Biological immunoassays without bound/free separation utilizing magnetic marker and HTS SQUID

We have developed a magnetic immunoassay system utilizing a magnetic marker and HTS SQUID. In this system, the magnetic marker was used to detect the biological material called antigen. The magnetic marker was designed so as to generate a remanence, and the remanence field of the markers that bound to the antigens was measured with the SQUID. The measurement was performed in a solution that contained both the bound and free (or unbound) markers, i.e., without using the so-called Bound/Free (BF) separation process. The Brownian rotation of the free markers in the solution was used to distinguish the bound markers from the free ones. Using the system, we conducted the detection of the biological material called human IgE. Good relationship was obtained between the detected signal and the weight of IgE. Minimum detectable weight of IgE was 2.4 pg (or 15 atto-mol). This sensitivity was limited by the background signal from the free markers.