Carbon nanostructures grow under extreme particle bombardment

Even at a plasma bombardment that is 10,000 times more intense than the standard production method, carbon nanostructures such as these can develop. 
Credit: K.Bystrov/DIFFER.

Nanostructures, such as graphene and carbon nanotubes, can develop under far extremer plasma conditions than was previously thought. Plasmas (hot, charged gases) are already widely used to produce interesting nanostructures. In the scientific journal Carbon, FOM PhD researcher Kirill Bystrov shows that carbon nanostructures can also develop under far extremer conditions than those normally used for this purpose.

DIFFER's Pilot-PSI device has been built to expose wall materials to plasmas that will rage in future fusion reactors. Such plasmas are 10,000 times more intense than those normally used for the construction of nanomaterials. Using Pilot-PSI, Bystrov's international team demonstrated that this extreme environment provides unexpected possibilities for producing nanostructures.

Out of equilibrium 

Plasmas offer major advantages for the controlled production of advanced materials. In the plasma ions and electrons can be brought far out of their thermal equilibria. Under these conditions, the deposition processes can proceed very differently from those at thermal equilibrium. In the widely used technique of plasma-enhanced chemical vapour deposition (PECVD) the plasma density and the quantity of material supplied (carbon) determine which nanostructures develop. The further plasma is from its thermal equilibrium, the more exotic the structures that develop.

Even at a plasma bombardment that is 10,000 times more intense than the standard production method, carbon nanostructures such as these can develop. 
Credit: K.Bystrov / DIFFER

Variation 

After they had exposed various materials such as tungsten, molybdenum and graphite to a plasma with a carbon supply, Bystrov's team discovered a layer full of exotic carbon nanostructures: multi-walled or extra long nanotubes, cauliflower structures and layers of graphene. Varying parameters such as the plasma density, temperature and composition yielded different structures each time. Bystrov: "It was most surprising that an enormous particle bombardment like that which occurs on the edge of a fusion reactor can yield such delicate structures". The influence of the material on which the deposited structures formed was found to be surprisingly small: on all three of the surfaces tested the same types of structures developed.

Versatile machines
 
With the research, Bystrov and his colleagues do not yet have a competitor for the PECVD technique. "Our interest is in demonstrating that you can allow interesting processes to occur in environments 10,000 times more intense than you would expect," Bystrov writes in his publication. Research leader dr. Greg De Temmerman from the Plasma Surface Interactions team at DIFFER: "We set up these experiments to investigate what happens with the wall materials in future fusion reactors. This research demonstrates that the conditions in Pilot-PSI and its big brother Magnum-PSI are also interesting far outside the fusion community. These are highly versatile machines".

Contact 

Kirill Bystrov, MSc, PhD researcher plasma-wall interaction, +31 (0)30 609 69 30.
Dr. Greg De Temmerman, research leader plasma wall interaction, +31 (0)30 609 69 44.
Gieljan de Vries, MSc, Head of Communication FOM Institute DIFFER, +31 (0)30 609 69 02.

Reference 

Spontaneous synthesis of carbon nanowalls, nanotubes and nanotips using high flux density plasmas, Carbon, 28 November 2013. DOI: 10.1016/j.carbon.2013.11.051 

Source: http://www.fom.nl/live/english/news/archives/pressreleases2013/artikel.pag?objectnumber=241874

Nanoscale Coatings Improve Stability and Efficiency of Devices for Renewable Fuel Generation

A graphic representation of how atomic layer
deposition can aid renewable hydrogen fuel
generation. Two papers published in
Proceedings of the National Academy of
Sciences show how atomic layer deposition
can make water-splitting devices more stable and
more efficient.

Splitting water into its components, two parts hydrogen and one part oxygen, is an important first step in achieving carbon-neutral fuels to power our transportation infrastructure – including automobiles and planes.

Now, North Carolina State University researchers and colleagues from the University of North Carolina at Chapel Hill have shown that a specialized coating technique can make certain water-splitting devices more stable and more efficient. Their results are published online this week in two separate papers in the Proceedings of the National Academy of Sciences.

Atomic layer deposition, or “ALD,” coats three-dimensional structures with a precise, ultra-thin layer of material. “An ALD coating is sort of like the chocolate glaze on the outside of a Klondike bar – just much, much thinner,” explains Dr. Mark Losego, research assistant professor of chemical and biomolecular engineering at NC State and a co-author on the work. “In this case, the layers are less than one nanometer thick – or almost a million times thinner than a human hair.”

Although extremely thin, these coatings improve the attachment and performance of surface-bound molecular catalysts used for water-splitting reactions in hydrogen-fuel-producing devices.

In the first paper, “Solar water splitting in a molecular photoelectrochemical cell,” the researchers used ALD coatings on nanostructured water-splitting cells to improve the efficiency of electrical current flow from the molecular catalyst to the device. The findings significantly improved the hydrogen generating capacity of these molecular-based solar water-splitting cells.

In the second paper, “Crossing the divide between homogeneous and heterogeneous catalysis in water oxidation,” the researchers used ALD to “glue” molecular catalysts to the surface of water-splitting electrodes in order to make them more impervious to detachment in non-acidic water solutions. This improved stability at high pH enabled a new chemical pathway to water splitting that is one million times faster than the route that had been previously identified in acidic, or low pH, environments. These findings could have implications in stabilizing a number of other molecular catalysts for other renewable energy pathways, including the conversion of carbon dioxide to hydrocarbon fuels.

“In these reports, we’ve shown that nanoscale coatings applied by ALD can serve multiple purposes in water-splitting technology, including increasing hydrogen production efficiency and extending device lifetimes,” Losego said. “In the future, we would like to build devices that integrate both of these advantages and move us toward other fuels of interest, including methanol production.”

