Electronic nose system, analysis

The performance of common multisensor arrays is ultimately determined by the properties of their constituent parts. Key parameters such as number, type and specificity of the sensors determine whether a specific instrument is suitable for a given application. The selection of an appropriate set of chemical sensors is of utmost importance if electronic nose classifications are to be utilised to solve an analytical problem. As this requires time and effort, the applicability of solid-state sensor technology is often limited. The time saved compared with classic analytical methods is questionable, since analysis times of electronic nose systems are generally influenced more by the sampling method utilised than the sensor response time [185]. 

VAN DEVENTER D and MALLiKARJUNAN P (2002), Comparative performance analysis of three electronic nose systems using different sensor technologies in odor analysis of retained solvents on printed packaging , J Food Sci, 67(8), 3170-3183. 

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. 

Keywords Electronic Nose System, Principal Component Analysis, Decision Tree, High Level Synthesis, Vivado, Zynq System on Chip... 

Scott SM, James D, All Z (2006) Data analysis for electronic nose systems. Microchim Acta 156 183... 

Arrays were introduced in the mid-eighties as a method to counteract the cross-selectivity of gas sensors. Their use has since become a common practice in sensor applications [1], The great advantage of this technique is that once arrays are matched with proper multivariate data analysis, the use of non-selective sensors for practical applications becomes possible. Again in the eighties, Persaud and Dodds argued that such arrays has a very close connection with mammalian olfaction systems. This conjecture opened the way to the advent of electronic noses [2], a popular name for chemical sensor arrays used for qualitative analysis of complex samples. 

Keywords electronic nose principal component analysis pattern recognition chemical sensors sensor arrays olfaction system multivariate data analysis. 

Cosio et al. (2006) used an electronic tongue system based on flow injection analysis (FIA) with two amperometric detectors, together with the use of an electronic nose, in order to classify olive oil samples on the basis of their geographical origin. Counter-propagation maps were used as classification tools. 

Given that an array sensor is being developed, how may they be validated I know of no system that has undergone validation for accreditation purposes. Even compared with environmental analysis, these sensors present difficulties that need to be resolved, before a consensus on suitable validation protocols is reached. Gardner and Bartlett have considered the problem of how to define the performance of electronic noses using standard odour mixtures [21]. They propose two indicators of performance, the range of different odours that may be detected by the array, and the ability to discriminate between similar odours (the resolving power). 

Nakabeppu et al. [58] describe the use of composite cantilevers made from tin or gold deposited on conventional silicon nitride AFM probes to detect spatial variations in temperature across an indium/tin oxide heater. Differential thermal expansion of the bimetallic elements causes the beam to bend. This movement is monitored using the AFM optical lever deflection detection system. In order to separate thermal deflection of the beam from displacement of the cantilever caused by the sample topography, an intermittent contact mode of operation is employed. Measurements were made under vacuum so as to minimize heat loss. A more practical use of this technology is in the form of miniature chemical and thermal sensors [59]. This approach has been used to perform thermal analysis on picolitre volumes of materisd deposited on the end of a bimetallic cantilever [60]. Arrays of such devices have applications as highly sensitive electronic noses . 

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