Manipulation of Dispersed Magnetic Beads for On-Chip Immunoassay

To provide a simple and low-cost mobile immunoassay platform, a test chip on which dispersed magnetic beads are manipulated was designed and fabricated by a 180 nm standard complementary metal–oxide–semiconductor (CMOS) process. In preliminary experiments, beads that have a diameter of 2.8 µm were successfully manipulated and their motion were captured and analyzed. Then, an immunoassay was conducted on the chip. First, the nonspecific binding of hydrophilic beads coated with an antibody was compared with that of hydrophobic beads that were used for the preliminary experiments. Next, comparison of an immunoassay of mouse IgG with a control assay and a test on the feasibility of the blocking process were conducted simultaneously. The beads coated with the antibody were successfully immobilized onto the chip surface in the presence of the target antigen, which was checked through bead manipulation. This indicates that an immunoassay on an inexpensive CMOS chip is feasible using an affordable amount of driving current.