Detection of magnetic nanoparticles with superconducting quantum interference device (SQUID) magnetometer and application to immunoassays

A system is developed to magnetically measure biological antigen-antibody r eactions with a superconducting quantum interference device (SQUID) magneto meter. In this system, antibodies are labeled with magnetic nanoparticles o f g-Fe2O3, and the antigen-antibody reactions are measured by detecting the magnetic field from the magnetic nanoparticles. A setup of the system is d escribed, and the sensitivity of the system is studied in terms of detectab le weight of nanoparticles. Magnetic particles as small as 600 pg can be de tected at present. An experiment is also conducted to measure antigen-antib ody reaction with the present system. It is shown that the sensitivity of t he present system is better than that of the conventional optical method. A one order of magnitude improvement of sensitivity will be realized by the sophistication of the present system.