Robert N. Grass

Gas phase synthesis of fcc-cobalt nanoparticles

Air stable cobalt nanoparticles have been prepared continuously at a production rate of 30 g h−1 by a modified flame synthesis method under highly reducing conditions. Nanoparticles of 20–60 nm in diameter consisted of metallic face-centered-cubic cobalt. The metal particles were protected against oxidation by a surface layer of less than 1 nm of cobalt oxide. The material was highly magnetic exhibiting a high saturation magnetisation (>124 emu g−1) together with a low (<100 Oe) coercivity. Experiments under varying fuel to oxygen ratio were combined with thermodynamic calculations to illustrate the necessity for highly reducing conditions and enhanced gas mixing to enable the formation of metallic cobalt nanoparticles in flames.

Robust Chemical Preservation of Digital Information on DNA in Silica with Error‐Correcting Codes

Information, such as text printed on paper or images projected onto microfilm, can survive for over 500 years. However, the storage of digital information for time frames exceeding 50 years is challenging. Here we show that digital information can be stored on DNA and recovered without errors for considerably longer time frames. To allow for the perfect recovery of the information, we encapsulate the DNA in an inorganic matrix, and employ error-correcting codes to correct storage-related errors. Specifically, we translated 83 kB of information to 4991 DNA segments, each 158 nucleotides long, which were encapsulated in silica. Accelerated aging experiments were performed to measure DNA decay kinetics, which show that data can be archived on DNA for millennia under a wide range of conditions. The original information could be recovered error free, even after treating the DNA in silica at 70 °C for one week. This is thermally equivalent to storing information on DNA in central Europe for 2000 years.

Permanent Pattern‐Resolved Adjustment of the Surface Potential of Graphene‐Like Carbon through Chemical Functionalization

The exceptional electronic and optical properties of graphene have caught the attention of physicists and materials scientists since the first effective preparation of this two-dimensional form of carbon by Novoselov et al. in 2004. Much effort is currently being invested in the large-scale production of graphene surfaces 3] and in the investigation of its peculiar quantum effects. Graphene is viewed as a potential alternative to silicon as a material for the construction of nanoscale electronic circuits. The use of graphene in this way would require control of its electronic band structure and the withdrawal or injection of electron density to adjust or tilt the Fermi level in a graphene sheet. Such pattern-resolved control of the energy level is the two-dimensional equivalent of n or p doping in classical semiconductors. In contrast to silicon, graphene has a continuous band structure with zero band gap. Thus, single adsorbed molecules modify the band structure and affect the electronic properties of graphene significantly, 10] which makes graphene difficult to handle. Device fabrication requires reliable and permanent control over the different electronic states and the Fermi energy of an air-stable material. The adsorption of organic molecules can result in p-type doping through a sandwichlike p-stacking arrangement on graphene. The injection of electrons is possible through n-type doping with potassium; however, such materials are highly sensitive to air and water. In the search for a robust and highly precise doping method, we investigated well-established protocols from organic radical chemistry to attach an air-stable dopant covalently and thus permanently alter the electronic structure of graphene sheets. The relative surface charge levels were measured by Kelvin force microscopy (KFM). The application of the linear free-enthalpy relationship for substituted aromatic compounds enabled the direct prediction of the charge-withdrawing or charge-injecting effect of graphene modification. We therefore concluded that this approach should enable direct control of the surface potential, Y, of modified graphene. Furthermore, the Hammett concept enabled a precise correlation between the observed change in the surface potential, DY, and the structure of the covalently bonded reagents. This concept was confirmed experimentally by using strongly electron withdrawing (p-nitrophenyl, s = 0.78) and electron donating substituents (p-methoxyphenyl, s = 0.23). For our experiments, we used the top graphene layer of highly ordered pyrolytic graphite (HOPG) as a model material. From a physical point of view, this model is not representative for detailed investigations on band structure or electronic effects. However, from a chemical point of view, the reactivity of the graphene stacks of HOPG is comparable to that of single-walled carbon nanotubes, which can be considered as rolls of graphene. For additional experimental validation, we also carried out the graphene modifications described herein on carbon-coated nanoparticles (two or three layers of graphene on copper). Detailed structural evidence was then provided by diffuse reflectance FTIR to characterize the products and confirm the direct covalent attachment of the modifying groups to the top graphene layer. This functionalization approach extends p and n doping based on adsorbed molecules or ions to make it a systematic and robust method with which molecular electronics elements can be attached perpendicular to the graphene plane in a third dimension. The experimental approach to covalent graphene modification is shown in Figure 1. The model material (top layer of a monocrystalline graphene stack) was first patterned by lithography, so that a plain (unfunctionalized) graphene surface would be preserved below the photoresist. The unmasked areas were functionalized by exposure to highly diluted diazonium reagents (see the Supporting Information). After removal of the photoresist, the graphene surface was investigated by scanning electron microscopy (SEM) and Kelvin force microscopy (KFM) in tapping mode to image the relative surface-potential levels of modified and native areas of the graphene surface. The chemical derivatization depends [*] MSc Chem. Eng. F. M. Koehler, MSc Mat. Sci. N. A. Luechinger, Dipl.-Chem.-Ing. E. K. Athanassiou, Dr. R. N. Grass, Prof. Dr. W. J. Stark Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences, ETH Zurich Wolfgang-Pauli-Strasse 10, 8093 Zurich (Switzerland) Fax: (+ 41)44-633-1083 E-mail: wendelin.stark@chem.ethz.ch Homepage: http://www.fml.ethz.ch

