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  • richardmitnick 3:09 pm on December 26, 2014 Permalink | Reply
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    From ANL: “Earth’s most abundant mineral finally has a name” 

    News from Argonne National Laboratory

    December 11, 2014
    Tona Kunz

    An ancient meteorite and high-energy X-rays have helped scientists conclude a half century of effort to find, identify and characterize a mineral that makes up 38 percent of the Earth.

    And in doing so, a team of scientists led by Oliver Tschauner, a mineralogist at the University of Las Vegas, clarified the definition of the Earth’s most abundant mineral – a high-density form of magnesium iron silicate, now called Bridgmanite – and defined estimated constraint ranges for its formation. Their research was performed at the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility located at DOE’s Argonne National Laboratory.

    The mineral was named after 1946 Nobel laureate and pioneer of high-pressure research Percy [Williams] Bridgman. The naming does more than fix a vexing gap in scientific lingo; it also will aid our understanding of the deep Earth.

    To determine the makeup of the inner layers of the Earth, scientists need to test materials under extreme pressure and temperatures. For decades, scientists have believed a dense perovskite structure makes up 38 percent of the Earth’s volume, and that the chemical and physical properties of Bridgmanite have a large influence on how elements and heat flow through the Earth’s mantle. But since the mineral failed to survive the trip to the surface, no one has been able to test and prove its existence – a requirement for getting a name by the International Mineralogical Association.

    Shock-compression that occurs in collisions of asteroid bodies in the solar system create the same hostile conditions of the deep Earth – roughly 2,100 degrees Celsius (3,800 degrees Farenheit) and pressures of about 240,000 times greater than sea-level air pressure. The shock occurs fast enough to inhibit the Bridgmanite breakdown that takes place when it comes under lower pressure, such as the Earth’s surface. Part of the debris from these collisions falls on Earth as meteorites, with the Bridgmanite “frozen” within a shock-melt vein. Previous tests on meteorites using transmission electron microscopy caused radiation damage to the samples and incomplete results.

    So the team decided to try a new tactic: non-destructive micro-focused X-rays for diffraction analysis and novel fast-readout area-detector techniques. Tschauner and his colleagues from Caltech and the GeoSoilEnviroCARS, a University of Chicago-operated X-ray beamline at the APS at Argonne National Laboratory, took advantage of the X-rays’ high energy, which gives them the ability to penetrate the meteorite, and their intense brilliance, which leaves little of the radiation behind to cause damage.

    The team examined a section of the highly shocked L-chondrite meteorite Tenham, which crashed in Australia in 1879. The GSECARS beamline was optimal for the study because it is one of the nation’s leading locations for conducting high-pressure research.

    t
    Ordinary chondrite meteorite found in Queensland, Australia, 1879. On display in the Natural History Museum, London

    Bridgmanite grains are rare in the Tenhma meteorite, and they are smaller than 1 micrometer in diameter. Thus the team had to use a strongly focused beam and conduct highly spatially resolved diffraction mapping until an aggregate of Bridgmanite was identified and characterized by structural and compositional analysis.

    This first natural specimen of Bridgmanite came with some surprises: It contains an unexpectedly high amount of ferric iron, beyond that of synthetic samples. Natural Bridgmanite also contains much more sodium than most synthetic samples. Thus the crystal chemistry of natural Bridgmanite provides novel crystal chemical insights. This natural sample of Bridgmanite may serve as a complement to experimental studies of deep mantle rocks in the future.

    Prior to this study, knowledge about Bridgmanite’s properties has only been based on synthetic samples because it only remains stable below 660 kilometers (410 miles) depth at pressures of above 230 kbar (23 GPa). When it is brought out of the inner Earth, the lower pressures transform it back into less dense minerals. Some scientists believe that some inclusions on diamonds are the marks left by Bridgmanite that changed as the diamonds were unearthed.

    The team’s results were published in the November 28 issue of the journal Science as Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite, by O. Tschauner at University of Nevada in Las Vegas, N.V.; C. Ma; J.R. Beckett; G.R. Rossman at California Institute of Technology in Pasadena, Calif.; C. Prescher; V.B. Prakapenka at University of Chicago in Chicago, IL.

    This research was funded by the U.S. Department of Energy, NASA, and NSF.

