical applications.

Robust superhydrophobic wood obtained by spraying silicone nanoparticles

Silica nanoparticles, usually synthesized via Stober reactions in the presence of a suitable amount of an ammonia catalyst, are frequently used in the fabrication of self-cleaning surfaces. However, to achieve superhydrophobicity, the nanosilica-modified surfaces need to be further functionalized with low-surface-energy materials. Here, we report the preparation of polymethylsiloxane nanoparticles in a facile way, i.e., the hydrolysis of trichloromethylsilane in toluene under ambient conditions in the absence of a catalyst. The resulting gel-like solution can be applied to substrate surfaces by the convenient method of spraying. Wood slides were used as substrates, and the spray-coated wood without any further surface elaboration became extremely superhydrophobic. Notably, it was observed that the superhydrophobicity of the coated wood is mechanically stable against repeated finger rubbing because of the macroscale and microscale roughness of the wood surfaces that serve as a barrier against mechanical damage.

Nanotechnology in the market: promises and realities

Nanotechnology is one of the key research areas of the 21st century affecting several different disciplines and industries. Amongst leading scientists there is growing awareness about the tremendous impact this field will have on society and the economy. It is forecast to become possibly even more important than for example the invention of the steam engine or the discovery of penicillin. However, the vast amount of research projects associated with nanotechnology makes it increasingly difficult to distinguish between promises for future products and real applications that are already in the market. The situation is even more complicated by the fact that nano is not a protected and well-defined term. Therefore it is also misused for marketing purposes of non-nano products. This paper is intended to contribute to a clearer picture about scientific developments and subsequently commercialised nanotechnological applications. In order to deliver a cohesive review, the focus was laid on six nanotechnology fields relevant for end-consumers (pharmaceutical, cosmetic, food, textile, automotive and construction). For the database search, a working definition was devised to discriminate nano from non-nano applications. In the present paper both scientific background information and market data about the nano-enabled products are presented, to reach the goal of combining economic analyses and chemical insights into nanotechnology. The results show that some commercialised technologies have several application fields, whereas others are only found in one market. Furthermore, it was demonstrated that regarding turnovers the pharmaceutical sector is currently the most important of the six considered nanotechnology markets, but all of them are expected to grow significantly in the future.