Standoff Sensing Enters New Realm With Dual-Laser Technique

 Identifying chemicals from a distance could take a step forward with the introduction of a two-laser system being developed at the Department of Energy's Oak Ridge National Laboratory.

In a paper published in the Journal of Physics D: Applied Physics, Ali Passian and colleagues present a technique that uses a quantum cascade laser to "pump," or strike, a target, and another laser to monitor the material's response as a result of temperature-induced changes. That information allows for the rapid identification of chemicals and biological agents.

"With two lasers, one serves as the pump and the other is the probe," said Passian, a member of ORNL's Measurement Science and Systems Engineering Division. "The novel aspect to our approach is that the second laser extracts information and allows us to do this without resorting to a weak return signal.

"The use of a second laser provides a robust and stable readout approach independent of the pump laser settings."

While this approach is similar to radar and lidar sensing techniques in that it uses a return signal to carry information of the molecules to be detected, it differs in a number of ways.

"First is the use of photothermal spectroscopy configuration where the pump and probe beams are nearly parallel," Passian said. "We use probe beam reflectometry as the return signal in standoff applications, thereby minimizing the need for wavelength-dependent expensive infrared components such as cameras, telescopes and detectors."

This work represents a proof of principle success that Passian and co-author Rubye Farahi said could lead to advances in standoff detectors with potential applications in quality control, forensics, airport security, medicine and the military. In their paper, the researchers also noted that measurements obtained using their technique may set the stage for hyperspectral imaging.

"This would allow us to effectively take slices of chemical images and gain resolution down to individual pixels," said Passian, who added that this observation is based on cell-by-cell measurements obtained with their variation of photothermal spectroscopy. Hyperspectral imaging provides not only high-resolution chemical information, but topographical information as well.

Other authors are ORNL's Laurene Tetard, a Wigner Fellow, and Thomas Thundat of the University of Alberta. Funding for this research was provided by ORNL's Laboratory Directed Research and Development program.

Swarming and Transporting

On its own, an ant is not particularly clever. But in a community, the insects can solve complicated tasks. Researchers intend to put this "swarm intelligence" to use in the logistics field. Lots of autonomous transport shuttles would provide an alternative to traditional materials-handling technology.

The orange-colored vehicle begins moving with a quiet whirr. Soon afterwards the next shuttles begin to move, and before long there are dozens of mini-transporters rolling around in the hall. As if by magic, they head for the high-rack storage shelves or spin around their own axis. But the Multishuttle Moves® -- is the name given to these driverless transport vehicles -- are not performing some robots' ballet. They are moving around in the service of science. At the Fraunhofer Institute for Material Flow and Logistics IML in Dortmund, Germany, researchers are working to harness swarm intelligence as a means of improving the flow of materials and goods in the warehouse environment. In a research hall 1000 square meters in size, the scientists have replicated a small-scale distribution warehouse with storage shelves for 600 small-part carriers and eight picking stations. The heart of the testing facility is a swarm of 50 autonomous vehicles. "In the future, transport systems should be able to perform all of these tasks autonomously, from removal from storage at the shelf to delivery to a picking station. This will provide an alternative to conventional materials-handling solutions," explains Prof. Dr. Michael ten Hompel, executive director at IML.

But how do the vehicles know what they should transport, and where, and which of the 50 shuttles will take on any particular order? "The driverless transport vehicles are locally controlled. The ›intelligence‹ is in the transporters themselves," Dipl.-Ing. Thomas Albrecht, head of the Autonomous Transport Systems department explains the researchers' solution approach. "We rely on agent-based software and use ant algorithms based on the work of Marco Dorigo. These are methods of combinational optimization based on the model behavior of real ants in their search for food." When an order is received, the shuttles are informed of this through a software agent. They then coordinate with one another via WLAN to determine which shuttle can take over the load. The job goes to whichever free transport system is closest.

The shuttles are completely unimpeded as they navigate throughout the space -- with no guidelines. Their integrated localization and navigation technology make this possible. The vehicles have a newly developed, hybrid sensor concept with signal-based location capability, distance and acceleration sensors and laser scanners. This way, the vehicles can compute the shortest route to any destination. The sensors also help prevent collisions.

