Natural olfaction

It has to be remarked that in spite of the widely accepted term electronic nose, current devices are still far from the structure and functions of natural olfaction sense. The unique common feature between artificial and natural system is that both are largely based on arrays of nonselective sensors. The concept underlying electronic nose systems has been demonstrated to be independent on the particular sensor mechanism indeed during the last two decades almost all the available sensor technologies have been utilized as electronic noses. Clearly, all these sensors are very different from the natural receptors. These dissimilarities make the perception of electronic nose very different from that of natural olfaction, so that the instrumental perception of the composition of air cannot be called odor measurement because odor is the sensation of smell as perceived by human olfaction. Nonetheless, the term odor analysis with electronic noses is now largely adopted, but it is important to keep in mind, especially in medical applications, that the electronic nose measurement may be very distant from the human perception. 

The methodology and currently developed devices are inspired by the natural olfaction system, where odours are sampled, detected and analysed. In the natural olfaction system of mammalians, odours are sampled by aspiration and condnced into the nasal cavity where they are detected by a series of olfaction cells that provide inpnt signals to the brain. The brain stores the signals in its memory and provides a comparison when a new odour is detected. 

The central point in electronic noses is that the individual gas sensors are completely unspecific, as are the olfactory cells in the natural olfaction system. This means, not only that an individual gas sensor may provide exactly the same electrical signal in the presence of two different pure gases, but also for two very different odours, hence one individual gas sensor is not able to discriminate between two complex odours (except in very simple cases which are not of interest). For example, an individual sensor may provide the same signal for someone smoking very close to the sensor and for something burning nearby hence, the sensor cannot discriminate between both situations. 

Duvall D. (1981). Western fence lizard (Sceloporus occidentalis) chemical signals, II a replication with naturally breeding adults and a test of the Cowles and Phelan hypothesis of rattlesnake olfaction. J Exp Zool 218, 351-361. 

Olfaction, once thought to be a primitive sense, is now recognized as an elaborate sensory system that deploys a large family of odorant receptors to analyse the chemical environment. Interactions between these receptors and their diverse natural binding molecules (ligands) translate the world of odors into a neural code. Humans have about 350 odorant receptors. Rodents have more than a thousand. 

Bang, B. G. (1965). Anatomical adaptations for olfaction in the snow petrel. Nature 205, 513-515. 

Vernet-Maury, E. (1980). Trimethylthiazoline in fox feces a natural alarming substance for the rat. InProceedings ofthe Vllth International Symposium on Olfaction and Taste, ed. H. van der Starre, p. 407. London IRL Press. 

A knowledge of botany enriches the understanding of natural perfume materials and their production but is not essential to the perfumer s job. An interest in the physiology of olfaction and the mechanisms of odor detection is intellectually enriching, but at the current state of knowledge this discipline contributes little to the practice of perfumery. 

Davies P 1999 Aromatherapy an A to Z, 3rd edn. CW Daniel, London Devon T K, Scott A1 1972 Handbook of naturally occurring compounds terpenes, volume 2. Academic Press Inc, New York Doty R L 2003 Handbook of olfaction and gustation. Marcel Dekker, New York Ernst E 2006 The desktop guide to complementary and alternative medicine an evidence based approach. Mosby, London... 

Y. Pilpel and D. Lancet. Olfaction. Good reception in fruitfly antennae. Nature, 398, 285—287, 1999. 

Figure 8. Aromatic potential (concentration of extractives/perception thresholds = olfactive units) of oak wood after natural seasoning during three years (SN) or artificial drying (3 months) (SA), adapted from (5)...

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