The U.S. National Nanotechnology Initiative uses the term "nanotechnology" to describe: Research and technology development aimed to work at atomic and molecular scales
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Researchers use magnets to tune supercooled gallium arsenide semiconductors
HOUSTON -- Physicists from Rice University and Princeton University have discovered how to use one of the information technology industry's mainstay materials -- gallium arsenide semiconductors -- as an ultrasensitive microwave detector that could be suitable for next-generation computers. The discovery comes at a time when computer chip engineers are racing both to add nanophotonic devices directly to microchips and to boost processor speeds beyond 10 gigahertz (GHz).
"Tunable photon-detection technology in the microwave range is not well-developed," said Rice physicist Rui-Rui Du, the study's lead author. "Single-photon detectors based on superconductors in the 10-GHz to 100-GHz range are available, but their resonance frequency has been difficult to tune. Our findings suggest that tunable single-photon detection may be within reach with ultrapure gallium arsenide."
The study, which is available online and due to appear in print this week in Physical Review Letters, is the latest result from a long-term collaboration between Du and Princeton University physicist Loren Pfeiffer, whose group produces the world's purest samples of gallium arsenide.
From left, Rice University physicist Rui-Rui Du, graduate students Chi Zhang and Yanhua Dai, have found that odd groupings of ultracold electrons could be useful in making fault-tolerant quantum computers.
Jeff Fitlow/Rice University
For the new study, Rice graduate student Yanhua Dai cooled one of Pfeiffer's ultrapure samples to below 4 degrees Kelvin -- the temperature of liquid helium. She then bombarded the sample with microwaves while applying a weak magnetic field -- approximately the same strength as that of a refrigerator magnet. Du and Dai were surprised to find that microwaves of a specific wavelength resonated strongly with the cooled sample. They also found they could use the magnet to tune this resonance to specific microwave frequencies.
Du said previous experiments have typically measured weak resonance effects from microwaves. "A signal level of 1 percent is a common measurement. In our case, the change was a thousand times that much."
While the team does not yet understand the mechanism that leads to such a sensitive reaction, they are eagerly pursuing follow-up research to try to prove they can use the effect for single-photon measurements.
A photon is the smallest possible unit of light or electromagnetic radiation. By incorporating devices that create, transmit and measure digital information via photons, rather than with electrons, makers of computer chips hope to produce computers that are both faster and more powerful.
"The clock speed of a new computer right now is about 2 GHz," Du said. "For the next generation, the industry is shooting for around 100 GHz, which is a microwave device. The phenomenon we've observed is in this region, so we hope it may be useful for them." ###
Additional co-authors include Princeton scientist Ken West. The research was supported by the National Science Foundation.
WEST LAFAYETTE, Ind. - A Purdue University research team developed a nanoparticle that can hold and release an antimicrobial agent as needed for extending the shelf life of foods susceptible to Listeria monocytogenes.
Yuan Yao, an assistant professor of food science, altered the surface of a carbohydrate found in sweet corn called phytoglycogen, which led to the creation of several forms of a nanoparticle that could attract and stabilize nisin, a food-based antimicrobial peptide. The nanoparticle can then preserve nisin for up to three weeks, combating Listeria, a potentially lethal foodborne pathogen found in meats, dairy and vegetables that is especially troublesome for pregnant women, infants, older people and others with weakened immune systems.
Controlling Listeria at deli counters, for example, is especially problematic because meat is continually being opened, cut and stored, giving Listeria many chances to contaminate the food. Nisin alone is only effective at inhibiting Listeria for a short period - possibly only a few days - in many foods.
Yuan Yao, Assistant Professor Food Science. Department: Department of Food Sciences Phone: 765.494.6317
"People have been using nisin for a number of years, but the problem has been that it is depleted quickly in a food system," said Arun Bhunia, a Purdue professor of food science who co-authored a paper with Yao on the findings in the early online version of the Journal of Controlled Release. "This nanoparticle is an improved way to deliver the antimicrobial properties of nisin for extended use."
Yao used two strategies to attract nisin to the phytoglycogen nanopoarticles. First, he was able to negatively charge the surface of the nanoparticle and use electrostatic activity to attract the positively charged nisin molecules. Second, he created a partially hydrophobic condition on the surface of the nanoparticle, causing it to interact with partially hydrophobic nisin molecules.
When the particles are hydrophobic, or repel water, they become attracted to each other.
"Both strategies may work together to allow nanoparticles to attract and stabilize nisin," Yao said, "This could substantially reduce the depletion of nisin in various systems."
For practical use, Yao said a solution containing the nanoparticles and free nisin could be sprayed onto foods or included in packaging. The solution requires a balance of free nisin and nisin on the nanoparticles.
"When you reduce the amount of free nisin, it will trigger a release of more nisin from the nanoparticles to re-establish the equilibrium," Yao said. "There will be a substantial amount of nisin preserved to counteract the Listeria."
Using a model, Yao said a sufficient amount of nisin to combat Listeria could be preserved for up to 21 days.
Yao and his colleagues are working on using other food-based antimicrobial peptides and nano-constructs to combat Listeria other foodborne pathogens such as E. coli O157:H7 and salmonella. The U.S. Department of Agriculture and the National Science Foundation funded their research.
Technology licensed to Audax Medical, Here's the vision: an elderly woman comes into the emergency room after a fall. She has broken her hip. The orthopaedic surgeon doesn't come with metal plates or screws or shiny titanium ball joints. Instead, she pulls out a syringe filled with a new kind of liquid that will solidify in seconds and injects into the break. Over time, new bone tissue will take its place, encouraged by natural growth factors embedded in the synthetic molecules of the material.
Although still early in its development, the liquid is real. In the Brown engineering lab of professor Thomas Webster it's called TBL, for the novel DNA-like "twin-base linker" molecules that give it seemingly ideal properties. The biotech company Audax Medical Inc., based in Littleton, Mass., announced on Dec. 7 an exclusive license of the technology from Brown. It brands the technology as Arxis and sees similar potential for repairing broken vertebrae.
"The reason we're excited about this material is because it gets us away from metals," Webster said. "Metals are not in us naturally and they can have a lot of problems with surrounding tissues."
In some of his work, Webster employs nanotechnology to try to bridge metals to bone better than traditional bone cement. But TBL is an entirely new material, co-developed with longtime colleague and chemist Hicham Fenniri at the University of Alberta. Fenniri synthesized the molecules, while Webster's research has focused on ensuring that TBL becomes viable material for medical use.
A nonmetalic solution Nanomaterials engineer Thomas Webster is developing alternatives to metals, which do not occur naturally in the body and can cause problems with surrounding tissue. Credit: Webster Lab/Brown University
The molecules are artificial, but made from elements that are no strangers to the body: carbon, nitrogen, and oxygen. At room temperature their aggregate form is a liquid, but the material they form solidifies at body temperature. The molecules look like nanoscale tubes (billionths of a meter wide), and when they come together, it is in a spiraling ladder-shaped arrangement reminiscent of DNA or collagen. That natural structure makes it easy to integrate with bone tissue.
In the space within the nanotubes, the team, which includes graduate student Linlin Sun, has managed to stuff in various drugs including antibiotics, anti-inflammatory agents, and bone growth factors, which the tubes release over the course of months. Even better, different recipes of TBL, or Arxis, can be chemically tuned to become as hard as bone or as soft as cartilage, and can solidify in seconds or minutes, as needed. Once it is injected, nothing else is needed.
"We really like the fact that it doesn't need anything other than temperature to solidify," Webster said. Other compounds that people have developed require exposure to ultraviolet light and cannot therefore be injected through a tiny syringe hole. They require larger openings to be created.
For all of TBL's apparent benefits, they have only been demonstrated in cow bone fragments in incubators on the lab bench top, Webster said. TBL still needs to be proven in vivo and, ultimately, in human trials. Part of the agreement with Audax will include support to continue the material's clinical development. Audax research and development director Whitney Sharp, a Brown alumna (Sc.B., 2008; Sc.M., 2009), is now working with Webster's group.
