Darwin on a chip

UT researchers develop (r)evolutionary circuits

Researchers of the MESA+ Institute for Nanotechnology and the CTIT Institute for ICT Research at the University of Twente in The Netherlands have demonstrated working electronic circuits that have been produced in a radically new way, using methods that resemble Darwinian evolution. The size of these circuits is comparable to the size of their conventional counterparts, but they are much closer to natural networks like the human brain. The findings promise a new generation of powerful, energy-efficient electronics, and have been published in the leading British journal Nature Nanotechnology.

One of the greatest successes of the 20th century has been the development of digital computers. During the last decades these computers have become more and more powerful by integrating ever smaller components on silicon chips. However, it is becoming increasingly hard and extremely expensive to continue this miniaturisation. Current transistors consist of only a handful of atoms. It is a major challenge to produce chips in which the millions of transistors have the same characteristics, and thus to make the chips operate properly. Another drawback is that their energy consumption is reaching unacceptable levels. It is obvious that one has to look for alternative directions, and it is interesting to see what we can learn from nature. Natural evolution has led to powerful ‘computers’ like the human brain, which can solve complex problems in an energy-efficient way. Nature exploits complex networks that can execute many tasks in parallel.

Moving away from designed circuits

The approach of the researchers at the University of Twente is based on methods that resemble those found in Nature. They have used networks of gold nanoparticles for the execution of essential computational tasks. Contrary to conventional electronics, they have moved away from designed circuits. By using 'designless' systems, costly design mistakes are avoided. The computational power of their networks is enabled by applying artificial evolution. This evolution takes less than an hour, rather than millions of years. By applying electrical signals, one and the same network can be configured into 16 different logical gates. The evolutionary approach works around - or can even take advantage of - possible material defects that can be fatal in conventional electronics.

Powerful and energy-efficient

It is the first time that scientists have succeeded in this way in realizing robust electronics with dimensions that can compete with commercial technology. According to prof. Wilfred van der Wiel, the realized circuits currently still have limited computing power. “But with this research we have delivered proof of principle: demonstrated that our approach works in practice. By scaling up the system, real added value will be produced in the future. Take for example the efforts to recognize patterns, such as with face recognition. This is very difficult for a regular computer, while humans and possibly also our circuits can do this much better."  Another important advantage may be that this type of circuitry uses much less energy, both in the production, and during use. The researchers anticipate a wide range of applications, for example in portable electronics and in the medical world.

University of Twente

First Complete Pictures of Cells' DNA-Copying Machinery

The first-ever images of the protein complex that unwinds, splits, and copies double-stranded DNA reveal something rather different from the standard textbook view. The electron microscope images, created by scientists at the U.S. Department of Energy's Brookhaven National Laboratory with partners from Stony Brook University and Rockefeller University, offer new insight into how this molecular machinery functions, including new possibilities about its role in DNA "quality control" and cell differentiation. The images and implications are described in a paper published online by the journal Nature Structural & Molecular Biology, November 2, 2015.

"This work is a continuation of our long-standing research using electron microscopy to understand the mechanism of DNA replication, an essential function for every living cell," said Huilin Li, a biologist with a joint appointment at Brookhaven Lab and Stony Brook University.

"These new images show the fully assembled and fully activated 'helicase' protein complex—which encircles and separates the two strands of the DNA double helix as it passes through a central pore in the structure—and how the helicase coordinates with the two 'polymerase' enzymes that duplicate each strand to copy the genome."

Three-dimensional structure of the active DNA helicase bound to the front-end DNA polymerase (Pol epsilon). The DNA polymerase epsilon (green) sits on top rather than the bottom of the helicase.

Studying this molecular machinery, known collectively as a "replisome," and the details of its DNA-copying process can help scientists understand what happens when DNA is miscopied—a major source of mutation that can lead to cancer—or learn more about how a single cell can eventually develop into the many cell types that make up a multicellular organism. But no one has produced a real structure of a replisome at any resolution for any organism until now.

