The electronic nose described in this paper uses a cross-reactive sensor array based on fluorescence sensors. The sensors are fabricated by attaching solvatochromic dyes to different microspheres. The microspheres are then placed into wells chemically etched on the distal end of an optical fibre bundle. The system uses an olfactometer to deliver a pulse of analyte vapour to the sensors. An optical imaging system is employed to monitor fluorescence intensity over time. We use a heterogeneous array that contains different types of sensors, which allows us to classify a large number of analytes and complex odours. The array is formed by randomly distributing microspheres on the end of the fibre array. The position of each microsphere is determined by using a method that compares different sensor responses to their responses to known analytes. The electronic nose has been used to detect explosives and explosive-like vapours at low levels, and was able to detect nitro aromatic compound (NAC) vapour concentrations as low as 5 ppb. In addition, by fabricating a model of a nasal cavity and placing identical sensors at different positions, we demonstrated how the flow environment affects sensor response. By using the information from multiple sensors placed in different spatial positions in the complex flow environment, we demonstrated it is possible to obtain better discrimination between analytes.
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