Electric Tongue Takes First Licks

Cameras mimic eyesight, and tape recorders mimic hearing. Now even the sense of taste has gone electronic. A rudimentary electronic tongue, described in the 1 July issue of the Journal of the American Chemical Society, lays the groundwork for future versions that can monitor beer and wine production or analyze blood samples in one quick step instead of a variety of individual tests.

Tongues are dotted with taste buds, which detect sweet, salty, sour, and bitter tastes. The taste buds blend these sensations to create a distinct pattern that the brain recognizes as a flavor, such as chocolate. Thus tastes differ, for example, from many scents that are "hardwired to mean important events, like a dog smelling a female in heat," says Eric Anslyn, a chemist at the University of Texas, Austin.

Anslyn and his colleagues wondered if they could outfit an electronic device with an array of sensors that could sample flavors in a solution, just like the tongue does. To build their device, the team drilled an array of wells, each about 250 micrometers wide, into a silicon wafer. Each hole contained a mini "taste bud"--a polystyrene resin bead, each coated with one of five organic compounds that change color when they react chemically with different types of substances. The "tongue" was then exposed to cocktails of varying pH, containing different combinations of calcium, cerium, and sugar. The beads produced distinct colored patterns, which the researchers could analyze to tell what was in the solution.

Although it is impossible for now to make a single "tongue" that senses everything from beer to french fry grease, even crude electronic "taste testers" could be useful for taking a snapshot of chemicals in a solution rather than laboriously testing for substances individually. "What's really nice about [this experiment] is that it's gone beyond the basic science," says Richard McCullough, a chemist at Carnegie Mellon University in Pittsburgh. He predicts there will soon be an "explosion" of devices using organic compounds as sensors because they are cheap and easy to make, and much of the basic science about how these compounds react is already known.