Saturday, April 23, 2011

An atomic electrical field sensor

Electrical fields play a pivotal role in numerous cases in both nature and technical areas: by changing the electrical field, impulses of nerves are transmitted and modern data storage operates by saving electrical charges the so-called Flash Memories. An ultra-precise reading of electrical fields, however, is still a challenge for physical measurement techniques. Researchers from the University of Stuttgart succeeded in measuring electrical fields with the aid of one single defect center in diamond.

This research report has now been published by Nature Physics.

There are different ways in which electrical charges control almost all physical, chemical or biological processes. For example, the exact distribution of electrons on DNA is crucial for the precise transmission of genetic information and modern electric circuits actuate electric currents up to single electrons.

However, measuring those minor electronic fields connected to the charge is still one of the most challenging tasks of measurement technology. Researchers from Stuttgart developed a novel sensor consisting of just one single atom. This nitrogen atom is an impurity captured in diamond. The diamond lattice fixes the atom, simultaneously allowing a laser to address the nuclear vacancy center. The interaction of the atom with the measured field can be determined by the light emitted by the impurity and, therefore, electrical fields can be measured which are just a fracture of the electrical field of an elementary charge in 0,1 µm distance. Since the sensor itself is only about the size of an atom, electrical fields can also be measured with the same spacial precision.

The optical readout by the sensors allows it to be placed in any geometry as desired and, furthermore, the process reaches its sensitivity and resolution at room temperature and ambient conditions. The existence of small magnetic fields has been demonstrated in the past; however, this new combination of both measurement techniques now allows measuring of the electrical as well as the magnetic field in one place without changing the sensor. This unique combination discloses new applications such as, for example, the simultaneous measuring of the magnetic moments' distribution of the chemical compounds' nuclei or the distribution of electrons in single molecules. This way, the structure of a substance and its chemical reactivity can be determined at the same time.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Stuttgart, via AlphaGalileo.

Journal Reference:

F. Dolde, H. Fedder, M. W. Doherty, T. Nöbauer, F. Rempp, G. Balasubramanian, T. Wolf, F. Reinhard, L. C. L. Hollenberg, F. Jelezko, J. Wrachtrup. Electric-field sensing using single diamond spins. Nature Physics, 2011; DOI: 10.1038/NPHYS1969

Material that if scratched, you can quickly and easily fix yourself, with light not heat

 Imagine you're driving your own new car--or a rental car--and you need to park in a commercial garage. Maybe you're going to work, visiting a mall or attending an event at a sports stadium, and you're in a rush. Limited and small available spots and concrete pillars make parking a challenge. And it happens that day: you slightly misjudge a corner and you can hear the squeal as you scratch the side of your car--small scratches, but large anticipated repair costs.

Now imagine that that you can repair these unsightly scratches yourself--quickly, easily and inexpensively. . . . or that you can go through a car wash that can detect these and other more minor scratches and fix them as the car goes through the washing garage. Fantasy? Not exactly. Not anymore. Not according to a new discovery detailed in the April 21 issue of the journal Nature, and depicted in a short video interview and simulation:

A team of researchers in the United States and Switzerland have developed a polymer-based material that can heal itself with the help of a widely used type of lighting. Called "metallo-supramolecular polymers," the material is capable of becoming a supple liquid that fills crevasses and gaps left by scrapes and scuffs when placed under ultraviolet light for less than a minute and then resolidifying.

"This is ingenious and transformative materials research," said Andrew Lovinger, polymers program director in NSF's Division of Materials Research. "It demonstrates the versatility and power of novel polymeric materials to address technological issues and serve society while creating broadly applicable scientific concepts."

The team involves researchers at Case Western Reserve University in Cleveland, Ohio, led by Stuart J. Rowan; the Adolphe Merkle Institute of the University of Fribourg in Switzerland, led by Christoph Weder; and the Army Research Laboratory at Aberdeen Proving Ground in Maryland, led by Rick Beyer.