"All the textbook drawings and descriptions of how a replisome should look and work are based on biochemical and genetic studies," Li said, likening the situation to the famous parable of the three blind men trying to describe an elephant, each looking at only one part. Those textbook drawings show the helicase moving along the DNA, separating the two strands of the double helix, with two polymerases located at the back where the DNA strand is split. In this configuration, the polymerases would add nucleotides (molecules containing the complementary A, T, G, and C bases of the genetic code) to the side-by-side split ends as they move out of the helicase to form two new complete double helix DNA strands.

Collaborating scientists and study coauthors Zuanning Yuan, a graduate student at Stony Brook University (standing), Huilin Li of Stony Brook and Brookhaven Lab (seated, back), and Jingchuan Sun of Brookhaven Lab (seated, front) examining protein structures.

To test these assumptions, Li's group turned to the technique they had previously used to study individual components of the helicase, electron microscopy (EM). Jingchuan Sun, an EM expert in Li's lab, was essential to the success of the work. He studied samples of replisomes from baker's yeast cells—a model for all nucleus-containing cells—prepared and provided by Roxana Georgescu in Michael O'Donnell's research group at Rockefeller University. O'Donnell's group had previously published biochemical results related to this work.

"DNA replication is one of the most fundamental processes of life, so it is every biochemist's dream to see what a replisome looks like," Sun said. "Our lab has expertise and a decade of experience using electron microscopy to study DNA replication, which has prepared us well to tackle the highly mobile therefore very challenging replisome structure. Working together with the O'Donnell lab, which has done beautiful functional studies on the yeast replisome, our two groups brought perfectly complementary expertise to this project," he said.

The team's first-ever images of an intact replisome revealed that only one of the polymerases is located at the back of the helicase. The other is on the front side of the helicase, where the helicase first encounters the double-stranded helix. This means that while one of the two split DNA strands is acted on by the polymerase at the back end, the other has to thread itself back through or around the helicase to reach the front-side polymerase before having its new complementary strand assembled.

The scientists were so surprised by this finding that they asked another group at Rockefeller, led by Brian Chait, to perform additional structural studies using mass spectrometry. Yi Shi, a postdoctoral fellow in Chait's group performed this work, which confirmed the electron-microscopy-based conclusion about the unexpected architecture of the replisome.

The counterintuitive position of one polymerase at the front of the helicase suggests that it may have an unforeseen function. The authors suggest several possibilities including keeping the two "daughter" strands separate to help organize them during replication and cell division. It might also be possible that, as the single strand moves over other portions of the structure, some "surveillance" protein components check for lesions or mistakes in the nucleotide sequence before it gets copied—a sort of molecular quality control.

This architecture could also potentially play an important role in developmental biology by providing a pathway for treating the two daughter strands differently. Many modifications to DNA, including how it is packaged with other proteins, control which of the many genes in the sequence are eventually expressed in cells. An asymmetric replisome may result in asymmetric treatment of the two daughter strands during cell division—an essential step for making different tissues within a multicellular organism.

As the paper concludes, "Clearly, further studies will be required to understand the functional implications of the unexpected replisome architecture reported here."

This research was funded by the National Institutes of Health (GM103314, GM109824, GM74985, AG29979, and GM38839) and by the Howard Hughes Medical Institute.

Brookhaven National Laboratory

Detecting HIV diagnostic antibodies with DNA nanomachines

A nanoscale machine composed of synthetic DNA can be used for the rapid, sensitive and low-cost diagnosis of many diseases, including HIV

New research may revolutionize the slow, cumbersome and expensive process of detecting the antibodies that can help with the diagnosis of infectious and auto-immune diseases such as rheumatoid arthritis and HIV. An international team of researchers have designed and synthetized a nanometer-scale DNA "machine" whose customized modifications enable it to recognize a specific target antibody. Their new approach, which they described this month in Angewandte Chemie, promises to support the development of rapid, low-cost antibody detection at the point-of-care, eliminating the treatment initiation delays and increasing healthcare costs associated with current techniques.

