domenica 12 aprile 2009

Tracking Down The Effect Of Nanoparticles

ScienceDaily (Apr. 12, 2009) — Cerium oxide is a ceramic nano-abrasive. Scientists have now examined, under conditions close to reality, what happens when it is breathed in and deposited on the lung surface. Initially, the result was rather reassuring.
Synthetic nanoparticles are ubiquitous in today's world: either as an additive to building materials, whose properties they improve; in cosmetics, mainly in sun creams and toothpaste; or in foodstuffs, to thicken them or brighten their color. However, nano-safety research, i.e. knowledge of how nanoparticles interact with their environment and specifically with a living organism, is still largely in its infancy.
However, this is one of the central topics for the research group led by Wendelin Stark, Assistant Professor at the Institute for Chemical and Bio-engineering of ETH Zurich. The group carries out tests over and over again to investigate the effect nanoparticles have on their surroundings.
Conditions close to reality
Together with the research group led by Peter Gehr, Professor of Histology at the University of Bern, the scientists have now used a completely new method and a new type of lung cell culture to examine how cerium oxide nanoparticles act on the cells. The aim was to study the toxicity of cerium oxide, which is used in large amounts as an abrasive, mainly in the manufacture of semiconductor chips. Although, as a rule, this takes place in a hermetically sealed room from which people are excluded, the researchers now simulated a situation in which ceramic nanomaterial is inhaled directly, for example if nanoparticles are manufactured without protection or the powder is handled incorrectly.
The researchers did this by using what is called flame spray synthesis to spray cerium oxide nanoparticles in a closed glove box, thus simulating aerosols. A fan distributed the aerosols uniformly in the box, about 2.5 cubic meters in size, in which the aerosols were sprayed on to the cultured lung cells for ten, twenty and thirty minutes. The ETH researches hit upon the idea when they spoke to Barbara Rothen-Rutishauser, a scientist from Bern and first author of the paper. She told them about the new type of cell culture.
The innovative aspect of the method is the special cell culture combined with the use of flame spray synthesis. The cell culture of lung epithelial cells grows on a permeable membrane. The lower surface of the epithelial cells is immersed in a medium and their upper surface is covered with a natural liquid layer. Thus the cell culture is very similar to the surface of the lung. As a result of the aerosol production, the spray process is also close to reality. The combination of these two techniques showed how inhaled nanoparticles are deposited on the lung surface. In conventional methods for such experiments up to now, cell cultures were bathed in nanoparticle solutions. However, this can cause the nanoparticles to agglomerate, which alters their properties; moreover, the lung surface is wet in a different way. Consequently, the behavior of the cells might also change.
No cell death
The scientists chose cerium oxide for their study, mainly because the material does not occur physiologically in cells, meaning that only the effect of the nanoparticle on the cell is observed. The longer the cultures were sprayed for, the more nanoparticles were deposited on the lung cells. The scientists observed that the cells were not destroyed, i.e. they did not die. However, the permeability of the cell layer increased. Therefore, the researchers suspect that certain structures of particular proteins that seal the interstices between the epithelial cells had altered under the influence of the nanoparticles. The production of a substance in the cell which is associated with oxidative stress and which could result in DNA damage could also be observed.
Long-term effects unknown
Robert Grass, group leader in Wendelin Stark’s group, explains: “However, we were unable to observe the effect of the particles on the cells over a prolonged time.” This is because the cultures must be subjected to further processing to allow them to be examined under a microscope. In a next step, the researchers plan to replicate even more realistic conditions by using what are known as triple cell co-cultures that simulate human cellular respiratory tract barriers. For example, they want to find out how the body’s phagocytes and “waste disposal agents”, known as macrophages, deal with nanoparticles.
Journal reference:
Rothen-Rutishauser et al. Direct Combination of Nanoparticle Fabrication and Exposure to Lung Cell Cultures in a Closed Setup as a Method To Simulate Accidental Nanoparticle Exposure of Humans. Environmental Science & Technology, 2009; 43 (7): 2634 DOI: 10.1021/es8029347
Adapted from materials provided by ETH Zurich.