The scientists envision widespread uses in the not-so-distant future for re-healable materials like theirs, primarily as coatings for consumer goods such as automobiles, floors and furniture. While their polymers are not yet ready for commercial use, they acknowledge, they now have proved that the concept works. And with that, what happens next is up to the market place. Necessity, the mother of invention, will expand the possibilities for commercial applications.

"These polymers have a Napoleon Complex," explains lead author Stuart Rowan, a professor of macromolecular engineering and science and director of the Institute for Advanced Materials at Case Western Reserve University. "In reality they're pretty small but are designed to behave like they're big by taking advantage of specific weak molecular interactions."

"Our study is really a fundamental research study," said Christoph Weder, a professor of polymer chemistry and materials and the director of the Adolphe Merkle Institute. "We tried to create materials that have a unique property matrix, that have unique functionality and that in principle could be very useful."

Specifically, the new materials were created by a mechanism known as supramolecular assembly. Unlike conventional polymers, which consist of long, chain-like molecules with thousands of atoms, these materials are composed of smaller molecules, which were assembled into longer, polymer-like chains using metal ions as "molecular glue" to create the metallo-supramolecular polymers.

While these metallo-supramolecular polymers behave in many ways like normal polymers, when irradiated with intense ultraviolet light the assembled structures become temporarily unglued. This transforms the originally solid material into a liquid that flows easily. When the light is switched off, the material re-assembles and solidifies again; its original properties are restored.

Using lamps such as those dentists use to cure fillings, the researchers repaired scratches in their polymers. Wherever they waved the light beam, the scratches filled up and disappeared, much like a cut that heals and leaves no trace on skin. While skin's healing process can be represented by time-lapse photography that spans several days or weeks, self-healing polymers heal in just seconds.

In addition, unlike the human body, durability of the material does not seem to be compromised by repeated injuries. Tests showed the researchers could repeatedly scratch and heal their materials in the same location.

Further, while heat has provided a means to heal materials for a long time, the use of light provides distinct advantages, says Mark Burnworth, a graduate student at Case Western Reserve University. "By using light, we have more control as it allows us to target only the defect and leave the rest of the material untouched."

The researchers systematically investigated several new polymers to find an optimal combination of mechanical properties and healing ability. They found that metal ions that drive the assembly process via weaker chemical interactions serve best as the light-switchable molecular glue.

They also found the materials that assembled in the most orderly microstructures had the best mechanical properties. But, healing efficiency improved as structural order decreased.

"Understanding these relationships is critical for allowing us improve the lifetime of coatings tailored to specific applications, like windows in abrasive environments" Beyer said.

And what's next? According to Rowan, "One of our next steps is to use the concepts we have shown here to design a coating that would be more applicable in an industrial setting."

Film director and art curator Aaron Rose was at least partially right when he said, "In the right light, at the right time, everything is extraordinary." Self-healing polymers certainly are extraordinary.

The research was funded by the Army Research Office of the U.S. Army Research Laboratory, the U.S. National Science Foundation, and the Adolphe Merkle Foundation.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by National Science Foundation.

Journal Reference:

Mark Burnworth, Liming Tang, Justin R. Kumpfer, Andrew J. Duncan, Frederick L. Beyer, Gina L. Fiore, Stuart J. Rowan, Christoph Weder. Optically healable supramolecular polymers. Nature, 2011; 472 (7343): 334 DOI: 10.1038/nature09963

Researchers now one step closer to controlled engineering of nanocatalysts

Currently, some 20 percent of the world's industrial production is based on catalysts -- molecules that can quicken the pace of chemical reactions by factors of billions. Oil, pharmaceuticals, plastics and countless other products are made by catalysts.

Many are hoping to make current catalysts more efficient, resulting in less energy consumption and less pollution. Highly active and selective nanocatalysts, for example, can be used effectively in efforts to break down pollution, create hydrogen fuel cells, store hydrogen and synthesize fine chemicals. The challenge to date has been developing a method for producing nanocatalysts in a controlled, predictable way.