NC State’s Gregory Parsons, Alcoa Professor of Chemical and Biomolecular Engineering, and Ph.D student Berc Kalanyan co-authored both papers with Losego. Thomas J. Meyer, the Arey Distinguished Professor of Chemistry at UNC-Chapel Hill, is the corresponding author on both papers; UNC researchers Dr. Aaron K. Vannucci and Dr. Leila Alibabaei were leading authors. The research was funded by the U.S. Department of Energy, the Research Triangle Solar Fuels Institute and the University of North Carolina Energy Frontier Research Center.

Source: http://news.ncsu.edu/releases/nanocoatings-improve-efficiency-stability/

Genetic mutation increases risk of Parkinson’s disease from pesticides

Healthy (left) and mutated (right) neurons exposed to pesticides.
The green color indicates cell death, the red color indicates
dopamine

A team of researchers has brought new clarity to the picture of how gene-environmental interactions can kill nerve cells that make dopamine. 

Dopamine is the neurotransmitter that sends messages to the part of the brain that controls movement and coordination. Their discoveries, described in a paper published online today in Cell, include identification of a molecule that protects neurons from pesticide damage.

“For the first time, we have used human stem cells derived from Parkinson’s disease patients to show that a genetic mutation combined with exposure to pesticides creates a ‘double hit’ scenario, producing free radicals in neurons that disable specific molecular pathways that cause nerve-cell death,” says Stuart Lipton, M.D., Ph.D., professor and director of Sanford-Burnham’s Del E. Webb Center for Neuroscience, Aging, and Stem Cell Research and senior author of the study.

Until now, the link between pesticides and Parkinson’s disease was based mainly on animal studies and epidemiological research that demonstrated an increased risk of disease among farmers, rural populations, and others exposed to agricultural chemicals.

In the new study, Lipton, along with Rajesh Ambasudhan, Ph.D., research assistant professor in the Del E. Webb Center, and Rudolf Jaenisch, M.D., founding member of Whitehead Institute for Biomedical Research and professor of biology at the Massachusetts Institute of Technology (MIT), used skin cells from Parkinson’s patients that had a mutation in the gene encoding a protein called alpha-synuclein. Alpha-synuclein is the primary protein found in Lewy bodies—protein clumps that are the pathological hallmark of Parkinson’s disease.

Using patient skin cells, the researchers created human induced pluripotent stem cells (hiPSCs) containing the mutation, and then “corrected” the alpha-synuclein mutation in other cells. Next, they reprogrammed all of these cells to become the specific type of nerve cell that is damaged in Parkinson’s disease, called A9 dopamine-containing neurons—thus creating two sets of neurons—identical in every respect except for the alpha-synuclein mutation.

“Exposing both normal and mutant neurons to pesticides—including paraquat, maneb, or rotenone—created excessive free radicals in cells with the mutation, causing damage to dopamine-containing neurons that led to cell death,” said Frank Soldner, M.D., research scientist in Jaenisch’s lab and co-author of the study.

“In fact, we observed the detrimental effects of these pesticides with short exposures to doses well below EPA-accepted levels,” said Scott Ryan, Ph.D., researcher in the Del E. Webb Center and lead author of the paper.

Having access to genetically matched neurons with the exception of a single mutation simplified the interpretation of the genetic contribution to pesticide-induced neuronal death. In this case, the researchers were able to pinpoint how cells with the mutation, when exposed to pesticides, disrupt a key mitochondrial pathway—called MEF2C-PGC1alpha—that normally protects neurons that contain dopamine. The free radicals attacked the MEF2C protein, leading to the loss of function of this pathway that would otherwise have protected the nerve cells from the pesticides.

“Once we understood the pathway and the molecules that were altered by the pesticides, we used high-throughput screening to identify molecules that could inhibit the effect of free radicals on the pathway,” said Ambasudhan. “One molecule we identified was isoxazole, which protected mutant neurons from cell death induced by the tested pesticides. Since several FDA-approved drugs contain derivatives of isoxazole, our findings may have potential clinical implications for repurposing these drugs to treat Parkinson’s.”

While the study clearly shows the relationship between a mutation, the environment, and the damage done to dopamine-containing neurons, it does not exclude other mutations and pathways from being important as well. The team plans to explore additional molecular mechanisms that demonstrate how genes and the environment interact to contribute to Parkinson’s and other neurodegenerative diseases, such as Alzheimer’s and ALS.

“In the future, we anticipate using the knowledge of mutations that predispose an individual to these diseases in order to predict who should avoid a particular environmental exposure. Moreover, we will be able to screen for patients who may benefit from a specific therapy that can prevent, treat, or possibly cure these diseases,” Lipton said. 

Source:  http://beaker.sanfordburnham.org/2013/11/genetic-mutation-increases-risk-of-parkinsons-disease-from-pesticides/#sthash.lPPYudgV.dpuf

Slowly cooled DNA transforms disordered nanoparticles into orderly crystal

Nature builds flawless diamonds, sapphires and other gems. Now a Northwestern University research team is the first to build near-perfect single crystals out of nanoparticles and DNA, using the same structure favored by nature.

“Single crystals are the backbone of many things we rely on -- diamonds for beauty as well as industrial applications, sapphires for lasers and silicon for electronics,” said nanoscientist Chad A. Mirkin. “The precise placement of atoms within a well-defined lattice defines these high-quality crystals.

“Now we can do the same with nanomaterials and DNA, the blueprint of life,” Mirkin said. “Our method could lead to novel technologies and even enable new industries, much as the ability to grow silicon in perfect crystalline arrangements made possible the multibillion-dollar semiconductor industry.”

