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

In this paper, we showed that it is possible to conduct the pretreatment reaction procedure for the disease diagnosis by using just single chip with nanoliter sample consumption. A polydimethylsiloxane (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 nl volume (3 mm × 1 mm × 30 μm). The reaction chamber was filled with micro beads and then biotin, streptavidin and antibody were flowed to react with each other on the bead surface using micro-fluidic flow. Alpha feto protein (AFP) which is the target application was analyzed by the confocal laser microscope followed by conjugating with fluorescein. We successfully demonstrated that 10−9 to 10−6 g/ml AFP which is over the desired range of AFP concentration in clinic could be detected. These bead reactions are three-dimensional reaction unlike the two-dimensional 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. It took about just 20 min to make antibody immobilization. We could also demonstrate that it is possible to concentrate AFP over 50 folded times by continuous AFP flowing while injecting it into microchip.