Smell and taste are chemical senses, so-called because they detect the presence of different chemicals as molecules in the
air (smell) or dissolved in liquids (taste). At present, electronic sensors for both are in their infancy.
Smells are simply chemical molecules small enough and light
enough to vaporise into the air. A smell may be just one type of molecule or a mixture of many different types. Over 600 different molecules wafting into your nose make up the delicious aroma of fresh coffee, for example.
Smell is a vital part of our daily lives and it uses more of
the brain than any of the other senses. Smell lets us sample our surroundings and check for danger. Think of the smell of smoke, for example. Molecules of smoke can travel long distances on the wind, showing that smell can act as an early warning system.
Even though the human sense of smell is poor compared with many
animals, we can easily detect just parts per billion of the toxic gas hydrogen sulphide - the smell of rotten eggs. With training and experience, human noses can check products such as wine, cheese, fish and many other foodstuffs, for quality and freshness. Doctors can diagnose certain diseases from their smell alone.
Human noses are sensitive and self-repairing but they are not
suited to boring or repetitive tasks. They are also subjective, prone to catching colds and cannot be used to check situations that may be hazardous. Humans cannot smell the fatal presence of carbon monoxide, for example. What we need is an electronic or E-nose, to give an objective readout of the smell-scape that surrounds us.
Scientists have been working on E-nose development since the
1980s, their first step being to understand how our biological sense of smell works. How do volatile odour molecules reaching your nose trigger recognition of a smell in your brain?
