High-T-c SQUID system for biological immunoassays

A high-T-c SQUID system is developed for the application to biological immu noassay, i.e., for the detection of an antigen with a magnetically labeled antibody. In order to improve the system performance, two issues are studie d. One is the use of a gradiometer to suppress the system noise due to resi dual environmental noise. It is shown that the noise of the gradiometer sys tem is five times smaller than that of the magnetometer system. The other i s to increase the signal field from the magnetic marker. The signal can be increased by increasing an applied field B-cx or by using remanence of the marker. If these improvements were fully developed, it will be possible to develop the system that is 100 times more sensitive than the conventional o ptical method. (C) 2001 Elsevier Science B.V. All rights reserved.