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Zürich, Switzerland

Sotiriou G.A.,Institute of Process Engineering | Franco D.,Institute of Energy Technology | Poulikakos D.,Institute of Energy Technology | Ferrari A.,Institute of Energy Technology
ACS Nano

Nanophosphors are light-emitting materials with stable optical properties that represent promising tools for bioimaging. The synthesis of nanophosphors, and thus the control of their surface properties, is, however, challenging. Here, flame aerosol technology is exploited to generate Tbactivated Y 2O 3 nanophosphors (∼25 nm) encapsulated in situ by a nanothin amorphous inert SiO 2 film. The nanocrystalline core exhibits a bright green luminescence following the Tb 3+ ion transitions, while the hermetic SiO 2-coating prevents any unspecific interference with cellular activities. The SiO 2-coated nanophosphors display minimal photobleaching upon imaging and can be easily functionalized through surface absorption of biological molecules. Therefore, they can be used as bionanoprobes for cell detection and for long-term monitoring of cellular activities. As an example, we report on the interaction between epidermal growth factor (EGF)-functionalized nanophosphors and mouse melanoma cells. The cellular uptake of the nanophosphors is visualized with confocal microscopy, and the specific activation of EGF receptors is revealed with biochemical techniques. Altogether, our results establish SiO 2-coated Tb-activated Y 2O 3 nanophosphors as superior imaging tools for biological applications. © 2012 American Chemical Society. Source

Camenzind A.,Institute of Process Engineering | Caseri W.R.,ETH Zurich | Pratsinis S.E.,Institute of Process Engineering
Nano Today

Processing of flame-made nanoparticles into polymers is reviewed including surface modification and compounding. Recent advances in combustion and aerosol science enable scalable synthesis of such nanoparticles way beyond today's commercially available nanostructured carbon black and fumed silica. As a result, sophisticated filler nanoparticles with closely controlled size, morphology (aggregates or agglomerates) and composition (segregated or mixed phases or nanothin coatings onto core particles) become available motivating research for their surface functionalization and dispersion. Emphasis is placed on nanocomposite mechanics and optics. Quantitative relations for optimal nanocomposite structure are presented: from the particle-polymer interface to the formation of a percolation network. © 2010 Elsevier Ltd. All rights reserved. Source

Eggersdorfer M.L.,Institute of Process Engineering | Kadau D.,Institute of Building Materials | Herrmann H.J.,Institute of Building Materials | Pratsinis S.E.,Institute of Process Engineering

Multiparticle sintering is encountered in almost all high temperature processes for material synthesis (titania, silica, and nickel) and energy generation (e.g., fly ash formation) resulting in aggregates of primary particles (hard-or sinter-bonded agglomerates). This mechanism of particle growth is investigated quantitatively by mass and energy balances during viscous sintering of amorphous aerosol materials (e.g., SiO2 and polymers) that typically have a distribution of sizes and complex morphology. This model is validated at limited cases of sintering between two (equally or unequally sized) particles, and chains of particles. The evolution of morphology, surface area and radii of gyration of multiparticle aggregates are elucidated for various sizes and initial fractal dimension. For each of these structures that had been generated by diffusion limited (DLA), cluster-cluster (DLCA), and ballistic particle-cluster agglomeration (BPCA) the surface area evolution is monitored and found to scale differently than that of the radius of gyration (moment of inertia). Expressions are proposed for the evolution of fractal dimension and the surface area of aggregates undergoing viscous sintering. These expressions are important in design of aerosol processes with population balance equations (PBE) and/or fluid dynamic simulations for material synthesis or minimization and even suppression of particle formation. © 2011 American Chemical Society. Source

Tricoli A.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Nature Nanotechnology

The enhanced performance and reduced scale that nanoparticles can bring to a device are frequently compromised by the poor electrical conductivity of nanoparticle structures or assemblies. Here, we demonstrate a unique nanoscale electrode assembly in which conduction is carried out by one set of nanoparticles, and other device functions by another set. Using a scalable process, nanoparticles with tailored conductivity are stochastically deposited above or below a functional nanoparticle film, and serve as extensions of the bulk electrodes, greatly reducing the total film resistance. We apply this approach to solid-state gas sensors and achieve controlled device resistance with an exceptionally high sensitivity to ethanol of 20 ppb. This approach can be extended to other classes of devices such as actuators, batteries, and fuel and solar cells. © 2010 Macmillan Publishers Limited. All rights reserved. Source

Buesser B.,Institute of Process Engineering | Pratsinis S.E.,Institute of Process Engineering
Annual Review of Chemical and Biomolecular Engineering

Aerosol synthesis of materials is a vibrant field of particle technology and chemical reaction engineering. Examples include the manufacture of carbon blacks, fumed SiO 2, pigmentary TiO 2, ZnO vulcanizing catalysts, filamentary Ni, and optical fibers, materials that impact transportation, construction, pharmaceuticals, energy, and communications. Parallel to this, development of novel, scalable aerosol processes has enabled synthesis of new functional nanomaterials (e.g., catalysts, biomaterials, electroceramics) and devices (e.g., gas sensors). This review provides an access point for engineers to the multiscale design of aerosol reactors for the synthesis of nanomaterials using continuum, mesoscale, molecular dynamics, and quantum mechanics models spanning 10 and 15 orders of magnitude in length and time, respectively. Key design features are the rapid chemistry; the high particle concentrations but low volume fractions; the attainment of a self-preserving particle size distribution by coagulation; the ratio of the characteristic times of coagulation and sintering, which controls the extent of particle aggregation; and the narrowing of the aggregate primary particle size distribution by sintering. Copyright © 2012 by Annual Reviews. All rights reserved. Source

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