His research group developed the “recipe” for using nanomaterials as atoms, DNA as bonds and a little heat to form tiny crystals. This single-crystal recipe builds on superlattice techniques Mirkin’s lab has been developing for nearly two decades.

In this recent work, Mirkin, an experimentalist, teamed up with Monica Olvera de la Cruz, a theoretician, to evaluate the new technique and develop an understanding of it. Given a set of nanoparticles and a specific type of DNA, Olvera de la Cruz showed they can accurately predict the 3-D structure, or crystal shape, into which the disordered components will self-assemble. 

Mirkin is the George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences. Olvera de la Cruz is a Lawyer Taylor Professor and professor of materials science and engineering in the McCormick School of Engineering and Applied Science. The two are senior co-authors of the study.

The results will be published Nov. 27 in the journal Nature. 

Chad Mirkin

The general set of instructions gives researchers unprecedented control over the type and shape of crystals they can build. The Northwestern team worked with gold nanoparticles, but the recipe can be applied to a variety of materials, with potential applications in the fields of materials science, photonics, electronics and catalysis. 

A single crystal has order: its crystal lattice is continuous and unbroken throughout. The absence of defects in the material can give these crystals unique mechanical, optical and electrical properties, making them very desirable.

In the Northwestern study, strands of complementary DNA act as bonds between disordered gold nanoparticles, transforming them into an orderly crystal. The researchers determined that the ratio of the DNA linker’s length to the size of the nanoparticle is critical.

“If you get the right ratio it makes a perfect crystal -- isn’t that fun?” said Olvera de la Cruz, who also is a professor of chemistry in the Weinberg College of Arts and Sciences. “That’s the fascinating thing, that you have to have the right ratio. We are learning so many rules for calculating things that other people cannot compute in atoms, in atomic crystals.”

The ratio affects the energy of the faces of the crystals, which determines the final crystal shape. Ratios that don’t follow the recipe lead to large fluctuations in energy and result in a sphere, not a faceted crystal, she explained. With the correct ratio, the energies fluctuate less and result in a crystal every time.

“Imagine having a million balls of two colors, some red, some blue, in a container, and you try shaking them until you get alternating red and blue balls,” Mirkin explained. “It will never happen.

“But if you attach DNA that is complementary to nanoparticles -- the red has one kind of DNA, say, the blue its complement -- and now you shake, or in our case, just stir in water, all the particles will find one another and link together,” he said. “They beautifully assemble into a three-dimensional crystal that we predicted computationally and realized experimentally.”

Monica Olvera de la Cruz

To achieve a self-assembling single crystal in the lab, the research team reports taking two sets of gold nanoparticles outfitted with complementary DNA linker strands. Working with approximately 1 million nanoparticles in water, they heated the solution to a temperature just above the DNA linkers’ melting point and then slowly cooled the solution to room temperature, which took two or three days.

The very slow cooling process encouraged the single-stranded DNA to find its complement, resulting in a high-quality single crystal approximately three microns wide. “The process gives the system enough time and energy for all the particles to arrange themselves and find the spots they should be in,” Mirkin said.

The researchers determined that the length of DNA connected to each gold nanoparticle can’t be much longer than the size of the nanoparticle. In the study, the gold nanoparticles varied from five to 20 nanometers in diameter; for each, the DNA length that led to crystal formation was about 18 base pairs and six single-base “sticky ends. 

“There’s no reason we can’t grow extraordinarily large single crystals in the future using modifications of our technique,” said Mirkin, who also is a professor of medicine, chemical and biological engineering, biomedical engineering and materials science and engineering and director of Northwestern’s International Institute for Nanotechnology.

The Air Force Office of Scientific Research (Multidisciplinary University Research Initiative, grant FA9550-11-1-0275) supported the research.

The title of the paper is “DNA-mediated nanoparticle crystallization into Wulff polyhedra.”

In addition to Mirkin and Olvera de la Cruz, authors of the paper are Evelyn Auyeung (first author), Ting I. N. G. Li, Andrew J. Senesi, Abrin L. Schmucker and Bridget C. Pals, all from Northwestern.

Source: http://www.mccormick.northwestern.edu/news/articles/2013/11/making-a-gem-of-a-tiny-crystal.html

Nanocrystals bond silicone to PTFE

Tetrapod shape aids bonding (CAU, Xin Jin)

The potential for silicone in medical applications keeps growing.

In the newest development, researchers in Germany have discovered a way to join silicone and polytetrafluoroethylene (PTFE) using nano-scaled crystal linkers as internal staples. A major side benefit is that it's a purely mechanical process, ensuring no change in the chemical structure of the polymers.

Potential applications include breathing masks, implants or sensors.

"If the nano staples make even extreme polymers like Teflon (PTFE) and silicone stick to each other, they can join all kinds of other plastic materials", says Professor Rainer Adelung, who runs the functional nano materials group at the Institute of Materials Science in Kiel that participated in the announcement of the discovery.

The key to the approach is the use of very tiny crystals made of zinc oxide that are shaped like tetrapods with four legs protruding from the point of origin. They interlock and form strong bonds, and have been used in larger forms in coastal protection.

Here's how it works:  zinc oxide crystals are distributed carefully on a heated layer of PTFE, kind of like sprinkling sugar on partially baked cookies. After silicone is poured on top, the polymer sandwich is heated to 100°C for less than sixty minutes.

"It's like stapling two non-sticky materials from the inside with the crystals: When they are heated up, the nano tetrapods in between the polymer layers pierce the materials, sink into them, and get anchored", says Xin Jin, the first author of the publication, who is currently working on her PhD thesis. Her supervisor, Yogendra Kumar Mishra, adds: "If you try to pull out a tetrapod on one arm from a polymer layer, the shape of the tetrapod will simply cause three arms to dig in deeper and to hold on even firmer."

