Your dog knows in a sniff if you have been cavorting with the despised feline next door or fingering his favorite treats. He knows because his nose is replete with more than 100,000 sensory cells that bind to chemicals wafting through the air. Humans have harnessed this fine canine sense for sniffing out bombs, drugs and fugitives, but there are many smelly jobs for which Fido won't do--including discerning if the food on the conveyor belt at the dog food plant smells exactly the same as it did yesterday. Or if a pigsty is too fetid, or treated sewage is odor-free. Human testers traditionally have pulled such pungent duties.

Electronic noses are now poised to fill these roles. The devices are collections of diverse detectors analogous to the sensing cells in a hound's nose. Each aroma pumped across the array induces a unique pattern of responses that is fed into a computer. The electronic nose "recognizes that pattern, draws it from its memory banks and says, ¿Aha, that's root beer or a rose or some other vapor that I've smelled before,'" explains chemist David R. Walt of Tufts University.

   
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