Transfer curve models for synthetic AHL-receiver devices

The input-output function of the AHL-receiver devices was determined by fitting cell fluorescence data with the following four-parameter logistical curve model:

GFP = b + ( a-b ) / 1 +10^( ( log(EC50)-log([AHL]) )*h)

where a is the maximal GFP output, b is the basal GFP output, [AHL] is the AHL inducer concentration, GFP is the green fluorescence response of the device for that inducer concentration, EC50 is the inducer concentration that results in half maximal activation of the device, and h is proportional to the value of the steepest slope along the curve (Hill coefficient) that indicates the responsiveness of the device to the input.