Supersensitive device for measuring the magnetic nanoparticles, based on the nonlinear magnetization of MP at the two frequencies and recording the response to the combinatorial frequencies.

The threshold of sensitivity of this instrument is 3 ng. of Fe₃O₄ nanoparticles in a volume of 0.1-0.5 ml, which is consistent with the level of sensitivity of the MP on the basis of isotope 59^Fe by γ-radiation.

Linear range of quantitative registration of MP is 4-5 orders of magnitude. On the basis of the registrar different formats of magnetic immunoassay has been developed using magnetic nanoparticles as markers of biochemical reactions.