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. 2011 Apr 8;6(4):e18231. doi: 10.1371/journal.pone.0018231

Figure 6. The chemoattractant concentration profile.

Figure 6

(A) To visualize the concentration profile of serine, a micropipette was filled with Inline graphic fluorescein and a small hydrostatic pressure was applied by a water column to maintain a continuous flow of dye into the sample chamber. The height of the water column was set to Inline graphic and kept fixed in all measurements. The fluorescence intensity distribution after the background subtraction is displayed in (A) and in the inset. In (B), the measured intensity Inline graphic is plotted against Inline graphic, where Inline graphic is along the radial direction as delineated in (A). In the far field, Inline graphic is proportional to Inline graphic as displayed by the dashed green line, which is expected from the calculation. The solid line is the fit to Eq. 6, which captures both the near- and far-field behaviors. The inset is a computer generated plot of the dye distribution according to Eq. 3, where Inline graphic and the same coordinate system is used as in the calculation. In (C and D), the fluorescence peak intensity (Inline graphic) and the half-width at half-height (Inline graphic) were measured as a function of the water column height Inline graphic. In (E), the micropipette was filled with Inline graphic of fluorescein, and the mean fluorescein concentration in the sample chamber (with a total volume of Inline graphic) was measured as a function of time Inline graphic.