Figure 4.

Bioinspired approaches for odor delivery and chemical sensor array design. (a) A realistic physical model of the canine nasal cavity. When odorants were introduced through the model’s nares, five identical sensors placed at different spatial locations in the model (numbered 1–5) yielded different spatiotemporal responses. These results show that complex flow dynamics in the nasal cavity could enhance the separation of different chemical species, potentially giving rise to diverse neural responses. (Reprinted with permission from ref (62). Copyright 2003 American Chemical Society). (b) An artificial mucosa to simulate fluid found within the nose employs microfluidic channels coated with polymers. This model could separate odor components like the stationary phase of a gas chromatography column. (Adapted with permission from (61). Copyright 2007 The Institution of Engineering Technology). (c) Temperature modulation of metal-oxide sensors to increase sensor dimensionality. A voltage profile is applied across the resistive heater, and the sensor resistance is continually recorded. Because interactions between metal-oxide chemiresistors and various chemical species are temperature dependent, the response of a sensor at a particular temperature can be treated as a separate “pseudo-sensor” or a “virtual sensor” and used to simulate a large population of ORNs. (Adapted with permission from ref (64). Copyright 1998 IEEE). (d) Odor sensing by microbead arrays: Odor vapor is delivered to the distal end of the fiber. Exposure to odor vapor induces a change in fluorescence that is recorded and plotted over time. Inset A: Microspheres coated with a polymer matrix onto which solvatochromic dye (e.g., Nile red) is immobilized and randomly filled at the distal end of the fiber. Inset B: Distal end of the optical fiber from which the response is read. (Adapted with permission from ref (70). Copyright 1996 Nature Publishing Group). Benefits of incorporating redundancy or diversity into a sensor array: (e) Responses of a single temperature modulated metal-oxide sensor to different background conditions and five target toxic industrial chemicals are shown. Each three-dimensional color-coded sphere indicates a sensor measurement after dimensionality reduction. (f) Responses from four identical copies of the sensor after dimensionality reduction are shown. (g) Responses from four different chemiresistors are shown for comparison. Both sensor redundancy and diversity improve detection and recognition of target chemicals from the background. (Reprinted with permission from ref (74). Copyright 2009 Elsevier).