Portable geosmin detection system based on sensor cells expressing insect odorant receptors

A technology that allows on-site targeting of odorants with high sensitivity and selectivity without using sophisticated instruments would have various useful applications from water quality testing to disease diagnosis. Here, we report a portable technology in which Sf21 cells expressing Drosophila melanogaster odorant receptors, co-receptors, and calcium-sensitive fluorescent proteins are used for detecting geosmin, a natural compound with a distinct musty odor. Cartridges were fabricated by immobilizing the sensor cells on the glass surface of a tube. The system, coupled with a portable fluorometer, was able to detect geosmin at a concentration of 100 pM (18.3 ppt) without the use of concentration techniques. Moreover, the system, which was introduced in the dam lakeside, was able to detect geosmin in actual field samples. This is the first successful detection of target odorants in the field using a biosensor based on sensor cells that were transfected with the desired odorant receptor gene as sensing elements. This study demonstrates the practicality of sensor cells expressing insect odorant receptors and the potential of this technology for a variety of applications, such as the quality inspection of food, beverages, and water where on-site detection of odorants is required.