The binding of the antibody to the DNA machine causes a structural change (or switch), which generates a light signal. The sensor does not need to be chemically activated and is rapid - acting within five minutes - enabling the targeted antibodies to be easily detected, even in complex clinical samples such as blood serum.

"One of the advantages of our approach is that it is highly versatile," said Prof. Francesco Ricci, of the University of Rome, Tor Vergata, senior co-author of the study. "This DNA nanomachine can be in fact custom-modified so that it can detect a huge range of antibodies, this makes our platform adaptable for many different diseases".

"Our modular platform provides significant advantages over existing methods for the detection of antibodies," added Prof. Vallée-Bélisle of the University of Montreal, the other senior co-author of the paper. "It is rapid, does not require reagent chemicals, and may prove to be useful in a range of different applications such as point-of-care diagnostics and bioimaging".

"Another nice feature of our this platform is its low-cost," said Prof. Kevin Plaxco of the University of California, Santa Barbara. "The materials needed for one assay cost about 15 cents, making our approach very competitive in comparison with other quantitative approaches."

"We are excited by these preliminary results, but we are looking forward to improve our sensing platform even more" said Simona Ranallo, a PhD student in the group of Prof. Ricci at the University of Rome and first-author of the paper. "For example, we could adapt our platform so that the signal of the nanoswitch may be read using a mobile phone. This will make our approach really available to anyone! We are working on this idea and we would like to start involving diagnostic companies."

University of Montreal

Nanotechnology World Association

Tracking nanowalkers with light

A gold cylinder with DNA feet can climb over DNA-primed hills made from folded DNA strands. The second cylinder (red) serves as a point of reference for observing the nanowalker. © MPI for Intelligent Systems, Stuttgart

A tiny gold rod walks across a surface guided by DNA and can be tracked step by step

Nanotechnology is taking its first steps. Researchers from the Max Planck Institute for Intelligent Systems in Stuttgart have developed a gold nanocylinder equipped with discrete DNA strands as ‘feet’ that can walk across a DNA origami platform. They are able to trace the movements of the nanowalker, which is smaller than the optical resolution limit, by exciting plasmons in the gold nanocylinder. Plasmons are collective oscillations of numerous electrons. The excitation changes the ray of light, thus allowing the researchers to actually observe the nanowalker. Their main objective is to use such mobile plasmonic nanoobjects to study how miniscule particles interact with light.

The body of the nanowalker consists of a gold cylinder that is 35 nanometres long and ten nanometres wide. “The cylinder’s surface is primed with numerous identical strands of DNA that effectively serve as feet,” Group Leader Liu explains. These DNA strands stick out from the gold cylinder like the bristles of a bottle brush. “They allow the gold cylinder to make contact with the surface underneath and travel across it.”Nanomachines – i.e. mechanical devices with dimensions of nanometers – could one day carry out specific tasks in fields such as medicine, information processing, chemistry or scientific research, according to nanotechnology experts. Yet miniature machines that are thousands of times smaller than the diameter of a human hair pose significant challenges for scientists: firstly, the individual constituents merely consist of a small number of atoms; it is barely possible to handle such components, let alone assemble them in a precise manner. Moreover, the machines would then need to be supplied with energy. And ultimately, the researchers cannot simply check to see if their device is in fact working. The microscopy techniques necessary for such observation are complex and require for example vacuum chambers, in which the devices would be destroyed. At the Max Planck Institute for Intelligent Systems in Stuttgart, a team of researchers including Chao Zhou and Xiaoyang Duan, headed by Laura Na Liu has now created a nanowalker that they can observe with the help of a nanooptical effect.

