Key to Safer Remote Detection of Dangerous Materials

Clough, a student in the Department of Electrical, Computer, and Systems Engineering at Rensselaer, is one of three finalists for the 2011$30,000 Lemelson-MIT Rensselaer Student Prize.  Clough's project is titled"Terahertz Enhanced Acoustics," and his faculty adviser is Xi-Cheng Zhang, the J. Erik Jonsson Professor of Science at Rensselaer and director of the university's Center for Terahertz Research.

The Rensselaer Center for Terahertz Research is one of the most active groups worldwide to apply terahertz wave technology for security and defense applications. Sensors using terahertz waves can penetrate packaging materials or clothing and identify the unique terahertz"fingerprints" of many hidden materials. Terahertz waves occupy a large segment of the electromagnetic spectrum between the infrared and microwave bands. Unlike X-rays and microwaves, terahertz radiation is very low energy and poses no known health threat to humans.

A key practical limitation of terahertz technology, however, is that it only works over short distances. Naturally occurring moisture in air absorbs terahertz waves, weakening the signal and sensing capabilities. This distance limitation is not ideal for applications in bomb or hazardous material detection, where the human operator wants to be as far away as possible from the potential threat.

Clough's patent-pending solution to this problem is a new method for using sound waves to remotely"listen" to terahertz signals from a distance. Focusing two laser beams into air creates small bursts of plasma, which in turn create terahertz pulses. Another pair of lasers is aimed near the target of interest to create a second plasma for detecting the terahertz pulses after they have interacted with the material. This detection plasma produces acoustic waves as it ionizes the air. Clough discovered that by using a sensitive microphone to"listen" to the plasma, he could detect terahertz wave information embedded in these sound waves. This audio information can then be converted into digital data and instantly checked against a library of known terahertz fingerprints, to determine the chemical composition of the mystery material.

So far, Clough has successfully demonstrated the ability to use acoustics to identify the terahertz fingerprints from several meters away. He has separately demonstrated plasma acoustic detection from 11 meters, limited only by available lab space. Along with the increased distance from the potentially hazardous material, an additional advantage is that his system does not require a direct line of sight to collect signals, as the microphone can still capture the audio information. Potential applications of Clough's invention, which circumvents the fundamental limitations of remote terahertz spectroscopy, include environmental monitoring of atmospheric conditions, monitoring smokestack emissions, inspecting suspicious packages, or even detecting land mines -- all from a safe distance.

Clough has presented his findings at several international conferences, and the details of his work have been published inOptics LettersandPhysical Review E.His new method for terahertz sensing has created the possibility to obtain terahertz spectroscopic information from a distance, bypassing a key limitation of high terahertz absorption by water vapor in air.

A National Science Foundation Integrative Graduate Education and Research Traineeship (IGERT) fellow, Clough is deeply committed to his research activities.

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Advanced NASA Instrument Gets Close-Up on Mars Rocks

The Alpha Particle X-Ray Spectrometer (APXS) instrument, designed by physics professor Ralf Gellert of the University of Guelph in Ontario, Canada, uses the power of alpha particles, or helium nuclei, and X-rays to bombard a target, causing the target to give off its own characteristic alpha particles and X-ray radiation. This radiation is"read by" an X-ray detector inside the sensor head, which reveals which elements and how much of each are in the rock or soil.

Identifying the elemental composition of lighter elements such as sodium, magnesium or aluminum, as well as heavier elements like iron, nickel or zinc, will help scientists identify the building blocks of the Martian crust. By comparing these findings with those of previous Mars rover findings, scientists can determine if any weathering has taken place since the rock formed ages ago.

All NASA Mars rovers have carried a similar instrument -- Pathfinder's rover Sojourner, Spirit and Opportunity, and now Curiosity, too. Improvements have been made with each generation, but the basic design of the instrument has remained the same.

"APXS was modified for Mars Science Laboratory to be faster so it could make quicker measurements. On the Mars Exploration Rovers {Spirit and Opportunity} it took us five to 10 hours to get information that we will now collect in two to three hours," said Gellert, the instrument's principal investigator."We hope this will help us to investigate more samples."

Another significant change to the next-generation APXS is the cooling system on the X-ray detector chip. The instruments used on Spirit and Opportunity were able to take measurements only at night. But the new cooling system will allow the instrument on Curiosity to take measurements during the day, too.