In a move in this direction, Yu Huang, an assistant professor of materials science and engineering at the UCLA Henry Samueli School of Engineering and Applied Science, and her research team have proposed and demonstrated a new approach to producing nanocrystals with predictable shapes by utilizing surfactants, biomolecules that can bind selectively to certain facets of the crystals' exposed surfaces.

Their new study can be found online in the journal Nature Chemistry.

At the nanoscale, the physical and chemical properties of materials depend on the materials' size and shape. The ultimate goal has been to rationally engineer materials to achieve programmable structures and predictable properties, thereby producing the desired functions. Yet shaped nanocrystals are still generally synthesized by trial-and-error, using non-specific molecules as surfactants -- a result of the inability to find appropriate molecules to control crystal formation.

Huang's team's innovative new work could change that, potentially leading to the ability to rationally produce nanocatalysts with desired shapes and, hence, catalytic properties.

"In our study, we were able to identify specific biomolecules -- peptide sequences, in our case -- which can recognize a desired crystal surface and produce nanocrystals exposed with a particular surface to control the shape," said Chin-Yi Chiu, a UCLA Engineering graduate student and lead author of the study.

"Facet-specific biomolecules can be used to direct the growth of nanocrystals, and most importantly, now we can do it in a predictable fashion," said Huang, senior author of the study. "This is still a first step, but we have overcome the challenges by finding the most specific and selective peptide sequences through a rational selection process."

Huang's team accomplished this by using a phage library that generated a pool of peptide sequences. The team was then able to identify the selectivity of peptide sequences on different crystal surfaces. The next step, the researchers say, is to figure out what exactly is happening on the interface and to be able to describe the characterizations of the interface.

"We don't know the molecular details yet -- that's like the holy grail of molecular biomimetics," Huang said. "Take the catalyst, for example. If we can predict the synthesized catalyst for just one surface, it could have much more improved activity and selectivity. We are still in the initial phase of what we really want to do, which is to see whether or not we can eventually program the synthesis of material structures."

"It's always been a personal interest to learn from the natural evolutionary selection process and apply it to research," Chiu said. "It is especially satisfying to be able to engineer a rational selection process for nanoscale materials to create nanocrystals with desired shapes."

The study was funded by the U.S. Office of Naval Research; the U.S. Army Research Office, through the Presidential Early Career Award for Scientists and Engineers (PECASE); and a Sloan Research Fellowship.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of California - Los Angeles. The original article was written by Wileen Wong Kromhout.

Journal Reference:

Chin-Yi Chiu, Yujing Li, Lingyan Ruan, Xingchen Ye, Christopher B. Murray, Yu Huang. Platinum nanocrystals selectively shaped using facet-specific peptide sequences. Nature Chemistry, 2011; DOI: 10.1038/nchem.1025

'Impossible' feat: Certain materials can exhibit ferromagnetism and superconductivity at same time

 It actually seems impossible: Scientists from the Helmholtz-Zentrum Dresden-Rossendorf and the TU Dresden were able to verify with an intermetallic compound of bismuth and nickel that certain materials actually exhibit the two contrary properties of superconductivity and ferromagnetism at the same time. A phenomenon that had only been demonstrated around the globe on a small number of materials and which might provide highly interesting technological opportunities in future.

Just in time for the 100th anniversary to commemorate the discovery of superconductivity by the Dutch physicist Heike Kamerlingh Onnes on April 8, 1911, scientists from the Helmholtz-Zentrum Dresden-Rossendorf and the TU Dresden published their research results in the journal Physical Review B.