The peel strength of the composite structure is 200 Newtons per meter, which is described as similar to peeling sticky tape off glass. "The stickiness we have achieved with the nano tetrapods is remarkable, because as far as we could verify, no one has ever made silicone and Teflon stick to each other at all," says co-author Lars Heepe, PhD student from the Zoological Institute of Kiel University. 

Adelung said fundamental research on the project will continue as practical applications are pursued. One of the business partners, nanoproofed GmbH, is currently developing a product for painting on top of silicone.

The work was conducted within the German Research Foundation (DFG)-funded Collaborative Research Center 677"Function by Switching".

Source: http://www.plasticstoday.com/articles/nanocrystals-bond-silicone-ptfe0829201201

Nanotubes can solder themselves, markedly improving device performance

University of Illinois researchers have developed a way to heal gaps in wires too small for even the world’s tiniest soldering iron.

Led by electrical and computer engineering professor Joseph Lyding and graduate student Jae Won Do, the Illinois team published its results in the journal Nano Letters. 

Carbon nanotubes are like tiny hollow wires of carbon just 1 atom thick – similar to graphene but cylindrical. Researchers have been exploring using them as transistors instead of traditional silicon, because carbon nanotubes are easier to transport onto alternate substrates, such as thin sheets of plastic, for low-cost flexible electronics or flat-panel displays. 

Carbon nanotubes themselves are high-quality conductors, but creating single tubes suitable to serve as transistors is very difficult. Arrays of nanotubes are much easier to make, but the current has to hop through junctions from one nanotube to the next, slowing it down. In standard electrical wires, such junctions would be soldered, but how could the gaps be bridged on such a small scale?

VIEW VIDEO | Illinois professor Joseph Lyding narrates an animation demonstrating the process of nano-soldering, which improves nanotube transistors. Metal self-deposits onto hotspot junctions, healing gaps between nanotubes.  | Video courtesy of Joe Lyding

“It occurred to me that these nanotube junctions will get hot when you pass current through them,” said Lyding, “kind of like faulty wiring in a home can create hot spots. In our case, we use these hot spots to trigger a local chemical reaction that deposits metal that nano-solders the junctions.”

Lyding’s group teamed with Eric Pop, an adjunct professor of electrical and computer engineering, and John Rogers, Swanlund professor in materials science and engineering, experts on carbon nanotube synthesis and transfer, as well as chemistry professor Greg Girolami. Girolami is an expert in a process that uses gases to deposit metals on a surface, called chemical vapor deposition (CVD).

The nano-soldering process is simple and self-regulating. A carbon nanotube array is placed in a chamber pumped full of the metal-containing gas molecules. When a current passes through the transistor, the junctions heat because of resistance as electrons flow from one nanotube to the next. The molecules react to the heat, depositing the metal at the hot spots and effectively “soldering” the junctions. Then the resistance drops, as well as the temperature, so the reaction stops. (See video for demonstration of the process.)

The nano-soldering takes only seconds and improves the device performance by an order of magnitude – almost to the level of devices made from single nanotubes, but much easier to manufacture on a large scale.

“It would be easy to insert the CVD process in existing process flows,” Lyding said. “CVD technology is commercially available off-the-shelf. People can fabricate these transistors with the ability to turn them on so that this process can be done. Then when it’s finished they can finish the wiring and connect them into the circuits. Ultimately it would be a low-cost procedure.”

Now, the group is working to refine the process.

“We think we can make it even better,” Lyding said. “This is the prelude, we hope, but it’s actually quite significant.”

The National Science Foundation and the Office of Naval Research supported this work.  Lyding and Rogers also are affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I.

Source: http://news.illinois.edu/news/13/1125nanosoldering_JosephLyding.html

Creating synthetic antibodies

MIT chemical engineers created this sensor that can recognize
riboflavin by coating a carbon nanotube with amphiphilic polymers.

Synthetic polymers coating a nanoparticle surface can recognize specific molecules just like an antibody.

MIT chemical engineers have developed a novel way to generate nanoparticles that can recognize specific molecules, opening up a new approach to building durable sensors for many different compounds, among other applications. 

To create these “synthetic antibodies,” the researchers used carbon nanotubes — hollow, nanometer-thick cylinders made of carbon that naturally fluoresce when exposed to laser light. In the past, researchers have exploited this phenomenon to create sensors by coating the nanotubes with molecules, such as natural antibodies, that bind to a particular target. When the target is encountered, the carbon nanotube’s fluorescence brightens or dims. 

The MIT team found that they could create novel sensors by coating the nanotubes with specifically designed amphiphilic polymers — polymers that are drawn to both oil and water, like soap. This approach offers a huge array of recognition sites specific to different targets, and could be used to create sensors to monitor diseases such as cancer, inflammation, or diabetes in living systems.

“This new technique gives us an unprecedented ability to recognize any target molecule by screening nanotube-polymer complexes to create synthetic analogs to antibody function,” says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and senior author of the study, which appears in the Nov. 24 online edition ofNature Nanotechnology.

Lead authors of the paper are recent PhD recipient Jingqing Zhang, postdoc Markita Landry, and former postdocs Paul Barone and Jong-Ho Kim.

Synthetic antibodies

The new polymer-based sensors offer a synthetic design approach to the production of molecular recognition sites — enabling, among other applications, the detection of a potentially infinite library of targets. Moreover, this approach can provide a more durable alternative to coating sensors such as carbon nanotubes with actual antibodies, which can break down inside living cells and tissues. Another family of commonly used recognition molecules are DNA aptamers, which are short pieces of DNA that interact with specific targets, depending on the aptamer sequence. However, there are not aptamers specific to many of molecules that one might want to detect, Strano says.

