Study and development of an "electronic nose" and comparison with mammalian olfaction

Citation

Doleman, Brett James (1999) Study and development of an "electronic nose" and comparison with mammalian olfaction. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/R6QQ-NX09. https://resolver.caltech.edu/CaltechTHESIS:09172012-133347649

Abstract

Arrays of broadly responsive vapor detectors (i.e., electronic noses) are receiving an increasing amount of scientific attention for their potential as analytical devices, as models for studying mammalian olfaction, and perhaps for someday ultimately duplicating or surpassing the mammalian olfactory sense. Herein, research was primarily focused on an electronic nose composed of an array of carbon black-polymer composite detectors while arrays of tin oxide detectors and organic conducting polymer detectors were used only in a comparison study. The research determined the odorant resolving power of electronic nose sensor arrays, explored the dependence of the electronic nose array response intensity on odorant vapor pressure, compared the odorant detection thresholds and odorant classification properties of the electronic nose to the mammalian olfactory sense, and attempted to predict human odor quality judgements using electronic nose detector responses.

The Fisher linear discriminant statistical metric was utilized to quantify the performance of arrays composed of carbon black-insulating polymer composite detectors, tin oxide detectors and bulk conducting organic polymer detectors in resolving nineteen odorant vapors. The odorant resolving power of the sensor arrays as a function of the chemical composition of the detectors and the number of detectors they contained was studied. The results provided insights into optimizing the chemical diversity and size of a chemical vapor sensor array for various tasks.

Response data were collected for a carbon black-polymer composite electronic nose array during exposure to homologous series of 1-alcohol and n-alkane odorants. The mean response intensity of the electronic nose detectors, and the response intensity of the most strongly-driven set of electronic nose detectors, was essentially constant for members of a chemically homologous odorant series when the concentration of each odorant in the gas phase was maintained at a constant fraction of the odorant's vapor pressure. A similar trend is observed in human odor detection threshold values for these same odorants. The data imply that the trends in detector responses and human detection thresholds can be understood based on the thermodynamic tendency to establish a relatively constant concentration of sorbed odorant into each of the polymeric films of the electronic nose and into the olfactory epithelium of humans at a constant fraction of the odorant's vapor pressure.

Experiments were performed to compare the detection thresholds and trends in discrimination abilities of the electronic nose to those of the mammalian olfactory sense, and to develop models predicting human odor quality judgements from electronic nose detector responses. The detection thresholds for the electronic nose and the human nose were compared for series of n-alkanes and 1-alcohols. Trends in the odorant-discriminating abilities of an electronic nose and mammalian noses were compared for series of esters, alcohols and carboxylic acids. Electronic nose response data were collected for a diverse set of odorants which had previously been quantitatively characterized by human panelists according to many categories of odor quality. The responses of the electronic nose detectors were then used in attempts at predicting the human odor quality judgements.

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