Fast detection of biological targets with magnetic marker and SQUID

We have been developing a SQUID system for the detection of biological targets. In this system, magnetic markers are bound to the targets, and the magnetic signal from the bound markers is detected with the SQUID. In order to realize fast detection of the targets, we developed a liquid-phase detection method. First, we used large polymer beads as material to capture the targets. Since the polymer beads are uniformly dispersed in liquid, biological targets on the surface of the polymer bead can be easily coupled to the markers, which results in the fast reaction time. Next, we detected the bound markers without using the washing process to separate the bound and unbound markers, which was realized by using the difference in the Brownian relaxation time between them. Using this procedure, we demonstrated the detection of the target called IgE, as well as biotin-coated polymer beads. We obtained a good relationship between the amount of IgE and the magnetic signal. The result was the same as that obtained using the conventional procedure. The reaction time for the coupling between the magnetic marker and the target was 4 min, which was much shorter than the conventional method. These results show the usefulness of the present method.