In the new paper, the researchers describe molecular recognition sites that enable the creation of sensors specific to riboflavin, estradiol (a form of estrogen), and L-thyroxine (a thyroid hormone), but they are now working on sites for many other types of molecules, including neurotransmitters, carbohydrates, and proteins.

Their approach takes advantage of a phenomenon that occurs when certain types of polymers bind to a carbon nanotube. These polymers, known as amphiphilic, have both hydrophobic and hydrophilic regions. These polymers are designed and synthesized such that when the polymers are exposed to carbon nanotubes, the hydrophobic regions latch onto the tubes like anchors and the hydrophilic regions form a series of loops extending away from the tubes.

These loops form a new layer surrounding the nanotube, known as a corona. The MIT researchers found that the loops within the corona are arranged very precisely along the tube, and the spacing between the anchors determines which target molecule will be able to wedge into the loops and alter the carbon nanotube’s fluorescence. 

Molecular interactions

What is unique about this approach, the researchers say, is that the molecular recognition could not be predicted by looking at the structure of the target molecule and the polymer before it attaches to the nanotube. 

“The idea is that a chemist could not look at the polymer and understand why this would recognize the target, because the polymer itself can’t selectively recognize these molecules. It has to adsorb onto the nanotube and then, by having certain sections of the polymer exposed, it forms a binding site,” Strano says.

Laurent Cognet, a senior scientist at the Institute of Optics at the University of Bordeaux, says this approach should prove useful for many applications requiring reliable detection of specific molecules.

“This new concept, being based on the molecular recognition from the adsorbed phase itself, does not require the use of antibodies or equivalent molecules to achieve specific molecule recognitions and thus provides a promising alternative route for ‘on demand’ molecular sensing,” says Cognet, who was not part of the research team.

The researchers used an automated, robot-assisted trial and error procedure to test about 30 polymer-coated nanotubes against three dozen possible targets, yielding three hits. They are now working on a way to predict such polymer-nanotube interactions based on the structure of the corona layers, using data generated from a new type of microscope that Landry built to image the interactions between the carbon nanotube coronas and their targets.

“What’s happening to the polymer and the corona phase has been a bit of a mystery, so this is a step forward in getting more data to address the problem of how to design a target for a specific molecule,” Landry says.

The research was funded by the National Science Foundation and the Army Research Office through MIT’s Institute for Soldier Nanotechnologies.

Source: http://web.mit.edu/newsoffice/2013/creating-synthetic-antibodies-1124.html

Turning plastic bags into high-tech materials

Nanotechnological Recycling

University of Adelaide researchers have developed a process for turning waste plastic bags into a high-tech nanomaterial.

The innovative nanotechnology uses non-biodegradable plastic grocery bags to make 'carbon nanotube membranes' ‒ highly sophisticated and expensive materials with a variety of potential advanced applications including filtration, sensing, energy storage and a range of biomedical innovations.

"Non-biodegradable plastic bags are a serious menace to natural ecosystems and present a problem in terms of disposal," says Professor Dusan Losic, ARC Future Fellow and Research Professor of Nanotechnology in the University's School of Chemical Engineering.

"Transforming these waste materials through 'nanotechnological recycling' provides a potential solution for minimising environmental pollution at the same time as producing high-added value products."

Carbon nanotubes are tiny cylinders of carbon atoms, one nanometre in diameter (1/10,000 the diameter of a human hair). They are the strongest and stiffest materials yet discovered - hundreds of times stronger than steel but six times lighter - and their unique mechanical, electrical, thermal and transport properties present exciting opportunities for research and development. They are already used in a variety of industries including in electronics, sports equipment, long-lasting batteries, sensing devices and wind turbines.

The University of Adelaide's Nanotech Research Group has 'grown' the carbon nanotubes onto nanoporous alumina membranes. They used pieces of grocery plastic bags which were vaporised in a furnace to produce carbon layers that line the pores in the membrane to make the tiny cylinders (the carbon nanotubes). The idea was conceived and carried out by PhD student Tariq Altalhi.

"Initially we used ethanol to produce the carbon nanotubes," says Professor Losic. "But my student had the idea that any carbon source should be useable."

The huge potential market for carbon nanotubes hinges on industry's ability to produce large quantities more cheaply and uniformly. Current synthesis methods usually involve complex processes and equipment, and most companies on the market measure production output in only several grams per day.

"In our laboratory, we've developed a new and simplified method of fabrication with controllable dimensions and shapes, and using a waste product as the carbon source," says Professor Losic.

The process is also catalyst and solvent free, which means the plastic waste can be used without generating poisonous compounds.

This research has been published online ahead of print in the journal Carbon.

Source: http://www.adelaide.edu.au/news/news65022.html?q=carbon%20nanotubes

Water-Like Properties of Soft Nanoparticle Suspensions

A schematic of soft nanocolloidal suspensions comprising 

of soft polyethylene glycol (PEG) tethered silica nanoparticles 

suspended in PEG oligomers. The pictures show the variation 

in physical characteristics with increasing particle loading 

and the electron micrograph shows the well-dispersed 

particles in these suspensions.

The unusual properties of water, including its anomalous thermal expansion and density anomaly, have intrigued researchers for decades. These properties are notoriously hard to investigate experimentally owing to the inherently small length scales and complex interactions that appear to govern the physics of these materials. Studies of small particles (colloids) dispersed in solvents, known as colloidal suspensions, used as models for atomic and molecular liquids have shown that some of these anomalies can be engineered in colloidal suspensions of soft particles. 

