Towards a truly biomimetic olfactory microsystem: an artificial olfactory mucosa

Today, the capability of the human olfactory system is still, in many ways, superior to that of artificial detection or the so- called electronic nose. Although electronic noses are often compared to their biological counterpart, they neither mimic its complex neural architecture nor achieve its performance in discriminating between complex odours. Recent developments in our understanding of the human olfactory system suggest that the olfactory mucosa (the lining of the nasal cavity comprising of a mucous layer and the olfactory epithelium) behaves like a gas chromatograph. Thus receptor cells distributed beneath the mucous layer (within the olfactory epithelium) provide both spatial and temporal chemosensory information. Here we report on the development of an artificial olfactory microsystem that replicates the basic structure of the olfactory mucosa. Our system employs an 80 element chemoresistive microsensor array fabricated on a 10 mm × 10 mm silicon die. The microsensors possess carbon black/polymer nanocomposite films as the odour-sensitive elements. In addition, a micro-fluidic package has been fabricated by micro- stereolithography, with an integrated channel to act as the nasal cavity (channel dimensions 500 μm × 500 μm × 2.4 m). This channel has been coated with Parylene C, as the retentive layer, in order to mimic the partitioning mucous layer of the olfactory mucosa. The fluidic package has been placed directly on top of the sensor array and has evenly spaced openings along the channel that encompass blocks of 5 sensing elements. Results show that this biomimetic system yields both spatial and temporal odorant signals, with a temporal chemical retention period of up to 110 seconds. Data analysis has revealed improvements in its ability to discriminate between two simple odours and a set of complex odours (i.e. essential oils). We conclude that closer emulation of the olfactory mucosa and nasal cavity could yield better odour discrimination and hence be superior to existing electronic nose technologies.