"They see the future where hopefully we will get to the point where we won't be implanting these huge pieces of metal into people," Webster said. "Instead we'll be implanting things through a needle that could be used to heal a hip that's more natural." ###
In calculating energies for graphene, Rice researchers find clues to chiral control
New research at Rice University could ultimately show scientists the way to make batches of nanotubes of a single type.
A paper in the online journal Physical Review Letters unveils an elegant formula by Rice University physicist Boris Yakobson and his colleagues that defines the energy of a piece of graphene cut at any angle.
Yakobson, a professor in mechanical engineering and materials science and of chemistry, said this alone is significant because the way graphene handles energy depends upon the angle -- or chirality -- of its edge, and solving that process for odd angles has been extremely challenging. But, he wrote, the research has "profound implications in the context of nanotube growth, offering rational ways to control their chiral symmetry, a tantalizing yet so far elusive goal."
Graphene is the single-atom-thick form of carbon that has become of tremendous interest for its potential to revolutionize electronics, optics, sensing and mechanical devices. Getting a handle on how this chicken-wire-shaped sheet of carbon atoms transports electricity has been the focus of intense study.
Boris Yakobson
A sheet of graphene with zigzag or armchair edges squares up nicely. Zigzags are metallic, armchairs are semiconductors, and their atoms march in rank, evenly spaced, along the edges. A full 30 degrees of rotation separates one from the other.
But if the hexagons that make up a sheet are offset less than 30 degrees, atoms along a straight edge are unevenly spaced. "That makes analysis of the energy very complicated, because it's a large irregular structure. It's like noise," Yakobson said. "We've found a way to calculate the energies in these arbitrary angles," he said.
Yakobson and his co-authors, Yuanyue Liu, a graduate student in his lab, and Alex Dobrinsky, a former graduate student and now a postdoctoral researcher at Brown University, soon wondered how these findings applied to carbon nanotubes.
"There are as many ways to roll graphene into a nanotube as there are ways to roll a newspaper," Yakobson said. "The text can be aligned circumferentially or run straight along the axis or spiral at an angle."
While rolling a newspaper makes it hard to read, rolling carbon into a nanotube makes it relatively easy to "read" its type -- whether armchair or zigzag or some variation in between. What's impossible is controlling how the tube will roll. The process tends to be willy-nilly, leaving researchers the task of separating the nanotubes they need from the bulk through ultracentrifugation or other expensive procedures.
Yakobson said it would be a real game-changer if they could, for instance, grow batches of pure armchair nanotubes for use in such projects as armchair quantum nanowire (AQW). As imagined by Rice's late Nobel Laureate Richard Smalley, AQW could revolutionize the nation's power grid by carrying 10 times the amount of electricity as copper at only one-sixth the weight.
Yakobson's work may open a path to do so. A nanotube's chirality is determined by the combination of energies at play in its nucleation. "When it just emerges from the 'primordial soup' of carbon, the edge of the tube is essentially the same as the edge of graphene," he said.
"At first, it's just a cap. There's no stem yet. You're frying these caps on a skillet, and they're bubbling," he said. "The probability for different bubbles to emerge is controlled by energy around the edge."
The chirality of the nascent nanotube is set when atoms in the cap self-assemble a sixth pentagon (necessary to mold the hexagons into a dome). "That's where we can, I think for the first time, make some quantitative judgment about how different chiral structures emerge," Yakobson said.
It may be worth chemists' efforts to look more closely at the energy between the catalyst and carbon structure. "This has some promise," he said. "If you can tweak this preference, if you can change energy from the catalyst side, you change the preference of the chirality. And then you can tell these self-assembling carbons, 'Please dance this way; don't dance that way.'"
Yakobson hopes the new work helps solve the long-standing problem of nanotube chirality. "For almost two decades, we didn't have a good understanding of this process," he said. "Actually, we didn't have a clue. I'm not saying this is a full solution, but this is the first time we've seen a quantitative approach, an order in the seeming chaos. It just feels satisfying.
"The bottom line is simple. We figured out the graphene edge and bridged it to the holy grail of nanotubes, which is chirality control." ###
Located in Houston, Rice University is consistently ranked one of America's best teaching and research universities. Known for its "unconventional wisdom," Rice is distinguished by its: size -- 3,279 undergraduates and 2,277 graduate students; selectivity -- 12 applicants for each place in the freshman class; resources -- an undergraduate student-to-faculty ratio of 5-to-1; sixth largest endowment per student among American private research universities; residential college system, which builds communities that are both close-knit and diverse; and collaborative culture, which crosses disciplines, integrates teaching and research, and intermingles undergraduate and graduate work.
Working in a multidisciplinary team that includes groups from other universities and the MER Corporation, Horacio Espinosa, James N. and Nancy J. Farley Professor in Manufacturing & Entrepreneurship at the McCormick School of Engineering and Applied Science, and his group have created a high performance fiber from carbon nanotubes and a polymer that is remarkably tough, strong, and resistant to failure. Using state-of-the-art in-situ electron microscopy testing methods, the group was able to test and examine the fibers at many different scales — from the nano scale up to the macro scale — which helped them understand just exactly how tiny interactions affect the material’s performance. Their results were recently published in the journal ACS Nano.
“We want to create new-generation fibers that exhibit both superior strength and toughness,” said Espinosa said. “A big issue in engineering fibers is that they are either strong or ductile — we want a fiber that is both. The fibers we fabricated show very high ductility and a very high toughness. They can absorb and dissipate large amounts of energy before failure. We also observed that the strength of the material stays very, very high, which has not been shown before. These fibers can be used for a wide variety of defense and aerospace applications.”
Horacio Espinosa
The project is part of the Department of Defense’s Multidisciplinary University Research Initiative (MURI) program, which supports research by teams of investigators that intersect more than one traditional science and engineering discipline. Espinosa and his collaborators received $7.5 million from the U.S. Army Research Office for the study of disruptive fibers, which could be used in bulletproof vests, parachutes, or composite materials used in vehicles, airplanes and satellites.
To create the new fiber, researchers began with carbon nanotubes —cylindrical-shaped carbon molecules, which individually have one of the highest strengths of any material in nature. When you bundle nanotubes together, however, they lose their strength — the tubes start to laterally slip between each other.
Working with the MER Corporation and using the corporation’s CVD reactor, the team added a polymer to the nanotubes to bind them together, and then spun the resulting material into yarns. Then they tested the strength and failure rates of the material using in-situ SEM testing, which uses a powerful microscope to observe the deformation of materials under a scanning electron beam. This technology, which has only been available in the past few years, allows researchers to have extremely high resolution images of materials as they deform and fail and allows researchers to study materials on several different scales. They can examine individual bundles of nanotubes and the fiber as a whole.
“We learned on multiple scales how this material functions,” said Tobin Filleter, a postdoctoral researcher in Espinosa’s group. “We’re going to need to understand how molecules function at these nanometer scales to engineer stronger and tougher fibers in the future.”
The result is a material that is tougher than Kevlar — meaning it has a higher ability to absorb energy without breaking. But Kevlar is still stronger — meaning it has a higher resistance to failure. Next, researchers hope to continue to study how to engineer the interactions between carbon nanotube bundles and between the nanotubes within the bundle itself.
“Carbon nanotubes, the nanoscale building blocks of the developed yarns, are still 50 times stronger than the material we created,” said Mohammad Naraghi, a postdoctoral researcher in Espinosa’s group. “If we can better engineer the interactions between bundles, we can make the material stronger.”
The group is currently looking at techniques — like covalently crosslinking tubes within bundles using high-energy electron radiation – to help better engineer those interactions.
Filleter and Naraghi said this work wouldn’t have been possible without the interdisciplinary team that includes merging academia with industry.
“To work in an environment where we can trade information back and forth is a unique opportunity that will push the technology farther,” Naraghi said. “MER has given us a unique raw material and a commercial perspective on the project. In turn, we provide the fundamental scientific understanding.”
The research was also funded by the Office of Naval Research.
The Defense Advanced Research Projects Agency (DARPA) has awarded the UCLA Henry Samueli School of Engineering and Applied Science an $8.4 million grant for research on a technology known as non-volatile logic, which enables computers and electronic devices to keep their state even while powered off, then start up and run complex programs instantaneously.
