[Show abstract][Hide abstract] ABSTRACT: We investigated the uptake of cerium (Ce) dioxide nanoparticles (NPs) by hydroponically grown wheat, pumpkin and sunflower plants. The presence of plant roots in nutrient solution led to a substantial increase in the dissolution of CeO2-NP compared to plant-free medium. Experiments with Zr/CeOx-NP revealed that Ce was not only taken up in the form of NPs, but simultaneously to a significant degree also as dissolved Ce(iii) ions, which then re-precipitated in the form of CeO2-NPs inside the leaves. The contribution of dissolved Ce uptake was particularly large for particles smaller than 10 nm due to their higher dissolution rate. Our data also indicate that the translocation of Ce resulting from NP-root-exposure is species dependent. When Ce was supplied as dissolved ions, sunflower had the highest capacity of Ce-ion accumulation inside the leaves, while there was no significant difference between pumpkin and wheat. We found no Ce translocation from roots into shoots when only NPs bigger than 20 nm were applied. This study highlights that plant root activity can have a significant impact on the dissolution of CeO2-NPs in soil solution and that uptake of dissolved Ce(iii) followed by re-precipitation needs to be considered as an important pathway in studies of CeO2-NP uptake by plants.
[Show abstract][Hide abstract] ABSTRACT: Iron oxide doped tricalcium phosphate (Fe2O3@TCP) nanoparticles were designed as transfection vehicles and prepared by flame spray synthesis. Both components are known to be non-toxic and biocompatible. Calcium phosphate (CaP) facilitates DNA entry into cells without the need for toxic cationic mediators, while magnetic iron oxide allows for particle localization at a target site. Flame spray synthesis ensures easy and low-cost nanoparticle production in a reproducible way. Fe2O3@TCP nanoparticles, exhibiting DNA-binding capacity in the presence of CaCl2, were tested for transfection of a green fluorescent protein (GFP) encoding plasmid with Human Embryonic Kidney 293 (HEK 293) cells. Commercial magnetic agents, polyethylenimine (PEI) and standard calcium phosphate-mediated transfection were used for comparison. Transfection efficiency was estimated by GFP expression detected by fluorescence microscopy, while hoechst/ethidium homodimer-1 staining allowed the evaluation of method toxicity. We were able to efficiently transfect HEK 293 cells, and showed that Fe2O3@TCP particles and bound DNA can be concentrated in specific sites in a culture plate through the application of a magnetic field gradient to achieve localized transfection. While the commercial magnetic controls strongly affected cell growth and morphology, Fe2O3@TCP particles did not show marked toxicity and had only limited effects on cell proliferation. Overall performance in terms of transfection efficiency, cell proliferation and viability, were comparable to that of CaP and PEI, which lack magnetic targeting capability. The newly synthetized Fe2O3@TCP are, therefore, improved tools to deliver nucleic acids into cells and achieve spatial control of transfection.
[Show abstract][Hide abstract] ABSTRACT: Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.
[Show abstract][Hide abstract] ABSTRACT: A novel solvent evaporation based process that exploits template-particle stabilized bicontinuous emulsions for the formation of previously unreached membrane morphologies is reported in this article. Porous membranes have a wide range of applications spanning from water filtration, pharmaceutical purification and battery separators to scaffolds for tissue engineering. Different situations require different membrane morphologies including various pore sizes and pore gradients. However, most of the previously reported membrane preparation procedures are restricted to specific morphologies and morphology alterations require an extensive optimization process. The tertiary system presented in this article, which consists of a polyethersulfone/dimethylacetamide (PES/DMAc) solution, glycerol and ZnO-nanoparticles, allows simple and exact tuning of pore diameters ranging from sub-20 nm, up to 100 nm. At the same time, the pore size gradient is controlled from 0 up to 840 %/µm yielding extreme asymmetry. In addition to structural analysis, water flux rates of over 5600 L m-2 h-1 are measured for membranes retaining 45 nm silica beads.