Interaction between Human Cathepsins K, L, and S and Elastins MECHANISM OF ELASTINOLYSIS AND INHIBITION BY MACROMOLECULAR INHIBITORS

Proteolytic degradation of elastic fibers is associated with a broad spectrum of pathological conditions such as atherosclerosis and pulmonary emphysema. We have studied the interaction between elastins and human cysteine cathepsins K, L, and S, which are known to participate in elastinolytic activity in vivo. The enzymes showed distinctive preferences in degrading elastins from bovine neck ligament, aorta, and lung. Different susceptibility of these elastins to proteolysis was attributed to morphological differences observed by scanning electron microscopy. Kinetics of cathepsin binding to the insoluble substrate showed that the process occurs in two steps. The enzyme is initially adsorbed on the elastin surface in a nonproductive manner and then rearranges to form a catalytically competent complex. In contrast, soluble elastin is bound directly in a catalytically productive manner. Studies of enzyme partitioning between the phases showed that cathepsin K favors adsorption on elastin; cathepsin L prefers the aqueous environment, and cathepsin S is equally distributed among both phases. Our results suggest that elastinolysis by cysteine cathepsins proceeds in cycles of enzyme adsorption, binding of a susceptible peptide moiety, hydrolysis, and desorption. Alternatively, the enzyme may also form a new catalytic complex without prior desorption and re-adsorption. In both cases the active center of the enzymes remains at least partly accessible to inhibitors. Elastinolytic activity was readily abolished by cystatins, indicating that, unlike enzymes such as leukocyte elastase, pathological elastinolytic cysteine cathepsins might represent less problematic drug targets. In contrast, thyropins were relatively inefficient in preventing elastinolysis by cysteine cathepsins.

Flame synthesis of calcium-, strontium-, barium fluoride nanoparticles and sodium chloride

Non-oxidic salts such as NaCl, CaF2, SrF2 and BaF2 were synthesised using a flame spray method; optional doping of such fluorides with rare earth elements suggests possible applications in optics.

Thermoresponsive Polymer Induced Sweating Surfaces as an Efficient Way to Passively Cool Buildings

Buildings can be effectively cooled by a bioinspired sweating-like action based on thermoresponsive hydrogels (PNIPAM), which press out their stored water when exceeding the lower critical solution temperature. The surface temperature is reduced by 15 °C compared to that of a conventional hydrogel (pHEMA) and by 25 °C compared to the bare ground.

Chemical Aerosol Engineering as a Novel Tool for Material Science: From Oxides to Salt and Metal Nanoparticles

Aerosol nanotechnology has rapidly evolved in the past years. This fascinating technology has resulted in the development of functional nanomaterials providing novel solutions in industrial applications. The extensive research on the physical understanding of gas phase processes has strongly contributed to the present industrial use of single and mixed oxides and the design of industrial aerosol reactors. Recent advances have shown that chemical aerosol engineering can be established on the interface between classical aerosol science and chemical engineering. The emerging new methods give access to a much broader class of functional materials including salt and metal nanoparticles. The latter implies that aerosol production units can now be considered as chemical reactors. The incorporation of thermodynamic considerations and chemical kinetics in the modelling of gas phase processes will further boost the development of aerosol engineering and will provide deeper understanding of the fundamentals of particle formation mechanisms. This will ultimately enable access to new multi-component materials with various structures or morphologies and the development of more sustainable, energy efficient gas phase processes.