The nanowalker strides across a carpet of DNA strands

The gold cylinder’s walkway is composed of DNA as well – a DNA origami template, to be precise. Extended from this folded DNA scaffold like fibres from a carpet are longitudinal rows of short strands that are parallel to the cylinder and serve as footholds for the walker’s tiny feet. Each row in the DNA carpet comprises a different combination of bases, and each row represents one station. Initially, the walker’s feet bind with two neighbouring rows, while the footholds of the other rows remain blocked.

“The walker moves forward in a rolling motion, from station to station,” says Liu. In order to make this possible, the researchers must constantly add short snippets of DNA to the fluid in which the action is taking place. These snippets are designed to match the DNA of the individual rows. First they break up a row of connections linking the walker’s feet and the DNA of the platform and block the footholds of that particular station. On the opposite side of the walker, they then unblock a separate row, to which the cylinder’s feet can now attach.

“Depending on what is added, the walker moves either in one direction or in the other,” explains Liu. “We are inspired by naturally occurring molecular motors: The fluid moves the cylinder and its feet back and forth by means of thermal motion.” Due to the fact that the feet only ever redock on one side, the walker slowly moves forward. Each step is seven nanometres long, which is over one hundred thousand times smaller than the single stride of a wood ant.

Researchers use plasmon resonance to trace the nanocylinder’s path

In order to trace the tiny machine’s path, the researchers relied on a nanooptical effect called plasmon resonance. Plasmons are collective oscillations of numerous electrons and are often present in metals, among other materials. “Light can interact with the plasmons in the gold,” Liu explains. “Light is partially absorbed in the process in our case, resulting in what is known as plasmon resonance.” By analysing the light beam, the researchers can measure this phenomenon.

Determining the cylinder’s exact location, however, required placing a second, stationary gold nanocylinder on the underside of the DNA origami platform. Broadly speaking, this second cylinder serves as a point of reference. The reason for this is because together, the two cylinders bring about a change in the circular polarisation of the light beam: Light consists of an oscillating electromagnetic field. The polarisation is equivalent to the direction in which the field oscillates; in circularly polarised light, it turns either clockwise or counterclockwise. By observing the spectral changes resulting from the interaction with circular polarized light, the researchers can determine the walker’s current position.

“By using this approach we were able to trace every single step. That’s why the walker is more than just a mobile element – it also provides information about its location,” says Liu. Sophisticated microscope technology thus became redundant for observing the plasmonic walker, which Liu deems a precursor of a “new generation of nanomachines with customised optical properties”. The researcher now aims to use this tool to further study the interaction of light and matter on a nanoscale, as well as the mechanical behaviour of nanoparticles. Because if the gold walker is indeed destined to one day reach its goal and complete various tasks, it still needs to take quite a few strides – and not just on DNA origami.

Max Planck

Read more on Nanotechnology World Association

Bacterial Armor Holds Clues for Self-Assembling Nanostructures

Many bacteria and archaea encase themselves within a self-assembling protective shell of S-layer proteins, like chainmail armor. The process is a model for the self-assembly of 2D and 3D organic and inorganic nanostructures.

Imagine thousands of copies of a single protein organizing into a coat of chainmail armor that protects the wearer from harsh and ever-changing environmental conditions. That is the case for many microorganisms. In a new study, researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have uncovered key details in this natural process that can be used for the self-assembly of nanomaterials into complex two- and three-dimensional structures.

Caroline Ajo-Franklin, a chemist and synthetic biologist at Berkeley Lab’s Molecular Foundry, led this study in which high-throughput light scattering measurements were used to investigate the self-assembly of 2D nanosheets from a common bacterial surface layer (S-layer) protein. This protein, called “SbpA,” forms the protective armor for Lysinibacillus sphaericus, a soil bacterium used as a toxin to control mosquitoes. Their investigation revealed that calcium ions play a key role in how this armor assembles. Two key roles actually.