The research has broad implications across a range of technologies, including portable electronics, remote sensors, unmanned aerial vehicles and high-performance computing.
UCLA Engineering researchers will conduct studies into the materials, design, fabrication and tools used to develop such technologies.
"The technologies developed in this project will form the basis for a paradigm shift, not only in spintronics, but in the electronics industry as a whole," said Kang Wang, UCLA's Raytheon Professor of Electrical Engineering and joint principal investigator on the project. "The support from DARPA is critical, since it will allow the U.S. to take the lead in developing this new non-volatile electronic technology."
Kang Wang
Today's digital electronics rely on complimentary metal-oxide semiconductor (CMOS) integrated circuits, which use an electron's charge to store and transfer information. But as devices and chips have become smaller and more compact, down to the nanometer scale, the fundamental limits of CMOS are being approached. The emerging field of spintronics exploits another aspect of electrons — their spin — to transfer information, taking advantage of ferromagnetic materials, which are inherently magnetic.
Devices using ferromagnetic materials can be non-volatile, maintaining their computational state even when power is removed, and they consume much less power when switched on.
The UCLA researchers are aiming to develop a prototype non-volatile logic circuit, which could lead to the development of new classes of ultra–low-power, high-performance electronics. The research program will explore three technical areas: the behavior of nanoscale magnetic materials; the fabrication and testing of a non-volatile logic circuit; and the development of novel circuits and circuit-design tools.
Researchers at the Western Institute of Nanoelectronics (WIN) and the Center for Functional Engineered Nano-Architectronics (FENA), both housed at UCLA Engineering and both led by Wang, have made several research breakthroughs in spintronics materials and design over the past several years. This research will be leveraged into the DARPA-funded non-volatile logic program.
"To achieve the ambitious goals of this program, we are planning to introduce key innovations in terms of both material and device structures. This is an opportunity to study new nano-magnetic physics while developing an exciting technology," said research associate Pedram Khalili, who will be the project manager at UCLA.
The project will be led by UCLA under principal investigators Kang Wang and Alex Khitun, an assistant research engineer, and will involve researchers from UCLA, UC Irvine, Yale University and the University of Massachusetts.
The UCLA Henry Samueli School of Engineering and Applied Science, established in 1945, offers 28 academic and professional degree programs and has an enrollment of almost 5,000 students. The school’s distinguished faculty are leading research to address many of the critical challenges of the 21st century, including renewable energy, clean water, health care, wireless sensing and networking, and cyber-security. Ranked among the top 10 engineering schools at public universities nationwide, UCLA Engineering is home to seven multimillion-dollar interdisciplinary research centers in wireless sensor systems, nanoelectronics, nanomedicine, renewable energy, customized computing, and the smart grid, all funded by federal and private agencies.
Rice University scientists find a little ozone goes a long way for fluorescence
Rice University researchers have discovered a simple way to make carbon nanotubes shine brighter.
The Rice lab of researcher Bruce Weisman, a pioneer in nanotube spectroscopy, found that adding tiny amounts of ozone to batches of single-walled carbon nanotubes and exposing them to light decorates all the nanotubes with oxygen atoms and systematically changes their near-infrared fluorescence.
Chemical reactions on nanotube surfaces generally kill their limited natural fluorescence, Weisman said. But the new process actually enhances the intensity and shifts the wavelength.
He expects the breakthrough, reported online in the journal Science, to expand opportunities for biological and material uses of nanotubes, from the ability to track them in single cells to novel lasers.
Best of all, the process of making these bright nanotubes is incredibly easy -- "simple enough for a physical chemist to do," said Weisman, a physical chemist himself.
He and primary author Saunab Ghosh, a graduate student in his lab, discovered that a light touch was key. "We're not the first people to study the effects of ozone reacting with nanotubes," Weisman said. "That's been done for a number of years.
CAPTION: Single-walled carbon nanotubes treated with ozone incorporate oxygen atoms that shift and intensify the nanotubes' near-infrared fluorescence emission. The discovery by Rice University scientists should lead to new uses of nanotubes in biomedicine and materials science. (Credit: Bruce Weisman/Rice University)
"But all the prior researchers used a heavy hand, with a lot of ozone exposure. When you do that, you destroy the favorable optical characteristics of the nanotube. It basically turns off the fluorescence. In our work we only add about one oxygen atom for 2,000-3,000 carbon atoms, a very tiny fraction."
Ghosh and Weisman started with a suspension of nanotubes in water and added small amounts of gaseous or dissolved ozone. Then they exposed the sample to light. Even light from a plain desk lamp would do, they reported.
Most sections of the doped nanotubes remain pristine and absorb infrared light normally, forming excitons, quasiparticles that tend to hop back and forth along the tube -- until they encounter oxygen.
"An exciton can explore tens of thousands of carbon atoms during its lifetime," Weisman said. "The idea is that it can hop around enough to find one of these doping sites, and when it does, it tends to stay there, because it's energetically stable. It becomes trapped and emits light at a longer (red-shifted) wavelength.
"Essentially, most of the nanotube is turning into an antenna that absorbs light energy and funnels it to the doping site. We can make nanotubes in which 80 to 90 percent of the emission comes from doped sites," he said.
Lab tests found the doped nanotubes' fluorescent properties to be stable for months.
Weisman said treated nanotubes could be detected without using visible light. "Why does that matter? In biological detection, any time you excite at visible wavelengths, there's a little bit of background emission from the cells and from the tissues. By exciting instead in the infrared, we get rid of that problem," he said.
The researchers tested their ability to view doped nanotubes in a biological environment by adding them to cultures of human uterine adenocarcinoma cells. Later, images of the cells excited in the near-infrared showed single nanotubes shining brightly, whereas the same sample excited with visible light displayed a background haze that made the tubes much more difficult to spot.
His lab is refining the process of doping nanotubes, and Weisman has no doubt about their research potential. "There are many interesting scientific avenues to pursue," he said. "And if you want to see a single tube inside a cell, this is the best way to do it. The doped tubes can also be used for biodistribution studies.
"The nice thing is, this isn't an expensive or elaborate process," Weisman said. "Some reactions require days of work in the lab and transform only a small fraction of your starting material. But with this process, you can convert an entire nanotube sample very quickly." ###
The paper's co-authors include Rice research scientist Sergei Bachilo, research technician Rebecca Simonette and Kathleen Beckingham, a Rice professor of biochemistry and cell biology.
The National Science Foundation, the Welch Foundation and NASA supported the research.
CAPTION: Single-walled carbon nanotubes treated with ozone incorporate oxygen atoms that shift and intensify the nanotubes' near-infrared fluorescence emission. The discovery by Rice University scientists should lead to new uses of nanotubes in biomedicine and materials science. (Credit: Bruce Weisman/Rice University)
Located in Houston, Rice University is consistently ranked one of America's best teaching and research universities. Known for its "unconventional wisdom," Rice is distinguished by its: size -- 3,279 undergraduates and 2,277 graduate students; selectivity -- 12 applicants for each place in the freshman class; resources -- an undergraduate student-to-faculty ratio of 5-to-1; sixth largest endowment per student among American private research universities; residential college system, which builds communities that are both close-knit and diverse; and collaborative culture, which crosses disciplines, integrates teaching and research, and intermingles undergraduate and graduate work.
Fine control of DNA translocation is essential component of nanopore-based DNA strand sequencing.
Santa Cruz, CA, USA and Oxford, UK, 2 December 2010: Research published this week in JACS shows continuous and controlled translocation of a single stranded DNA (ssDNA) polymer through a protein nanopore by a DNA polymerase enzyme. The paper by researchers at the University of California Santa Cruz (UCSC) provides the foundation for a molecular motor, an essential component of Strand Sequencing using nanopores. Researchers at UCSC are collaborating with the UK-based company Oxford Nanopore Technologies, developers of a nanopore DNA sequencing technology.
The new research advances previous work showing that DNA could be moved through a nanopore using a polymerase. DNA movement in the previous study was performed by a series of polymerases and required complex electronics for control. Improvements noted in the JACS paper include techniques to allow continuous ssDNA movement, giving an uninterrupted signal as the strand was moved through the nanopore in real time. The enzyme-nanopore construct was active and measurable in a constant electronic field without complex electronics.