A report published in Physical Review Letters describes research carried out at the U.S. Department of Energy Office of Science’s Advanced Photon Source (APS) at Argonne National Laboratory that elucidates the arrangements and mobility of soft nanoparticles in dense suspensions that mirror the anomalies observed in complex liquids like water. This discovery, which is the first instance of experimental observation of such behavior in a colloidal suspension, allows for an extension of the toolbox of the experimental physicist interested in employing suspensions to mimic molecular liquids, with the added advantage of readily accessible length and time scales.

The unusual properties of water, including its anomalous thermal expansion and density anomaly, have intrigued researchers for decades. These properties are notoriously hard to investigate experimentally owing to the inherently small length scales and complex interactions that appear to govern the physics of these materials. Studies of small particles (colloids) dispersed in solvents, known as colloidal suspensions, used as models for atomic and molecular liquids have shown that some of these anomalies can be engineered in colloidal suspensions of soft particles. A report published in Physical Review Letters describes research carried out at the U.S. Department of Energy Office of Science’s Advanced Photon Source (APS) at Argonne National Laboratory that elucidates the arrangements and mobility of soft nanoparticles in dense suspensions that mirror the anomalies observed in complex liquids like water. This discovery, which is the first instance of experimental observation of such behavior in a colloidal suspension, allows for an extension of the toolbox of the experimental physicist interested in employing suspensions to mimic molecular liquids, with the added advantage of readily accessible length and time scales.

The research team, with members from Cornell University and Argonne, synthesized soft nanoparticles by densely tethering small polymers onto the surface of silica nanoparticles. Small-angle x-ray scattering (SAXS) and x-ray photon correlation spectroscopy (XPCS) measurements were carried out at X-ray Science Division beamlines 12-ID-B and 8-ID-I at the APS to reveal the equilibrium structure and the characteristics of particle motion, respectively.

It was found that the particle arrangements become more disordered and move faster when more particles are added into the suspension beyond a critical particle volume fraction, coinciding with a sharp increase in the resistance by the system of grafted nanoparticles to physical deformations.

Evolution of structure factor (S(q)) and relaxation times (τ) with particle loading (ϕ) for soft nanoparticle suspensions. The appearance of maxima in the height of the first peak of S(q) clearly indicates the structural anomaly, while the maxima in relaxation times indicates the transport anomaly in the soft nanocolloidal suspensions. These results were obtained from SAXS and XPCS measurements, respectively.

This is in contrast to the usual situation where increasing the concentration of particles in a dilute suspension decreases the space available for placing new particles, thus increasing particle ordering and slowing them down.

“It becomes easier for any particle in these suspensions to diffuse when they are more surrounding by their neighbors; the counterintuitive nature of this situation can be illustrated with the following analogy - it is easier to make a run and score a touch down when the opposing team has fifteen people in defense,” said Samanvaya Srivastava, a senior graduate student at Cornell University and lead author of thePhysical Review Letters article.

The anomalous behavior of particles suspended in water and other complex liquids has been long argued to exist for systems with soft repulsion, which is characterized by a potential energy that exhibits a finite width over which particle interaction occurs. These empirical findings lend support to an emerging consensus from simulation studies and provide for a model system for studying systems with soft repulsive interactions.

Source: http://www.aps.anl.gov/Science/Highlights/Content/APS_SCIENCE_20131125.php

Ultra-Sensitive Force Sensing With Levitating Nanoparticle

Thermal nonlinearities in a nanomechanical oscillator in Nature Physics.

In a recent study, researchers of the Plasmon nano-optics group led by ICREA Prof. at ICFO Romain Quidant in collaboration with Prof. Lukas Novotny at ETH, achieved the highest force sensitivity ever observed with a nano-mechanical resonator. The scientific results of this study have been published in Nature Physics.

Despite recent advances in the design and fabrication of mechanical resonators, their Q-factor has so far been limited by coupling to the environment through physical contact to a support. To overcome this limitation, the present work has proposed to use optically levitated objects in vacuum that do not suffer from clamping losses.

ICFO researchers have optically levitated nanoparticles in high vacuum conditions and measured the highest Q-factor ever observed in nano- or micromechanical systems. The combination of an ultra-high Q-factor with the tiny mass of the nanoparticles leads to an unprecedented force sensitivity at room temperature. The system is so sensitive that the weak forces arising from collisions between the nanoparticle and the residual air molecules are enough to drive it into the nonlinear regime. This study demonstrates for the first time that ultra-high Q-factor nano-resonators intrinsically behave nonlinearly.

The advent of this new class of nano-mechanical oscillators will open new avenues for ultrasensitive force sensing and benefit the experimental investigation of quantum physics.

Source: http://www.icfo.eu/newsroom/news2.php?id_news=2156&subsection=home

Researchers discover roots of superfluorescent bursts from quantum wells

Spontaneous bursts of light from a solid block illuminate the unusual way interacting quantum particles behave when they are driven far from equilibrium. The discovery by Rice University scientists of a way to trigger these flashes may lead to new telecommunications equipment and other devices that transmit signals at picosecond speeds.

The Rice University lab of Junichiro Kono found the flashes, which last trillionths of a second, change color as they pulse from within a solid-state block. The researchers said the phenomenon can be understood as a combination of two previously known many-body concepts: superfluorescence, as seen in atomic and molecular systems, and Fermi-edge singularities, a process known to occur in metals.

The team previously reported the first observation of superfluorescence in a solid-state system by strongly exciting semiconductor quantum wells in high magnetic fields. The new process – Fermi-edge superfluorescence – does not require them to use powerful magnets. That opens up the possibility of making compact semiconductor devices to produce picosecond pulses of light.

The results by Rice, Florida State University and Texas A&M University researchers were reported this month in Nature’s online journal, Scientific Reports.

The semiconducting quantum wells at the center of the experiment contain particles – in this case, a dense collection of electrons and holes – and confine them to wiggle only within the two dimensions allowed by the tiny, stacked wells, where they are subject to strong Coulomb interactions.