    See the full article here

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    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

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  • richardmitnick 7:30 pm on December 4, 2014 Permalink | Reply
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    From ANL: “Atomic ‘mismatch’ creates nano ‘dumbbells'” 

    News APS at Argonne National Laboratory

    December 4, 2014
    Jared Sagoff

    Like snowflakes, nanoparticles come in a wide variety of shapes and sizes. The geometry of a nanoparticle is often as influential as its chemical makeup in determining how it behaves, from its catalytic properties to its potential as a semiconductor component.

    Thanks to a new study from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, researchers are closer to understanding the process by which nanoparticles made of more than one material – called heterostructured nanoparticles – form. This process, known as heterogeneous nucleation, is the same mechanism by which beads of condensation form on a windowpane.

    Heterostructured nanoparticles can be used as catalysts and in advanced energy conversion and storage systems. Typically, these nanoparticles are created from tiny “seeds” of one material, on top of which another material is grown. In this study, the Argonne researchers noticed that the differences in the atomic arrangements of the two materials have a big impact on the shape of the resulting nanoparticle.

    “Before we started this experiment, it wasn’t entirely clear what’s happening at the interface when one material grows on another,” said nanoscientist Elena Shevchenko of Argonne Center for Nanoscale Materials, a DOE Office of Science user facility.

    In this study, the researchers observed the formation of a nanoparticle consisting of platinum and gold. The researchers started with a platinum seed and grew gold around it. Initially, the gold covered the platinum seed’s surface uniformly, creating a type of nanoparticle known as “core-shell.” However, as more gold was deposited, it started to grow unevenly, creating a dumbbell-like structure.

    m
    This picture combines a transmission electron microscope image of a nanodumbbell with a gold domain oriented in direction. The seed and gold domains in the dumbbell in the image on the right are identified by geometric phase analysis. Image credit: Soon Gu Kwon.

    Thanks to state-of-the-art X-ray analysis provided by Argonne’s Advanced Photon Source (APS), a DOE Office of Science user facility, the researchers identified the cause of the dumbbell formation as “lattice mismatch,” in which the spacing between the atoms in the two materials doesn’t align.

    “Essentially, you can think of lattice mismatch as having a row of smaller boxes on the bottom layer and larger boxes on the top layer. When you try to fit the larger boxes into the space for a smaller box, it creates an immense strain,” said Argonne physicist Byeongdu Lee.

    While the lattice mismatch is only fractions of a nanometer, the effect accumulates as layer after layer of gold forms on the platinum. The mismatch can be handled by the first two layers of gold atoms – creating the core-shell effect – but afterwards it proves too much to overcome. “The arrangement of atoms is the same in the two materials, but the distance between atoms is different,” said Argonne postdoctoral researcher Soon Gu Kwon. “Eventually, this becomes unstable, and the growth of the gold becomes unevenly distributed.”

    As the gold continues to accumulate on one side of the seed nanoparticle, small quantities “slide” down the side of the nanoparticle like grains of sand rolling down the side of a sand hill, creating the dumbbell shape.

    The advantage of the Argonne study comes from the researchers’ ability to perform in situ observations of the material in realistic conditions using the APS. “This is the first time anyone has been able to study the kinetics of this heterogeneous nucleation process of nanoparticles in real-time under realistic conditions,” said Argonne physicist Byeongdu Lee. “The combination of two X-ray techniques gave us the ability to observe the material at both the atomic level and the nanoscale, which gave us a good view of how the nanoparticles form and transform.” All conclusions made based on the X-ray studies were further confirmed using atomic-resolution microscopy in the group of Professor Robert Klie of the University of Illinois at Chicago.

    This analysis of nanoparticle formation will help to lay the groundwork for the formation of new materials with different and controllable properties, according to Shevchenko. “In order to design materials, you have to understand how these processes happen at a very basic level,” she said.

    The research was funded in part by the National Science Foundation and the University of Illinois at Chicago Research Resources Center.

    An article based on the research, Heterogeneous nucleation and shape transformation of multicomponent metallic nanostructures,” appeared in the Nov. 2 online issue of Nature Materials.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future.

    With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

    See the full article here.