Physicists Discover Important Step For Making Light Crystals

ScienceDaily (Apr. 13, 2009) — Ohio State University researchers have developed a new strategy to overcome one of the major obstacles to a grand challenge in physics.
What they’ve discovered could eventually aid high-temperature superconductivity, as well as the development of new high-tech materials.
In 2008, the Defense Advanced Research Projects Agency (DARPA) chose three multi-university teams to tackle an ambitious problem: trap atoms inside a light crystal -- also called an “optical lattice” -- that can simulate exotic materials and answer fundamental questions in physics.
The deadline for the first phase of the challenge -- June 2009 -- is fast approaching, and the teams have been unable to make the atoms cold enough for their experiments to work.
In the recent online edition of the Proceedings of the National Academy of Sciences, Ohio State university physicist Tin-Lun Ho and doctoral student Qi Zhou present a potential solution.
Their calculations suggest that it’s possible to compress the atoms in an optical lattice until the heat is squeezed out of them -- and into a surrounding pool of ultra-cold Bose-Einstein condensate (BEC), which will absorb the heat and evaporate it away.
“It is absolutely essential to achieve very low temperatures for this program to succeed. All three teams have made much progress, but until now, temperature has been a bottleneck for the whole enterprise,” said Ho, Distinguished Professor of Mathematical and Physical Sciences at Ohio State.
“Ours is the first proposal to show how the temperature can be lowered dramatically. In fact, we believe it can be made much lower that what is considered achievable today.”
A Bose-Einstein Condensate is a collection of atoms cooled with laser light to a temperature just above absolute zero (0 Kelvin, −273 degrees Celsius, or −460 degrees Fahrenheit). The first BEC ever produced was 170 nanokelvin, or 170 billionths of a Kelvin. Researchers have since produced condensates as cold as 500 picokelvin, or 500 trillionths of a Kelvin.
Ho pioneered theoretical studies of BEC. He has made a wide range of contributions in the field, for which he was awarded the 2008 Lars Onsager Prize of the American Physical Society. Recently, he has worked on the physics of cold atoms in optical lattices, and has pointed out the amount of cooling needed to meet the DARPA challenge.
The new method cools the atoms in an optical lattice by literally squeezing the heat out of them and into a surrounding BEC, which acts as a heat sink.
Ho has already shared the cooling method with the three teams in recent DARPA Meetings. The teams are led by the Massachusetts Institute of Technology, Rice University, and the University of Maryland. Each team is approaching the problem a little differently, and Ho is a member of two of the teams: Rice and Maryland.
All are working to create an optical lattice -- a three-dimensional cubic structure made of laser light which contains many smaller cubes, or “cells,” inside it. Each cell in the lattice is supposed to contain one atom.
If the researchers succeed, they will have made an adjustable crystal out of laser light, and will be able to emulate different solid materials.
Physicists think of heat in terms of entropy, or disorder, Ho explained. His cooling method involves boosting the laser intensity to force the atoms into a very orderly arrangement.
The researchers are trying to trap atomic particles called fermions, which have an internal angular momentum called spin. When fermions are hot, they spin chaotically. The hotter the atoms, the more disordered these spins become.
Ho and Zhou discovered that by raising the laser intensity, researchers could compress the fermions into a so-called “band insulator,” where each cell in the lattice contains two fermions instead of one. Each fermion will naturally pair up with one that is spinning in the opposite direction, so that the two spins cancel each other out. This two-fermion state would have no entropy, or heat.
But according to the laws of thermodynamics, the heat has to go somewhere. Ho calculates that it would be pressed outward to the surface of the lattice, where a Bose-Einstein Condensate could absorb it.
After the BEC evaporated away, the researchers could turn down the intensity of the laser, so that the lattice could expand and the atoms could return to their original locations, with one per cell. Only this time, the whole lattice would be much colder than before.
“Effectively, this is a two-part solution -- divide and conquer,” Ho said. “The ‘divide’ part is to push the entropy out of the interior of the system. The ‘conquer’ part is to get rid of the entropy by evaporating away the BEC. Next, we’d like to reduce it to a one-step process, and eliminate the need for the BEC entirely.” Recently, Ho and Zhou have come up with another method which they believe may be even simpler.
Physicists hope that the light crystal will be able to simulate new materials, and perhaps even reveal the key to high-temperature superconductivity. Ho is optimistic that such applications will be achievable in the next decade.
This work was funded by DARPA and by the National Science Foundation.
Adapted from materials provided by Ohio State University.

