Abstract 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.

Morgan, C. L., Newman, D. J., & Price, C. P. (1996). Immunosensors: technology and opportunities in laboratory medicine. Clinical Chemistry, 42(2), 193–209.