A mobile immunoassay system which carries out all its procedure on a CMOS chip is proposed. This method utilizes magnetic beads as its assay marker and provides a simplified protocol. The chip is fabricated in a 0.35 μm standard complementary metal-oxide-semiconductor (CMOS) process. Just one post processing, etch back Hall sensor area, enhances its sensitivity and an RF drain current across it lowers the noise floor. The system reduces the assay cost as low as 10's cents per a test and ready for ordinary people use. It might enable a regional scale screening and disease control.