There is considerable interest in developing sensors that act as analogs of the mammalian olfactory system (1–3). Such sensors have proven useful in the detection of small molecules and odorants. The potential application of electronic nose technology with particular regard to the detection of vapors from explosives has been described in a monograph (4). The measurement of air content for the detection of contaminants has become a growing concern both in the workplace, e.g., factories and laboratories, as well as in residential neighborhoods and homes.
Perception of odor is a physical mechanism by which information is processed in the brain. Humans are able to detect essentially an unlimited number of dissimilar odors and in dilutions in the ppb range (5).
It is believed that the brain is able to evaluate and identify tens or possibly hundreds of thousands of different odors. The brain is able to recognize these odors and associate them with likes, dislikes, events and experiences. According to the chemical theory of olfaction, molecules of odors, or odorants, are conveyed to the olfactory epithelium by convection, diffusion or both and directly or indirectly induce changes in the olfactory receptors.
It is believed that the human nose detects smells when odorants strike a region on the olfactory neurons, the cells that contain the odorant receptors. Axons extend from these cells to the olfactory bulb, ...