Previous experiments by Rice and Florida State showed the ability to create superfluorescent bursts from a stack of quantum wells excited by a laser in extreme cold and under the influence of a strong magnetic field, both of which further quenched the electrons’ motions and made an atom-like system. The basic features were essentially the same as those known for superfluorescence in atomic systems.

That was a first, but mysteries remained, especially in results obtained at low or zero magnetic fields. Kono said the team didn’t understand at the time why the wavelength of the burst changed over its 100-picosecond span. Now they do. The team included co-lead authors Timothy Noe, a Rice postdoctoral researcher, and Ji-Hee Kim, a former Rice postdoctoral researcher and now a research professor at Sungkyunkwan University in the Republic of Korea.

In the new results, the researchers not only described the mechanism by which the light’s wavelength evolves during the event (as a Fermi-edge singularity), but also managed to record it without having to travel to the National High Magnetic Field Laboratory at Florida State.

Kono said superfluorescence is a well-known many-body, or cooperative, phenomenon in atomic physics. Many-body theory gives physicists a way to understand how large numbers of interacting particles like molecules, atoms and electrons behave collectively. Superfluorescence is one example of how atoms under tight controls collaborate when triggered by an external source of energy. However, electrons and holes in semiconductors are charged particles, so they interact more strongly than atoms or molecules do.

The quantum well, as before, consisted of stacked blocks of an indium gallium arsenide compound separated by barriers of gallium arsenide. “It’s a unique, solid-state environment where many-body effects completely dominate the dynamics of the system,” Kono said.

“When a strong magnetic field is applied, electrons and holes are fully quantized – that is, constrained in their range of motion — just like electrons in atoms,” he said. “So the essential physics in the presence of a high magnetic field is quite similar to that in atomic gases. But as we decrease and eventually eliminate the magnetic field, we’re entering a regime atomic physics cannot access, where continua of electronic states, or bands, exist.”

The Kono team’s goal was to keep the particles as dense as possible at liquid helium temperatures (about -450 degrees Fahrenheit) so that their quantum states were obvious, or “quantum degenerate,” which happens when the so-called Fermi energy is much larger than the thermal energy. When pumped by a strong laser, these quantum degenerate particles gathered energy and released it as light at the Fermi edge: the energy level of the most energetic particles in the system. As the electrons and holes combined to release photons, the edge shifted to lower-energy particles and triggered more reactions until the sequence played out.

The researchers found the emitted light shifted toward the higher red wavelengths as the burst progressed.

“What’s cool about this is that we have a material, we excite it with a 150-femtosecond pulse, wait for 100 picoseconds, and all of a sudden a picosecond pulse comes out. It’s a long delay,” Kono said. “This may lead to a new method for producing picosecond pulses from a solid. We saw something essentially the same previously, but it required high magnetic fields, so there was no practical application. But now the present work demonstrates that we don’t need a magnet.”

Co-authors are Stephen McGill, an associate scholar and scientist with the National High Magnetic Field Laboratory at Florida State University, and researchers Yongrui Wang and Aleksander Wójcik and Professor Alexey Belyanin of Texas A&M University.

The National Science Foundation and the state of Florida supported the research.

Source: http://news.rice.edu/2013/11/25/flashes-of-brilliance/

Scientists capture 'redox moments' in living cells

Better understanding of hardy bacteria enhances tool for biofuel creation

Scientists have charted a significant signaling network in a tiny organism that's big in the world of biofuels research. The findings about how a remarkably fast-growing organism conducts its metabolic business bolster scientists' ability to create biofuels using the hardy microbe Synechococcus, which turns sunlight into useful energy.

The team at the Department of Energy's Pacific Northwest National Laboratory glimpsed key chemical events, known as redox reactions, inside living cells of the organism. The publication in ACS Chemical Biology marks the first time that redox activity, a very fast regulatory network involved in all major aspects of a cell's operation, has been observed in specific proteins within living cells.

The findings hone scientists' control over a common tool in the biofuels toolbox. At a more basic level, the work gives researchers the newfound ability to witness a basic biological process that occurs every moment in everything from bacteria to people.

"Redox activity tells us where the action is going on within a cell," said chemist Aaron Wright, the leader of the PNNL team whose project was funded by DOE's Office of Science. "We've been able to get a look at the redox system while it's still operating in a living cell, without destroying the cell first. This allows us to tell who the players are when the cells are engaged in the activity of our choice, like making components for biofuels."

Redox activity is one of the most powerful tools an organism has to sense and adapt to a changing environment; it's particularly active in plants that must respond constantly to changing conditions, such as light and dark.

The PNNL study was aimed at ferreting out proteins that are potential redox players in the cyanobacterium Synechococcus. Cyanobacteria absorb light energy from the sun and use it to convert carbon dioxide into food and other molecules, while also giving off oxygen. Redox reactions play a role in directing where the harvested energy goes.

Scientists believe the organism and its plant-like cousins, including algae, were responsible for producing the first oxygen on Earth, more than 2.5 billion years ago. It's a sure bet that you have inhaled oxygen molecules produced by Synechococcus, which today contributes a significant proportion of the oxygen available on Earth.

The organism is attractive to scientists for a number of reasons. It's adept at converting carbon dioxide into other molecules, such as fatty acids, that are of interest to energy researchers. Synechococcus is easy for scientists to change and manipulate as they explore new ideas. And it grows quickly, doubling in approximately two hours. A patch just two feet wide by seven feet long — roughly the area of a typical dining room table — could blossom into an area the size of a football field in just one day.

