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Aircraft Biosensor Detects Pathogens in Flight January 2008
In 2006, more than 720 million passengers flew to and within the U.S. on over 30 million flights that moved through more than 62 hub airports. Unfortunately, many of those passengers carried more than just luggage—some of them brought illnesses that can spread during the journey. With easy access to air travel by just about anybody, the danger of infectious diseases crossing borders via air travelers is a real threat. The danger of international disease transmission was highlighted in March 2003 when 22 out of 120 passengers were infected by Severe Acute Respiratory Syndrome (SARS) during a three-hour flight from Hong Kong to Beijing. The SARS outbreak of 2002-2003 affected five continents and 18 countries and resulted in 774 fatalities. The economic impact on Asia alone was $11 billion. By chance, SARS didn't spread to the United States. Closer to home, however, Andrew Speaker created an international scare in spring 2007 when he traveled from Greece to the U.S. by first going to Canada and without alerting border officials that he had a rare variety of tuberculosis originally thought to be extremely drug-resistant. These types of incidents show that you can't always rely on airline passengers to know about the status of their own health—or to make the right decisions when they do. To protect the health of travelers, more must be done using onboard technology.
In 2006, a study by the National Research Council evaluated two types of systems to counter bio-threats in airlines: a continuous air decontamination system for the near-term and a detect-to-prevent system for the longer term. As a feasibility study, MITRE is addressing the detect-to-prevent system, which would discover infectious diseases and assist with containment strategies. In the study, our researchers are exploring the use of a miniature biosensor system that can be placed at strategic locations throughout an aircraft. MITRE has been expanding its work in this area for some time—see "MITRE's Work in Biosecurity," below. Safeguarding the Nation's Health "Designing a biosensor system for homeland security, as well as for the health of the nation in general, is a complex project," says Richard Sciambi, chief engineer for the Center for Enterprise Modernization (CEM), a federally funded research and development center (FFRDC) managed by MITRE. "We're using our expertise in bioengineering to design the sensor. And because the sensor is one part of a larger system, we'll be using our core experience in systems engineering to develop a total solution." That expertise will be pulled from all parts of the company. "The Federal Aviation Administration [FAA] doesn't have the technical resources in-house for this particular problem, so we're able to help," adds Andy Lacher, a senior principal systems engineer for the Center for Advanced Aviation System Development (CAASD), an FFRDC managed by MITRE for the FAA. "We try to anticipate potential sponsor needs, so this research is right on target. We're collaborating with an FAA Center of Excellence for Air Cabin Environmental Research [ACER] group along with industry and academia." A Four-Pronged Attack Detecting pathogens on an aircraft involves developing and combining
innovations in four research areas:
"It's a tough problem, but the kind of work that MITRE does," says Glenn Roberts, chief engineer for CAASD. "We have a long history of working in sensors and we're also tapping into a lot of our new expertise in biology and biotechnology." To bring together the many aspects of the sensor design, Grace Hwang, CEM's lead biosensors scientist, is directing a team of scientists and engineers in systems analysis, device integration, sensor prototyping, model building, and infrastructure development. MITRE is also collaborating with a network of 10 institutions, including the University of Massachusetts Lowell, Harvard University, Auburn University, University of California San Diego, NASA's Jet Propulsion Laboratory, and Kansas State University. Detecting Bugs During Flight Although sensors and analysis techniques that can detect pathogens in air samples already exist, many systems give false alarms about once every 100 tests. "If the system we envision is to be deployable, the biosensor will have to operate at very high fidelity and have a very low probability of false alarm," says Hwang. "We're aiming for one false alarm per million flights." Another problem with current sensors is that getting results can take up to a week—much too slow for airline passengers. The research is aimed at detecting a threat while the aircraft is still enroute to its destination. It's likely that multiple biosensors would be placed throughout the aircraft to optimize detection probabilities and minimize false alarms. The MITRE team will study how air flows in an airplane cabin, how to collect and concentrate the air, and how to extract the pathogens so the sensors can be tested enroute in the future. Hwang notes that before pilots start warning a destination airport of the presence of an incoming bio-threat, the sensor system must be reliable, rapid, small, and relatively inexpensive. With today's technology, the sensor is expected to be about 4-inches long x 4-inches wide x 3-inches thick in its final form. Hwang is developing an optics-based sensor in collaboration with biologist Elaine Mullen and biomedical engineer Songeeta Palchaudhuri. The sensor is based on a design by Lin Pang and Yeshaiahu Fainman, UC San Diego.