Headed by Dr. Thomas Herrmannsdörfer, the team from the HZDR's High Magnetic Field Laboratory (HLD) examined a material consisting of the elements bismuth and nickel (Bi3Ni) with a diameter of only a few nanometers -- which is unique since it has not been achieved elsewhere so far. This was made possible through a new chemical synthesis procedure at low temperatures which had been developed at the TU Dresden under the leadership of Prof. Michael Ruck. The nano scale size and the special form of the intermetallic compound -- namely, tiny fibers -- caused the physical properties of the material, which is non-magnetic under normal conditions, to change so dramatically. This is a particularly impressive example of the excellent opportunities modern nanotechnology can provide today, emphasizes Dr. Thomas Herrmannsdörfer. "It's really surprising to which extend the properties of a substance can vary if one manages to reduce their size to the nanometer scale."

There are numerous materials which become superconducting at ultralow temperatures. However, this property competes with ferromagnetism which normally suppresses superconductivity. This does not happen with the analyzed compound: Here, the Dresden researchers discovered with their experiments in high magnetic fields and at ultralow temperatures that the nanostructured material exhibits completely different properties than larger-sized samples of the same material. What's most surprising: The compound is both ferromagnetic and superconducting at the same time. It is, thus, one of those rarely known materials which exhibit this unusual and physically not yet completely understood combination. Perhaps bismuth-3-nickel features a special type of superconductivity, says Dr. Herrmannsdörfer. The physicist and doctoral candidate Richard Skrotzki, who has just turned 25, is making a vital contribution to the research results and describes the phenomenon as "the bundling of contrary properties in a single strand."

The TU Dresden and the HZDR are partners in the research alliance DRESDEN-concept which pursues the objective of making visible the excellence of Dresden research.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Helmholtz Association of German Research Centres, via EurekAlert!, a service of AAAS.

Journal Reference:

T. Herrmannsdörfer, R. Skrotzki, J. Wosnitza, D. Köhler, R. Boldt, M. Ruck. Structure-induced coexistence of ferromagnetic and superconducting states of single-phase Bi_{3}Ni seen via magnetization and resistance measurements. Physical Review B, 2011; 83 (14) DOI: 10.1103/PhysRevB.83.140501

Collecting the sun's energy: Novel electrode for flexible thin-film solar cells

Conventional silicon-based rigid solar cells generally found on the market are not suitable for manufacturing moldable thin-film solar cells, in which a transparent, flexible and electrically conductive electrode collects the light and carries away the current. A woven polymer electrode developed by Empa has now produced first results which are very promising, indicating that the new material may be a substitute for indium tin oxide coatings.

The scarcity of raw materials and increasing usage of rare metals is making electronic components and devices more and more costly. Such rare metals are used, for example, to make the transparent electrodes found in mobile phone touchscreen displays, liquid-crystal displays, organic LEDs and thin-film solar cells. The material of choice in these cases is indium tin oxide (ITO), a largely transparent mixed oxide. Because ITO is relatively expensive, however, it is uneconomic to use in large area applications such as solar cells.

The search for alternatives

Indium-free transparent oxides do exist, but with demand for them increasing they too are tending to become scarce. In addition, the principal disadvantages such as brittleness remain. The search for alternative coatings which are both transparent and electrically conductive is therefore intense, with materials such as conductive polymers, carbon nanotubes or graphenes coming under scrutiny. Carbon-based electrodes, however, generally show excessive surface resistance values which make them poor electrical conductors. If a metallic grid is integrated into the organic layer, it reduces not just its resistance but also its mechanical stability. If a solar cell made out of this material is bent, the electrode layers break and are no longer conductive. The challenge thus consists of manufacturing flexible yet stable conductive substrates, ideally in a cost-effective industrial rolling process.

One solution: woven electrodes

One particularly promising possibility is the use of a transparent flexible woven polymer, which Empa has developed together with the company Sefar AG in a project financially supported by the Swiss Commission for Technology and Innovation (CTI). Sefar, which specializes in precision fabrics, is able to produce the woven polymer economically and in large quantities using a roll to roll process similar to the way newspapers are printed. Metal wires woven into the material ensure that it is electrically conductive. In a second process step the material is embedded in an inert plastic layer which does not, however, completely cover the metal filaments, thus retaining its conductivity. The electrode which results is transparent, stable and yet flexible. The Empa researchers then applied a series of coatings to this new substrate to create a novel organic solar cell whose efficiency is compatible to conventional ITO-based cells. In addition, the woven electrode is significantly more stable when deformed than commercially available flexible plastic substrates to which a thin layer of conductive ITO has been applied.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Empa.