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  • richardmitnick 1:52 pm on November 7, 2014 Permalink | Reply
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    From FNAL: “Multilaboratory collaboration brings new X-ray detector to light” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, Nov. 7, 2014
    Troy Rummler

    A collaboration blending research in DOE’s offices of High-Energy Physics (HEP) with Basic Energy Sciences (BES) will yield a one-of-a-kind X-ray detector. The device boasts Brookhaven Lab sensors mounted on Fermilab integrated circuits linked to Argonne Lab data acquisition systems. It will be used at Brookhaven’s National Synchrotron Light Source II and Argonne’s Advanced Photon Source. Lead scientists Peter Siddons, Grzegorz Deptuch and Robert Bradford represent the three laboratories.

    BNL NSLS II PhotoBNL NSLS-II Interior
    BNL NSLS II

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    “This partnership between HEP and BES has been a fruitful collaboration, advancing detector technology for both fields,” said Brookhaven’s Peter Siddons.

    team
    These researchers work on the VIPIC prototype. Peter Siddons of Brookhaven National Laboratory (fifth from the left), Grzegroz Deptuch of Fermilab (third from the right) and Robert Bradford of Argonne National Laboratory (far right) lead the effort. Photo courtesy of Argonne National Laboratory

    This detector is filling a need in the X-ray correlation spectroscopy (XCS) community, which has been longing for a detector that can capture dynamic processes in samples with microsecond timing and nanoscale sensitivity. Available detectors have been designed largely for X-ray diffraction crystallography and are incapable of performing on this time scale.

    det
    The 64-by-64 pixel VIPIC prototype, pictured with a sensor on the bottom and solder bump-bonding bump on top, ready to be received on the printed circuit board. Photo: Reidar Hahn

    In 2006, Fermilab’s Ray Yarema began investigating 3-D integrated chip technology, which increases circuit density, performance and functionality by vertically stacking rather than laterally arranging silicon wafers. Then in 2008 Deptuch, a member of Yarema’s group and Fermilab ASIC [Application Specific Integrated Circuit] Group leader since 2011, met with Siddons, a scientist at Brookhaven, at a medical imaging conference. They discussed applying 3-D technology to a new, custom detector project, which was later given the name VIPIC (vertically integrated photon imaging chip). Siddons was intrigued by the 3-D opportunities and has since taken the lead on leveraging Fermilab expertise toward the longstanding XCS problem. As a result, the development of the device at Fermilab — where 97 percent of research funds come through HEP — receives BES funding.

    A 64-by-64-pixel VIPIC prototype tested at Argonne this summer flaunted three essential properties: timing resolution within one microsecond; continuous new-data acquisition with simultaneous old-data read-out; and selective transmission of only pixels containing data.

    The results achieved with the prototype have attracted attention from the scientific community.

    Deptuch noted that this partnership between BES and HEP reflects the collaborative nature of such efforts at the national labs.

    “It truly is a cooperative effort, combining the expertise from three national laboratories toward one specific goal,” he said.

    The team will grow their first VIPIC prototype tiled, seamless array of chips on a sensor to form a 1-megapixel detector. The collaboration is targeting a completion date of 2017 for the basic functionality detector. Ideas for expanded capabilities are being discussed for the future.

    See the full article here.

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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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  • richardmitnick 9:05 pm on July 7, 2014 Permalink | Reply
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    From Argonne Lab: “Unprecedented detail of intact neuronal receptor offers blueprint for drug developers “ 

    News from Argonne National Laboratory

    July 7, 2014
    Tona Kunz

    Scientists succeeded in obtaining an unprecedented view of a type of brain-cell receptor that is implicated in a range of neurological illnesses, including Alzheimer’s disease, Parkinson’s disease, depression, schizophrenia, autism, and ischemic injuries associated with stroke.

    cell
    The NMDA receptor is a massive, multi-subunit complex. CSHL researchers found that it looks much like a hot air balloon. The upper, balloon-like portion of the structure is found outside the cell and responds to chemical messengers. Those messengers act like a key to unlock the lower portion of the receptor. This lower portion, corresponding to the basket of the hot air balloon, is embedded in the neuron’s membrane. It creates a narrow channel that allows ions, or electrically charged atoms, to flow into the cell. These many subunit interactions are potential targets for drug discovery.

    The team of biologists at Cold Spring Harbor Laboratory used the U.S. Department of Energy’s Advanced Photon Source at Argonne National Laboratory to get an atomic-level picture of the intact NMDA (N-methyl, D-aspartate) receptor should serve as template and guide for the design of therapeutic compounds.