Biofuels makers and other scientists are trying to exploit this ability to churn out quantities of materials that might serve as biofuel. Synechococcus is also remarkably hardy, capable of tolerating the stress caused by intense sunlight, which kills many other cyanobacteria. Redox reactions that take place throughout the organism are at the core of this ability, and understanding them gives scientists a treasured global view of how the cell lives and responds to change.

Some researchers are working to get the bacteria itself to create biofuel, growing an organism with more fatty acids that could be converted to diesel fuel. Others, like Wright, are working to understand the organism more completely, to direct the organism to create fuels using light and carbon dioxide.

Wright's team found the signals by keeping the bacteria hungry, then suddenly flooding it with food — a massive, immediate change in environment. Within 30 seconds, the team detected redox activity, which changes the way proteins operate by adding or subtracting electrons.

His team uncovered an extensive network of redox activity, identifying 176 proteins that are sensitive to signaling in this manner. Before this study, just 75 of those proteins were known to be part of a redox signaling network. The scientists found that the system is involved in all the major processes of a cell — which genes are turned on and off, for example, as well as how the cell maintains its molecular machinery and converts energy into fuel.

Central to the work are the chemical probes Wright developed that are able to cross the cell membrane and get into the cytoplasm of the cell. The probes flag redox events by binding to certain forms of the amino acid cysteine, which is a known player in many of these interactions. Then the probes and the interactions they flag are subjected to scrutiny at EMSL, the DOE's Environmental Molecular Sciences Laboratory on the PNNL campus, where instruments detect redox activity through various means, such as through fluorescent imaging and mass spectrometry. The analysis tells scientists about when and where within the cell redox activity occurred.

"Knowing the proteins that are sensitive to redox signaling lets us know where to look as we test out new methods for working with this organism," said Wright. "We can tinker with a specific protein, for instance, and then watch the effects immediately.

"This is the type of information we really must have if we want organisms like this to produce substances that make a difference, like biofuels, chemicals or potential medicines," he added.


Source: http://www.pnnl.gov/news/release.aspx?id=1024

Researchers Use Nanoscale ‘Patches’ to Sensitize Targeted Cell Receptors

Researchers from North Carolina State University and Duke University have developed nanoscale “patches” that can be used to sensitize targeted cell receptors, making them more responsive to signals that control cell activity. The finding holds promise for promoting healing and facilitating tissue engineering research.

The research takes advantage of the fact that cells in a living organism can communicate via physical contact. Specifically, when targeted receptors on the surface of a cell are triggered, the cell receives instructions to alter its behavior in some way. For example, the instructions may cause a stem cell to differentiate into a bone cell or a cartilage cell.

These receptors respond to specific ligands, or target molecules. And those ligands have to be present in certain concentrations in order to trigger the receptors. If there aren’t enough target ligands, the receptors won’t respond.

Now researchers have developed nanoscale patches that are embedded with tiny protein fragments called peptides. These peptides bond to a specific cell receptor, making it more sensitive to its target ligand – meaning that it takes fewer ligand molecules to trigger the receptor and its resulting behavior modification.

“This study shows that our concept can work, and there are a host of potential applications,” says Dr. Thom LaBean, an associate professor of materials science at NC State and senior author of a paper describing the work. “For example, if we identify the relevant peptides, we could create patches that sensitize cells to promote cartilage growth on one side of the patch and bone growth on the other side. This could be used to expedite healing or to enable tissue engineering of biomedical implants.”

“What’s important about this is that it allows us to be extremely precise in controlling cell behavior and gene expression,” says Ronnie Pedersen, a Ph.D. student at Duke University and lead author of the paper. “By controlling which peptides are on the patch, we can influence the cell’s activity. And by manipulating the placement of the patch, we can control where that activity takes place.”

The patch itself is made of DNA that researchers have programmed to self-assemble into flexible, two-dimensional sheets. The sheets themselves incorporate molecules called biotin and streptavidin which serve to hold and organize the peptides that are used to sensitize cell receptors.

“These peptides can bind with cell receptors and sensitize them, without blocking the interaction between the receptors and their target ligands,” Pedersen says. “That’s what makes this approach work.”

The paper, “Sensitization of Transforming Growth Factor-β Signaling by Multiple Peptides Patterned on DNA Nanostructures,” was published online Nov. 8 in the journal Biomacromolecules. The paper was co-authored by Dr. Elizabeth Loboa, associate professor of the joint biomedical engineering program at NC State and UNC-Chapel Hill. The work was supported by National Science Foundation grants DMS-CDI-0835794 and 1133427; National Institute of Biomedical Imaging and Bioengineering grant 1R03EB008790; and the Danish National Research Foundation.

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Note to Editors: The study abstract follows.

“Sensitization of Transforming Growth Factor-β Signaling by Multiple Peptides Patterned on DNA Nanostructures”

Authors: Ronnie O. Pedersen, Duke University; Elizabeth G. Loboa, North Carolina State University and UNC-Chapel Hill; and Thomas LaBean, North Carolina State University

Published: online Nov. 8, Biomacromolecules

DOI: 10.1021/bm4011722

Abstract: We report sensitization of a cellular signaling pathway by addition of functionalized DNA nanostructures. Signaling by transforming growth factor β (TGFβ) has been shown to be dependent on receptor clustering. By patterning a DNA nanostructure with closely spaced peptides that bind to TGF? receptor, we observe increased sensitivity of NMuMG cells to TGFβ ligand. This is evidenced by translocation of secondary messenger proteins to the nucleus and stimulation of an inducible luciferase reporter at lower concentrations of TGFβ ligand. We believe this represents an important initial step toward realization of DNA as a self-assembling and biologically compatible material for use in tissue engineering and drug delivery.

Source: http://news.ncsu.edu/releases/wms-labean-nanopatch2013/