Journal Reference:

William Kylberg, Fernando Araujo de Castro, Peter Chabrecek, Uriel Sonderegger, Bryan Tsu-Te Chu, Frank Nüesch, Roland Hany. Woven Electrodes for Flexible Organic Photovoltaic Cells. Advanced Materials, 2011; 23 (8): 1015 DOI: 10.1002/adma.201003391

Innovative screening method identifies possible new treatment for fatal childhood disease

Many genes that cause human diseases have parallel genes in other organisms, including yeast. Now Columbia University researchers have used an innovative yeast-based screening method to identify a possible treatment for the fatal childhood disease Niemann-Pick C (NP-C). This "exacerbate-reverse" approach can potentially be used to study any disease. The findings were published online in the Journal of Chemical Biology on April 13, 2011.

NP-C is one of a group of called lipid storage disorders. Lipids are fat-like substances (which include fat and cholesterol) that are in all of the body's cells. With NP-C, an inability to metabolize lipids properly causes dangerous levels of lipids to accumulate in the liver, spleen, and brain. NP-C is an autosomal recessive disorder; that is, both parents must have the for their child to have the disease. Tragically, a couple may have several children before realizing that they are carriers. Some families have lost three out of four children to the disease.

NP-C is a rare but devastating disease. The symptoms, which usually appear between the ages of four and ten, begin with problems with balance and gait, slurred speech, and developmental delays and inevitably progress to severe , dementia, and, ultimately, death. Frustrated families may spend several years seeking a proper diagnosis, when symptoms are misattributed to learning disabilities or "clumsiness."

Stephen L. Sturley, PhD, associate professor of clinical pediatrics, and Andrew B. Munkacsi, PhD, associate research scientist, both at Columbia University Medical Center, and their colleagues have shown that the existing cancer drug SAHA (developed by Columbia researchers) has the potential to improve three diagnostic criteria of NP-C: accumulation of cholesterol, 2) accumulation of sphingolipids, and 3) defective esterification of LDL-derived cholesterol (esterification is the formation of esters, fatty compounds derived from acids). The discovery of a new use for a drug already on the market is always good news, as the drug has already been tested for safety.

Sturley and his team took advantage of the fact that the gene responsible for 95% of NP-C cases has been present throughout evolution, including in the evolutionarily distant yeast. They used what is called a "synthetic lethality screen" on a yeast model of NC-P. Synthetic lethality occurs when the combination of otherwise insignificant mutations in two or more genes leads to cell death. In other words, they determined which combination of mutations was lethal to the yeast.

The cell nucleus contains proteins called histones. During histone acetylation, a group of atoms called an acetyl group is substituted for a hydrogen atom, and during histone deacetylation, it is removed. When deletion of genes responsible for histone acetylation in the yeast model led to an accumulation of lipids, the researchers hypothesized that an imbalance in histone acetylation caused NP-C disease.

They found that the majority of the 11 histone deacetylase (HDAC) genes were impaired. They then discovered that the cancer drug, an HDAC inhibitor, repaired the genes. Sturley and his team concluded that the genetic pathways that exacerbate lethality in the yeast model could be reversed in human cells, providing a novel treatment for NP-C. In short, using their "exacerbate-reverse" approach, they identified the pathways that exacerbate lethality in their yeast model and then used drugs to manipulate those pathways in the opposite direction.

The next step is to test this new use of the cancer drug on mice and, eventually, hopes Sturley, in clinical trials. Although scientific curiosity originally led Sturley to study NP-C, he is now motivated by the search for a cure. "Once you get to know some of these kids and their families," he says, "it can't be otherwise."