    The NMDA receptor is a massive multi- subunit complex that integrates both chemical and electrical signals in the brain to allow neurons to communicate with one another. These conversations form the basis of memory, learning, and thought, and critically mediate brain development. The receptor’s function is tightly regulated: both increased and decreased NMDA activities are associated with neurological diseases.

    Despite the importance of NMDA receptor function, scientists have struggled to understand how it is controlled. In work published recently in Science, CSHL Associate Professor Hiro Furukawa and Erkan Karakas, Ph.D., a postdoctoral investigator, use a type of molecular photography known as X-ray crystallography to determine the structure of the intact receptor. Their work identifies numerous interactions between the four subunits of the receptor and offers new insight into how the complex is regulated. The X-ray work was done with the National Institute for General Medical Sciences and National Cancer Institute Collaborative Access Team (GM/CA) beamline at the APS and a beamline at SPring 8.

    “Previously, our group and others have crystallized individual subunits of the receptor – just fragments – but that simply was not enough,” says Furukawa. “To understand how this complex functions you need to see it all together, fully assembled.”

    For such a large complex, this was a challenging task. Using an exhaustive array of protein purification methods, Furukawa and Karakas were able to isolate the intact receptor. Their crystal structure reveals that the receptor looks much like a hot air balloon. “The ‘basket’ is what we call the transmembrane domain. It forms an ion channel that allows electrical signals to propagate through the neuron,” explains Furukawa.

    An ion channel is like a gate in the neuronal membrane. Ions, small electrically charged atoms, are unable to pass through the cell membrane. When the ion channel “gate” is closed, ions congregate outside the cell, creating an electrical potential across the cell membrane.

    When the ion channel “gate” opens, ions flow in and out of the cell through the channel pores. This generates an electrical current that sums up to create pulses that rapidly propagate through the neuron. But the current can’t jump from one neuron to the next. Rather, the electrical pulse triggers the release of chemical messengers, called neurotransmitters. These molecules traverse the distance between the neurons and bind to receptors, such as the NMDA receptor, on the surface of neighboring cells. There, they act much like a key, unlocking ion channels within the receptor and propelling the electrical signal across another neuron and, ultimately, across the brain.

    The “balloon” portion of the receptor that Furukawa describes is found outside the cell. This is the region that binds to neurotransmitters. The structure of the assembled multi-subunit receptor complex, including the elusive ion channel, helps to explain some of the existing data about how NMDA receptors function. “We are able to see how one domain on the exterior side of the receptor directly regulates the ion channel within the membrane,” says Furukawa. “Our structure shows why this particular domain, called the amino terminal domain, is important for the activity of the NMDA receptor, but not for other related receptors.”

    This information will be critical as scientists work to develop drugs that control the NMDA receptor. “Our structure defines the interfaces where multiple subunits and domains contact one another,” says Furukawa. “In the future, these will guide the design of therapeutic compounds to treat a wide range of devastating neurological diseases.”

    This work was supported by the National Institutes of Health, a Mirus Research Award, and the Robertson Research Fund of Cold Spring Harbor Laboratory.

    Crystal structure of a heterotetrameric NMDA receptor ion channel appears online in Science on May 30, 2014. The authors are Erkan Karakas and Hiro Furukawa. The paper can be obtained online at: http://www.sciencemag.org

    The APS beamline is funded by the National Institutes of Health’s National Institute of General Medical Sciences and the National Cancer Institute. The APS is funded by the U.S. Department of Energy’s Office of Science.

    See the full article here.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

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  • richardmitnick 4:16 am on May 7, 2014 Permalink | Reply
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    From APS at Agonne Lab: “Advanced Photon Source to remain leader in protein structure research for years” 

    News from APS at Argonne National Laboratory

    May 5, 2014
    Brian Grabowski

    Proteins are involved in virtually every process in all living cells on the planet, be it a bacterium or yourself. In humans, antibodies defend against invading bacteria, viruses and other infectious agents. Insulin helps regulate how your body uses carbohydrates and fats. Lactase helps digest lactose from dairy products.

    ps
    The world’s first protein characterization research facility directly attached to a light source will open in the near future at the Advanced Photon Source. The Advanced Protein Characterization Facility will use state-of-the-art robotics for gene cloning, protein expression, protein purification and protein crystallization.