The vehicles are based on the components of the shelf-bound Multishuttle already successfully in use for several years. The researchers at IML have worked with colleagues at Dematic to develop the system further. The special feature about the Multishuttle Move®: the transporters can navigate in the storage area and in the hall. To accomplish this, the shuttles are fitted with an additional floor running gear. But what benefits do these autonomous transporters offer compared with conventional steady materials-handling technology with roller tracks? "The system is considerably more flexible and scalable," Albrecht points out. It can grow or contract depending on the needs at hand. This is how system performance can be adapted to seasonal and daily fluctuation. Another benefit: It considerably shortens transportation paths. In conventional storage facilities, materials-handling equipment obstructs the area between high-rack storage and picking stations. Packages must travel two to three times farther than the direct route. "It also makes shelf-control units and steady materials-handling technology," Albrecht adds. Researchers are now trying to determine how these autonomous transporters can improve intralogistics. "We want to demonstrate that cellular materials-handling technology makes sense not only technically but also economically as an alternative to classic materials-handling technology and shelf-control units," institute executive director ten Hompel observes. If this succeeds, the autonomous vehicles could soon be going into service in warehouses.

New Theory On Size of Black Holes: Gas-Guzzling Black Holes Eat Two Courses at a Time

Astronomers have put forward a new theory about why black holes become so hugely massive -- claiming some of them have no 'table manners', and tip their 'food' directly into their mouths, eating more than one course simultaneously.

Researchers from the UK and Australia investigated how some black holes grow so fast that they are billions of times heavier than the sun.

The team from the University of Leicester (UK) and Monash University in Australia sought to establish how black holes got so big so fast.

Professor Andrew King from the Department of Physics and Astronomy, University of Leicester, said: "Almost every galaxy has an enormously massive black hole in its center. Our own galaxy, the Milky Way, has one about four million times heavier than the sun. But some galaxies have black holes a thousand times heavier still. We know they grew very quickly after the Big Bang.''

"These hugely massive black holes were already full--grown when the universe was very young, less than a tenth of its present age."

Black holes grow by sucking in gas. This forms a disc around the hole and spirals in, but usually so slowly that the holes could not have grown to these huge masses in the entire age of the universe. `We needed a faster mechanism,' says Chris Nixon, also at Leicester, "so we wondered what would happen if gas came in from different directions."

Nixon, King and their colleague Daniel Price in Australia made a computer simulation of two gas discs orbiting a black hole at different angles. After a short time the discs spread and collide, and large amounts of gas fall into the hole. According to their calculations black holes can grow 1,000 times faster when this happens.

"If two guys ride motorbikes on a Wall of Death and they collide, they lose the centrifugal force holding them to the walls and fall," says King. The same thing happens to the gas in these discs, and it falls in towards the hole.

This may explain how these black holes got so big so fast. "We don't know exactly how gas flows inside galaxies in the early universe," said King, "but I think it is very promising that if the flows are chaotic it is very easy for the black hole to feed."

The two biggest black holes ever discovered are each about ten billion times bigger than the Sun.

Their research is due to published in the Monthly Notices of the Royal Astronomical Society. The research was funded by the UK Science and Technology Facilities Council.

Shiny New Tool for Imaging Biomolecules

At the heart of the immune system that protects our bodies from disease and foreign invaders is a vast and complex communications network involving millions of cells, sending and receiving chemical signals that can mean life or death. At the heart of this vast cellular signaling network are interactions between billions of proteins and other biomolecules. These interactions, in turn, are greatly influenced by the spatial patterning of signaling and receptor molecules. The ability to observe signaling spatial patterns in the immune and other cellular systems as they evolve, and to study the impact on molecular interactions and, ultimately, cellular communication, would be a critical tool in the fight against immunological and other disorders that lead to a broad range of health problems including cancer. Such a tool is now at hand.

Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley, have developed the first practical application of optical nanoantennas in cell membrane biology. A scientific team led by chemist Jay Groves has developed a technique for lacing artificial lipid membranes with billions of gold "bowtie" nanoantennas. Through the phenomenon known as "plasmonics," these nanoantennas can boost the intensity of a fluorescent or Raman optical signal from a protein passing through a plasmonic "hot-spot" tens of thousands of times without the protein ever being touched.

