(Invited) Biological Applications of Magnetic Nanoparticles for Magnetic Immunoassay and Magnetic Particle Imaging

Here, we introduce the application of magnetic nanoparticles (MNPs) for magnetic immunoassay and magnetic particle imaging (MPI). First, we present a liquid-phase magnetic immunoassay system that uses the difference in Brownian relaxation between bound and unbound magnetic particles. We found that the minimum detectable molecular number concentration of the developed magnetic immunoassay system is 3.6 × 10−18 mol/mL. We then studied the effect of the alignment of the easy axes on the performance of the MPI. Although the detection sensitivity can be improved by using an aligned MNP sample, the spatial resolution of the aligned sample strongly depends on the direction of alignment of the easy axes.