What's an Electronic Nose?

Yesterday, Dr. B told you about a job some people have in which they can tell what is in a mixture by smelling. They're called "noses". Well, scientists have developed a laboratory instrument that can "smell", too! It's called an "electronic nose", or Enose for short. Here's a picture of a small, handheld Enose made by the Princeton Applied Research Company:

It looks like a walkie-talkie, doesn't it? It doesn't look at all like a nose! Of course, an Enose doesn't actually smell the same way our noses do. To use an Enose, you would put the "snout" into the area to be sniffed, then push the right buttons. Then your results would appear on the little screen!

Inside the Enose, the sniffed gases are blown over tiny devices called chemical sensors. These little devices, which look a little like computer chips, create a small electrical current when they are exposed to certain types of molecules. So you load up the Enose with sensors that can "see" the kinds of molecules you want to sniff, and each sensor will detect slightly different molecules. Now here's the important part - Enoses are pretty stupid when you first take them out of the boxes, so you have to "teach" them what certain smells are. For example, let say that there are five sensors that we'll call A, B, C, D, and E. Lemons are detected by A and D, and limes, by C, D, and E. What would the scent of lemon-lime soda do? Right - you'd get signals from A, C, D (really strong) and E. Sensor B wouldn't do anything. Now you basically understand how an Enose works!