Peering Into Nanowires To Measure Dopant Properties

ScienceDaily (Apr. 13, 2009) — Semiconductor nanowires — tiny wires with a diameter as small as a few billionths of a meter — hold promise for devices of the future, both in technology like light-emitting diodes and in new versions of transistors and circuits for next generation of electronics.
But in order to utilize the novel properties of nanowires, their composition must be precisely controlled, and researchers must better understand just exactly how the composition is determined by the synthesis conditions.
Nanowires are synthesized from elements that form bulk semiconductors, whose electrical properties are in turn controlled by adding minute amounts of impurities called dopants. The amount of dopant determines the conductivity of the nanowire.
But because nanowires are so small — with diameters ranging from 3 to 100 nanometers — researchers have never been able to see just exactly how much of the dopant gets into the nanowire during synthesis. Now, using a technique called atom probe tomography, Lincoln Lauhon, assistant professor of materials science and engineering at Northwestern University’s McCormick School of Engineering and Applied Science, has provided an atomic-level view of the composition of a nanowire. By precisely measuring the amount of dopant in a nanowire, researchers can finally understand the synthesis process on a quantitative level and better predict the electronic properties of nanowire devices.
The results were published online March 29 in the journal Nature Nanotechnology.
“We simply mapped where all the atoms were in a single nanowire, and from the map we determined where the dopant atoms were,” he says. “The more dopant atoms you have, the higher the conductivity.”
Previously, researchers could not measure the amount of dopant and had to judge the success of the synthesis based on indirect measurements of the conductivity of nanowire devices. That meant that variations in device performance were not readily explained.
“If we can understand the origin of the electrical properties of nanowires, and if we can rationally control the conductivity, then we can specify how a nanowire will perform in any type of device,” he says. “This fundamental scientific understanding establishes a basis for engineering.”
Lauhon and his group performed the research at Northwestern’s Center for Atom Probe Tomography, which uses a Local Electrode Atom ProbeTM microscope to dissect single nanowires and identify their constituents. This instrumentation software allows 3-D images of the nanowire to be generated, so Lauhon could see from all angles just how the dopant atoms were distributed within the nanowire.
In addition to measuring the dopant in the nanowire, Lauhon’s colleague, Peter Voorhees, Frank C. Engelhart Professor of Materials Science and Engineering at Northwestern, created a model that relates the nanowire doping level to the conditions during the nanowire synthesis. The researchers performed the experiment using germanium wires and phosphorous dopants — and they will soon publish results using silicon — but the model provides guidance for nanowires made from other elements, as well.
“This model uses insight from Lincoln’s experiment to show what might happen in other systems,” Voorhees says. “If nanowires are going to be used in device applications, this model will provide guidance as to the conditions that will enable us to add these elements and control the doping concentrations.”
Both professors will continue working on this research to broaden the model.
“We would like to establish the general principles for doping semiconductor nanowires,” Lauhon says.
In addition to Lauhon and Voorhees, the other authors are Daniel E. Perea, Eric R. Hemesath, Edwin J. Schwalbach, and Jessica L. Lensch-Falk, all from Northwestern.
The research was supported by the Office of Naval Research and the National Science Foundation.
Journal reference:
Perea et al. Direct measurement of dopant distribution in an individual vapour–liquid–solid nanowire. Nature Nanotechnology, 2009; DOI: 10.1038/nnano.2009.51
Adapted from materials provided by Northwestern University.