The sensor detects the presence of a pathogen by monitoring how a polarized laser beam interacts with a gold-coated surface that's perforated with nanoholes. The gold-coated surface is in a tiny chamber, which allows a fluid containing the suspected pathogen to flow over the surface. Because gold is a highly conductive metal, the electrons at its surface are mobile and not strongly attached to individual atoms or molecules. The laser beam, through electromagnetic coupling, interacts with the mobile electrons, creating surface plasmon polaritons (SPPs). These SPPs can be thought of as waves that ripple across the gold surface much like waves propagate across the surface of a pond when a stone is thrown into it. Nanohole Spacing is Critical The amount of electromagnetic coupling between the laser energy and the SPPs reaches an optimal point when the distance between the nanoholes matches the laser beam's wavelength. Once there is optimal coupling, the liquid with suspected pathogens is flowed over the gold layer. When a pathogen binds to the surface, there is a shift in the optimal coupling at the gold-liquid interface. The change in the shift can be converted to a concentration that tells you how much of a specific pathogen is present. Introducing a specific pathogen to the sensor is another part of the problem. Currently, the device takes advantage of a biological phenomenon where complex sugars on proteins called glycoproteins bind to bacteria and viruses. The UC San Diego researchers helped analyze surrogates of pathogens in solution form that are conveyed over a layer of custom-designed glycoproteins attached to the gold surface. When a target pathogen such as avian influenza comes in contact with the glycoprotein layer, for example, adhesive structures studding the surface of the pathogen bind to complementary sugars. Again, the binding of virus particles to the gold surface changes the optimal coupling point between the polarized laser light and the plasmons, and the shift in coupling measures how much pathogen is present. A major advantage of the sensor is that it can test for multiple pathogens at the same time. Currently, the biosensor requires a liquid solution to introduce test samples. The UC San Diego team has been assisting MITRE with experiments using liquid solutions. Later, the researchers will try to detect the presence of pathogens by using the air's own moisture, which eliminates the need to bring extra fluids onboard an aircraft. To get an idea of the sensor's sensitivity, an early-stage test will involve putting a small number of sensors in a short wind tunnel constructed by mechanical engineers Marc Pepi, Steve Mitchell, and Joe Giannetti. An atomized mist of a biological simulant will be pulled through the wind tunnel by a fan. Working at a facility at the University of Massachusetts Lowell, the team, alongside university colleagues, will measure airflow velocity, humidity, temperature, and particle sizes to see how the sensor is affected by different variables. Collecting Airborne Particles Another part of the project involves the study of collection methods for airborne particles, because the output from the collector is also the input to the detector. Modeling the collector allows the team to test different collection strategies, including tradeoffs between efficiency for various particle sizes, concentration factors, and flow rates. Hwang and team members Matt Peterson, Michael Harkin, and Charles Laljer will apply the science of aerobiology—the study of how bacteria, viruses, and droplets are spread through the air. Later on, the prototype sensors and particle collectors will be tested in a mock-up of an aircraft cabin at Kansas State University. After the team completes its first-year goals (demonstrating the feasibility of biodetection using aerosol technology and establishing error rates), the focus will turn to biological receptor molecules. When combined with multiple optical detection techniques, these receptor molecules help decrease the probability of false alarms. "I think it has a lot of promise," says CAASD's Roberts. "When we prove that an accurate sensor can be built affordably, then we'll want to see what sort of concept of operation would make sense and work on that with our government sponsors."
—by David A. Van Cleave Related Information Articles and News
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January 14, 2008 | Top of page
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