Printed protection: Low-cost paper-based wireless sensor could help detect explosive devices

ScienceDaily (Oct. 27, 2011) — Researchers at the Georgia Institute of Technology have developed a prototype wireless sensor capable of detecting trace amounts of a key ingredient found in many explosives.

The device, which employs carbon nanotubes and is printed on paper or paper-like material using standard inkjet technology, could be deployed in large numbers to alert authorities to the presence of explosives, such as improvised explosive devices (IEDs).

"This prototype represents a significant step toward producing an integrated wireless system for explosives detection," said Krishna Naishadham, a principal research scientist who is leading the work at the Georgia Tech Research Institute (GTRI). "It incorporates a sensor and a communications device in a small, low-cost package that could operate almost anywhere."

Other types of hazardous gas sensors are based on expensive semiconductor fabrication and gas chromatography, Naishadham said, and they consume more power, require human intervention, and typically do not operate at ambient temperatures. Furthermore, those sensors have not been integrated with communication devices such as antennas.

The wireless component for communicating the sensor information -- a resonant lightweight antenna -- was printed on photographic paper using inkjet techniques devised by Professor Manos Tentzeris of Georgia Tech's School of Electrical and Computer Engineering. Tentzeris is collaborating with Naishadham on development of the sensing device.

The sensing component, based on functionalized carbon nanotubes (CNTs), has been fabricated and tested for detection sensitivity by Xiaojuan (Judy) Song, a GTRI research scientist. The device relies on carbon-nanotube materials optimized by Song.

A presentation on this sensing technology was given in July at the IEEE Antennas and Propagation Symposium (IEEE APS) in Spokane, Wash., by Hoseon Lee, a Ph.D. student in ECE co-advised by Tentzeris and Naishadham. The paper received the Honorable Mention Award in the Best Student Paper competition at the symposium.

This is not the first inkjet-printed ammonia sensor that has been integrated with an antenna on paper, said Tentzeris. His group produced a similar integrated sensor last year in collaboration with the research group of C.P. Wong, who is Regents professor and Smithgall Institute Endowed Chair in the School of Materials Science and Engineering at Georgia Tech.

"The fundamental difference is that this newest CNT sensor possesses dramatically improved sensitivity to miniscule ammonia concentrations," Tentzeris said. "That should enable the first practical applications to detect trace amounts of hazardous gases in challenging operational environments using inkjet-printed devices."

Tentzeris explained that the key to printing components, circuits and antennas lies in novel "inks" that contain silver nanoparticles in an emulsion that can be deposited by the printer at low temperatures -- around 100 degrees Celsius. A process called sonication helps to achieve optimal ink viscosity and homogeneity, enabling uniform material deposition and permitting maximum operating effectiveness for paper-based components.

"Ink-jet printing is low-cost and convenient compared to other technologies such as wet etching," Tentzeris said. "Using the proper inks, a printer can be used almost anywhere to produce custom circuits and components, replacing traditional clean-room approaches."

Low-cost materials -- such as heavy photographic paper or plastics like polyethylene terephthalate -- can be made water resistant to ensure greater reliability, he added. Inkjet component printing can also use flexible organic materials, such as liquid crystal polymer (LCP), which are known for their robustness and weather resistance. The resulting components are similar in size to conventional components but can conform and adhere to almost any surface.

Naishadham explained that the same inkjet techniques used to produce RF components, circuits and antennas can also be used to deposit the functionalized carbon nanotubes used for sensing. These nanoscale cylindrical structures -- about one-billionth of a meter in diameter, or 1/50,000th the width of a human hair -- are functionalized by coating them with a conductive polymer that attracts ammonia, a major ingredient found in many IEDs.

Sonication of the functionalized carbon nanotubes produces a uniform water-based ink that can be printed side-by-side with RF components and antennas to produce a compact wireless sensor node.

"The optimized carbon nanotubes are applied as a sensing film, with specific functionalization designed for a particular gas or analyte," Song said. "The GTRI sensor detects trace amounts of ammonia usually found near explosive devices, and it can also be designed to detect similar gases in household, healthcare and industrial environments at very low concentration levels."

The sensor has been designed to detect ammonia in trace amounts -- as low as five parts per million, Naishadham said.

The resulting integrated sensing package can potentially detect the presence of trace explosive materials at a distance, without endangering human lives. This approach, called standoff detection, involves the use of RF technology to identify explosive materials at a relatively safe distance. The GTRI team has designed the device to send an alert to nearby personnel when it detects ammonia.

The wireless sensor nodes require relatively low power, which could come from a number of technologies including thin-film batteries, solar cells or power-scavenging and energy-harvesting techniques. In collaboration with Tentzeris's and Wong's groups, GTRI is investigating ways to make the sensor operate passively, without any power consumption.

"We are focusing on providing standoff detection for those engaged in military or humanitarian missions and other hazardous situations," Naishadham said. "We believe that it will be possible, and cost-effective, to deploy large numbers of these detectors on vehicles or robots throughout a military engagement zone."

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The above story is reprinted from materials provided by Georgia Institute of Technology Research News. The original article was written by Rick Robinson.

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Using math and light to detect misshapen red blood cells

ScienceDaily (Oct. 31, 2011) — Misshapen red blood cells (RBCs) are a sign of serious illnesses, such as malaria and sickle cell anemia. Until recently, the only way to assess whether a person's RBCs were the correct shape was to look at them individually under a microscope -- a time-consuming process for pathologists. Now researchers from the University of Illinois at Urbana-Champaign (UIUC) have pioneered a technique that will allow doctors to ascertain the healthy shape of red blood cells in just a few seconds, by analyzing the light scattered off hundreds of cells at a time.