"Our technique is minimally invasive since enhancement of optical signals is achieved without requiring the molecules to directly interact with the nanoantenna," Groves says. "This is an important improvement over methods that rely on adsorption of molecules directly onto antennas where their structure, orientation, and behavior can all be altered."

Groves holds joint appointments with Berkeley Lab's Physical Biosciences Division and UC Berkeley's Chemistry Department, and is also a Howard Hughes Medical Institute investigator. He is the corresponding author of a paper that reports these results in the journal NanoLetters. The paper is titled "Single Molecule Tracking on Supported Membranes with Arrays of Optical Nanoantennas." Co-authoring the paper were Theo Lohmuller, Lars Iversen, Mark Schmidt, Christopher Rhodes, Hsiung-Lin Tu and Wan-Chen Lin.

Fluorescent emissions, in which biomolecules of interest are tagged with dyes that fluoresce when stimulated by light, and Raman spectroscopy, in which the scattering of light by molecular vibrations is used to identify and locate biomolecules, are work-horse optical imaging techniques whose value has been further enhanced by the emergence of plasmonics. In plasmonics, light waves are squeezed into areas with dimensions smaller than half-the-wavelength of the incident photons, making it possible to apply optical imaging techniques to nanoscale objects such as biomolecules. Nano-sized gold particles in the shape of triangles that are paired in a tip-to-tip formation, like a bow-tie, can serve as optical antennas, capturing and concentrating light waves into well-defined hot spots, where the plasmonic effect is greatly amplified. Although the concept is well-established, applying it to biomolecular studies has been a challenge because gold particle arrays must be fabricated with well-defined nanometer spacing, and molecules of interest must be delivered to plasmonic hot-spots.

"We're able to fabricate billions of gold nanoantennas in an artificial membrane through a combination of colloid lithography and plasma processing," Groves says. "Controlled spacing of the nanoantenna gaps is achieved by taking advantage of the fact that polystyrene particles melt together at their contact point during plasma processing. The result is well-defined spacing between each pair of gold triangles in the final array with a tip-to-tip distance between neighboring gold nanotriangles measuring in the 5-to-100 nanometer range."

Until now, Groves says, it has not been possible to decouple the size of the gold nanotriangles, which determines their surface plasmon resonance frequency, from the tip-to-tip distance between the individual nanoparticle features, which is responsible for enhancing the plasmonic effect. With their colloidal lithography approach, a self-assembling hexagonal monolayer of polymer spheres is used to shadow mask a substrate for subsequent deposition of the gold nanoparticles. When the colloidal mask is removed, what remains are large arrays of gold nanoparticles and triangles over which the artificial membrane can be formed.

The unique artificial membranes, which Groves and his research group developed earlier, are another key to the success of this latest achievement. Made from a fluid bilayer of lipid molecules, these membranes are the first biological platforms that can combine fixed nanopatterning with the mobility of fluid bilayers. They provide an unprecedented capability for the study of how the spatial patterns of chemical and physical properties on membrane surfaces influence the behavior of cells.

"When we embed our artificial membranes with gold nanoantennas we can trace the trajectories of freely diffusing individual proteins as they sequentially pass through and are enhanced by the multiple gaps between the triangles," Groves says. "This allows us to study a realistic system, like a cell, which can involve billions of molecules, without the static entrapment of the molecules."

As molecules in living cells are generally in a state of perpetual motion, it is often their movement and interactions with other molecules rather than static positions that determine their functions within the cell. Groves says that any technique requiring direct adsorption of a molecule of interest onto a nanoantenna intrinsically removes that molecule from the functioning ensemble that is the essence of its natural behavior. The technique he and his co-authors have developed allows them to look at individual biomolecules but within the context of their surrounding community.

"The idea that optical nanoantennas can produce the kinds of enhanced signals we are observing has been known for years but this is the first time that nanoantennas have been fabricated into a fluid membrane so that we can observe every molecule in the system as it passes through the antenna array," Groves says. "This is more than a proof-of-concept we've shown that we now have a useful new tool to add to our repertoire."

This research was primarily supported by the DOE Office of Science.

Laser Hints at How Universe Got Its Magnetism

Scientists have used a laser to create magnetic fields similar to those thought to be involved in the formation of the first galaxies; findings that could help to solve the riddle of how the Universe got its magnetism.

