When we use a Programmable Microfluidic Device (PMD), we need to wash some contaminated area to use the chip for further experiments. Recently, a novel washing technique called Block-Flushing has been proposed. Block-Flushing washes contaminated area in PMDs by using buffer flows. In Block-Flushing, we need to keep a buffer flow from an input port to an output port of a PMD for a long period to dissolve residual contaminants. Thus, we may need a lot of buffer fluids and washing time even if the contaminated area is small. Another disadvantage of the washing method by Block-Flushing is such that we may not able to clean residual contaminants at valves completely by only buffer flows. To address the above-mentioned issues, this paper proposes a totally new idea to wash PMDs; our method does not use buffer flows, but washes contaminated area by using mixers. By using a mixer, we can dissolve residual contaminants at valves in the area of the mixer very efficiently. In this paper, we propose two methods to wash PMDs by using mixers. The first method can wash the whole chip area by using only four times of a single 2x2-mixer time. We also propose the second method which is a heuristic to reduce the number of moving valves because valves may wear down if they are used many times. We also show some experimental results to confirm that the second method can indeed decrease the number of used valves.

We report a real time method to monitor the chemical reaction in microdroplets, which contain an organic dye, 5(6)-carboxynaphthofluorescein and a CdSe/ZnS quantum dot using fluorescence spectra. Especially, the relationship between the droplet size and the reaction rate of the two reagents was investigated by changing an injection speed.