To facilitate the exchange of solutions, we formed an array of plugs of necessary solutions in a flow channel and mobilized the plugs to a sensing area one by one. Plug-based microfluidic transport has many advantages in that the consumption of sample and reagent solutions is extremely small, handling of many solutions is easy, and mixing of solutions is rapid. We demonstrated that the handling of the plugs can be carried out using the integrated pumps. As an application to practical analyses, the device was also used for the detection of a tumor marker, α-fetoprotein (AFP) .

　Fig. 1 shows the fabricated device. Six solution injectors were formed and the reservoir for each injector was connected to the main channel. Fig. 2 shows the procedure to form a plug in the main flow channel. Following the volume change by produced hydrogen bubbles, the diaphragm is deformed and the solution in the reservoir is injected into the main channel. Fig. 3 shows the injection and transport of liquid plugs in the main flow channel. The device was used for immunoassay. With the device, proteins to be detected, antibodies, and rinsing solutions can be mobilized to the sensing area, incubated, and rinsed. After the series of procedures, FITC was immobilized as a part of the antigen-antibody complex and the fluorescence intensity was measured. The intensity increased with the increase in the concentration of AFP.