    But scientists know the structures and functions of only a small fraction of the proteins in living systems. The vast majority remain a mystery. The backlog of uncharacterized proteins grows quickly every day as scientists continue to determine the genetic makeups of thousands of new organisms, using astonishingly efficient techniques of genome sequencing.

    No X-ray facility in the world has supported more protein structure research and characterized more proteins than the Advanced Photon Source (APS) at the U.S. Department of Energy’s Argonne National Laboratory. Soon this 2/3-mile-in-circumference X-ray instrument will get a boost in efficiency that likely will translate into a big boon for the discovery of new pharmaceuticals and the control of genetic disorders and other diseases, as well as advancing the biotech industry.

    The world’s first protein characterization research facility directly attached to a light source will open in the near future at the APS. The Advanced Protein Characterization Facility (APCF) will use state-of-the-art robotics for gene cloning, protein expression, protein purification and protein crystallization.

    robotics
    Not beautiful, but very efficient

    “The net result will be more protein structures analyzed per year, higher resolution structures and more research into protein function,” said Andrzej Joachimiak, an Argonne Distinguished Fellow who also is director of the Structural Biology Center’s (SBC’s) Sector 19 beamlines and the Midwest Center for Structural Genomics. “This facility has been designed to integrate systems biology and molecular biology with gene cloning, protein expression, protein purification, protein crystallization and crystal testing and delivery to the APS. There is nothing like this anywhere in the world right now.”

    When a new protein structure is discovered and verified, the data are deposited in the Protein Data Bank repository to make it available to researchers around the world. For the last 11 consecutive years, the APS has been far and away the world leader in protein structure deposits. The APS has 14 beamlines dedicated to the study of protein crystals through a technique called macromolecular crystallography.

    “Two Nobel Prizes for Chemistry were awarded in the past four years for APS-based research involving crystallography,” said Joachimiak, “One Nobel Prize was for research into the structure and function of ribosomes on SBC’s 19-ID beamline, and another was awarded in 2012 for studies of G-protein-coupled receptors at a GM/CA-CAT micro-focus beamline.”

    Ribosomes make proteins in all living cells. Improved knowledge about bacterial ribosomes, for example, is speeding development of new antibiotics that combat bacterial infections by interfering with protein production. G-protein-coupled receptor (GPCR) proteins help cells stay in constant communication with each other, thereby facilitating resource sharing. When normal cells become cancerous, GPCRs are changed, too. The change can corrupt the lines of communication, allowing the cancerous cells to grow without limits. The first discovery of the structure of a human GPCR was made at the APS as part of the Nobel Prize-winning research. In fact, the structure was captured at the exact moment the GPCR was signaling across a cell membrane.

    The APCF will be available for use by the more than 5,500 scientists who visit the APS annually, but it will have a particularly strong connection to Argonne’s SBC and the beamline it operates at Sector 19. In 2013, more than 660 crystallographers used the SBC facility to collect data on hundreds of projects, including proteins from the Ebola virus. More than 4,100 protein structures have been deposited into the Protein Data Bank from SBC.

    Protein structures are analyzed by crystalling the proteins and then placing the single crystals into an X-ray beam for analysis using X-ray diffraction. The results depend on the quality of both the protein crystal and the X-ray beam. The APS provides some of the most brilliant X-ray beams in the Western Hemisphere. Additionally, the APS generates a highly parallel beam, which enables tight focusing of the X-rays. Staff at the National Institute of General Medical Sciences and National Cancer Institute structural biology facility (GM/CA-CAT) beamline capitalized on this and created the world’s first micro X-ray beam at the request of visiting researchers. “The micro-beam was essential for the GPCR research,” said Joachimiak.

    The crystallography capabilities of the APS will increase with a planned upgrade. “After the upgrade, the brilliance of the X-ray beam will increase by two to three orders of magnitude,” Joachimiak said. “The beam will be more parallel, too, so we will be able to focus down to a very small beam size. This beam will also be two to three times more intense. The upgrade should help ensure APS leadership in macromolecular crystallography for many years to come.”

    See the full article here.