Mass Spec Technique Analyzes Defensive Chemicals On Seaweed Surfaces For Potential Drugs

ScienceDaily (Apr. 13, 2009) — A new analytical technique is helping scientists learn how organisms as simple as seaweed can mount complex chemical defenses to protect themselves from microbial threats such as fungus. Known as desorption electrospray ionization mass spectrometry (DESI-MS), the technique for the first time allows researchers to study unique chemical activity taking place on the surfaces of these organisms.
Understanding this surface chemistry could one day allow scientists to borrow and adapt some of those defensive chemical compounds for use against cancer, HIV, malaria, drug-resistant bacteria and other diseases of humans. In a paper scheduled to be published online in the journal Proceedings of the National Academy of Sciences, researchers from the Georgia Institute of Technology describe a sophisticated chemical defense system that uses 28 different compounds to protect a species of seaweed against a single fungus.
"Plants and animals in the wild use chemistry as way to fight with one another," said Julia Kubanek, a professor in Georgia Tech's School of Biology. "Using this new technology, scientists can listen in on this fight to perhaps learn from what's going on and steal some of the strategies for human biomedical applications."
As part of a long-term project sponsored by the Natural Institutes of Health, Georgia Tech scientists have been cataloging and analyzing natural compounds from more than 800 species found in the waters surrounding the Fiji Islands. They have been particularly interested in Callophycus serratus, an abundant species of red seaweed that seems particularly successful – and adept at fighting off microbial infections.
Using the DESI-MS technique, the researchers analyzed recently-collected samples of the seaweed and found groups of potent anti-fungal compounds in light-colored microscopic surface patches covering what may be wounds on the surface of the seaweed. In laboratory testing, these bromophycolide compounds and callophycoic acids effectively inhibited the growth of Lindra thalassiae, a common marine fungus.
"It is possible that the alga is marshalling its defenses and displaying them in a way that blocks the entry points for microbes that might invade and cause disease," Kubanek said. "Seaweeds don't have B cells, T cells and immune responses like humans do. But instead they have some chemical compounds in their tissues to protect them."
Though all the seaweed they studied was from a single species, the researchers were surprised to find two distinct groups of anti-fungal chemicals. From one seaweed subpopulation, dubbed the "bushy" type for its appearance, 18 different anti-fungal compounds were identified. In a second group of seaweed, the researchers found 10 different anti-fungal compounds – all different from the ones seen in the first group.
"This species is producing some unique chemical compounds that other seaweeds don't produce, and it is producing a large number of compounds, each of which has a role to play in the overall defense against the fungus," Kubanek noted. "We think the compounds work together in an additive way."
Though chemically different, the compounds are structurally related and seem to arise from a similar metabolic pathway in the seaweed. Why one species of simple organism would produce 28 different anti-fungal compounds remains a mystery, though Kubanek believes the chemicals may also have other uses that are not yet understood.
The compounds have been tested for potential activity against drug-resistant bacteria, cancer, HIV, malaria and other human health threats. So far, preliminary testing suggests they have anti-malarial effects.
The DESI-MS technique allowed the researchers for the first time to analyze chemical activity occurring on the surface of the seaweed. Earlier techniques allowed identification of chemicals in the organism's tissue, but being able to confirm their location on the surface – the first line of defense against infection – confirms the role they play as defensive chemicals.
In DESI-MS, a charged stream of polar solvent is directed at the surface of a sample under study at ambient pressure and temperature. The spray desorbs molecules, which are then ionized and delivered to the mass spectrometer for analysis.
"This technique allows us to examine intact organisms and see how the chemical compounds are distributed," Kubanek explained. "For our research with seaweed, this is important because we'd like to understand how an organism distributes these compounds to protect itself from enemies."
In addition to Kubanek, others researchers contributing to the study included Leonard Nyadong, Asiri Galhena, Tonya Shearer, E. Paige Stout, R. Mitchell Parry, Mark Kwasnik, May Wang, Mark Hay, and Facundo Fernandez – all from Georgia Tech – and Amy Lane, now at Scripps Institution of Oceanography. Beyond the National Institutes of Health support, the research has also been sponsored by the National Science Foundation.
For the future, Kubanek and a graduate student are working to modify the most promising of the anti-malarial compounds, replacing some oxygen atoms for nitrogen atoms and bromine for chlorine and fluorine. The hope is to create a compound more potent against the malaria organism with less toxicity for humans.
"We are doing reaction chemistry using these 28 compounds as a starting point," she explained. "Learning about how other species avoid diseases may give us something we can use to avoid or treat our own diseases."
Adapted from materials provided by Georgia Institute of Technology, via EurekAlert!, a service of AAAS.

