SmoColi cells are engineered to sense toxic substances found in cigarette smoke. They are immobilized in a microfluidic channel, in which a concentration gradient of the toxic substance is established. The sensor is linked to a band-pass filter that leads to input-concentration-dependent GFP expression. Continuous increase of the input concentration and its detection, therefore, establishes a moving fluorescent band in the channel. Finally, if the input concentration exceeds a certain threshold, cells produce RFP and the device turns red.
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