From: The Washington Post, Monday, March 22, 1999, p. A09.

Original URL: http://www.washingtonpost.com/wp-srv/WPlate/1999-03/22/096l-032299-idx.html .


Artificial Tongue Has a Taste for Many Tasks

By Louis Jacobson
Special to The Washington Post
Monday, March 22, 1999; Page A09

AUSTIN—It looks more like a microchip than the organ we use for speaking, slurping and licking. In fact, the "artificial tongue" is no bionic spare part. But once it's perfected, researchers hope it will change fields as far-flung as medical diagnostics, food and pharmaceutical manufacturing and environmental cleanups.

Medical technicians could use the tongue to instantaneously "taste" blood samples for the prevalence of cholesterol--or glucose, or any of a thousand other bloodstream chemicals. Alternately, one could install electronic tongues in beverage production lines or chlorinated swimming pools to make sure--by "tasting"--that the liquids have precisely the right chemical balance, 24 hours a day.

The creators of the artificial tongue got their idea from researchers who created "artificial noses." "What impressed us about the artificial nose is that one could use fairly rudimentary chemical principles to create a system with a very sophisticated ability to measure odors," says John McDevitt, a University of Texas chemist and a co-designer of the artificial tongue. "We thought that was fantastic, but we realized there would be a bigger influence on society if we could do the same for liquid solutions." The reason, McDevitt says, is that more chemicals important to human activity are found in liquid form than in vapors.

"Ten years ago, people were thinking about" doing what McDevitt and his team are doing, said Richard McCullough, a Carnegie Mellon University chemist. "But no one had been able to deliver. They really made a quantum leap. What's nice about this is that their process has a very high sensitivity and is very selective."

Scientists have long been able to detect chemicals--even in minute concentrations--within other liquids. Technicians can isolate the natural components of blood using centrifuges--machines that spin a sample repeatedly at increasing speeds to separate out its components by weight. Or they can treat a liquid with a chemical known to produce a visible reaction if a desired chemical is present.

But the Texas scientists say these methods are labor-intensive and time-consuming. They're also narrow: Searching for each desired substance requires a different test. "Until now you haven't been able to test for three or 12 or 100 things in one simultaneous analysis," says biochemist Eric Anslyn, another team member. "This would be a major breakthrough."

The tongue starts as a small metal chip the size of a dime. The current generation of the chip is pitted with 100 holes--or, more precisely, holes in the form of inverted pyramids. Placed inside the inverted-pyramid shapes, and held snugly by a glass plate, are translucent, permeable beads made by engineer Dean Neikirk. The spherelike beads, formed from a plasticlike composite, are roughly the width of a human hair and as roly-poly as ball bearings.

Onto these spheres the team attaches specially made artificial taste buds--lots of them, as many as 1 trillion per sphere. The artificial taste buds are based on the principle that molecules can serve as receptors--that is, if the receptor molecule comes into contact with a particular target molecule, the two of them will bind together in a predictable, lock-and-key fashion. But rather than sending nerve signals to the brain, as natural buds would do, the artificial buds are wired so that they produce a detectable glow when a target molecule is found.

Some taste buds--typically those that detect salty, sweet, bitter and sour sensations--are relatively easy to fabricate by mimicking the chemistry of real human taste buds. But the kinds of substances the Texas team is most interested in, from cholesterol to chlorine to toxic chemicals, do not appear commonly enough in our diets to have spawned specialized human taste buds that recognize them.

So to "taste" these less-familiar flavors, the scientists have to create their own receptor molecules. "Molecular recognition" specialists, such as Anslyn, use computers to tailor workable receptors for molecules they want to target--designer taste buds, if you will. Then Anslyn mixes organic chemicals together, purifies them and creates and breaks molecular bonds using heat, chemical reactions and light.

"The challenge is creating these receptors," Anslyn says. "Sometimes they're quite difficult and time-consuming to create. But they're getting much faster, and although it's expensive to create the first one, once you've done that, they're cheap to produce. Once you've figured out the manufacturing process, it takes only two to three months to make the world supply."

To use the artificial tongue, a technician--or a continuous-process flowline--would inject a sample of liquid under the glass plate that holds the spheres in place. Due to capillary action, the sample liquid washes automatically over the buds, stimulating the proper receptor molecules and triggering them to glow. That glow is then picked up by a computer that monitors the chip.

"We can analyze a complex mixture very rapidly," says team member Jason B. Shear, an assistant professor of chemistry and biochemistry. "You can get simultaneous signals from the array nearly instantaneously. With the old separation procedures, you'd be waiting tens of minutes until the chemicals migrated out one at a time."

So far the team has synthesized rudimentary taste buds for sweetness (which detect sugars), sourness (which sense acidity) and water hardness (which measure dissolved chemicals). Already the team has achieved a sensitivity of 0.1 parts per million in the lab; the goal is to reach 1 part per trillion. The scientists say their standard is far better than the 10 parts per million threshold that the real human tongue can manage. In addition, the glow from the electronic tongue--unlike the sensation from a real tongue--is precisely calibrated to the intensity of the "taste."

Eventually the dime-size chips will be custom-fitted with as many different kinds of taste buds as an assignment demands. Though the scientists say the artificial taste buds are hardy, they expect the users will dispose of them after every use, particularly when they are used for medical diagnostics.

"The engineering challenge is producing something that someone can use in the real world, not just in the lab," says Neikirk, an engineering professor. "We would like to allow physicians to have a hand-held device at the patient's side. If a patient had a heart attack, the physician could measure changes in blood chemistry, either by taking and measuring a sample, or by doing a constant flow."

Such a product, the scientists acknowledge, is "five to 10 years away."

 


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