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"Electronic Tongue" Mimics Human Taste Organ

Mark Anderson
for National Geographic News
September 1, 2009
 
An "electronic tongue" that can digitally measure the taste of sweetness has been created, a new study says.

The technique uses a postage stamp-size piece of paper dotted with colored pigments.

A computer compares scans of the array of dots before and after the paper is wetted with an eyedropper full of liquid.

After running dozens of samples of mystery artificial sweeteners dissolved in water or tea, the research team reported that their tongue could pick out the sweetener used with with 100 percent accuracy.

But the array only works collectively: No single dot—each made of a tiny gel coated with a pigment that reacts to different sweeteners—detected any single sugar or sugar substitute, according to study leader Kenneth Suslick, a chemistry professor at the University of Illinois at Urbana-Champaign.

"It's not like a key that only fits one lock," Suslick said.

"That's not the way our tongue works—that's not the way our nose works. And that's not the way this array works."

Bitter End

The human tongue also detects saltiness, sourness, bitterness, and savoriness.

Sourness is just another word for acidity, Suslick said, which any high school chemistry student can test for using litmus paper.

Savoriness—also called "umami"—and saltiness can already be measured by handheld devices sensitive to protein levels and sodium and potassium ions.

The final dimension of taste that remains to be cracked is bitterness, which is still somewhat of an unknown.

"We lump a whole bunch of things into that one word," said Suslick, whose study appeared August 1 in the journal Analytical Chemistry. "It just isn't clear yet what the bitterness receptors [in the tongue] are and what they respond to."

(Related: "For Frog-Licking Scientist, the Tongue Says It All.")

Still, Suslick and colleagues' past research has helped California-based company iSense to develop technology that can sense noxious gases for emergency first responders and military personnel.

Other applications down the road, Suslick said, include a kind of breathalyzer that could detect harmful bacteria, and biomolecules, which could provide people with an early warning of diseases such as pneumonia and lung cancer. (Learn more about human diseases.)

Missing Out

Eric Anslyn, a chemistry professor at the University of Texas at Austin, said in an email that an artificial tongue that sensed just these five flavors would still miss a lot.

Much of what we experience as taste is really smell, said Anslyn, who was not involved in the new research.

"You plug your nose and hold your breath to eat food you don't like—we all know this," he said.

"Hence, we are missing the vast majority of taste when not including the dimensionality that smell brings."

The sweetness sensor, said study leader Suslick, is "only one small part of a much broader program to create a new technology to imitate both our sense of taste and of smell."
 

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