Caption: A protein nanopore (blue) embedded in a lipid bilayer is coupled with a DNA polymerase (green). The polymerase sequentially adds complementary bases to single stranded DNA, thus ratcheting it upwards through the nanopore.
Controlled initiation of the polymerase processing at the site of the nanopore-enzyme complex allowed sequential measurement of multiple ssDNA molecules using a single experimental setup . Furthermore the polymerase exhibited tenacious binding with the DNA polymer, unlike previous enzymes researched in similar conditions. These results demonstrate that qualities of the phi29 DNA polymerase are commensurate with a strand sequencing technology.
In the 'strand sequencing' method of nanopore DNA sequencing, ionic current through a protein nanopore is measured and current disruptions used to identify bases on a ssDNA polymer in sequence, as it translocates the pore. Two key challenges for this method are: engineering a nanopore to enable identification of individual bases when a ssDNA polymer spans the pore and a mechanism for controlling translocation of ssDNA at a consistent and appropriate speed to enable base identification through electronic measurements.
Translocation techniques described in this paper are compatible with base identification technology being performed in the laboratories of Oxford Nanopore Technologies and its collaborators.
"This work with the phi29 polymerase has allowed us to make important progress on a key element of DNA strand sequencing," said investigator Professor Mark Akeson of the University of California, Santa Cruz. "While previous work showed that translocation control was possible in theory, this work shows that DNA translocation control is achievable in conditions that are compatible with an electronic sequencing technology. We look forward to further collaboration with Oxford Nanopore to realise this research."
"The 'strand sequencing' method of DNA sequencing using a nanopore has been studied for many years, but this paper shows for the first time that DNA can be translocated by an enzyme using methods that are consistent with a high throughput electronic technology," said Dr Gordon Sanghera, CEO of Oxford Nanopore. "We are excited by this work and its potential when coupled with additional recent developments in DNA base identification on DNA strands, the other critical element for strand sequencing." ###
Work conducted in this paper
In this JACS paper, single stranded DNA (ssDNA) was translocated through an alpha hemolysin nanopore using the enzyme bacteriophage phi29 DNA polymerase (phi29DNAP). The enzyme had been chosen due its favourable processivity and high binding strength with DNA substrates. The nanopore-enzyme construct was shown to be stable in an electric field under a 180 mV applied potential, a level that is compatible with simultaneous identification of DNA bases using a nanopore. In the presence of deoxynucleoside triphosphates, processing of the ssDNA could be initiated specifically at the nanopore, with real time addition of nucleotides resulting in ssDNA translocation through the pore. The nanopore used in this research was not engineered for nucleotide discrimination and therefore an abasic area within the ssDNA was introduced to allow observation of its passage through the pore.
Base identification during strand sequencing
In addition to achieving fine control of DNA translocation through a nanopore, a key challenge for strand sequencing is accurate identification of individual nucleotides on ssDNA. When passing through AHL,10-15 bases on a ssDNA polymer will span the pore's central channel. Strategies are in development for distinguishing single bases, for example researchers at the University of Oxford have previously published methods (1, 2) to correctly identify individual nucleotides on ssDNA immobilised within an AHL nanopore and to identify modified bases on a DNA strand. Further work continues at Oxford Nanopore and in the laboratories of the Company's collaborators and this work is compatible with the methods described in the JACS paper.
Oxford Nanopore Technologies Ltd
Oxford Nanopore Technologies Ltd is developing a revolutionary technology for direct, electronic detection and analysis of single molecules. The platform is designed to offer substantial benefits in a variety of applications. The Company's lead application is DNA sequencing, but the platform is also adaptable for protein analysis for diagnostics and drug development and identification of a range of other molecules for security & defence and environmental monitoring. The technology is modular and highly scalable, driven by electronics rather than optics.
The Company's first generations of DNA sequencing technology, Exonuclease sequencing and Strand sequencing, combine a protein nanopore with a processive enzyme, multiplexed on a silicon chip. In exonuclease sequencing, individual bases are cleaved from a strand of DNA and identified as they pass through a protein nanopore. In strand sequencing a DNA polymer is analysed as it translocates the nanopore. This elegant and scalable system has unique potential to transform the speed and cost of DNA sequencing. Oxford Nanopore also has collaborative projects in the development of solid state nanopores for further improvements in speed and cost. For further information please. visit www.nanoporetech.com.
Notes to Editors
Reference: Processive Replication of Single DNA Molecules in a Nanopore Catalyzed by phi29 DNA Polymerase (subscription needed). Available online at at pubs.acs.org/doi/abs/10.1021/ja1087612 (subscription needed for full article)
Feds fund CWRU researcher's capacitor design. Need has caught up with Gerhard Welsch's ideas.
Welsch, a professor of materials science and engineering at Case Western Reserve University, began patenting designs for a small, light, powerful and reliable capacitor in 2000.
Now it's just the kind of energy storage device makers of hybrid cars, computer power supplies, pacemakers and more are seeking to absorb and provide surges of electricity.
Funded with a recent $2.25 million stimulus grant from the U.S. Dept. of Energy's Advanced Research Projects Agency – Energy, or ARPA-E, Welsch will try to make a capacitor ready for market within three years.
Working with him are colleagues Chung-Chiun Liu, professor of chemical engineering, and Frank Merat, professor of computer science and electrical engineering.
Gerhard Welsch
ARPA-E is especially interested in the capacitor for hybrids and all-electric cars. A battery, which is a tortoise to this hare, can't supply or absorb energy nearly as fast as a capacitor. To accomplish this, capacitor-enabled power inverters convert the DC electricity from batteries, solar panels or fuel cells to high frequency AC power.
"Electric vehicles need power inverters to convert battery power into higher voltage AC power for their electric motors and to harvest braking power," Welsch said.
His capacitor would provide a 10-fold or higher increase in energy density over current models, yet would be a fraction of the size and weight. And, this model could greatly increase reliability because it can heal leaks of electrical current that plague models now in use.
The keys are the materials and design of the device.
Capacitors, like batteries, have two poles: an anode and a cathode. The anode of Welsch's capacitor is made of a titanium alloy so finely textured that it absorbs almost all the light falling on it. (It looks black.) A large surface area squeezed into a small volume enables high capacitance and a high energy density.
The fine porous structure is laid out on a spine with many branches, further increasing the surface area.
A layer of titanium oxide, made by coating the porous surface with metal oxide, creates a barrier called a dielectric. The dielectric separates positive and negative electrical charges with a certain voltage, which holds the energy. Next comes a layer of an ion-conducting electrolyte followed by a metallic layer, probably of carbon or titanium, which serves as the cathode.
"A capacitor is the equivalent of an electron pressure tank, and the trick is to make the dielectric film (or the wall of the pressure tank), impenetrable to electrons by making it strong and as perfect as possible," Welsch said. "Perfect is not possible, but we can make a material that's close."
Typically, defects in the dielectric allow electrons to leak between the anode and cathode, limiting the energy density or leading to failure of the device. A new synthesis process reduces the size and number of defects in the dielectric formed. When a defect does form, the same forces that store energy in the dielectric draw ions from titanium and the electrolyte, forming a new oxide in or near the defect, sealing the leak.
The spine and branches' design, high surface area, synergistic materials and the instant healing of the dielectric would provide unmatched efficiency and high energy in a small space, the researchers believe.
In addition to demonstrating the capacitor in power supplies for electric cars and LED lighting, Welsch's group aims to show how it can be used in a miniaturized implantable defibrillator. When a sensor detects uncontrolled contraction of heart muscle, a battery will send energy to the capacitor, which will in turn jolt the muscle with a pulse of electricity lasting a microsecond, restoring a normal beat. ###
A five-year project led by the Georgia Institute of Technology has developed a novel approach to space electronics that could change how space vehicles and instruments are designed. The new capabilities are based on silicon-germanium (SiGe) technology, which can produce electronics that are highly resistant to both wide temperature variations and space radiation.
