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MEETING NEWS Kris Christen reports from the Detector/Sensor Research and Technology for Homeland and National Security Workshop—Gatlinburg, Tenn.
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ZHIYU HU, ORNL
spread deployment is just a matter of time, Thundat says. And integration of these Terrorists currently enjoy a sensors onto chips sets the large economic advantage in stage for a rapid increase in their methods of attack, be it the number of sensors per chemical, biological, radiologidevice. This increase is akin cal, or explosive. But tiny meto Moore’s law, the obserchanical “noses” could shift this vation that the number of advantage back to law enforcetransistors on a semiconducment officials and countertertor chip doubles roughly rorism experts. every 18 months. In this Microelectromechanical sencase, Thundat predicts a sors fit the bill of an ideal sensor Moore’s law in homeland platform because they are inexdefense, with these sensors pensive and could be deployed becoming both more affordalmost anywhere, according to able and more complex. various workshop speakers. In Increased complexity will addition, their high sensitivity then allow researchers to (down to subparts-per-trillion make these sensors mimic levels), high selectivity, low the behavior of the nose. power consumption, real-time Just as humans don’t have response capability, and robustsensors for the scent of a ness meet many of the technical specific flower, for example, requirements laid out by the Micromachined cantilevers for atomic force microscopy, such as it won’t be necessary to deTransportation Security Adminthe one shown here, can be turned into sensitive chemical detecvelop a sensor for each comistration under the U.S. Depart- tors. ORNL researchers use cantilever arrays to simultaneously deplex chemical, Thundat exment of Homeland Security. tect multiple chemicals. plains. Instead, patterns in Oak Ridge National Laborathe simultaneous response of a large The sensitivity of detection is greatly tory (ORNL) was among the first facilinumber of different sensors could be enhanced because these tiny cantilevers ties to propose and develop such an apanalyzed to accurately determine the naproach, based on cantilever arrays, which bend easily as a consequence of minute ture of a specific threat. changes in surface stresses and their dehas been accepted by researchers worldAnd the future looks promising. flection can be detected by integrated wide, says Thomas Thundat, the ORNL Lawrence Bottomley of the Georgia piezoresistive or capacitive elements, physicist spearheading this work. The Institute of Technology presented reThundat explains. For such bending to principle is based on coatings that selecsearch at the workshop on plastic canbe obtained, one side of each cantilever tively bind a specific chemical, such as tilevers that would bring the cost down must be coated with a specific layer that an explosive or a poison gas, which can even further. Zhiyu Hu from ORNL binds the chemical in question; the dethen be detected. reported on efforts pushing the limits velopment of these materials is key to It’s not that chemical sensors based the success of this approach. Fortunate- of miniaturization to the point where on selective coatings haven’t existed bean entire sensor array could fit onto a ly, techniques similar to ink-jet printing fore. Conventional methods such as shirt button. But that’s not all. Accordcould eventually be used to efficiently quartz crystal microbalances and surface ing to Thundat, the real breakthrough mass-produce these coatings, Thundat acoustic wave devices rely on the same will come when someone, somewhere, adds. principle, Thundat notes. But compared discovers an approach for detecting Moreover, with a cost in the range of with these approaches, microcantilevers chemicals without chemistry. In other a few hundred dollars for a prototype are extremely small; hence, they can revapor sensor dubbed SniffEx, which can words, if there were a way for direct spond to much smaller amounts of a detection, the coatings that bind the detect and locate a variety of explosives, chemical and many more of them can be species wouldn’t be necessary. including plastic-based explosives, wideput together in a small integrated device. D E C E M B E R 1 , 2 0 0 4 / A N A LY T I C A L C H E M I S T R Y
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