venerdì 10 aprile 2009

Red-Hot Research Could Lead To New Materials

ScienceDaily (Apr. 11, 2009) — Recent experiments to create a fast-reacting explosive by concocting it at the nanoscopic level could result in more spectacular firework displays. But more impressive to the Missouri University of Science and Technology professor who led the research, the method used to mix chemicals at that tiny scale could lead to new strong porous materials for high temperature applications, from thermal insulation in jet engines to industrial chemical reactors.
Researchers led by Dr. Nicholas Leventis, a professor of chemistry at Missouri S&T, reported in the April 8 Journal of the American Chemical Society that they created a new type of flammable nanomaterial by combining an oxidizer (copper oxide) with an organic fuel (a resorcinol-formaldehyde polymer, or RF). Nanomaterials are made from substances that are one billionth of a meter – the size of a few molecules. This achievement has been highlighted in the online edition of Nature Chemistry.
The new nanomaterial burned rapidly when ignited by a flame, leaving behind minimal residue, Nature Chemistry’s April 3 Research Highlights section reported on the Leventis research.
While the Leventis research is based on the hypothesis that the performance of so-called low-order explosives such as gunpowder can be improved by mixing the oxidizer and fuel as closely as possible – at the nano level, nanoparticle to nanoparticle – Leventis is more excited about the “very far-reaching implications” of the experiment.
“The broader impact of this research is in the methodology of making intimate mixtures of nanoparticles that can react efficiently and fast. That will most certainly lead to future innovations in materials science. Energetic materials is just an example,” he says.
Mixing materials at the nano level may lead to stronger substances, because the two materials may be more closely woven together. Leventis sees this approach leading to such materials engineering breakthroughs as the development of microporous ceramics that can hold up under extremely high temperatures.
The more immediate application of this research could be in pyrotechnics, Leventis explains. Fireworks are considered low-order explosives, meaning that their reaction rate can be improved by mixing the oxidizer and fuel as closely as possible.
With this research, Leventis and his Missouri S&T colleagues worked with Dr. Hongbing Lu, a professor of mechanical and aerospace engineering at Oklahoma State University, to create a fluffy, low-density mixed aerogel from the copper oxide and the RF nanoparticles.
To make the mixed network of nanoparticles, the researchers devised a one-pot sol-gel method, in which they used the gelling colloidal solution (“sol”) of one component (copper oxide) as the catalyst for the gelation of the second component (RF). In the final product, copper oxide acted as the fuse to catalyze, or ignite, the RF fuel.
The research was originally published March 17 in the online in the Journal of the American Chemical Society. Working with Leventis at S&T were Dr. Chariklia Sotirou-Leventis, professor of chemistry, and Naveen Chandrasekaran and Anand G. Sadekar, both graduate students in chemistry.
Journal references:
Leventis et al. One-Pot Synthesis of Interpenetrating Inorganic/Organic Networks of CuO/Resorcinol-Formaldehyde Aerogels: Nanostructured Energetic Materials. Journal of the American Chemical Society, 2009; 131 (13): 4576 DOI: 10.1021/ja809746t
Neil Withers. Energetic materials: Burn baby burn. Nature Chemistry, 2009; DOI: 10.1038/nchem.205
Adapted from materials provided by Missouri University of Science and Technology.