Titled "SiGe Integrated Electronics for Extreme Environments," the $12 million, 63-month project was funded by the National Aeronautics and Space Administration (NASA). In addition to Georgia Tech, the 11-member team included academic researchers from the University of Arkansas, Auburn University, University of Maryland, University of Tennessee and Vanderbilt University. Also involved in the project were BAE Systems, Boeing Co., IBM Corp., Lynguent Inc. and NASA's Jet Propulsion Laboratory.
"The team's overall task was to develop an end-to-end solution for NASA – a tested infrastructure that includes everything needed to design and build extreme-environment electronics for space missions," said John Cressler, who is a Ken Byers Professor in Georgia Tech's School of Electrical and Computer Engineering. Cressler served as principal investigator and overall team leader for the project.
Caption: A five-year project led by the Georgia Institute of Technology has developed a novel approach to space electronics that could change how space vehicles and instruments are designed. The new capabilities are based on silicon-germanium (SiGe) technology, which can produce electronics that are highly resistant to both wide temperature variations and space radiation.
Credit: Credit: Georgia Tech/Inertia Films with NASA video/still images. Usage Restrictions: None.
Caption: This close-up image shows a remote electronics unit 16-channel sensor interface, developed for NASA using silicon-germanium microchips by an 11-member team led by Georgia Tech.
Credit: Credit: Gary Meek. Usage Restrictions: None.
A paper on the project findings will appear in December in IEEE Transactions on Device and Materials Reliability, 2010. During the past five years, work done under the project has resulted in some 125 peer-reviewed publications.
Unique Capabilities
SiGe alloys combine silicon, the most common microchip material, with germanium at nanoscale dimensions. The result is a robust material that offers important gains in toughness, speed and flexibility.
That robustness is crucial to silicon-germanium's ability to function in space without bulky radiation shields or large, power-hungry temperature control devices. Compared to conventional approaches, SiGe electronics can provide major reductions in weight, size, complexity, power and cost, as well as increased reliability and adaptability.
"Our team used a mature silicon-germanium technology – IBM's 0.5 micron SiGe technology – that was not intended to withstand deep-space conditions," Cressler said. "Without changing the composition of the underlying silicon-germanium transistors, we leveraged SiGe's natural merits to develop new circuit designs – as well as new approaches to packaging the final circuits – to produce an electronic system that could reliably withstand the extreme conditions of space."
At the end of the project, the researchers supplied NASA with a suite of modeling tools, circuit designs, packaging technologies and system/subsystem designs, along with guidelines for qualifying those parts for use in space. In addition, the team furnished NASA with a functional prototype – called a silicon-germanium remote electronics unit (REU) 16-channel general purpose sensor interface.
The device was fabricated using silicon-germanium microchips and has been tested successfully in simulated space environments.
A New Paradigm
Andrew S. Keys, center chief technologist at the Marshall Space Flight Center and NASA program manager, said the now-completed project has moved the task of understanding and modeling silicon-germanium technology to a point where NASA engineers can start using it on actual vehicle designs.
"The silicon-germanium extreme environments team was very successful in doing what it set out to do," Keys said. "They advanced the state-of-the-art in analog silicon-germanium technology for space use – a crucial step in developing a new paradigm leading to lighter weight and more capable space vehicle designs."
Keys explained that, at best, most electronics conform to military specifications, meaning they function across a temperature range of minus- 55 degrees Celsius to plus-125 degrees Celsius. But electronics in deep space are typically exposed to far greater temperature ranges, as well as to damaging radiation. The Moon's surface cycles between plus-120 Celsius during the lunar day to minus-180 Celsius at night.
The silicon-germanium electronics developed by the extreme environments team has been shown to function reliably throughout that entire plus-120 to minus-180 Celsius range. It is also highly resistant or immune to various types of radiation.
The conventional approach to protecting space electronics, developed in the 1960s, involves bulky metal boxes that shield devices from radiation and temperature extremes, Keys explained. Designers must place most electronics in a protected, temperature controlled central location and then connect them via long and heavy cables to sensors or other external devices.
By eliminating the need for most shielding and special cables, silicon-germanium technology helps reduce the single biggest problem in space launches – weight. Moreover, robust SiGe circuits can be placed wherever designers want, which helps eliminate data errors caused by impedance variations in lengthy wiring schemes.
"For instance, the Mars Exploration Rovers, which are no bigger than a golf cart, use several kilometers of cable that lead into a warm box," Keys said. "If we can move most of those electronics out to where the sensors are on the robot's extremities, that will reduce cabling, weight, complexity and energy use significantly."
A Collaborative Effort
NASA currently rates the new SiGe electronics at a technology readiness level of six, which means the circuits have been integrated into a subsystem and tested in a relevant environment. The next step, level seven, involves integrating the SiGe circuits into a vehicle for space flight testing. At level eight, a new technology is mature enough to be integrated into a full mission vehicle, and at level nine the technology is used by missions on a regular basis.
Successful collaboration was an important part of the silicon-germanium team's effectiveness, Keys said. He remarked that he had "never seen such a diverse team work together so well."
Professor Alan Mantooth, who led a large University of Arkansas contingent involved in modeling and circuit-design tasks, agreed. He called the project "the most successful collaboration that I've been a part of."
Mantooth termed the extreme-electronics project highly useful in the education mission of the participating universities. He noted that a total of 82 students from six universities worked on the project over five years.
Richard W. Berger, a BAE Systems senior systems architect who collaborated on the project, also praised the student contributions.
"To be working both in analog and digital, miniaturizing, and developing extreme-temperature and radiation tolerance all at the same time – that's not what you'd call the average student design project," Berger said.
Miniaturizing an Architecture
BAE Systems' contribution to the project included providing the basic architecture for the remote electronics unit (REU) sensor interface prototype developed by the team. That architecture came from a previous electronics generation: the now cancelled Lockheed Martin X-33 Spaceplane initially designed in the 1990s.
In the original X-33 design, Berger explained, each sensor interface used an assortment of sizeable analog parts for the front end signal receiving section. That section was supported by a digital microprocessor, memory chips and an optical bus interface – all housed in a protective five-pound box.
The extreme environments team transformed the bulky X-33 design into a miniaturized sensor interface, utilizing silicon germanium. The resulting SiGe device weighs about 200 grams and requires no temperature or radiation shielding. Large numbers of these robust, lightweight REU units could be mounted on spacecraft or data-gathering devices close to sensors, reducing size, weight, power and reliability issues.
Berger said that BAE Systems is interested in manufacturing a sensor interface device based on the extreme environment team's discoveries.
Other space-oriented companies are also pursuing the new silicon-germanium technology, Cressler said. NASA, he explained, wants the intellectual-property barriers to the technology to be low so that it can be used widely.
"The idea is to make this infrastructure available to all interested parties," he said. "That way it could be used for any electronics assembly – an instrument, a spacecraft, an orbital platform, lunar-surface applications, Titan missions – wherever it can be helpful. In fact, the process of defining such an NASA mission-insertion road map is currently in progress." ###
Applied physics professor Chris Marianetti figures out how to shatter the world's strongest material
New York, NY November 29, 2010 In 2008, experiments at The Fu Foundation School of Engineering and Applied Science at Columbia University established pure graphene, a single layer of graphite only one atom thick, as the strongest material known to mankind. This raised a question for Chris Marianetti, Assistant Professor in Columbia Engineering's Department of Applied Physics and Applied Mathematics: how and why does graphene break?
Using quantum theory and supercomputers, Marianetti has revealed the mechanisms of mechanical failure of pure graphene under tensile stress. In a paper recently accepted for publication in the journal Physical Review Letters, he shows that, when graphene is subject to strain equal in all directions, it morphs into a new structure which is mechanically unstable.
Marianetti says this failure mechanism is a novel soft-mode phonon instability. A phonon is a collective vibrational mode of atoms within a crystal, similar to a wave in a liquid.
A schematic of the soft phonon-mode in graphene. The undistorted graphene lattice is shown in yellow. Image credit: Chris Marianetti.
