Figure 9. Density distribution of 2 μm sPsL particles for the urease pump.

The data are for 100 mM urea (green) and 500 mM urea (purple). For ∼0.5 mm² areas along the centre of the pattern, the number of particles settled on the surface was determined by image analysis software as the per cent area covered by particles, which was then normalized. For 100 mM urea concentration, a fivefold increase in tracer particles was observed at a distance of ∼6 mm away from the reagent source. Increasing the urea concentration to 500 mM changed the maximum to ∼9 mm away from the reagent source, with a 10-fold increase in particle density. The observed shift in maximum for the tracer density distribution qualitatively agrees with simulated shifts presented in Fig. 5 with increasing amount of reagent.