Magnetic fields exist throughout galactic and intergalactic space, what is puzzling is how they were originally created and how they became so strong.

A team, led by Oxford University physicists, used a high-power laser to explode a rod of carbon, similar to pencil lead, in helium gas. The explosion was designed to mimic the cauldron of plasma -- an ionized gas containing free electrons and positive ions -- out of which the first galaxies formed.

The team found that within a microsecond of the explosion strong electron currents and magnetic fields formed around a shock wave. Astrophysicists took these results and scaled them through 22 orders-of-magnitude to find that their measurements matched the 'magnetic seeds' predicted by theoretical studies of galaxy formation.

A report of the research is published in a recent issue of the journal Nature.

'Our experiment recreates what was happening in the early Universe and shows how galactic magnetic fields might have first appeared,' said Dr Gianluca Gregori of Oxford University's Department of Physics, who led the work at Oxford. 'It opens up the exciting prospect that we will be able to explore the physics of the cosmos, stretching back billions of years, in a laser laboratory here on Earth.'

The results closely match theories which predict that tiny magnetic fields -- 'magnetic seeds' -- precede the formation of galaxies. These fields can be amplified by turbulent motions and can strongly affect the evolution of the galactic medium from its early stages.

Dr Gregori said: 'In the future, we plan to use the largest lasers in the world, such as the National Ignition Facility at the Lawrence Livermore National Laboratory in California (USA), to study the evolution of cosmic plasma.'

The experiments were conducted at the Laboratoire pour l'Utilisation de Lasers Intenses laser facility in France.

Materials Inspired by Mother Nature: One-Pound Boat That Could Float 1,000 Pounds

Combining the secrets that enable water striders to walk on water and give wood its lightness and great strength has yielded an amazing new material so buoyant that, in everyday terms, a boat made from 1 pound of the substance could carry five kitchen refrigerators, about 1,000 pounds.

One of the lightest solid substances in the world, which is also sustainable, it was among the topics of a symposium in San Diego March 25 at the 243rd National Meeting & Exposition of the American Chemical Society, the world's largest scientific society. The symposium focused on an emerging field called biomimetics, in which scientists literally take inspiration from Mother Nature, probing and adapting biological systems in plants and animals for use in medicine, industry and other fields.

Olli Ikkala, Ph.D., described the new buoyant material, engineered to mimic the water strider's long, thin feet and made from an "aerogel" composed of the tiny nano-fibrils from the cellulose in plants. Aerogels are so light that some of them are denoted as "solid smoke." The nanocellulose aerogels also have remarkable mechanical properties and are flexible.

"These materials have really spectacular properties that could be used in practical ways," said Ikkala. He is with Helsinki University of Technology in Espoo, Finland. Potential applications range from cleaning up oil spills to helping create such products as sensors for detecting environmental pollution, miniaturized military robots, and even children's toys and super-buoyant beach floats.

Ikkala's presentation was among almost two dozen reports in the symposium titled, "Cellulose-Based Biomimetic and Biomedical Materials," that focused on the use of specially processed cellulose in the design and engineering of materials modeled after biological systems. Cellulose consists of long chains of the sugar glucose linked together into a polymer, a natural plastic-like material. Cellulose gives wood its remarkable strength and is the main component of plant stems, leaves and roots. Traditionally, cellulose's main commercial uses have been in producing paper and textiles -- cotton being a pure form of cellulose. But development of a highly processed form of cellulose, termed nanocellulose, has expanded those applications and sparked intense scientific research. Nanocellulose consists of the fibrils of nanoscale diameters so small that 50,000 would fit across the width of the period at the end of this sentence.

"We are in the middle of a Golden Age, in which a clearer understanding of the forms and functions of cellulose architectures in biological systems is promoting the evolution of advanced materials," said Harry Brumer, Ph.D., of Michael Smith Laboratories, University of British Columbia, Vancouver. He was a co-organizer of the symposium with J. Vincent Edwards, Ph.D., a research chemist with the Agricultural Research Service, U.S. Department of Agriculture in New Orleans, Louisiana. "This session on cellulose-based biomimetic and biomedical materials is really very timely due to the sustained and growing interest in the use of cellulose, particularly nanoscale cellulose, in biomaterials."