“Calcium ions not only trigger the folding of the protein into the correct shape for nanosheet formation, but also serve to bind the nanosheets together,” Ajo-Franklin says. “By establishing and using light scattering as a proxy for SbpA nanosheet formation, we were able to determine how varying the concentrations of calcium ions and SbpA affects the size and shape of the S-layer armor.”

Caroline Ajo-Franklin, Steve Whitelam and Behzad Rad led a team at Berkeley Lab’s Molecular Foundry that uncovered key details by which bacterial proteins self-assemble into a protective armor coating. (Photo by Roy Kaltschmidt)

Details on this study have been published in the journal ACS Nano in a paper titled “Ion-Specific Control of the Self-Assembly Dynamics of a Nanostructured Protein Lattice.” Ajo-Franklin is the corresponding author. Co-authors are Behzad Rad, Thomas Haxton, Albert Shon, Seong-Ho Shin and Stephen Whitelam.

In the microbial world of bacteria and archaea, external threats abound. Their surrounding environment can transition from extreme heat to extreme cold, or from highly acidic to highly basic. Predators are everywhere. To protect themselves, many bacteria and archaea encase themselves within a shell of S-layer proteins. While scientists have known about this protective coating for many years, how it forms has been a mystery.

Ajo-Franklin and her colleagues have been exploring self-assembling proteins as a potential means of creating nanostructures with complex structure and function.

“At the Molecular Foundry, we’ve gotten really good at making nanomaterials into different shapes but we are still learning how to assemble these materials into organized structures,” she says. “S-layer proteins are abundant biological proteins known to self-assemble into 2D crystalline nanosheets with lattice symmetries and pore sizes that are about the same dimensions as quantum dots and nanotubes. This makes them a compelling model system for the creation of nanostructured arrays of organic and inorganic materials in a bottom-up fashion.”

The binding of calcium ions to SbpA proteins starts the process
by which the SbpA self-assembles into nanosheets. Ca2+ binds to
SbpA with an affinity of 67 μM.

In this latest study, light-scattering measurements were used to map out diagrams that revealed the relative yield of self-assembled nanosheets over a wide range of concentrations of SbpA and calcium ions. In addition, the effects of substituting manganese or barium ions for calcium ions were examined to distinguish between a chemically specific and generic divalent cation role for the calcium ions. Behzad Rad, the lead author of the ACS Nano paper, and co-workers followed light-scattering by light in the visible spectrum. They then correlated the signal to nanosheet formation by using electron microscopy and Small Angle X-ray Scattering (SAXS), a technology that can provide information on molecular assemblies in just about any type of solution. The SAXS measurements were obtained at the “SIBYLS beamline (12.3.1) of Berkeley Lab’s Advanced Light Source.

“We learned that only calcium ions trigger the SbpA self-assembly process and that the concentrations of calcium ions inside the cell are too low for nanosheets to form, which is a good thing for the bacterium,” says Rad. “We also found that the time evolution of the light scattering traces is consistent with the irreversible growth of sheets from a negligibly small nucleus. As soon as five calcium ions bind to a SbpA protein, the process starts and the crystal grows really fast. The small nucleus is what makes our light-scattering technique work.”

Ajo-Franklin, Rad and their co-authors believe their light-scattering technique is applicable to any type of protein that self-assembles into 2D nanosheets, and can be used to monitor growth from the nanometer to the micrometer scales.

Given the rugged nature of the S-layer proteins and their adhesive quality – bacteria use their S-layer armor to attach themselves to their surroundings – there are many intriguing applications awaiting further study.

“One project we’re exploring is using SbpA proteins to make adhesive nanostructures that could be used to remove metals and other contaminants from water,” Ajo-Franklin says. “Now that we have such a good handle on how SbpA proteins self-assemble, we’d like to start mixing and matching them with other molecules to create new and useful structures.”

http://newscenter.lbl.gov/2015/02/11/bacterial-armor/

Engineers Build World’s Smallest, Fastest Nanomotor

Researchers at the Cockrell School of Engineering at The University of Texas at Austin have built the smallest, fastest and longest-running tiny synthetic motor to date. The team’s nanomotor is an important step toward developing miniature machines that could one day move through the body to administer insulin for diabetics when needed, or target and treat cancer cells without harming good cells.

