Figure 2. Chemotaxis assays based on parallel-flow.

(A) Numerical simulation of diffusion gradient at the interface of parallel-flow in the main channel, assuming a total flow rate of 0.53 μL/min. (B,C) Fluorescent imaging of the diffusion gradients for fluorescein in the main channel, at the inlet and 4 mm downstream from the inlet. (D) Experimental validation of cross-sectional diffusion profiles at 0 mm (red line) and 4 mm (blue line) below the junction were compared with theoretical simulations. (E) Representative fluorescent image showing response of E. coli RP437 to the gradient of 10 mM aspartic acid (Asp). (F) Zoom-in view shows that some cells were not clearly imaged (indicated by the white arrows). The experiments were performed at a total flow rate of 0.53 μL/min.