The main electronics portion of the tissue-box-sized instrument lives in the rover's body, while the sensor head, the size of a soft drink can, is mounted on the robotic arm. With the help of Curiosity's remote sensing instruments -- the Chemistry and Camera (ChemCam) instrument and the Mastcam -- the rover team will decide where to drive Curiosity for a closer look with the instruments, including APXS. Measurements are taken with the APXS by deploying the sensor head to make direct contact with the desired sample.

The rover's brush will be used to remove dust from rocks to prepare them for inspection by APXS and by MAHLI, the rover's arm-mounted, close-up camera. Whenever promising samples are found, the rover will then use its drill to extract a few grains and feed them into the rover's analytical instruments, SAM and CheMin, which will then make very detailed mineralogical and other investigations.

Scientists will use information from APXS and the other instruments to find the interesting spots and to figure out the present and past environmental conditions that are preserved in the rocks and soils.

"The rovers have answered a lot of questions, but they've also opened up new questions," said Gellert."Curiosity was designed to pick up where Spirit and Opportunity left off."

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Science Laboratory mission for the NASA Science Mission Directorate, Washington.

For more information about the mission, visithttp://mars.jpl.nasa.gov/msl/. To watch the spacecraft being assembled and tested, visithttp://www.ustream.tv/nasajpl.

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Sentries in the Garden Shed: Plants That Can Detect Environmental Contaminants, Explosives

The stuff of science fiction you say? Not so, says a Colorado State University biologist whose research is funded in part by Homeland Security's Science and Technology Directorate (DHS S&T), as well as by the Defense Advanced Research Projects Agency (DARPA), the Office of Naval Research (ONR), and others.

Dr. June Medford and her team in the Department of Biology at Colorado State have shown that plants can serve as highly specific sentries for environmental pollutants and explosives. She's enabled a computer-designed detection trait to work in plants. How? By rewiring the plant's natural signaling process so that a detection of the bad stuff results in the loss of green color.

Based on research so far, Medford says the detection abilities of some plants (tobacco is an example) are similar to, or even better, than those of a dog's snout, long the hallmark of a good detector. Best of all, the training time is nothing compared to that of a dog.

"The idea comes directly from nature," Medford said."Plants can't run or hide from threats, so they've developed sophisticated systems to detect and respond to their environment. We've 'taught' plants how to detect things we're interested in and respond in a way anyone can see, to tell us there is something nasty around, by modifying the way the plant's proteins process chlorophyll. Our system, with improvements, may allow plants to serve as a simple and inexpensive means to monitor human surroundings for substances such as pollutants, explosives, or chemical agents."

The detection traits could be used in any plant and could detect multiple pollutants at once -- changes that can also be detected by satellite. While visible change in the plant is apparent after a day, the reaction can be remotely sensed within a couple of hours. A spectral imaging system designed specifically for the detection of de-greening biosensors would provide the fastest indication of a threat detected by the plants.

Computational design of the detection trait was initially done in collaboration with Professor Homme Hellinga at Duke University, and more recently with Professor David Baker at the University of Washington. The Baker and Hellinga laboratories used a computer program to redesign naturally-occurring proteins called receptors. These redesigned receptors specifically recognize a pollutant or explosive. Medford's lab then modifies these computer redesigned receptors to function in plants, and targets them to the plant cell wall where they can recognize pollutants or explosives in the air or soil near the plant. Once the substance is detected, an internal signal causes the plant to turn white.

Medford and her team want to speed up detection time. The initial or first-generation plants respond to an explosive in hours, but improvements are underway to reduce the response time to just a few minutes. A faster response time increases the likelihood of identifying the threat and preventing an attack.

"At this point in the research, it takes hours to achieve a visible change in the foliage," says Doug Bauer, DHS S&T's program manager on the research."Ideally, we'd want the reaction to be considerably faster." In addition to faster response times, Bauer says, in the next generation of the research, the indicators may take place in a non-visible spectrum, such as infrared, by using color-changing methods other than the suppression of chlorophyll. That way, law enforcement equipped with the appropriate sensors would be alerted, but a terrorist would not be tipped off.

A decentralized, ubiquitous detection capability could allow the early detection of bomb-manufacturing sites, instead of waiting for a potential bomber to show up at a transportation hub or other target zone.

There are still many, many years of research to go before any possible deployment of plant sentinels. Once the research achieves a point where it may be possible to deploy, there are other considerations that will have to be taken into account and additional studies to be conducted. For example, USDA regulations stipulate that genetically-altered plants must go through a rigorous study on their impact to and interaction with the environment before they can be cultivated or planted in the United States.