The fact that a phonon becomes "soft" under tensile strain means that the system can lower its energy by distorting the atoms along the vibrational mode and transitioning to a new crystalline arrangement. Under sufficient strain, graphene develops a particular soft-mode that causes the honeycomb arrangement of carbon atoms to be driven towards isolated hexagonal rings. This new crystal is structurally weaker, resulting in the mechanical failure of the graphene sheet.
"This is exciting on many different levels," Marianetti notes. "Soft modes were first recognized in the 1960s in the context of ferroelectric phase transitions, but they have never been directly linked to fracture. Typically, defects in a material will always cause failure to happen prematurely, but the pristine nature of graphene allows one to test our prediction. We have already outlined some interesting new experiments to directly observe our theoretical prediction of the soft mode."
Marianetti added that this is the first time a soft optical phonon has ever been linked to mechanical failure and that therefore it is likely that this novel failure mechanism is not exclusive to graphene but may be prevalent in other very thin materials. "With nanotechnology becoming increasingly ubiquitous, understanding the nature of mechanical behavior in low dimensional systems such as graphene is of great importance. We think strain may be a means to engineer the properties of graphene, and therefore understanding its limits is critical." The research was funded by the National Science Foundation.
Marianetti's research interests lie in the use of classical and quantum mechanics to model the behavior of materials at the atomic scale. In particular, he is focused on applying these techniques to materials with potential for energy storage and conversion. Current applications in his research program range from nuclear materials such as plutonium to rechargeable battery materials such as cobalt oxides. ###
Marianetti received his BS and MS degrees from Ohio State University and his PhD in materials science and engineering from MIT. Before joining the faculty at Columbia Engineering, he did post-doctoral research in the Department of Physics at Rutgers University and in the Materials Chemistry Division of Lawrence Livermore National Laboratory.
Columbia Engineering
Columbia University's Fu Foundation School of Engineering and Applied Science offers programs to both undergraduate and graduate students who undertake a course of study leading to the bachelor's, master's, or doctoral degree in engineering and applied science. With facilities specifically designed and equipped to meet the laboratory and research needs of faculty and students, Columbia Engineering is home to a broad array of basic and advanced research installations, from the Columbia Center for Electron Transport in Molecular Nanostructures to the Columbia Genome Center. These interdisciplinary centers in science and engineering, materials research, nanoscale research, and genomic research are leading the way in their respective fields while individual groups of engineers and scientists collaborate to solve some of society's more vexing challenges. www.engineering.columbia.edu/
Universal microfluidics connector could find broad use.
Biomedical engineers at UC Davis have developed a plug-in interface for the microfluidic chips that will form the basis of the next generation of compact medical devices. They hope that the "fit to flow" interface will become as ubiquitous as the USB interface for computer peripherals.
UC Davis filed a provisional patent on the invention Nov. 1. A paper describing the devices was published online Nov. 25 by the journal Lab on a Chip.
"We think there is a huge need for an interface to bridge microfluidics to electronic devices," said Tingrui Pan, assistant professor of biomedical engineering at UC Davis. Pan and graduate student Arnold Chen - invented the chip and co-authored the paper.
Microfluidic devices use channels as small as a few micrometers across, cut into a plastic membrane, to carry out biological or chemical tests on a miniature scale. They could be used, for example, in compact devices used for medical diagnosis, food safety or environmental monitoring.
Caption: The clear block to the right is the Fit-to-Flow connector, with a microfluidic chip inserted. Channels take red and blue fluid through the connector to the chip. USB flash drive shown for scale.
Credit: Tingrui Pan, UC Davis. Usage Restrictions: May be used with acknowledgement of the source.
Cell phones with increasingly sophisticated cameras could be turned into microscopes that could read such tests in the field.
But it is difficult to connect these chips to electronic devices that can read the results of a test and store, display or transmit it.
Pan thinks that the fit-to-flow connectors can be integrated with a standard peripheral component interconnect (PCI) device commonly used in consumer electronics, while an embedded micropump will provide on-demand, self-propelled microfluidic operations. With this standard connection scheme, chips that carry out different tests could be plugged into the same device -- such as a cell phone, PDA or laptop -- to read the results. ###
The work was supported by a National Science Foundation CAREER award to Pan, and a fellowship to Chen from UC Davis.
MU scientists make strides in green nanotechnology.
COLUMBIA, Mo. ¬¬¬–Gold nanoparticles, tiny pieces of gold so small that they can't be seen by the naked eye, are used in electronics, healthcare products and as pharmaceuticals to fight cancer. Despite their positive uses, the process to make the nanoparticles requires dangerous and extremely toxic chemicals. While the nanotechnology industry is expected to produce large quantities of nanoparticles in the near future, researchers have been worried about the environmental impact of the global nanotechnological revolution.
Now, a study by a University of Missouri research team, led by MU scientist Kattesh Katti, curators' professor of radiology and physics in the School of Medicine and the College of Arts and Science, senior research scientist at the University of Missouri Research Reactor and director of the Cancer Nanotechnology Platform, has found a method that could replace nearly all of the toxic chemicals required to make gold nanoparticles. The missing ingredient can be found in nearly every kitchen's spice cabinet – cinnamon.
Caption: University of Missouri researcher Kattesh Katti has found a method that could replace nearly all of the toxic chemicals required to make gold nanoparticles.
Credit: University of Missouri. Usage Restrictions: None.
The usual method of creating gold nanoparticles utilizes harmful chemicals and acids that are not environmentally safe and contain toxic impurities. In the MU study, Katti and researchers Raghuraman Kannan, the Michael J and Sharon R. Bukstein Distinguished Faculty Scholar in Cancer Research, assistant professor of radiology and director of the Nanoparticle Production Core Facility; and Nripen Chanda, a research associate scientist, mixed gold salts with cinnamon and stirred the mixture in water to synthesize gold nanoparticles. The new process uses no electricity and utilizes no toxic agents.
"The procedure we have developed is non-toxic," Kannan said. "No chemicals are used in the generation of gold nanoparticles, except gold salts. It is a true 'green' process."
"From our work in green nanotechnology, it is clear that cinnamon — and other species such as herbs, leaves and seeds — will serve as a reservoir of phytochemicals and has the capability to convert metals into nanoparticles," Katti said. "Therefore, our approach to 'green' nanotechnology creates a renaissance symbolizing the indispensable role of Mother Nature in all future nanotechnological developments."
During the study, the researchers found that active chemicals in cinnamon are released when the nanoparticles are created. When these chemicals, known as phytochemicals, are combined with the gold nanoparticles, they can be used for cancer treatment. The phytochemicals can enter into cancer cells and assist in the destruction or imaging of cancer cells, Katti said.
"Our gold nanoparticles are not only ecologically and biologically benign, they also are biologically active against cancer cells," Katti said.
As the list of applications for nanotechnology grows in areas such as electronics, healthcare products and pharmaceuticals, the ecological implications of nanotechnology also grow. When considering the entire process from development to shipping to storage, creating gold nanoparticles with the current process can be incredibly harmful to the environment, Chanda said.
"On one hand, you are trying to create a new, useful technology. However, continuing to ignore the environmental effects is detrimental to the progress," Kannan said.
Katti, who is considered to be father of green nanotechnology, and Nobel prize winner Norman Borlaug have shared similar views on the potential of green nanotechnology in medicine, agricultural and life sciences. Borlaug predicted a connection between medical and agricultural sciences. Katti, who is the editor of The International Journal of Green Nanotechnology, said that as more uses for nanotechnology are created, scientists must develop ways to establish the connection between nanotechnology and green science. The study was published this fall in Pharmaceutical Research. ###
Penn neurosurgeons, engineers developing inexpensive, easy way to relate soldiers' exposure to possible brain injury.
PHILADELPHIA - Mimicking the reflective iridescence of a butterfly's wing, investigators at the University of Pennsylvania School of Medicine and School of Engineering and Applied Sciences have developed a color-changing patch that could be worn on soldiers' helmets and uniforms to indicate the strength of exposure to blasts from explosives in the field. Future studies aim to calibrate the color change to the intensity of exposure to provide an immediate read on the potential harm to the brain and the subsequent need for medical intervention. The findings are described in the ahead-of-print online issue of NeuroImage.
