MEMS tongue mimics taste buds

By R. Colin Johnson
EE Times
(11/09/98, 3:31 p.m. EDT)

AUSTIN, Texas — An artificial tongue that can "taste" the chemicals in substances has been created by researchers at the University Of Texas here.

The researchers combined microelectromechanical systems (MEMS) with budding chemical-engineering technologies to create the tongue. It not only mimics the ability to classify flavors composed of sweet, sour, salt and bitter-as real tongues do-but also identifies the specific chemical elements, using a wide range of substance samples.

The artificial taste buds are mounted on a silicon chip using MEMS technology, with a CCD imager feeding data to a pattern-recognition learning algorithm. The National Institute of Health recently awarded the research group a $600,000 grant to develop the technology.

"We have combined the kind of MEMS technology used in the accelerometer of an airbag switch with microfluidics to make arrays of miniature test tubes where we can identify chemical substances in real-time," said electrical and computer engineering professor Dean Neikirk.

Neikirk had been developing the MEMS technology for pressure transducers and magnetic proximity sensors when he was approached by chemistry professor Eric Anslyn, who was identifying substances with tiny detection beads that change color. Chemists were mixing the beads in with the substance to be identified, but were having difficulty tracking them as they swirled around inside normal test tubes. Neikirk suggested putting the beads behind bars, in a silicon-chip-based "jail."

Since the beads change color to identify the substance under test, Neikirk suggested using a CCD camera to track the bead's color, along with pattern-recognition software to reveal the elements of the substance under test based on the color changes in the beads.

Neikirk calls his MEMS chip a jail because he attaches a wire mesh over an array of beads, each of which occupies an etched pit in the silicon chip. Typical arrays employ tens to hundreds of beads deposited in pits measuring about 100 microns across and spaced at about 500 microns apart to achieve a density of 100 sensors/mm2.

"The trick is to keep them in jail while they absorb the substance under test, because they swell up. We etch a pit shaped like an upside-down four-sided pyramid with sides at a 54° angle with the surface. We use a pick-and-place machine to put the beads in the pits, then attach a wire mesh over them that acts like bars on a jail door," said Neikirk.

For the prototype system, an inspection microscope is used to observe the change in color of the beads when milliliters of a test substance wash over its surface. Eventually the CCD will go on top of the chip, with tiny valves and pumps conducting picoliters of a test substance. Now, an off-the-shelf frame grabber captures the image of the artificial tongue, and humans inspect the color changes.

The group has applied for several patents for the artificial tongue and envisions industrial uses that range from screening new foods for "good taste" to testing blood samples and dangerous chemicals.

Researchers at the University of Texas at Austin have applied MEMS technology to chemical sensing.

All material on this site Copyright © 1998 CMP Media Inc. All rights reserved.

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