This work could eventually be used for a wide range of applications such as security in airports or monitoring for pollutants such as radon, a carcinogenic gas that can be found in basements. Harnessing plants as bio-sensors allows for distributed sensing without the need for a power supply."One day, plants may assist law enforcement officers in detecting meth labs or help emergency responders determine where hazardous chemicals are leaking," Bauer says."The fact that DoD, DHS and a variety of other agencies contributed to funding this research is an indicator of the breadth of possibilities."

Financial support for this research was provided by the Defense Advanced Research Projects Agency (DARPA), the Office of Naval Research (ONR), the Bioscience Discovery Evaluation Grant Program through the Colorado Office of Economic Development and International Trade, the National Science Foundation (NSF), Department of Homeland Security Science and Technology Directorate (DHS S&T), and Gitam Technologies. Most recently, Medford and her team received a three-year,$7.9 million grant from the DoD's Defense Threat Reduction Agency.

The research from Medford's team appeared in the peer-reviewed journalPLoS ONE.

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Scientists Elevate Warfighter Readiness Against Invisible Threats

A research team, led by Drs. Joshua Caldwell and Orest Glembocki, scientists at the U.S. Naval Research Laboratory, Electronic Science and Technology Division, has overcome this limitation with surface enhanced Raman scattering (SERS) using optically stimulated plasmon oscillations in nanostructured substrates.

Shown to provide enhancements of the Raman signal, large-area gold (Au) coated silicon (Si) nanopillar arrays are over 100 million times (10⁸) more sensitive than Raman scattering sensing alone, while maintaining a very uniform response with less than 30 percent variability across the sensor area.

"These arrays are over an order-of-magnitude more sensitive than the best reported SERS sensors in the literature and the current state-of-the-art large-area commercial SERS sensors," said Caldwell."These arrays can be a key component of fully integrated, autonomously operating chemical sensors that detect, identify and report the presence of a threat at trace levels of exposure."

Raman devices use laser light to excite molecular vibrations, which in turn causes a shift in the energy of the scattered laser photons, up or down, creating a unique visual pattern. In the case of trace amounts of molecules in gases or liquids, detection through ordinary Raman scattering is virtually impossible. However, the Raman signal can be enhanced via the SERS effect using metal nanoparticles.

Despite surface-enhanced Raman scattering being first observed in the late 1970s, efforts to provide reproducible SERS-based chemical sensors has been hindered by the inability to make large-area devices with a uniform SERS response. The ability to reproducibly pattern nanometer-sized particles in periodic arrays has finally allowed this requirement to be met.

"While many tools are currently available to detect trace amounts of chemical warfare and biological agents and explosive compounds, a device using SERS can be used to identify these minute quantities of the chemicals of interest by providing a 'fingerprint' of the material, which all but eliminates the prevalence of false alarms," says Glembocki.

SERS offers several potential advantages over other spectroscopic techniques because of its measurement speed, high sensitivity, portability, and simple maneuverability. SERS can additionally be used to enhance existing Raman technologies, such as the hand held and standoff units that are already in use in field applications.

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'Air Laser' May Sniff Bombs, Pollutants from a Distance

"We are able to send a laser pulse out and get another pulse back from the air itself," said Richard Miles, a professor of mechanical and aerospace engineering at Princeton, the research group leader and co-author on the paper."The returning beam interacts with the molecules in the air and carries their finger prints."

The new technique differs from previous remote laser-sensing methods in that the returning beam of light is not just a reflection or scattering of the outgoing beam. It is an entirely new laser beam generated by oxygen atoms whose electrons have been"excited" to high energy levels. This"air laser" is a much more powerful tool than previously existed for remote measurements of trace amounts of chemicals in the air.

The researchers, whose work is funded by the Office of Naval Research's basic research program on Sciences Addressing Asymmetric Explosive Threats, published their new method Jan. 28 in the journalScience.

Miles collaborated with three other researchers: Arthur Dogariu, the lead author on the paper, and James Michael of Princeton, and Marlan Scully, a professor with joint appointments at Princeton and Texas A&M University.