"We wanted to create a 'blast badge' that would be lightweight, durable, power-free, and perhaps most important, could be easily interpreted, even on the battlefield", says senior author Douglas H. Smith, MD, director of the Center for Brain Injury and Repair and professor of Neurosurgery at Penn. "Similar to how an opera singer can shatter glass crystal, we chose color-changing crystals that could be designed to break apart when exposed to a blast shockwave, causing a substantial color change."
Caption: Blast exposure disrupts the nanostructure of the blast injury dosimeter, resulting in clear changes in color. The color changes may be calibrated to denote the severity of blast exposure in relation to thresholds for blast-related traumatic brain injury.
Credit: Douglas Smith, MD, University of Pennsylvania School of Medicine, NeuroImage. Usage Restrictions: None.
D. Kacy Cullen, PhD, assistant professor of Neurosurgery, and Shu Yang, PhD, associate professor of Materials Science and Engineering, were co-authors with Smith.
Blast-induced traumatic brain injury is the "signature wound" of the current wars in Iraq and Afghanistan. However, with no objective information of relative blast exposure, soldiers with brain injury may not receive appropriate medical care and are at risk of being returned to the battlefield too soon.
"Diagnosis of mild traumatic brain injury [TBI] is challenging under most circumstances, as subtle or slowly progressive damage to brain tissue occurs in a manner undetectable by conventional imaging techniques," notes Cullen. There is also a debate as to whether mild TBI is confused with post-traumatic stress syndrome. "This emphasizes the need for an objective measure of blast exposure to ensure solders receive proper care," he says.
Sculpted by Lasers
The badges are comprised of nanoscale structures, in this case pores and columns, whose make-up preferentially reflects certain wavelengths. Lasers sculpt these tiny shapes into a plastic sheet.
Yang's group pioneered this microfabrication of three-dimensional photonic structures using holographic lithography. "We came up the idea of using three-dimensional photonic crystals as a blast injury dosimeter because of their unique structure-dependent mechanical response and colorful display," she explains. Her lab made the materials and characterized the structures before and after the blast to understand the color-change mechanism.
"It looks like layers of Swiss cheese with columns in between," explains Smith. Although very stable in the presence of heat, cold or physical impact, the nanostructures are selectively altered by blast exposure. The shockwave causes the columns to collapse and the pores to grow larger, thereby changing the material's reflective properties and outward color. The material is designed so that the extent of the color change corresponds with blast intensity.
The blast-sensitive material is added as a thin film on small round badges the size of fill-in-the-blank circles on a multiple-choice test that could be sewn onto a soldier's uniform.
In addition to use as a blast sensor for brain injury, other applications include testing blast protection of structures, vehicles and equipment for military and civilian use. ###
This research was funded by the Philadelphia Institute of Nanotechnology, and supported in part by the Office of Naval Research and the Air Force Office of Scientific Research.
Penn Medicine is one of the world's leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the University of Pennsylvania School of Medicine (founded in 1765 as the nation's first medical school) and the University of Pennsylvania Health System, which together form a $3.6 billion enterprise.
Penn's School of Medicine is currently ranked #2 in U.S. News & World Report's survey of research-oriented medical schools, and is consistently among the nation's top recipients of funding from the National Institutes of Health, with $367.2 million awarded in the 2008 fiscal year.
Penn Medicine's patient care facilities include:
The Hospital of the University of Pennsylvania – the nation's first teaching hospital, recognized as one of the nation's top 10 hospitals by U.S. News & World Report.
Penn Presbyterian Medical Center – named one of the top 100 hospitals for cardiovascular care by Thomson Reuters for six years.
Pennsylvania Hospital – the nation's first hospital, founded in 1751, nationally recognized for excellence in orthopaedics, obstetrics & gynecology, and psychiatry & behavioral health.
Additional patient care facilities and services include Penn Medicine at Rittenhouse, a Philadelphia campus offering inpatient rehabilitation and outpatient care in many specialties; as well as a primary care provider network; a faculty practice plan; home care and hospice services; and several multispecialty outpatient facilities across the Philadelphia region.
Penn Medicine is committed to improving lives and health through a variety of community-based programs and activities. In fiscal year 2009, Penn Medicine provided $733.5 million to benefit our community.
An international team of researchers has succeeded in creating artificial spin ice in a state of thermal equilibrium for the first time, allowing them to examine the precise configuration of this important nanomaterial.
Scientists from the University of Leeds, the US Department of Energy's Brookhaven National Laboratory and the UK Science and Technology Facilities Council's Rutherford Appleton Laboratory say the breakthrough will allow them to study in much greater detail a scientific phenomenon known as 'magnetic monopoles', which are thought to exist in such structures. Their findings are published today in the journal Nature Physics.
Artificial spin ice is built using nanotechnology and is made up of millions of tiny magnets, each thousands of times smaller than a grain of sand. The magnets exist in a lattice in what is known as a 'frustrated' structure. Like water ice, the geometry of the structure means that all of the interactions between the atoms cannot be satisfied at the same time.
"It's like trying to seat alternating male and female diners around a table with an odd number of seats – however much you re-arrange them you will never succeed," said Dr Christopher Marrows from the University of Leeds, co-author of the paper.
artificial spin ice
In spin ice, magnetic dipoles with a north and south pole are arranged in tetrahedron structures. Each dipole has magnetic moments, similar to the protons on H2O molecules in water ice, which attract and repel each other.
Consequently, the dipoles arrange themselves into the lowest possible energy state, which is two poles pointing in and two pointing out.
Dr Marrows said: "Spin ices have created a lot of excitement in recent years as it has been realised that they are a playground for physicists studying magnetic monopole excitations and Dirac string physics in the solid state. However, until now all of the samples of these artificial structures created in the lab have been what we call 'jammed'.
"What we have done is find a way to un-jam spin ice and get it into a well-ordered ground state known as thermal equilibrium. We can then freeze a sample into this state, and use a microscope to see which way all the little magnets are pointing. It's the equivalent of being able take a picture of every atom in a room as it allows us to inspect exactly how the structure is configured."
Jason Morgan, PhD student at the University of Leeds and lead author of the paper, was the first member of the team to observe the sample in equilibrium. He said: "Getting the sample to self-order in such a way has never been achieved experimentally before and for a while had been considered impossible. But when we looked at the sample using magnetic force microscopy and saw this beautiful periodic structure we knew instantly that we had achieved an ordered ground state."
The researchers have also been able to observe individual excitations out of this ground state within their sample, which they say is evidence for monopole dynamics within the lattice.
Magnetic monopoles – magnets with only a single north or south pole ¬¬– are former hypothetical particles that are now thought to exist in spin ice. There is hope among scientists that understanding these monopoles in more detail could lead to advances in a novel technology field known as 'magnetricity' – a magnetic equivalent to electricity.
Co-author Sean Langridge, a Science and Technology Facilities Council (STFC) Fellow and visiting Professor at the University of Leeds, added: "In the naturally occurring spin-ice systems this ground state is predicted but has not been experimentally observed.
"Now that is has been observed in an artificial system the next step is to observe dynamically the excitations from this ground state. We can only do this by controlling the interactions with state of the art lithographic techniques. This level of control will provide an even greater level of understanding in this fascinating system."
The team created "artificial" spin ice samples at Brookhaven using a state-of-the-art nanotechnology tool called an electron beam writer. A similar £4 million facility is shortly to be opened at the University of Leeds which will be unique to the UK and will allow continued collaboration with the researchers at Brookhaven. ###
The research was funded by the Engineering and Physical Sciences Research Council, the Science and Technology Facilities Council, and the US Department of Energy's Office of Science.
To request an interview with Dr Chris Marrows, or to request photographs of the spin ice sample, please contact Hannah Isom in the University of Leeds press office on 0113 343 4031 or email h.isom@leeds.ac.uk.