With the goal of powering these yet-to-be invented devices, UT Austin engineers focused on building a reliable, ultra-high-speed nanomotor that can convert electrical energy into mechanical motion on a scale 500 times smaller than a grain of salt.

Mechanical engineering assistant professor Donglei “Emma” Fan led a team of researchers in the successful design, assembly and testing of a high-performing nanomotor in a nonbiological setting. The team’s three-part nanomotor can rapidly mix and pump biochemicals and move through liquids, which is important for future applications. The team’s study was published in the April issue of Nature Communications.

Fan and her team are the first to achieve the extremely difficult goal of designing a nanomotor with large driving power.

With all its dimensions under 1 micrometer in size, the nanomotor could fit inside a human cell and is capable of rotating for 15 continuous hours at a speed of 18,000 RPMs, the speed of a motor in a jet airplane engine. Comparable nanomotors run significantly more slowly, from 14 RPMs to 500 RPMs, and have only rotated for a few seconds up to a few minutes.

Looking forward, nanomotors could advance the field of nanoelectromechanical systems (NEMS), an area focused on developing miniature machines that are more energy efficient and less expensive to produce. In the near future, the Cockrell School researchers believe their nanomotors could provide a new approach to controlled biochemical drug delivery to live cells.

Mechanical engineering assistant professor Donglei "Emma" Fan

To test its ability to release drugs, the researchers coated the nanomotor’s surface with biochemicals and initiated spinning. They found that the faster the nanomotor rotated, the faster it released the drugs.

“We were able to establish and control the molecule release rate by mechanical rotation, which means our nanomotor is the first of its kind for controlling the release of drugs from the surface of nanoparticles,” Fan said. “We believe it will help advance the study of drug delivery and cell-to-cell communications.”

The researchers address two major issues for nanomotors so far: assembly and controls. The team built and operated the nanomotor using a patent-pending technique that Fan invented while studying at Johns Hopkins University. The technique relies on AC and DC electric fields to assemble the nanomotor’s parts one by one.

In experiments, the researchers used the technique to turn the nanomotors on and off and propel the rotation either clockwise or counterclockwise. The researchers found that they could position the nanomotors in a pattern and move them in a synchronized fashion, which makes them more powerful and gives them more flexibility.

Fan and her team plan to develop new mechanical controls and chemical sensing that can be integrated into nanoelectromechanical devices. But first they plan to test their nanomotors near a live cell, which will allow Fan to measure how they deliver molecules in a controlled fashion.

Cockrell School graduate students Kwanoh Kim, Xiaobin Xu and Jianhe Guo co-authored the study. The National Science Foundation Career Award, the Welch Foundation and startup funds from the Cockrell School supported the study.

http://www.engr.utexas.edu/features/nanomotors

Scientists combine bacteria with liquid crystals

When swimming around, bacteria aren’t good with the “pool rules.”  In small quantities, they’ll follow the lanes, but put enough together and they’ll begin to create their own flow.

In a collaboration between the U.S. Department of Energy’s Argonne National Laboratory and the Liquid Crystal Institute at Kent State University, researchers combined bacteria with liquid crystals and observed how the bacteria swam around and interacted with the medium, forming “living liquid crystals” that may have interesting applications for new material design and fabrication.

Liquid crystals are intermediate materials that exhibit some of the behaviors of a liquid and some of those of a crystalline solid. For example, a liquid crystal has a liquid-like flow, but on the molecular level it may appear more crystalline.

When they are dissolved in water, the molecules that make up a liquid crystal tend to form long rod-like structures that prefer to organize along one dimension, called a director. The director is symmetrical -- it does not have poles along its axis.

