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Gels featured in talk on sensors and detectors

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Specially designed gels that shrink or swell in response to factors like temperature and pH, and "molecular wires" to detect various chemicals were the subjects of two talks at the Sensors, Actuators and Detectors session of the Industrial Liaison Program's Research Directors Conference last week.

Gels are jello-like materials made of cross-linked networks of polymers that contain a fluid. In response to different environmental factors they can be made to contract or swell -- processes that correspond to the folding and unfolding of the polymer.

They can also be designed to detect and capture specific molecules. In the latter case, "the gel absorbs the target molecule when collapsed, and releases it when swollen," said Toyoichi Tanaka, the Otto and Jane Morningstar Professor of Physics. "We have made such a 'target recovery' system."

Professor Timothy M. Swager of chemistry described an approach to creating ultra-sensitive detectors for chemicals such as TNT. Traditional chemosensors, or individual molecular devices that can detect chemicals, are useful, but only to a point. "If you want to go to very, very low concentrations of the chemical of interest, it becomes much more difficult," he said.

His solution? "Hard-wire" individual chemosensor molecules together into a "molecular wire." This results in a much more sensitive device due to the "additive effects of all these different receptors," Professor Swager said. His team has developed several different types of molecular wires.

Also at the session, Professor Stephen D. Senturia talked about the remote detection of chemical agents, pollutants and other compounds using microelectrome-chanical systems (MEMS). The MEMS device he and his colleagues are developing is key to an advanced spectroscopy technique for detecting such compounds. Dr. Senturia is the Barton L. Weller Professor of Electrical Engineering.

Associate Professor Kenneth S. Breuer of the Department of Aeronautics and Astronautics concluded the session with a talk on "MEMS Sensors and Actuators for Measurement and Control of Flows."

A version of this article appeared in MIT Tech Talk on May 13, 1998.

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