Notes to editors
The 2008 Research Assessment Exercise showed the University of Leeds to be the UK's eighth biggest research powerhouse. The University is one of the largest higher education institutions in the UK and a member of the Russell Group of research-intensive universities. The University's vision is to secure a place among the world's top 50 by 2015. www.leeds.ac.uk
One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry, and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation of the State University of New York, for and on behalf of Stony Brook University, the largest academic user of Laboratory facilities; and Battelle Memorial Institute, a nonprofit, applied science and technology organization. Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more (www.bnl.gov/bnlweb/pubaf/pr/newsroom), or follow Brookhaven Lab on Twitter (twitter.com/BrookhavenLab).
The Science and Technology Facilities Council ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange partnerships.
The Council has a broad science portfolio including Astronomy, Particle Physics, Particle Astrophysics, Nuclear Physics, Space Science, Synchrotron Radiation, Neutron Sources and High Power Lasers. www.stfc.ac.uk
Accurate gene distribution during cell division depends on stable set-up.
Scientists have discovered an amazingly simple way that cells stabilize their machinery for forcing apart chromosomes. Their findings are reported Nov. 25 in Nature.
When a cell gets ready to split into new cells, this stable set-up permits its genetic material to be separated and distributed accurately. Otherwise, problem cells – like cancer cells— arise.
The human body contains more than a trillion cells, and every single cell needs to have the exact same set of chromosomes. Mistakes in moving chromosomes during cell division can lead to babies being born with genetic conditions like Down syndrome, where cells have an extra copy of chromosome 21.
"A striking hallmark of cancer cells," said one of the senior authors of the study, Sue Biggins, an investigator in the Basic Science Division, Fred Hutchinson Cancer Research Center in Seattle, "is that they contain the wrong number of chromosomes, so it is essential that that we understand how chromosome separation is controlled. This knowledge would potentially lead to ways to correct defects before they occur, or allow us to try to target cells with the wrong number of chromosomes to prevent them from dividing again."
Caption: If microtubules don't line up correctly on either side of a chromosome pair, the tension is weak and the attachment is released and fixed. A proper alignment secures the attachment through mechanical tension, and helps assure the chromosomes will separate accurately during cell division.
Credit: Charles Asbury lab. Usage Restrictions: For use by news media, schools and museums only.
The machine inside cells that moves the chromosomes is the kinetochore.
These appear on the chromosomes and attach to dynamic filaments during cell division. Kinetochores drive chromosome movement by keeping a grip on the filaments, which are constantly remodeling. The growth and shortening of the filaments tugs on the kinetochores and chromosomes until they separate.
"The kinetochore is one of the largest cellular machines but had never been isolated before," Biggins said, "Our labs isolated these machines for the first time. This allowed us to analyze their behavior outside of the cell and find out how they control movement."
"We demonstrated that attachments between kinetochores and microtubule filaments become more stable when they are placed under tension," noted Dr. Charles "Chip" Asbury, a University of Washington (UW) associate professor of physiology and biophysics. Originally trained in mechanical engineering, Asbury studies molecular motors in cells. He is also a senior author on the Nov. 25 Nature paper.
Asbury likened the stabilizing tension on the filament to a Chinese finger trap toy – the harder you try to pull away, the stronger your knuckles are gripped.
Asbury explained how this tension-dependent stabilization helps chromosomes separate according to plan. As cell division approaches, a mitotic spindle forms, so named by 19th century scientists because the gathering microfilaments resemble a wheel spinning thread.
When chromosome pairs are properly connected to the spindle, with one attached to microtubules on the right and the other to microtubules on the left, the kinetochore comes under mechanical tension and the attachment becomes stabilized, sort of like steadying a load by tightening ropes on either side. This is a simple, primitive mechanism.
"On the other hand," Asbury said," if the chromosome pair is not properly attached, the kinetochores do not come under full tension. The attachments are unstable and release quickly, giving another chance for proper connections to form." Kinetochores are not just connectors, but also are regulatory hubs. They sense and fix errors in attachment. They emit "wait" signals until the microtubule filaments are in the right place.
The research team conducted this study using techniques to manipulate single molecules to see how they worked. These methods allow scientists to take measurements not possible in living cells. The native kinetochore particles were purified from budding yeast cells.
To the best of his knowledge, Asbury said, "Intact, functional kinetochores had not previously been isolated from any organism." The purification of the kinetochores allowed the research team to make the first direct measurements of coupling strength between individual kinetechore particles and dynamic microtubules.
The results of this study contribute to wider efforts to understand a puzzling phenomenon on which all life depends: How are motion and force produced to move duplicated chromosomes apart before cells divide?
###
The research was funded by grants from the National Institute of General Science at the National Institutes of Health, the National Science Foundation, the Packard Foundation, the Kinship Foundation and the Beckman Foundation.
In addition to senior authors Biggins and Asbury, the lead authors on this study are Bungo Akiyoshi, from the Molecular and Cellular Biology Program at the UW and the Division of Basic Sciences, Fred Hutchinson Cancer Research Center; and Krishna K, Sarangapani and Andrew F. Powers, both of the UW Department of Physiology & Biophysics. The research team included Christian R. Nelson, Fred Hutchinson Cancer Research Center; Steve L. Reichow, UW Department of Biochemistry; Hugo Arellano-Santoyo, Fred Hutchinson Cancer Research Center, UW Molecular and Cellular Biology Program, and UW Department of Physiology & Biophysics; Tamir Gonen of the UW Department of Biochemistry and the Howard Hughes Medical Institute; and Jeffrey N. Ranish of the Institute for Systems Biology in Seattle.
A new chemical analysis technique developed by a research group at the National Institute of Standards and Technology (NIST) uses the shifting ultrasonic pitch of a small quartz crystal to test the purity of only a few micrograms of material. Since it works with samples close to a thousand times smaller than comparable commercial instruments, the new technique should be an important addition to the growing arsenal of measurement tools for nanotechnology, according to the NIST team.
As the objects of scientific research have gotten smaller and smaller—as in nanotechnology and gene therapy—the people who worry about how to measure these things have been applying considerable ingenuity to develop comparable instrumentation.* This new NIST technique is a riff on thermogravimetric analysis (TGA), an imposing name for a fairly straightforward concept. A sample of material is heated, very slowly and carefully, and changes in its mass are measured as the temperature increases. The technique measures the reaction energy needed to decompose, oxidize, dehydrate, or otherwise chemically change the sample with heat.
TGA can be used, for example, to characterize complex biofuel mixtures because the various components vaporize at different temperatures.
Quartz Crystal Microbalances Enable New Microscale Analytic Technique.
Caption: A NIST researcher prepares quartz crystal microbalance disks with samples of carbon nanotubes for microscale thermogravimetric analysis. Typical sample sizes are about 2 microliters, or about 1 microgram.
Credit: Kar/NIST. Usage Restrictions: None.
The purity of an organic sample can be tested by the shape of a TGA plot because, again, different components will break down or vaporize at different temperatures. Conventional TGA, however, requires samples of several milligrams or more of material, which makes it hard to measure very small, laboratory-scale powder samples—such as nanoparticles—or very small surface chemistry features such as thin films.
What's needed is an extremely sensitive "microbalance" to measure the minute changes in mass. The NIST group found one in the quartz crystal microbalance, essentially a small piezoelectric disk of quartz sandwiched between two electrodes. An alternating current across the electrodes causes the crystal to vibrate at a stable and precise ultrasonic frequency—the same principle as a quartz crystal watch.
Added mass (a microsample) lowers the resonant frequency, which climbs back up as the microsample is heated and breaks down.
In a new paper.** the NIST materials science group demonstrates that their microbalance TGA produces essentially the same results as a conventional TGA instrument, but with samples about a thousand times smaller. They can detect not only the characteristic curves for carbon black, aluminum oxide and a sample organic fluid, but also the more complex curves of mixtures.
"We started this work because we wanted to analyze the purity of small carbon nanotube samples," explains analytical chemist Elisabeth Mansfield. More recently, she says, they've applied the technique to measuring the organic surface coatings biologists put on gold nanoparticles to modify them for particular applications. "Measuring how much material coats the particles surface is very hard to do right now," she says, "It will be a really unique application for this technique."
The prototype apparatus requires that the frequency measurements be made in a separate step from the heating. Currently, the team is at work integrating the microbalance disks with a heating element to enable the process to be simultaneous. ###
