Electronic nose mechanism

Using the principles of biological olfaction, electronic nose systems contain arrays of different types of cross-reactive vapor-sensitive sensors. While it is difficult to discriminate analytes entirely by their responses to a single type of sensor, using an array of sensors yields response patterns that can readily distinguish many different vapors. Ideally, the response mechanisms of the sensors are highly varied and encompass both physical and chemical phenomena1. 

Particular cases are potassium selective potentiometric sensors based on cobalt [41] and nickel [38, 42] hexacyanoferrates. As mentioned, these hexacyanoferrates possess quite satisfactory redox activity with sodium as counter-cation [18]. According to the two possible mechanisms of such redox activity (either sodium ions penetrate the lattice or charge compensation occurs due to entrapment of anions) there is no thermodynamic background for selectivity of these sensors. In these cases electroactive films seem to operate as smart materials similar to conductive polymers in electronic noses. 

The major conceptual limitation of all regression techniques is that one can only ascertain relationships, but one can never be sure about underlying causal mechanism. The explanation of conclusions with the assistance of other sciences would avoid reaching nonsense conclusions. A hypothetical paradigm can be to use the electronic nose for detecting the adulteration of refined olive oil with refined seed oils when these kinds of oils do not contain volatiles (refined process of vegetable oils includes the deodorization). 

The development of instruments, an artificial nose or an electronic nose, that can evaluate the air quality as the human nose does is an ongoing activity. Many attempts have been made, some successful for the purpose they are designed for, others not. The reason is not only related to the still incomplete knowledge of the perception mechanism (information processes in the brain), but also to the fact that the nose is able to detect very low concentrations. 

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. 

Hahaut E, Peigney A, Laurent C, MarUere C, Chastel F, Rousset A (2000) Carbon nanotube-metal oxide nanocomposites microstructure, electrical conductivity and mechanical properties. Acta Mater 48 3803-3812 Freund MS, Lewis NS (1995) A chemically diverse conduction polymer-based electronic nose . Proc Natl Acad Sci USA 92 2652-2656... 

Drawing and cross-sectional view of a typical one-kilogram, Electron homb. Note blunt nose and awkward streamlining. With the exception of the sheet iron tail and firing mechanism, the bomb Is constructed entirely of incendiary materials... 

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