A compact device for measuring incubation of living cells with molecules attached to superparamagnetic nanoparticles consisting of iron cores by magnetizing the nanoparticles with an external pulsed field, measuring the time dependence of decaying magnetic fields of the nanoparticles as they attach to the cells by a magnetic sensor, extracting number of attached nanoparticles per cell and rate of incubation by mathematical analysis of the magnetic field emitted by the incubating cells versus time.