Preparation of polymer-coated ultrafine ferrite particles and evaluation as an immunoassay magnetic marker by a SQUID sensor

Polymer-coated ferrite particles having carboxyl groups were preparated by radical copolymerization of N-acryloyl-L-glutamic acid and Tri(2- acryloyloxyethyl)ammonium chloride to disperse in aqueous solution. Successive immobilization of antibodies to the particles using 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide hydrochloride gave a magnetic marker for quantitative detection of immunological reactions by a SQUID sensor. The marker immobilized anti-lgE or Streptavidin were able to monitor minimal amount 0.3 pg of lgE. Amounts of lgE in a human serum, determined by the present method, well agreed with ones by an ELISA test. Thus, it was confirmed that the present SQUID technique was applicable to immunoassay using a human serum.