[Show abstract][Hide abstract] ABSTRACT: Ferromagnetic nanoparticles are covalently modified in order to enhance the dispersion stability as well as the antifouling properties. Insertion of an azide moiety allows “click”-reaction of a relevant tag molecule. This and the high saturation magnetization of the presented nanocomposite offer a promising platform for magnetic biosensors.
Chemical Communications 12/2014; 51(10). DOI:10.1039/C4CC06126H · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, we demonstrate a two-step process where activated carbon based air purifier systems can be regenerated in situ and eliminate volatile organic compounds (VOCs) from indoor air in an energy efficient way. A carbon based adsorber was combined in series with a CeO2/TiO2 oxidative catalyst for total oxidation of the previously adsorbed and periodically released volatile organic compounds during regeneration runs. We investigated the adsorption and desorption behavior of five different VOCs (diethyl ether, limonene, linalool, hexanoic acid, triethylamine and n-decane) with thermogravimetric measurements, mass spectrometry and elemental analysis. Cyclic loading and regeneration experiments were carried out with selected VOCs (limonene, linalool and n-decane) for testing regeneration at elevated temperature. We showed that in situ thermal regeneration and subsequent oxidation of released VOC is a sustainable and easy applicable technology for indoor air purification. This two-step approach allows energy saving as the VOCs are eliminated discontinuously (enriching VOCs; periodic catalytic combustion), and is of high environmental and economic interest, as much less maintenance services are required.
[Show abstract][Hide abstract] ABSTRACT: Although silica particles are among the widest utilized engineered nanoparticles, the measurement of silica particles at low exposure concentrations is impeded by the high background concentrations of silicates in the environment. To circumvent this analytical limitation, we describe a new method for tracing submicrometer silica particles in water by the usage of silica particles fully encapsulating unique DNA codes. Because DNA can be detected at extremely low concentrations by quantitative polymerase chain reaction (PCR), the encapsulation of DNA in silica allows an indirect measure of the concentration of silica particles down to the sub-parts per billion range (micrograms per liter). To provide insight into the capability of this novel technology, we utilized DNA-loaded submicrometer silica particles to follow the fate of silica particles in the analytically most demanding biological stages of wastewater treatment solutions (activated sludge). At various initial particle concentrations ranging from 10 ppb (10 μg/L) to 10 ppm (10 mg/L) and under both aerobic and anoxic conditions, we are able to show that >97% of the particles were removed from the wastewater by incorporation into sludge biomass.
[Show abstract][Hide abstract] ABSTRACT: Magnetic hybrid materials have been synthesized as recyclable catalysts for alkene hydrogenation. The materials consist of magnetic nanobeads functionalized with imidazolium-based ionic liquids and optional polymer shells. Palladium nanoparticles (NPs) were synthesized on the surface of these supports by two different methods and evaluated as catalysts for alkene hydrogenation. Deposition of palladium(0) onto the magnetic nanobeads by microwave decomposition of Pd2(dba)(3)center dot CHCl3 leads to more efficient catalysts than the reduction of a Pd(II) precursor. Reactivity, recycling ability and ease of separation of the catalysts are compared. A hybrid material without polymer shells and a quite flexible ionic liquid was identified as the most promising for stabilizing Pd NPs resulting in a catalyst that shows high activity (TOF up to 330 h(-1)), good recycling ability, and minor metal leaching into the product. Notably, the activity of this catalyst increases with an enhanced Pd loading, contrasting related systems for which a decrease of activity is observed due to agglomeration. Therefore, this recyclable, highcapacity system is especially attractive for large-scale applications, requiring just a minimal amount of supporting material for the recycling of expensive Pd that is readily achieved by magnetic decantation.
