Figure 8.

Food coloring used as dye to visibly examine fluidic flow and back contamination. The initial state has green and blue colors dropped at the two channel inlets. During channel 1 actuation, it was observed that a small portion of the blue dye had flowed into the channel but not beyond the first actuation point (D). Also, a slight backflow of green dye occurred but not beyond the second actuation point (C). Next, during channel 2 actuation, a similar backflow of blue dye was observed, but it did not go beyond the second actuation point (B). Green dye was observed to occupy the first actuation point on channel 1 (A), but it stopped there, and no cross-contamination was observed. In channels 1 and 2, the backflow stopped at the valves even when the cycles were repeated three times more than the protocol requirement.