In addition to offering hope to NP-C sufferers and their families, research on NP-C and other lipid storage diseases may help scientists to understand the mechanisms of Alzheimer's disease and other common dementias.

Provided by Columbia University Medical Center (news : web)

Polarized microscopy technique shows new details of how proteins are arranged

Whether you're talking about genes, or neurons, or the workings of a virus, at the most fundamental level, biology is a matter of proteins. So understanding what protein complexes look like and how they operate is the key to figuring out what makes cells tick. By harnessing the unique properties of polarized light, Rockefeller scientists have now developed a new technique that can help deduce the orientation of specific proteins within the cell. By turning their instruments toward the nuclear pore complex, a huge cluster of proteins that serves as a gateway to a cell's nucleus, the scientists say they have filled in the gaps left by other techniques and made important new discoveries about how the complex works.

"Our new technique allows us to measure how components of large protein complexes are arranged in relation to one another," says Sandy Simon, head of the Laboratory of . "This has the potential to give us important new information about how the functions, but we believe it can also be applied to other multi-protein complexes such as those involved in DNA transcription, or ."

Although researchers have spent years studying the workings of the nuclear pore complex, there is still much that has remained mysterious. One problem is that there is a "resolution gap" between the two techniques primarily used to visualize protein complexes. can reveal the broad outlines of a large protein complex, but it can't show details. X-ray crystallography, meanwhile, can show minute detail but only of a small piece of the complex; it can't say how the individual pieces fit together. To further complicate matters, both techniques require fixed samples – while they can give you an idea of what something looks like at a moment in time, they can't tell you how its pieces might move.

The new technique was developed by Simon along with postdoc Alexa Mattheyses, graduate student Claire Atkinson and Martin Kampmann, a former a member of Günter Blobel's Laboratory of Cell Biology who is currently at the University of California, San Francisco. It takes advantage of the properties of polarized light to show how specific proteins are aligned in relation to one another. After genetically attaching fluorescent markers to individual components of the nuclear pore complex, the scientists replaced the cell's own copy of the gene that encodes the protein with the new form that has the fluorescent tag. Then, they used customized microscopes to measure the orientation of the waves of light the fluorescently tagged proteins emitted. By combining these measurements with known data about the structure of the complex, the scientists can confirm or deny the accuracy of previously suggested models.

"Our experimental approach to the structure is synergistic with other studies being conducted at Rockefeller, including analysis with X-ray crystallography in Günter's lab and electron microscopy and computer analysis in Mike Rout's lab," says Simon. "By utilizing multiple techniques, we are able to get a more precise picture of these complexes than has ever been possible before."

The scientists used the technique to study nuclear pore complexes in both budding yeast and human cells. In the case of the human cells, their new data shows that multiple copies of a key building block of the nuclear pore complex, the Y-shaped subcomplex, are arranged head-to-tail, rather than like fence posts, confirming a model proposed by Blobel in 2007.

"As a graduate student with Günter Blobel, I determined the three-dimensional structure of the Y-shaped subcomplex using electron microscopy," says Kampmann. "However, it was still a mystery how these 'Y's are arranged. The new technique we have developed reveals the orientation of building blocks in the cell, and we hope that it will eventually enable us to assemble individual crystal structures into a high-resolution map of the entire nuclear pore complex."

Eventually, the scientists say their technique could go even further. Because the proteins' fluorescence can be measured while the cells are still alive, it could give scientists new insights into how complexes react to varying environmental conditions, and how their configurations change over time.

"What happens when other proteins pass through the nuclear pore? Does the orientation of the nucleoporins change? With this technique, can find out not only what the pore looks like when it's sitting still, but what happens to it when it's active," Simon says. Their first characterization of the dynamics of the nuclear pore proteins was published recently in The Biophysical Journal.

Provided by Rockefeller University (news : web)