Fluorescence measurements of concentration profiles by confocal microscopy. (A) Scan field across the observation area with resulting confocal images stiched together into one large image. (B) Concentration profile in quasi-static conditions after twelve hours. The undulations are due to confocal imaging. The smooth line connects the local maxima of the measured intensity. (C) Time dependence of the concentration profile. Four hours after adding the fluorophore into one of the reservoirs approximately 50% of the overall maximum intensity is reached. The concentration profile changes very little during 48 hours. The size of error bars is twice the standard deviation of the C100 reference measurement. The main error of the repeated experiments is the result of different amounts of "chemoattractant solution" being filled into the reservoir. The amount of liquid filled into the reservoir defines the initial distance between chemoattractant-containing solution and the observation area in which the gradient is to be built.