Using a solution known as “Terrific Broth” – so known for its usefulness as a bacterial growth medium – the researchers cultured a colony ofBacillus subtilis bacteria and transferred it to a liquid crystal.

When the researchers looked at the bacteria in the liquid crystal using a powerful optical microscope, they saw that they moved in a surprising way. Each B. subtilis bacterium has a long, thin tail called a flagellum, which the bacterium spins like a screw to propel itself. Although the bacteria originally orient themselves parallel to the director, the spinning of the flagella as the bacteria swim locally changes the director’s alignment into a wave-like pattern.

As the researchers increased the density of bacteria in the liquid crystal solution, they saw a second surprising effect. Because of the collective effects, the swimming bacteria began to create “stripes” of different director orientations within the liquid crystal. These stripes could then be erased by depriving the bacteria of oxygen.

“The system is extremely sensitive,” said Argonne materials scientist Andrey Sokolov, one of the authors of the study. “There is always an interplay between the bacterial forces and liquid crystal forces, and the behavior of the material depends on which one wins in the end.”

According to Argonne materials scientist Igor Aronson, the study’s lead author, it only takes a bacterial concentration of 0.2% for the bacteria’s collective swimming to begin to overtake the natural order of the liquid crystal.

The researchers hope that eventually studies on living liquid crystals as well as other similar “living materials” will pay dividends for a number of different applications. “Our principal goal is understanding active materials,” Aronson said. “We want to see how we can design new ways to consume energy from the environment and use it for self-assembly and self-repair.”

The scientists also noted that their method may have other implications beyond the living liquid crystals themselves.  Because the wake created by the oscillations of the flagella in the liquid crystal is so much larger than the nanometer-wide flagella themselves, the researchers were able to observe the action of the flagella with an optical microscope. “The flagella are only a few tens of nanometers in diameter, and in the past we’ve had to use electron microscopes in order to see it,” Aronson said.

“This could have bigger implications in terms of ways to visualize other nanoscale objects,” Sokolov added.

Funding for the study was provided by DOE’s Office of Science and the National Science Foundation, and results appeared as a paper titled "Living liquid crystals" in the Proceedings of the National Academy of Sciences.

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 DOE 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. For more information, please visit http://science.energy.gov.

Source: http://www.anl.gov/articles/it-s-alive-scientists-combine-bacteria-liquid-crystals

Graphene-Based Nano-Antennas May Enable Networks of Tiny Machines

Networks of nanometer-scale machines offer exciting potential applications in medicine, industry, environmental protection and defense, but until now there’s been one very small problem: the limited capability of nanoscale antennas fabricated from traditional metallic components.

With antennas made from conventional materials like copper, communication between low-power nanomachines would be virtually impossible. But by taking advantage of the unique electronic properties of the material known as graphene, researchers now believe they’re on track to connect devices powered by small amounts of scavenged energy.

Based on a honeycomb network of carbon atoms, graphene could generate a type of electronic surface wave that would allow antennas just one micron long and 10 to 11 nanometers wide to do the work of much larger antennas. While operating graphene nano-antennas have yet to be demonstrated, the researchers say their modeling and simulations show that nano-networks using the new approach are feasible with the alternative material.

“We are exploiting the peculiar propagation of electrons in graphene to make a very small antenna that can radiate at much lower frequencies than classical metallic antennas of the same size,” said Ian Akyildiz, a Ken Byers Chair professor in Telecommunications in the School of Electrical and Computer Engineering at the Georgia Institute of Technology. “We believe that this is just the beginning of a new networking and communications paradigm based on the use of graphene.”

Sponsored by the National Science Foundation, the research is scheduled to be reported in the journalIEEE Journal of Selected Areas in Communications (IEEE JSAC). In addition to the nanoscale antennas, the researchers are also working on graphene-based nanoscale transceivers and the transmission protocols that would be necessary for communication between nanomachines.

