Box 17-2 What Is an Electronic Nose

In the old days. chemists prided themselves on their ability to identify compounds by odor. Smelling unknown chemicals is a bad idea because some vapors are toxic. Chemists are developing electronic noses to recognize odors to assess the freshness of meat, to find out if fruit is internally bruised, and to detect adulteration of food products.13 

One approach to recognize vapors is to coat interdigitated electrodes with an electronically conductive polymer, such as a derivative of polypyrrole. 

When gaseous odor molecules are absorbed by the polymer, the electrical conductivity of the polymer changes. Different gases affect conductivity in different ways. Other sensor coatings are polymers containing conductive particles of silver or graphite. 

When the polymer absorbs small molecules, it swells and the conductivity decreases. 

Interdigitated electrodes coated with conductive polymer to create an electronic nose. The conductivity of the polymer changes when it absorbs odor molecules. The spacing between fingers is 0.25 mm. 

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