From 2007.igem.org

Detector cell: this cell is designed to test the concentration of AHL signal. In this cell, LuxR gene under the control of tet promoter could produce LuxR protein which could activate the following Lux pR promoter when binding to certain amount of AHL signal, thus GFP expressed to make this cell green within the view of a fluorescence microscope. The intensity of fluorescence could be measured by a fluorescence spectrophotometer to decide the concentration of AHL signal roughly.