The new laser sensing method uses an ultraviolet laser pulse that is focused on a tiny patch of air, similar to the way a magnifying glass focuses sunlight into a hot spot. Within this hot spot -- a cylinder-shaped region just 1 millimeter long -- oxygen atoms become"excited" as their electrons get pumped up to high energy levels. When the pulse ends, the electrons fall back down and emit infrared light. Some of this light travels along the length of the excited cylinder region and, as it does so, it stimulates more electrons to fall, amplifying and organizing the light into a coherent laser beam aimed right back at the original laser.

Researchers plan to use a sensor to receive the returning beam and determine what contaminants it encountered on the way back.

"In general, when you want to determine if there are contaminants in the air you need to collect a sample of that air and test it," Miles said."But with remote sensing you don't need to do that. If there's a bomb buried on the road ahead of you, you'd like to detect it by sampling the surrounding air, much like bomb-sniffing dogs can do, except from far away. That way you're out of the blast zone if it explodes. It's the same thing with hazardous gases -- you don't want to be there yourself. Greenhouse gases and pollutants are up in the atmosphere, so sampling is difficult."

The most commonly used remote laser-sensing method, LIDAR -- short for light detection and ranging -- measures the scattering of a beam of light as it reflects off a distant object and returns back to a sensor. It is commonly used for measuring the density of clouds and pollution in the air, but can't determine the actual identity of the particles or gases. Variants of this approach can identify contaminants, but are not sensitive enough to detect trace amounts and cannot determine the location of the gases with much accuracy.

The returning beam is thousands of times stronger in the method developed by the Princeton researchers, which should allow them to determine not just how many contaminants are in the air but also the identity and location of those contaminants.

The stronger signal should also allow for detection of much smaller concentrations of airborne contaminants, a particular concern when trying to detect trace amounts of explosive vapors. Any chemical explosive emits various gases depending on its ingredients, but for many explosives the amount of gas is miniscule.

While the researchers are developing the underlying methods rather than deployable detectors, they envision a device that is small enough to be mounted on, for example, a tank and used to scan a roadway for bombs.

So far, the researchers have demonstrated the process in the laboratory over a distance of about a foot and a half. In the future they plan to increase the distance over which the beams travel, which they note is a straightforward matter of focusing the beam farther way. They also plan to fine-tune the sensitivity of the technique to identify small amounts of airborne contaminants.

In addition, the research group is developing other approaches to remote detection involving a combination of lasers and radar.

"We'd like to be able to detect contaminants that are below a few parts per billion of the air molecules," Miles said."That's an incredibly small number of molecules to find among the huge number of benign air molecules."

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Sensors to Detect Explosives, Monitor Food Being Developed

"There are many dangerous substances, pollutants and infectious bacteria we are constantly exposed to," said Rigoberto Advincula, a highly cited materials scientist at UH."Our work is poised to assist in such efforts as rapidly detecting explosives or banned substances in airports for homeland security, as well as monitoring commercial products like milk and pet food for substandard additive products. There is a need to measure this quantitatively and in a rapid manner."

In a two-stage effort on which a provisional patent has been filed, Advincula's team fabricated the polymer materials and then built a device that was used as a sensor. The work is based on what he calls"the artificial receptor concept." This is akin to an enzyme functioning as a biochemical catalyst within a cell, like an antibody, binding with specific molecules to produce a specific effect in the cell. The elements in Advincula's work, however, deal with metals and plastics and are called molecular imprinted polymers (MIP), a concept also used for making plastic antibodies. These polymers show a certain chemical affinity for the original molecule and can be used to fabricate sensors.

Based in electrochemistry, the films were prepared by electrodeposition, a process similar to electroplating used for metals in the automotive and metal industries. Their key innovation was to use a process called electropolymerization directly on a gold surface and attached to a digital read out. The group's next step is to put this film on portable devices, thus acting as sensors.

"Our materials and methods open up these applications toward portable devices and miniaturization. Our device will allow, in principle, the development of hand-held scanners for bomb detection or nerve agent detection in airports," Advincula said."This means accurate answers in a rapid manner without loss of time or use of complicated instruments. We can achieve very high sensitivity and selectivity in sensing. The design of our molecules and their fabrication methods have been developed in a simple, yet effective, manner."

The culmination of a year's work, the research being published simultaneously in three journals is a record for Advincula's group. These publications --Macromolecules, Applied Materials& Intefaces,andBiosensors& Bioelectronics- are among some of the most highly cited in this area of study.

