Biological immunoassay with high T-c superconducting quantum interference device (SQUID) magnetometer

A high T-c superconducting quantum interference device (SQUID) magnetometer system is developed for the application to biological immunoassay. In this application, magnetic nanoparticles are used as magnetic markers to perfor m immunoassay; i.e.. to detect binding reaction between an antigen and its antibody. The antibody is labeled with gamma -Fe2O3 nanoparticles. and the binding reaction can he magnetically detected by measuring the magnetic fie ld from the nanoparticles. Design and set up of the system is described, an d the sensitivity of the system is studied in terms of detectable,le number uf the magnetic markers. At present, we can detect 4 x 10(6) markers when the diameter of the marker is 50 nm. Total weight of the magnetic nanoparti cles becomes 520 pg ill this case. All experiment is also conducted to meas ure antigen-antibody reaction with the present system, It is shown that the sensitivity of the present system is 10 times better than that of the conv entional method using an optical marker. A one order of magnitude improveme nt of sensitivity will he realized by the sophistication of the present sys tem.