The communications challenge is that at the micron scale, metallic antennas would have to operate at frequencies of hundreds of terahertz. While those frequencies might offer advantages in communication speed, their range would be limited by propagation losses to just a few micrometers. And they’d require lots of power – more power than nanomachines are likely to have.

Akyildiz has studied nanonetworks since the late 1990s, and had concluded that traditional electromagnetic communication between these machines might not be possible. But then he and his Ph.D. student, Josep Jornet – who graduated in August 2013 and is now an assistant professor at the State University of New York at Buffalo – began reading about the amazing properties of graphene. They were especially interested in how electrons behave in single-layer sheets of the material.

“When electrons in graphene are excited by an incoming electromagnetic wave, for instance, they start moving back and forth,” explained Akyildiz. “Because of the unique properties of the graphene, this global oscillation of electrical charge results in a confined electromagnetic wave on top of the graphene layer.”

Known technically as a surface plasmon polariton (SPP) wave, the effect will allow the nano-antennas to operate at the low end of the terahertz frequency range, between 0.1 and 10 terahertz – instead of at 150 terahertz required by traditional copper antennas at nanoscale sizes. For transmitting, the SPP waves can be created by injecting electrons into the dielectric layer beneath the graphene sheet.

Materials such as gold, silver and other noble metals also can support the propagation of SPP waves, but only at much higher frequencies than graphene. Conventional materials such as copper don’t support the waves.

By allowing electromagnetic propagation at lower terahertz frequencies, the SPP waves require less power – putting them within range of what might be feasible for nanomachines operated by energy harvesting technology pioneered by Zhong Lin Wang, a professor in Georgia Tech’s School of Materials Science and Engineering.

“With this antenna, we can cut the frequency by two orders of magnitude and cut the power needs by four orders of magnitude,” said Jornet. “Using this antenna, we believe the energy-harvesting techniques developed by Dr. Wang would give us enough power to create a communications link between nanomachines.”

The nanomachines in the network that Akyildiz and Jornet envision would include several integrated components. In addition to the energy-harvesting nanogenerators, there would be nanoscale sensing, processing and memory, technologies that are under development by other groups. The nanoscale antenna and transceiver work being done at Georgia Tech would allow the devices to communicate the information they sense and process to the outside world.

“Each one of these components would have a nanoscale measurement, but in total we would have a machine measuring a few micrometers,” said Jornet. “There would be lots of tradeoffs in energy use and size.”

Beyond giving nanomachines the ability to communicate, hundreds or thousands of graphene antenna-transceiver sets might be combined to help full-size cellular phones and Internet-connected laptops communicate faster.

“The terahertz band can boost current data rates in wireless networks by more than two orders of magnitude,” Akyildiz noted. “The data rates in current cellular systems are up to one gigabit-per-second in LTE advanced networks or 10 gigabits-per-second in the so-called millimeter wave or 60 gigahertz systems. We expect data rates on the order of terabits-per-second in the terahertz band.”

The unique properties of graphene, Akyildiz says, are critical to this antenna – and other future electronic devices.  

“Graphene is a very powerful nanomaterial that will dominate our lives in the next half-century,” he said. “The European community will be supporting a very large consortium involving many universities and companies with an investment of one billion euros to conduct research into this material.”

The researchers have so far evaluated numerous nano-antenna designs using modeling and simulation techniques in their laboratory. The next step will be to actually fabricate a graphene nano-antenna and operate it using a transceiver also based on graphene.

“Our project shows that the concept of graphene-based nano-antennas is feasible, especially when taking into account very accurate models of electron transport in graphene,” said Akyildiz. “Many challenges remain open, but this is a first step toward creating advanced nanomachines with many applications in the biomedical, environmental, industrial and military fields.”

The research described here was supported by the National Science Foundation under award number CCF-1349828. Any opinions or conclusions are those of the authors and do not necessarily reflect the official views of the NSF.

Source: http://www.news.gatech.edu/2013/12/11/graphene-based-nano-antennas-may-enable-networks-tiny-machines