Quantitative Magnetic Immunoassays With a SQUID by Means of Mutual Inductance Calculations

We recently developed a SQUID system for magnetic immunoassays which allows fast measurements of the remanent magnetization of samples containing magnetic particles used as markers in biomedical applications. In this paper, we propose to quantify the immunoassays by estimating the specific magnetization of the samples, after magnetic flux measurements and remanent magnetic moment calculations. Since the SQUID and the sample have about the same size, we need to take into account their geometries in order to calculate properly their magnetic moments. This is accomplished by means of mutual inductance calculations. The values for the mass of particles obtained from the specific magnetization are compared with those estimated by using sample dilution factors.