Fluidigm of South San Francisco, Calif., has received US Patent No. 8,420,017, "Microfluidic reaction apparatus for high-throughput screening." The microfluidic device described has a slug mixing arrangement, where the reaction well has an input flow channel with a first valve near the well, and a second valve further from the well. A fluid source is connected to the segment in between the two valves. A second fluid source is connected behind the second valve.