Ikkala pointed out that cellulose is the most abundant polymer on Earth, a renewable and sustainable raw material that could be used in many new ways. In addition, nanocellulose promises advanced structural materials similar to metals, such as high-tech spun fibers and films.

"It can be of great potential value in helping the world shift to materials that do not require petroleum for manufacture," Ikkala explained. "The use of wood-based cellulose does not influence the food supply or prices, like corn or other crops. We are really delighted to see how cellulose is moving beyond traditional applications, such as paper and textiles, and finding new high-tech applications."

One application was in Ikkala's so-called "nanocellulose carriers" that have such great buoyance. In developing the new material, Ikkala's team turned nanocellulose into an aerogel. Aerogels can be made from a variety of materials, even the silica in beach sand, and some are only a few times denser than air itself. By one estimate, if Michelangelo's famous statue David were made out of an aerogel rather than marble, it would be less than 5 pounds.

The team incorporated into the nanocellulose aerogel features that enable the water strider to walk on water. The material is not only highly buoyant, but is capable of absorbing huge amounts of oil, opening the way for potential use in cleaning up oil spills. The material would float on the surface, absorbing the oil without sinking. Clean-up workers, then, could retrieve it and recover the oil.

The American Chemical Society is a non-profit organization chartered by the U.S. Congress. With more than 164,000 members, ACS is the world's largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.

Single Molecules in a Quantum Movie

The quantum physics of massive particles has intrigued physicists for more than 80 years, since it predicts that even complex particles can exhibit wave-like behaviour -- in conflict with our everyday ideas of what is real or local. An international team of scientists now succeeded in shooting a movie which shows the build-up of a matter-wave interference pattern from single dye molecules which is so large (up to 0.1 mm) that you can easily see it with a camera. This visualizes the dualities of particle and wave, randomness and determinism, locality and delocalization in a particularly intuitive way.

A quantum premiere with dye molecules as leading actors

Physicist Richard Feynman once claimed that interference effects caused by matter-waves contain the only mystery of quantum physics. Understanding and applying matter waves for new technologies is also at the heart of the research pursued by the Quantum Nanophysics team around Markus Arndt at the University of Vienna and the Vienna Center for Quantum Science and Technology.

The scientists now premiered a movie which shows the build-up of a quantum interference pattern from stochastically arriving single phthalocyanine particles after these highly-fluorescent dye molecules traversed an ultra-thin nanograting. As soon as the molecules arrive on the screen the researchers take live images using a spatially resolving fluorescence microscope whose sensitivity is so high that each molecule can be imaged and located individually with an accuracy of about 10 nanometers. This is less than a thousandth of the diameter of a human hair and still less than 1/60 of the wavelength of the imaging light.

A breath of nothing

In these experiments van der Waals forces between the molecules and the gratings pose a particular challenge. These forces arise due to quantum fluctuations and strongly affect the observed interference pattern. In order to reduce the van der Waals interaction the scientists used gratings as thin as 10 nanometers (only about 50 silicon nitride layers). These ultra-thin gratings were manufactured by the nanotechnology team around Ori Cheshnovski at the Tel Aviv University who used a focused ion beam to cut the required slits into a free-standing membrane.

Tailored nanoparticles

In this study the experiments could be extended to phthalocyanine heavier derivatives which were tailor-made by Marcel Mayor and his group at the University of Basel. They represent the most massive molecules in quantum far-field diffraction so far.

Motivation and continuation

The newly developed and combined micro- and nanotechnologies for generating, diffracting and detecting molecular beams will be important for extending quantum interference experiments to more and more complex molecules but also for atom interferometry.

The experiments have a strongly didactical component: they reveal the single-particle character of complex quantum diffraction patterns on a macroscopic scale that is visible to the eye. You can see them emerge in real-time and they last for hours on the screen. The experiments thus render the wave-particle duality of quantum physics particularly tangible and conspicuous.

The experiments have a practical side, too. They allow to access molecular properties close to solid interfaces and they show a way towards future diffraction studies at atomically thin membranes.

Seeing is believing: the movie by Thomas Juffmann et al. is published on March 25 in Nature Nanotechnology. This project was supported by the Austrian FWF Z149-N16 (Wittgenstein), ESF/FWF/SNF MIME (I146) and the Swiss SNF in the NCCR "Nanoscale Science."