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March 20, 2006 Vol. 77, no. 10S
An electronic
nose that knows
Imagine if the milk in your refrigerator could sniff itself, changing the color of the carton if its contents were spoiled. EECS graduate student Josephine Chang is building just such an “electronic nose.” Fabricated with a modified inkjet printer that squirts organic electronic inks, the e-nose could potentially beat the sensitivity of today’s commercial gas analyzers at the cost of tens rather than tens of thousands of dollars. “Right now, electronic noses are so expensive they’re mainly used by the military or sometimes in industry,” Chang says. “But if we can significantly lower the cost, they could be everywhere, inside toasters, medicine cabinets, possibly even food packaging.” Chang is a graduate student in the research group of EECS associate professor Vivek Subramanian. Subramanian and his students are pioneers in organic electronics, a form of electronics that uses conductive polymers, or plastics, in lieu of inorganic materials such as the copper or silicon found in traditional circuits. Previously, the researchers have demonstrated an inkjet printer and family of electronic inks that can pattern circuits onto paper, plastic or cloth without damaging the material. “One challenge with organic electronics is that they’re very sensitive to their environments,” says Chang. “It’s hard to keep them stable in air. But using organics for sensors takes advantage of that sensitivity. It flips around a weakness and turns it into a strength.” The basic component in the electronic nose is an organic thin film transistor (OTFT). These are similar to transistors on a computer chip, only much larger and slower. Because the OTFT’s electrical properties change in the presence of certain compounds, the devices are well-suited for sensing applications. Furthermore, the organic transistors can be chemically altered to make them respond to different substances, alcohols or acids, for example. As a result, the researchers were able to print an array of sensors, each tuned to measure a particular kind of gas, onto a single piece of silicon. The “all-purpose” electronic nose can then be “trained” to identify a particular odor based on the signature response of the sensors. “It’s pattern recognition,” says Chang, who worked on the project with Subramanian, undergraduate student Vincent Liu, and a team led by College of Chemistry professor Jean Fréchet. “Apple pies may smell differently, but you can know the general pattern of the odor.” Last December, the electronic nose research won Chang and graduate students Brian Mattis and Steve Molesa a top prize in the Berkeley Technology Breakthrough Competition, sponsored by the Center for Entrepreneurship and Technology. The aim of the competition is to showcase high-impact science research and discoveries that have the potential to be commercialized within the next five years. Right now though, Chang isn’t planning to take the electronic nose to market. After earning her Ph.D. later this year, she’ll move to the East Coast to join IBM’s famed Watson Research Center.
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