PDMS micro bead cage reactor for the detection of alpha feto protein (AFP)

In this paper, we describe that it is possible to conduct the pretreatment reaction procedure for the disease diagnosis by using just single chip with nanoliter sample consumption. A PDMS micro-pillar with a diameter and height of 30 μm was developed for bead platform. The micro reaction chamber that is surrounded by the PDMS pillar structure has 90 nanoliter volume. (3 mm × 1 mm × 30 μm) After filling the reaction chamber with micro beads, biotin, streptavidin and antibody are flowed to react with each other on the bead surface using microfluidic flow. It takes about just 20 minutes to make antibody immobilization. Alpha feto protein (AFP) was tested for the application of our micro chips. Fluorescein conjugated AFP was analyzed with confocal microscope. We successfully demonstrated the AFP detection capability from 10^-9 to 10^-6 g/ml which is over the desired range of AFP concentration in clinic. These bead reactions are 3D reaction unlike the 2D reaction of standard surface immobilization process. Therefore, the consumption of the sample and antibody solution is minimized and the sensitivity is enhanced. In addition, we have investigated the effects of parameters such as flow rate, pH and temperature, which are the crucial reaction parameters. We could also demonstrate that it is possible to concentrate AFP over 50 folded times by continuous AFP flowing while injecting it into microchip.