[Show abstract][Hide abstract] ABSTRACT: Limestone nanoparticles can be used as nanopore template to prepare porous polymeric films. Their application as membranes was so far strongly limited by the fact that these films were highly hydrophobic. In this study, a simple method is reported to directly produce self-wetting membranes by the template removal method. Triethyl citrate modified polyethersulfone and cellulose acetate membranes were produced using dissolvable limestone nanoparticles as pore templates. The nanoporous polymer films were used as dialysis membranes and characterized by means of buffer exchange rate, molecular weight cut-off, protein adsorption, pore size distribution and water contact angle. The herein prepared membranes were further benchmarked against commercially available dialysis membranes with comparable average pore size. They showed narrow pore size distributions, fast dialysis rates at low protein adsorption and molecular weight cut-off of around 12 kDa. Interestingly, the triethyl citrate modified polyethersulfone membranes displayed only moderate change in pore size distribution as a result of the plasticizer additive compared to pure polyethersulfone membranes. This is a matter of substantial interest considering the fact that additive modifications of membranes produced by the predominant phase inversion process typically show alterations in morphology that lead to undesired changes in membrane performance. Furthermore, dextran recovery analysis proved to meet the specific requirements for dialysis membrane characterization and benchmarking.
[Show abstract][Hide abstract] ABSTRACT: The effects of an exposure to three mass-produced metal oxide nanoparticles – similar in size and specific surface area, but different in redox activity and solubility – were studied in rat alveolar macrophages (MAC) and epithelial cells (AEC). We hypothesized that the cell response depends on the particle redox activity and solubility determining the amount of reactive oxygen species formation (ROS) and subsequent inflammatory response. MAC and AEC were exposed to different amounts of Mn3O4 (soluble, redox-active), CeO2 (insoluble, redox-active), and TiO2 (insoluble, redox-inert) up to 24 hours. Viability and inflammatory response were monitored with and without co-incubation of a free-radical scavenger (trolox). In MAC elevated ROS levels, decreased metabolic activity and attenuated inflammatory mediator secretion were observed in response to Mn3O4. Addition of trolox partially resolved these changes. In AEC, decreased metabolic activity and an attenuated inflammatory mediator secretion were found in response to CeO2 exposure without increased production of ROS, thus not sensitive to trolox administration. Interestingly, highly redox-active soluble particles did not provoke an inflammatory response. The data reveal that target and effector cells of the lung react in different ways to particle exposure making a prediction of the response depending from redox activity and intracellular solubility difficult.
[Show abstract][Hide abstract] ABSTRACT: Work-up in organic synthesis can be very time consuming, particularly when using reagents of solubility similar to the desired products and a low tendency to crystallize. In this respect, reactions involving organic bases would strongly profit from a tremendously simplified separation. Therefore, we synthesized a derivative of the superbasic proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) and covalently linked it to the strongest currently available nanomagnets based on carbon-coated cobalt metal nanoparticles. The immobilized magnetic superbase reagent was tested in Knoevenagel and Claisen-Schmidt type condensations and showed conversions up to 99%. In a particular example, high yields up to 97 % of isolated product could be obtained by simple recrystallization without using column chromatography. Recycling of the catalyst was simple and fast with insignificant decrease in catalytic activity.
The Journal of Organic Chemistry 10/2014; 79(22). DOI:10.1021/jo501913z · 4.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The capability of tracing a food product along its production chain is important to ensure food safety and product authenticity. For this purpose and as an application example, recently developed Silica Particles with Encapsulated DNA (SPED) were added to milk at concentrations ranging from 0.1 to 100 ppb (µg per kg milk). Thereby the milk, as well as the milk derived products yoghurt and cheese, could be uniquely labeled with a DNA tag. Procedures for the extraction of the DNA tags from the food matrixes were elaborated and allowed identification and quantification of previously marked products by quantitative polymerase chain reaction (qPCR) with detection limits below 1 ppb of added particles. The applicability of both synthetic as well as naturally occurring DNA sequences was shown. The usage of approved food additives as DNA carrier (silica = E551) and the low cost of the technology (< 0.1 USD per ton of milk labeled with 10 ppb of SPED) display the technical applicability of this food labeling technology.
