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Electronic Nose that Knows

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Josephine Chang with the sensor chamber apparatus used to test the electronic nose. In previous work, Chang wove an electric textile that incorporated organic transistors.

Imagine that the milk in your refrigerator could sniff itself, changing the color of the carton if its contents were spoiled, or tiny sensors throughout an airport unobtrusively screened for explosives, replacing the bulky, expensive machines that contribute to security checkpoint traffic jams. UC Berkeley graduate student Josephine Chang is building just such an "electronic nose." Fabricated with a modified inkjet printer squirting organic electronic inks, the e-nose could potentially beat the sensitivity of today's commercial gas analyzers while costing tens of dollars instead of tens of thousands.

"Right now, electronic noses are so expensive that 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 Vivek Subramanian, a professor of electrical engineering and computer sciences. 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.

Researchers in Subramanian's laboratory and elsewhere have experimented with printable organic electronics to create ultra-low cost "smart tags" that promise to replace the ubiquitous UPC bar code on products. Subramanian has also made headway on inexpensive plastic displays that could be rolled up. Still, a great many hurdles remain before organic electronics can provide the fast switching and high flow of current necessary for those applications. According to Chang though, the electronic nose technology is "very forgiving of organics' weaknesses."

"One challenge with organic electronics is they're very sensitive to their environments," she says. "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."

A microscope image of an organic thin film transistor sensor that the researchers printed using conductive ink. [view larger image]

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."

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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 with 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 PhD later this year, she'll move to the East Coast to join IBM's famed Watson Research Center.

Vivek Subramanian's Organic Electronics Group

"Organic Transistors and the Death of the Bar Code" by David Pescovitz (Lab Notes, Feb/March 2002)

"Dry Clean Only?: Josephine Chang (née Lee) and electronic textiles

Professor Jean M.J. Fréchet's home page

Center for Entrepreneurship & Technology

Lab Notes is published online by the Marketing and Communications Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow.

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