The team reports its results in the October issue of the Optical Society's (OSA) open-access journal Biomedical Optics Express.

A healthy RBC looks like a disc with a depression -- called a dimple -- in the top and bottom. Stressed RBCs often have deeper dimples than healthy ones, giving the cells a deflated look; others may have shallow dimples or no dimples at all. The UIUC researchers reasoned that if they shone light on a sample of blood and analyzed the light scattering off that sample, they would get a pattern -- a sort of signature produced by the way light interacts with itself in a three-dimensional space -- that would be different from the pattern collected from blood containing mostly misshapen cells. But these light-cell interactions were too complicated to analyze with the usual mathematical tools. So researchers made use of the Born approximation, a mathematical rule that can be used when the object of interest is small and transparent.

By running Fourier Transform Light Scattering (FTLS) -- a method developed by the same group three years ago -- on individual RBCs, the scientists found that the pattern changed significantly with the diameter and dimple width of the cells. Using this information, the UIUC team applied the Born approximation to their findings and calculated what the appropriate scattering signature for healthy cells should be. They then used this new "healthy cell signature" to identify the correct morphology of cells in a blood smear. The new technique may allow for faster, accurate blood tests that could help doctors diagnose various types of anemia, and could be especially useful in resource-poor areas of the world, the researchers say.

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Bartolomeo Della Ventura, Luigi Schiavo, Carlo Altucci, Rosario Esposito, Raffaele Velotta. Light assisted antibody immobilization for bio-sensing. Biomedical Optics Express, 2011; 2 (11): 3223 DOI: 10.1364/BOE.2.003223

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GPS stations can detect clandestine nuclear tests

ScienceDaily (June 8, 2011) — At the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), American researchers are unveiling a new tool for detecting illegal nuclear explosions: Earth's global positioning system (GPS).

Even underground nuclear tests leave their mark on the part of the upper atmosphere known as the ionosphere, the researchers discovered, when they examined GPS data recorded the same day as a North Korean nuclear test in 2009. Within minutes on that day, GPS stations in nearby countries registered a change in ionospheric electron density, as a bubble of disturbed particles spread out from the test site and across the planet.

"Its as if the shockwave from the underground explosion caused the earth to 'punch up' into the atmosphere, creating another shockwave that pushed the air away from ground zero," said Ralph von Frese, professor of earth sciences at Ohio State University and senior author on the study.

Jihye Park, a doctoral student in geodetic science at the university, is presenting the results of the study in a poster session at the CTBTO meeting in Vienna, Austria.

International authorities already possess several methods for detecting illegal nuclear tests, Park said. Seismic detectors pick up shockwaves through land, and acoustic sensors monitor for shockwaves through water and the air for tests that happen above ground. Chemical sensors detect airborne radioactive gas and dust as definitive evidence of a nuclear explosion. However, these particles may be lacking if the explosion is contained deeply below ground.

"GPS is a complement to these other methods, and can help confirm that a nuclear test has taken place -- especially when the test was underground, so that its effect in the air is very subtle, and otherwise nearly impossible to detect," she said.

While GPS was designed for location purposes, the technology has always been especially sensitive to atmospheric disturbances, said Dorota Grejner-Brzezinska, a professor of geodetic science at Ohio State and Park's advisor.

"GPS signals must pass from transmitters on satellites high above the planet down to ground-based receivers," Grejner-Brzezinska explained. "Air molecules -- more specifically, the electrons and other charged particles in the ionosphere -- interfere with the signal, generating position error. Part of our research concerns how to compensate for that vulnerability and make GPS work better. Jihye found a way to take that vulnerability and turn it into something useful."

Park wrote computer algorithms that search GPS signals for patterns indicating a sudden fluctuation in atmospheric electron density in specific locations, which is what happens when a shockwave pushes a bubble of air through the atmosphere. As the GPS signal passes through the edge of the bubble, the change in electron density disturbs the signal in a noticeable way.

Park was able to utilize data collected from GPS receivers that the International GNSS Service (IGS) has planted around the globe for research purposes. Five of the IGS receivers scattered in Eastern Asia provided data for this study, as did six receivers belonging to the South Korean GPS network.

When Park analyzed the data from the 11 GPS stations, she detected a sudden spike in atmospheric electron density after the May 25, 2009 underground test, which is believed to have happened just before 1:00 a.m. Coordinated Universal Time that day.

Within 25 minutes, the shockwave had traveled 225 miles to the nearest GPS station in the study, which was located in Inje County, in Gangwon Province, South Korea. That means that it was traveling through the air at 9 miles per minute, or 540 miles per hour. Within that first hour, it had reached all 11 stations.

Based on the timing of the shockwave, the researchers traced the origin of the explosion back to P'unggye, in Hamyong Province, North Korea. This finding agrees with seismic data from the event, which was collected by the CTBTO and the US Geological Survey.

The researchers will continue this work as Park earns her PhD, and they are seeking funding and partnerships to expand it further. In the meantime, they have submitted a paper on the discovery to the journal Geophysical Research Letters.

Collaborators on the study include Yu Morton, professor of electrical and computer engineering at Miami University in Oxford, Ohio, and Luis Gaya-Pique of CTBTO's On-Site Inspection Division.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Ohio State University. The original article was written by Pam Frost Gorder.

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