Ancient Diatoms Lead To New Technology For Solar Energy

ScienceDaily (Apr. 9, 2009) — Engineers at Oregon State University have discovered a way to use an ancient life form to create one of the newest technologies for solar energy, in systems that may be surprisingly simple to build compared to existing silicon-based solar cells.

The secret: diatoms.
These tiny, single-celled marine life forms have existed for at least 100 million years and are the basis for much of the life in the oceans, but they also have rigid shells that can be used to create order in a natural way at the extraordinarily small level of nanotechnology.
By using biology instead of conventional semiconductor manufacturing approaches, researchers at OSU and Portland State University have created a new way to make "dye-sensitized" solar cells, in which photons bounce around like they were in a pinball machine, striking these dyes and producing electricity. This technology may be slightly more expensive than some existing approaches to make dye-sensitized solar cells, but can potentially triple the electrical output.
"Most existing solar cell technology is based on silicon and is nearing the limits of what we may be able to accomplish with that," said Greg Rorrer, an OSU professor of chemical engineering. "There's an enormous opportunity to develop different types of solar energy technology, and it's likely that several forms will ultimately all find uses, depending on the situation."
Dye-sensitized technology, for instance, uses environmentally benign materials and works well in lower light conditions. And the new findings offer advances in manufacturing simplicity and efficiency.
"Dye-sensitized solar cells already exist," Rorrer said. "What's different in our approach are the steps we take to make these devices, and the potential improvements they offer."
The new system is based on living diatoms, which are extremely small, single-celled algae, which already have shells with the nanostructure that is needed. They are allowed to settle on a transparent conductive glass surface, and then the living organic material is removed, leaving behind the tiny skeletons of the diatoms to form a template.
A biological agent is then used to precipitate soluble titanium into very tiny "nanoparticles" of titanium dioxide, creating a thin film that acts as the semiconductor for the dye-sensitized solar cell device. Steps that had been difficult to accomplish with conventional methods have been made easy through the use of these natural biological systems, using simple and inexpensive materials.
"Conventional thin-film, photo-synthesizing dyes also take photons from sunlight and transfer it to titanium dioxide, creating electricity," Rorrer said. "But in this system the photons bounce around more inside the pores of the diatom shell, making it more efficient."
The physics of this process, Rorrer said, are not fully understood – but it clearly works. More so than materials in a simple flat layer, the tiny holes in diatom shells appear to increase the interaction between photons and the dye to promote the conversion of light to electricity, and improve energy production in the process.
The insertion of nanoscale tinanium oxide layers into the diatom shell has been reported in ACS Nano, a publication of the American Chemical Society, and the Journal of Materials Research, a publication of the Materials Research Society. The integration of this material into a dye-sensitized solar cell device was also recently described at the fourth annual Greener Nanoscience Conference.
The work is supported by the National Science Foundation and the Safer Nanomaterials and Nanomanufacturing Initiative, a part of the Oregon Nanoscience and Microtechnologies Institute.
Diatoms are ancient, microscopic organisms that are found in the fossil record as far back as the time of the dinosaurs. They are a key part of the marine food chain and help cycle carbon dioxide from the atmosphere.
But in recent years their tiny, silica shells have attracted increasing attention as a way to create structure at the nano level. Nature is the engineer, not high tech tools. This is providing a more efficient, less costly way to produce some of the most advanced materials in the world.
Journal reference:
Jeffryes et al. Metabolic Insertion of Nanostructured TiO2 into the Patterned Biosilica of the Diatom Pinnularia sp. by a Two-Stage Bioreactor Cultivation Process. ACS Nano, 2008; 2 (10): 2103 DOI: 10.1021/nn800470x
Adapted from materials provided by Oregon State University.