A cell-based odor sensing system using fluorescent technique and lock-in measurement robust against disturbance

We have developed an odor sensing system based on insect olfactory receptor (OR) and fluorescent instrumentation. When an odorant is captured by an OR (OR56a) expressed on Sf21 cell, calcium indicator protein (GCaMP6) is activated by calcium ion flowing through the OR into the cell. The intensity change of the fluorescent light can be regarded as a sensor output. Since fluorescent light from the cell was very weak, the measurement should be done in the dark condition. The measurement quality deteriorates if the ambient light is included. Thus, a lock-in measurement technique was incorporated to the system to overcome the problem of the ambient light together with the fluorescent image. The lock-in technique enables the detection of light synchronous with the modulated excitation light under the ambient light. This technique is also useful to improve the signal to noise ratio. In this work, we were successful in the detection of 500 nM geosmin even under the condition with the ambient light, whereas it was not clearly detected by the system without lock-in technique.