Highly sensitive detection of magneto-optical markers based on magneto-optical gate effect

In this paper, a new concept of magnetic nanoparticles (MNPs) as magneto-optical markers is proposed, and a "magneto-optical gate" effect is explored. High-sensitivity detection of MNPs was developed based on this principle. Under irradiation from monochromatic light with a wavelength much larger than the size of a given MNP, Rayleigh scattering occurs on the MNP surface. The MNPs anisotropic and orientate themselves into chains, meaning that the Rayleigh scattering now decreases under magnetic field excitation. After applying an AC magnetic field with a frequency of f, the transmitted light passing through the MNPs reagent generates an AC signal with a frequency of 2f. Moreover, the AC signal disappears after removal of the magnetic field. This creates a "magneto-optical gate" effect. The instantaneous and highly sensitive detection of magnetooptical markers with a concentration of 0.2 mu g/mL and an effective optical path length of 10 mu m is realized based on this "magnetooptical gate" effect.