Towards a Cell Based Bioelectronic Nose

Electronic noses are devices that combine gas sensors with a pattern recognition system. They have been advocated as a fast and cheap alterna-tive to human sensory panels or analytical instruments such as GC-MS. However, they cannot cope with presence of certain volatiles that, even in very low concentrations, impart a particular character to an aroma, giving it that specific note which makes it distinguishable from another similar scent. With the intention to combine the best of both biological and electronic systems, the main objective of this thesis was to investigate the potential of connecting the biological aroma sensors the olfactory receptor neurons with an optical or electronic transducer platform to measure their response to aroma components. In a first step, a system was constructed to produce different aromas in a controlled way to calibrate and train bioelectronic noses. Hereto the aroma space spanned by a large number of volatiles was projected onto a low dimensional space. An algorithm was developed to construct basic mixtures combinations of a limited number of specific volatiles that serve as basis vectors of this reduced order aroma space. A particular aroma that was an element of the original aroma space could then be reconstructed by blending specific amounts of the different basic mixtures. In order to test the concept, a real time aroma synthesizer was constructed. The device consisted of a sphere in which the basic mixtures were blended and vaporized using pressurized nozzles. The aroma of five citrus fruit species (orange, lemon, lime, grapefruit and mandarins) was measured by means of GC-MS and reconstructed using four basic mixtures. The reconstructed aromas for lime and lemon could be classified correctly by the statistical model that was used to define the relevant aroma components. The aromas for orange, tangerine and grapefruit had lower correct classification rates. Second, rat olfactory receptors were evaluated as building blocks of a bioe-lectronic nose. It was studied whether rat olfactory receptor neurons could be maintained in vitro and their response to aroma components was ana-lysed with calcium imaging. Two embryonic cultures from day 17 and day 20 were set up, both of them proved to be odorant responsive. On the other hand, it was concluded that the density of olfactory receptor neurons that could be reached in culture was not high enough to use these cultures in combination with micro electrode arrays and a new method needed to be developed to reach higher densities in olfactory neurons.Therefore, in a last step, acute olfactory epithelial slices were made and placed on top of a micro electrode array (MEA) device. This is a powerful platform to study the spatial electrical activity of the olfactory receptor neurons in sliced layers of the epithelium. By choosing a sagittal slicing direction for the olfactory epithelium, better signal-to-noise ratios could be obtained in comparison to transversal slices. The mean spike frequency of the olfactory receptor neurons inresponse to different concentrations of isoamyl acetate appeared to be following an exponential curve, saturating at higher levels of the odorant. Due to the low amount of points and re-peats of these measurements, the exponential curve might only be an approximation of the actual course of the receptor neurons responses. A spatial map also showed increasing spike frequencies with increasing iso-amyl acetate concentration over the different recording sites on the slice. When alternating the application of isoamyl acetate and L-carvone, two typical aroma volatiles, on the slices, the spatial map of the spike frequen-cies also showed a different activity pattern for both odorants.<w:latentstyles deflockedstate="false" defunhidewhenused="true"