Macromolecules is the most-cited journal on polymer science, and Applied Materials& Intefaces is an upcoming international forum for applied materials science and engineering. Both are put out by the American Chemical Society (ACS), which provides a comprehensive collection of well-cited, peer-reviewed journals in the chemical sciences. Biosensors& Bioelectronics is the principal international journal devoted to research, design, development and application of such devices and is published by Elsevier, one of the world's leading publishers of science and health information.

In the coming year, the researchers hope to expand the work to many other types of dangerous chemicals and also to proteins given off by pathogens. Ultimately, they plan to create portable hand-held devices for detection that will be made commercially available to the general public, as well as being of interest to the military. Advincula plans to seek additional funding and collaborators to reach these goals. Advincula currently has funding from the National Science Foundation and also works in collaboration with some companies.

Student success is another key element that Advincula emphasizes. In addition to becoming an ACS fellow last year, he received UH's undergraduate research mentoring award and is particularly committed to student success in a materials discovery environment. He says there are few labs like his that have the capability to develop all the chemistry in concert with developing the device and doing the surface analysis all in one location. The set-up provides students a unique environment for discovery.

The two students working on this project who are being trained in his lab are Roderick Pernites and Ramakrishna Ponnapati. Pernites, who is finishing his Ph.D. this semester, recently received the ACS best poster award in the colloids division and currently has eight publications in Advincula's group. Ponnapati, who studied under Advincula and received his Ph.D. in 2009, is now a postdoctoral researcher in UH's department of chemical and biomolecular engineering and previously received a best student award with the Society of Plastic Engineers chapter in Houston.

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Hunt for Dark Matter Closes in at Large Hadron Collider

The scientists have now carried out the first full run of experiments that smash protons together at almost the speed of light. When these sub-atomic particles collide at the heart of the CMS detector, the resultant energies and densities are similar to those that were present in the first instants of the Universe, immediately after the Big Bang some 13.7 billion years ago. The unique conditions created by these collisions can lead to the production of new particles that would have existed in those early instants and have since disappeared.

The researchers say they are well on their way to being able to either confirm or rule out one of the primary theories that could solve many of the outstanding questions of particle physics, known as Supersymmetry (SUSY). Many hope it could be a valid extension for the Standard Model of particle physics, which describes the interactions of known subatomic particles with astonishing precision but fails to incorporate general relativity, dark matter and dark energy.

Dark matter is an invisible substance that we cannot detect directly but whose presence is inferred from the rotation of galaxies. Physicists believe that it makes up about a quarter of the mass of the Universe whilst the ordinary and visible matter only makes up about 5% of the mass of the Universe. Its composition is a mystery, leading to intriguing possibilities of hitherto undiscovered physics.

Professor Geoff Hall from the Department of Physics at Imperial College London, who works on the CMS experiment, said:"We have made an important step forward in the hunt for dark matter, although no discovery has yet been made. These results have come faster than we expected because the LHC and CMS ran better last year than we dared hope and we are now very optimistic about the prospects of pinning down Supersymmetry in the next few years."

The energy released in proton-proton collisions in CMS manifests itself as particles that fly away in all directions. Most collisions produce known particles but, on rare occasions, new ones may be produced, including those predicted by SUSY -- known as supersymmetric particles, or 'sparticles'. The lightest sparticle is a natural candidate for dark matter as it is stable and CMS would only 'see' these objects through an absence of their signal in the detector, leading to an imbalance of energy and momentum.

In order to search for sparticles, CMS looks for collisions that produce two or more high-energy 'jets' (bunches of particles travelling in approximately the same direction) and significant missing energy.

Dr Oliver Buchmueller, also from the Department of Physics at Imperial College London, but who is based at CERN, explained:"We need a good understanding of the ordinary collisions so that we can recognise the unusual ones when they happen. Such collisions are rare but can be produced by known physics. We examined some 3 trillion proton-proton collisions and found 13 'SUSY-like' ones, around the number that we expected. Although no evidence for sparticles was found, this measurement narrows down the area for the search for dark matter significantly."

The physicists are now looking forward to the 2011 run of the LHC and CMS, which is expected to bring in data that could confirm Supersymmetry as an explanation for dark matter.

The CMS experiment is one of two general purpose experiments designed to collect data from the LHC, along with ATLAS (A Toroidal LHC ApparatuS). Imperial's High Energy Physics Group has played a major role in the design and construction of CMS and now many of the members are working on the mission to find new particles, including the elusive Higgs boson particle (if it exists), and solve some of the mysteries of nature, such as where mass comes from, why there is no anti-matter in our Universe and whether there are more than three spatial dimensions.

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