A 'Microfluidic Nose': Detection of Olfactory Sensory Neuron Responses to Odorants Across the Whole Olfactory Receptor Space

In vertebrates, odorant molecules are detected by olfactory sensory neurons (OSNs) present in the nasal epithelium. A large, G-protein coupled receptor gene family is responsible for transducing the detection of a cognate molecule for a given receptor. Each OSN appears to express only one of thousands of olfactory receptor (OR) genes in rodents. Odorants are perceived by combinatorial activation of a number of ORs (it is specific to a subset of odorants); each OR recognizes a range of odorants and odorants are typically recognized by a number of ORs. Given the approximately thousand OSN/OR types and the hundreds of thousands of potential ligands, measuring individual OSN activation with the usual in-vivo and in-vitro methods is a laborious task that is not suitable for interrogating the whole OR space. Hence a microfluidic and high-throughput system was developed to analyze these cells.Utilizing the techniques of soft-lithography, we developed a microwell array of ∼32,000 wells (20 um diameter, 10 um depth) to capture dissociated olfactory epithelia (OE) cells and sequentially exposing them to different odorants. Cell response was detected using the Fluo4AM calcium binding dye. By imaging the fluorescence change in each well, a response profile to each odorant can be constructed for thousands of individual OSNs simultaneously.