Magnetic Nanoparticle Relaxation Biosensor

Antibody-coated Fe₃O₄ nanoparticles are simulated as two live populations — free single particles and biomarker-cross-linked clusters — each rotating its magnetic moment toward a driving AC field with its own Brownian relaxation time. As biomarker concentration rises, more particles are pulled into slower-rotating clusters, the phase lag between field and moment grows, and the out-of-phase susceptibility signal — the actual readout of a real magnetic-relaxation immunoassay — climbs with it. Sliders for concentration, drive frequency, nanoparticle core size and solution viscosity let you explore why real assays are engineered around a narrow core-size window where Néel relaxation is frozen and only the biomarker-sensitive Brownian rotation carries the signal.