Immunosensors: technology and opportunities in laboratory medicine.

An immunosensor is a device comprising an antigen or antibody species coupled to a signal transducer, which detects the binding of the complementary species. An indirect immunosensor uses a separate labeled species that is detected after binding by, e.g., fluorescence or luminescence (i.e., a heterogeneous immunoassay). A direct device detects the binding by a change in potential difference, current, resistance, mass, heat, or optical properties (i.e., a homogeneous immunoassay). Although indirect sensors may encounter fewer problems due to nonspecific binding effects, the direct sensors are capable of real-time monitoring of the antigen-antibody reaction. A wide range of molecules can be detected with detection limits ranging between 10(-9) and 10(-13) mol/L. However, there are only a few successful commercial applications of direct immunosensors, these being of the optical type. This review describes the principles underlying the technologies, their merits, limitations, and applications.