Journal of Agricultural and Food Chemistry 10/2014; 62(43). DOI:10.1021/jf503413f · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: From environmental modeling of engineered nanomaterial (ENM) release, it is clear that ENMs will enter soils, where they interact with soil compounds as well as plant roots. We analyzed three different size groups of cerium dioxide nanoparticles (CeO2-NPs) in respect to chemical changes in the most common plant growth medium, Hoagland solution. We created a simple environmental model using liquid dispersions of 9-, 23-, and 64-nm-uncoated CeO2-NPs. We found that CeO2-NPs release dissolved Ce when the pH of the medium is below 4.6 and in the presence of strong chelating agents even at pH of 8. In addition, we found that in reaction with Fe2+-ions, equimolar amounts of Ce were released from NPs. We could elucidate the involvement of the CeO2-NPs surface redox cycle between Ce3+ and Ce4+ to explain particle transformation. The chemical transformation of CeO2-NPs was summarized in four probable reactions: dissolution, surface reduction, complexation, and precipitation on the NP surface. The results show that CeO2-NPs are clearly not insoluble as often stated but can release significant amounts of Ce depending on the composition of the surrounding medium.
Journal of Nanoparticle Research 10/2014; 16(10). DOI:10.1007/s11051-014-2668-8 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gelatin is an exceptional and versatile biopolymer with applications in various industries. As the most abundant structural protein in vertebrates it is available in megaton quantities. On these grounds, it would be a plausible substitute for synthetic polymers. Gelatin processing into fibers seems promising as continuous protein filaments do not have the limitation of natural fibers, i.e., small staple fiber length. Instead of spinning an aqueous gelatin solution, a protein precipitate from a phase-separated system is used. Robust wet spinning with subsequent fiber drawing allows production of a gelatin filament with similar mechanical properties as sheep wool. Different degrees of fiber drawing and addition of plasticizers enable to tailor the mechanical and thermal fiber properties and demonstrate the versatility of the proposed spinning process.
[Show abstract][Hide abstract] ABSTRACT: We present a design and parameter study on 3D-printed, lost-wax-casted and combustion-powered soft silicone pumps, which are internally cooled by the conveyed liquid. Important factors influencing the pumping performance such as gas mixtures, feed rates, and actuation frequencies were thoroughly studied. Furthermore, we reinforced some of the here presented pumps with aramid fabrics in order to achieve partial blocking of the elastomeric flexibility upon combustion expansion. This design measure dramatically increased the pumping capabilities and allowed continuous conveying of water to 13 m (corresponding to 42 ft) of height. We were able to stably operate these novel pumps for more than 30 000 combustion cycles. Therefore, they represent a further step toward long-term stable soft machines with dense power characteristics.
[Show abstract][Hide abstract] ABSTRACT: Objectives
To investigate chemo-mechanical effects of incorporating alkaline bioactive glass nanoparticles into a light-curable dental resin matrix.
An unfilled Bis-GMA/TEGDMA material was infiltrated with up to 20 wt% of ultrafine SiO2–Na2O–CaO–P2O5–Bi2O3 particles. The unfilled and filled resins were investigated regarding their viscosity before setting and compared to commercially available materials. Set specimens were immersed for 21 days in phosphate buffered saline at 37 °C. Water uptake, pH, Knoop hardness, and degree of conversion of freshly polymerized and stored samples were investigated. Resin surfaces were viewed and mapped in a scanning electron microscope for the formation of calcium phosphate (Ca/P) precipitates. In addition, Raman spectroscopy was performed. Numeric values were statistically compared (p < 0.01).
Viscosity increased with particle loading, but remained below that of a flowable dental composite material. Water uptake into and pH induction from the polymerized samples also increased with particle loading (p < 0.01). The addition of 20 wt% nanoparticles had no significant influence on microhardness, yet it slightly (p < 0.01) increased the degree of conversion after 21 days. Ca/P precipitates formed on specimens filled with 20 wt% of the particles, while they were scarce on counterparts loaded with 10 wt%, and absent on unfilled resin surfaces.
The results of the current study show that a Bis-GMA-based resin can be functionalized using alkaline nanoparticles. A material with bioactive properties and similar hardness as the unfilled resin was obtained by incorporating 20 wt% of ultrafine SiO2–Na2O–CaO–P2O5–Bi2O3 particles into the resin matrix.