    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

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  • richardmitnick 4:16 pm on March 21, 2014 Permalink | Reply
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    From Argonne APS: “A Layered Nanostructure Held Together By DNA” 

    News from Argonne National Laboratory

    March 18, 2014
    David Lindley

    Dreaming up nanostructures that have desirable optical, electronic, or magnetic properties is one thing. Figuring out how to make them is another. A new strategy uses the binding properties of complementary strands of DNA to attach nanoparticles to each other and builds up a layered thin-film nanostructure through a series of controlled steps. Investigation at the U.S. Department of Energy Office of Science’s Advanced Photon Source has revealed the precise form that the structures adopted, and points to ways of exercising still greater control over the final arrangement.

    dna
    DNA

    The idea of using DNA to hold nanoparticles was devised more than 15 years ago by Chad Mirkin and his research team at Northwestern University. They attached short lengths of single-stranded DNA with a given sequence to some nanoparticles, and then attached DNA with the complementary sequence to others. When the particles were allowed to mix, the “sticky ends” of the DNA hooked up with each other, allowing for reversible aggregation and disaggregation depending on the hybridization properties of the DNA linkers.

    sticky
    Nanoparticles linked by complementary DNA strands form a bcc superlattice when added layer-by-layer to a DNA coated substrate. When the substrate DNA is all one type, the superlattice forms at a different orientation (top row) than if the substrate has both DNA linkers (bottom row). GISAXS scattering patterns (right) and scanning electron micrographs (inset) reveal the superlattice structure. No image credit.

    Recently, this DNA “smart glue” has been utilized to assemble nanoparticles into ordered arrangements resembling atomic crystal lattices, but on a larger scale. To date, nanoparticle superlattices have been synthesized in well over 100 crystal forms, including some that have never been observed in nature.

    However, these superlattices are typically polycrystalline, and the size, number, and orientation of the crystals within them is generally unpredictable. To be useful as metamaterials, photonic crystals, and the like, single superlattices with consistent size and fixed orientation are needed.

    Northwestern researchers and a colleague at Argonne National Laboratory have devised a variation on the DNA-linking procedure that allows a greater degree of control.

    The basic elements of the superlattice were gold nanoparticles, each 10 nanometers across. These particles were made in two distinct varieties, one adorned with approximately 60 DNA strands of a certain sequence, while the other carried the complementary sequence.

    The researchers built up thin-film superlattices on a silicon substrate that was also coated with DNA strands. In one set of experiments, the substrate DNA was all of one sequence – call it the “B” sequence – and it was first dipped into a suspension of nanoparticles with the complementary “A” sequence.

    When the A and B ends connected, the nanoparticles formed a single layer on the substrate. Then the process was repeated with a suspension of the B-type nanoparticles, to form a second layer. The whole cycle was repeated, as many as four more times, to create a multilayer nanoparticle superlattice in the form of a thin film.

    Grazing incidence small-angle x-ray scattering (GISAXS) studies carried out at the X-ray Science Division 12-ID-B beamline at the Argonne Advanced Photon Source revealed the symmetry and orientation of the superlattices as they formed. Even after just three half-cycles, the team found that the nanoparticles had arranged themselves into a well-defined, body-centered cubic (bcc) structure, which was maintained as more layers were added.

    In a second series of experiments, the researchers seeded the substrate with a mix of both the A and B types of DNA strand. Successive exposure to the two nanoparticle types produced the same bcc superlattice, but with a different vertical orientation. That is, in the first case, the substrate lay on a plane through the lattice containing only one type of nanoparticle, while in the second case, the plane contained an alternating pattern of both types (see the figure).

    To get orderly superlattice growth, the researchers had to conduct the process at the right temperature. Too cold, and the nanoparticles would stick to the substrate in an irregular fashion, and remain stuck. Too hot, and the DNA linkages would not hold together.

    But in a temperature range of a couple of degrees on either side of about 40° C (just below the temperature at which the DNA sticky ends detach from each other), the nanoparticles were able to continuously link and unlink from each other. Over a period of about an hour per half-cycle, they settled into the bcc superlattice, the most thermodynamically stable arrangement.

    GISAXS also revealed that although the substrate forced superlattices into specific vertical alignments, it allowed the nanoparticle crystals to form in any horizontal orientation. The researchers are now exploring the possibility that by patterning the substrate in a suitable way, they can control the orientation of the crystals in both dimensions, increasing the practical value of the technique.

    See the full article here.

    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security.

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