But things are finally looking up for the electronic nose. Thanks to advances in chip technology and pattern-recognition techniques, increasingly tiny sniffers are beginning to live up to their moniker. Today e-noses are being tested for everything from disease detection to disaster prevention, and lower-priced models are starting to come on the market--including an $8,000 device called the Cyranose 320 being introduced this week by Cyrano Sciences of Pasadena, Calif.
Like our proboscises, e-noses are only as good as their sensors, and all of them operate on principles remarkably similar to those of a real nose. Humans detect odors with up to 650 types of receptors found on cells high up in the nasal passages, somewhere between our eyebrows. How the nose works is still something of a mystery, but it is believed that each receptor responds to a subtle characteristic of a molecule that carries odor--its peculiar shape, say, or degree of oiliness--rather than to the molecule itself. Working together, the receptors can generate unique "smell prints" of a wide variety of odors, which are then parceled off to the brain and stored.
In e-noses, chemical sensors replace the body's cellular receptors, and microprocessors substitute for the brain. "What limits these devices is how well the sensors are doing," explains Nathan Lewis, the Caltech chemist who helped invent the sensor technology licensed by Cyrano and who has since continued his research independently. He compares the power of e-noses to the resolution of computer monitors: "Are you seeing the world in eight shades of gray or in 16 million colors?"
If Cyrano's enthusiastic (and aptly named) ceo Steven Sunshine is to be believed, Cyranose is "seeing" in Technicolor. When properly trained, its 32-sensor Nose-Chip[TM] can sniff a particular variety of rice and tell you not only which one it is but also where it was grown. Does it smell as well as we do? Yes and no. It has trouble detecting some things to which human noses are acutely attuned--such as the stench of rotting eggs--but it can be trained to pick up others most people would never notice. There are limits, however, to how well the e-noses can be educated. Wine connoisseurs, for example, can distinguish fragrances beyond the ken of any chip.
No matter. E-noses have other, more practical uses. Osmetech, a British e-nose company, has dedicated itself to the detection of diseases. Its e-nose can sniff out six of the seven types of bacteria responsible for urinary-tract infections. Microsensor Systems of Orlando, Fla., makes a $9,800 portable device equipped with crystal sensors that can sniff out spoiling food and chemical weapons with equal ease. Caltech researchers sent one of their chips on John Glenn's space-shuttle mission last year to keep tabs on the quality of the cabin air. An adventurous Cyranose was even used to study how the scent of wild cats in Africa varies among species.
As the devices get smaller and prices come down, the applications are bound to multiply. "Miniaturization could significantly affect the e-nose market," says Harry Goldstein, who follows the business for Technical Insights. He imagines factories of the future filled with thousands of cheap, tiny sensors. "If there's a chemical spill, we could find out what's going on instantly instead of waiting until someone falls over."