[Show abstract][Hide abstract] ABSTRACT: There is a strong interest in studying the cellular uptake of silica nanoparticles, particularly at medically relevant concentrations (ppb-ppm range) to understand their toxicology. At present, uptake analysis at these exposure levels is impeded by the high silica background concentration. Here we describe the use of DNA encapsulated within silica particles as a tool to quantify silica nanoparticles in in vitro cell-uptake experiments at low concentrations (down to 10 fg cell-1). This journal is
Chemical Communications 07/2014; 50(73). DOI:10.1039/c4cc04480k · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Removal of volatile organic compounds (VOC) and indoor air quality regulation through adsorbers required exchange or maintenance of active materials. In this work, we combine well known VOC adsorbers with oxidation catalysts as intimate particulate mixtures. We demonstrate how typical VOC can subsequently adsorb on such mixed material fixed beds (usually days to weeks; the common state of the system, adsorption phase) using small organic compounds (diethyl ether, triethylamine), monoterpenes such as linalool and limonene, and hexanoic acid. Occasional regeneration runs through heat up of the fixed bed results in simultaneous desorption and oxidation of the accumulated VOC, thus regenerating full adsorption capacity for a next adsorption phase. We investigated both small pore zeolites (H-ZSM-5) and larger pore zeolites (13X) and found a distinct interplay between the pore size and the type of VOC. Thermogravimetry coupled with mass spectroscopy was used to quantitatively study the effects of mixing composition and temperature on adsorber performance and regeneration. The here investigated bi-functional systems combine very low maintenance costs and materials requirement with low air flow and exchange costs, thus suggesting mixed (two-functional) bed adsorbers with catalytic function as sustainable alternatives to currently used single use systems based on granulated zeolites or activated carbon. In this work we show the ability of zeolite/cerium oxide physical mixtures to adsorb and capture different classes of VOC at room temperature and release them for oxidation at higher temperatures in a regenerative and sustainable process.
[Show abstract][Hide abstract] ABSTRACT: Elastic silicone composites with mechanically switchable transparency are generated by incorporating micron‐sized aluminum platelets into a highly flexible silicone. Physisorbing Fe3O4 nanoparticles onto the platelets surface allow magnetic pre‐alignment during the polymer curing. One‐dimensional or two‐dimensional stretching of the resulting silicone composites permits orientation of the incorporated flakes and alters light transmittance of the polymer coating.
[Show abstract][Hide abstract] ABSTRACT: Objectives:
To investigate chemo-mechanical effects of incorporating alkaline bioactive glass nanoparticles into a light-curable dental resin matrix.
An unfilled Bis-GMA/TEGDMA material was infiltrated with up to 20 wt% of ultrafine SiO2-Na2O-CaO-P2O5-Bi2O3 particles. The unfilled and filled resins were investigated regarding their viscosity before setting and compared to commercially available materials. Set specimens were immersed for 21 days in phosphate buffered saline at 37°C. Water uptake, pH, Knoop hardness, and degree of conversion of freshly polymerized and stored samples were investigated. Resin surfaces were viewed and mapped in a scanning electron microscope for the formation of calcium phosphate (Ca/P) precipitates. In addition, Raman spectroscopy was performed. Numeric values were statistically compared (p<0.01).
Viscosity increased with particle loading, but remained below that of a flowable dental composite material. Water uptake into and pH induction from the polymerized samples also increased with particle loading (p<0.01). The addition of 20 wt% nanoparticles had no significant influence on microhardness, yet it slightly (p<0.01) increased the degree of conversion after 21 days. Ca/P precipitates formed on specimens filled with 20 wt% of the particles, while they were scarce on counterparts loaded with 10 wt%, and absent on unfilled resin surfaces.
The results of the current study show that a Bis-GMA-based resin can be functionalized using alkaline nanoparticles. A material with bioactive properties and similar hardness as the unfilled resin was obtained by incorporating 20wt% of ultrafine SiO2-Na2O-CaO-P2O5-Bi2O3 particles into the resin matrix.
Dental materials: official publication of the Academy of Dental Materials 06/2014; 30(8). DOI:10.1016/j.dental.2014.05.029 · 3.77 Impact Factor