Immobilized β-Cyclodextrin on Surface-Modified Carbon-Coated Cobalt Nanomagnets: Reversible Organic Contaminant Adsorption and Enrichment from Water

Surface-modified magnetic nanoparticles can be used in extraction processes as they readily disperse in common solvents and combine high saturation magnetization with excellent accessibility. Reversible and recyclable adsorption and desorption through solvent changes and magnetic separation provide technically attractive alternatives to classical solvent extraction. Thin polymer layered carbon-coated cobalt nanoparticles were tagged with β-cyclodextrin. The resulting material reversibly adsorbed organic contaminants in water within minutes. Isolation of the immobilized inclusion complex was easily carried out within seconds by magnetic separation due to the strong magnetization of the nanomagnets (metal core instead of hitherto used iron oxide). The trapped molecules were fully and rapidly recovered by filling the cyclodextrin cavity with a microbiologically well accepted substitute, e.g., benzyl alcohol. Phenolphthalein was used as a model compound for organic contaminants such as polychlorinated dibenzodioxins (PCDDs) or bisphenol A (BPA). Fast regeneration of nanomagnets (compared to similar cyclodextrin-based systems) under mild conditions resulted in 16 repetitive cycles (adsorption/desorption) at full efficiency. The high removal and regeneration efficiency was examined by UV-vis measurements at chemical equilibrium conditions and under rapid cycling (5 min). Experiments at ultralow concentrations (160 ppb) underline the high potential of cyclodextrin modified nanomagnets as a fast, recyclable extraction method for organic contaminants in large water streams or as an enrichment tool for analytics.

High-strength metal nanomagnets for diagnostics and medicine: carbon shells allow long-term stability and reliable linker chemistry

The rapidly growing applications of nanomagnets in magnetic drug delivery and separation in clinical diagnostics require strong and reliable magnetic vehicles. Strength conveys rapid processing, high delivery/targeting yield and rapid results when used in clinics. Reliability enables recycling of nanomagnets, regulatory-conforming drug formulations and efficient use of (expensive) antibodies in diagnostics, combined with reduced leaching (reagent loss). The present work illustrates how metal-based nanomagnets provide a two-three-times stronger magnetic particle than conventional magnetite-based materials. Ligands, antibodies or drugs can be anchored to such carbon/metal core/shell nanomagnets over covalent, hydrolysis-resistant carbon-carbon bonds. This linker chemistry resists strong acids, sterilization and prolonged storage or aggressive treatment. As dispersions, functional nanomagnets rapidly scan liquids/tissue by Brownian diffusion, capture/deliver/react at a target and are efficiently recollected after use. Metal iron-based, carbon-coated nanomagnets consist of particularly well-accepted materials and now open stable nanomagnets to a broad range of fascinating separation problems in biomedical research.

Magnetically Recoverable, Thermostable, Hydrophobic DNA/Silica Encapsulates and Their Application as Invisible Oil Tags

A method to encapsulate DNA in heat-resistant and inert magnetic particles was developed. An inexpensive synthesis technique based on co-precipitation was utilized to produce Fe2O3 nanoparticles, which were further functionalized with ammonium groups. DNA was adsorbed on this magnetic support, and the DNA/magnet nanocluster was surface coated with a dense silica layer by sol-gel chemistry. The materials were further surface modified with hexyltrimethoxysilane to achieve particle dispersibility in hydrophobic liquids. The hydrodynamic particle sizes were evaluated by analytical disc centrifugation, and the magnetic properties were investigated by vibrating sample magnetometry. The obtained nanoengineered encapsulates showed good dispersion abilities in various nonaqueous fluids and did not affect the optical properties of the hydrophobic dispersant when present at concentrations lower than 10(3) μg/L. Upon magnetic separation and particle dissolution, the DNA could be recovered unharmed and was analyzed by quantitative real-time PCR and Sanger sequencing. DNA encapsulated within the magnetic particles was stable for 2 years in decalin at room temperature, and the stability was further tested at elevated temperatures. The new magnetic DNA/silica encapsulates were utilized to developed a low-cost platform for the tracing/tagging of oils and oil-derived products, requiring 1 μg/L=1 ppb levels of the taggant and allowing quantification of taggant concentration on a logarithmic scale. The procedure was tested for the barcoding of a fuel (gasoline), a cosmetic oil (bergamot oil), and a food grade oil (extra virgin olive oil), being able to verify the authenticity of the products.