Giant magneto-resistance based immunoassay for the tumor marker carcinoembryonic antigen

We report on a giant magnetoresistance (GMR) based immunosensor for the carcinoembryonic antigen (CEA) labeled with superparamagnetic microparticles (Dynabeads). The GMR sensor contains 200 GMR strips and was fabricated by micro-electromechanical system (MEMS) technology. This system can detect Dynabeads in concentrations down to 10 ng⋅mL −1 . Sandwich immunoassays were employed on the surface of a gold film modified with a self-assembled monolayer and using biotinylated secondary antibody against CEA and streptavidinylated Dynabeads. With DC magnetic fields in the range of 40 to 90 Oe, CEA can be detected with a detection limit as low as 10 pg⋅mL −1 . Samples spiked with different concentrations of CEA can be distinguished clearly, and the method is deemed to be well suited for clinical use. Make use of antigen-antibody immune reaction, Dynabeads that conjugated with polyclonal CEA antibodies were captured onto the surface of Au film which immobilize of monoclonal CEA antibodies. Under the dc magnetic field magnetizing, the superparamagnetism Dynabeads induced a weak magnetic field that can be detected by the nearby GMR sensor, which reveals the presence of CEA. GMR: giant magneto-resistance CEA: carcinoembryonic antigens.