SQUID based remanence measurements for immunoassays

The use of fine magnetic particles as labels for antibodies and the measurement of their remanent magnetization for the preparation of immunoassays is presented. Antibodies were coupled with magnetic nanoparticles and samples were prepared by reaction of the magnetically labeled antibodies with their solid phase adsorbed antigen. After exposing the samples to a field of some mT a dc-SQUID system measures the remanent sample magnetization in the absence of an external field. The combination of high moment labels and SQUIDs yields ultrasensitive immunoassays with a wide range of detectable analyte concentrations. In contrast to most standard techniques in our method the detected magnetic signal is specific only for bound reaction partners, thus eliminating the need for separation of unbound components.