Electronic nose elements

Zuppa et al.60 have used SOMs in the assessment of data from an electronic nose. Six chemicals—water, propanol, acetone, acetonitrile, butanol, and methanol—were presented at varying concentrations to a 32-element conducting polymer gas sensor array. The output was used to train a group of SOMs, rather than a single SOM, to avoid the problems of parameter drift. One SOM was associated with each vapor, and with suitable use of smoothing filters, the SOM array was found to perform effectively. 

Figure 17. Concept of a spatio-temporal neuromorphic electronic nose chip [21]. The sensor stage has been fabricated [13] and the subsequent analogue VLSI implementation of the integrate-and-fire elements and neurons reported [21].

Aromas and odors are mixture of different classes of chemical species often found in foods, beverages, and medicines. It is difficult to use a single chemosensor to discriminate these analytes. Sensor arrays, in which different sensor elements are used with data analysis, and subsequent pattern recognition will make it possible to characterize gas mixtnres quantitatively or odors qualitatively. Sensors that incorporate pattern recognition software are usually referred to as electronic noses [74]. Recently, there has been much interest in the composition of the suites of organic vapors emitted by food products. 

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 . 

Sysoev, V. V, Goschnick, J., Schneider, T, Strelcov, E. and Kolmakov, A. (2007) A Gradient Microarray Electronic Nose Based on Percholating SnQ2 Nanowire Sensing Elements, NonoZeff., 7,3182. 

While samples enter a laboratory where they are analyzed, it is rare for the information to be used there the decision-makers usually reside outside of a laboratory. Therefore, a laboratory should integrate with its client departments to become an efficient part of an organization or enterprise. One element of this integration is to take the laboratory to the sample or process rather than the sample to the laboratory. When taking the laboratory to sample the analytical chemist can use conventional equipment or use some of the processes and techniques outlined in this article such as electronic noses and tongues, membranes, sensors of all descriptions, and continuous flow systems. 

Similarly, electronic noses were developed in order to take a picture of the complex gaseous mixtures, typically on the basis to their effect on the electrical conductivity of semiconducting metal oxides. A similar approach is followed in the so-called electronic tongues, which are stUl much less established than noses. In particular, potentiometric and amperometric sensors for blind analysis of liquid samples have been proposed. The more easily controlled environment consisting of a solution could constitute a favorable element with respect to gaseous mixtures, even tested in natural environment, with so many uncontrolled variables. 

The array approach has also been developed for amperometric sensing when used in solution. Change in amperometric responses in the presence of different ions is used as the signal transduction method. This has been used by us to discriminate between simple ions (34,35) and even proteins (36). The approach used is similar to the electronic nose in that none of the sensing elements is specific however, each polymer has a different selectivity series, giving rise to a unique pattern of responses for any given protein. 

Sysoev VV, Strelcov E, Sommer M, Bruns M, Kiselev I, Habicht W, Kar S, Gregoratti L, Kiskinova M, Kohnakov A (2010) Single-nanobelt electronic nose engineering and tests of the simplest analytical element. ACS Nano 4(8) 4487 94... 

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