Determination of the Agglutination Reactions Using Power Spectral Analysis of the Depolarized Light Intensity Fluctuations Scattered from Magnetic Particles

Presented here is a new optical method for evaluating the agglutination reactions of magnetic particles. Light intensity fluctuations scattered from the particles are detected by a cross-polarized optical measurement system. As soon as the electrolyte (NaCl)-induced coagulation of 2 min in a uniform magnetic field is completed, the sample data are gathered under the influence of a half-wave rectified magnetic field. The power spectral density has a strong peak at the frequency of the applied magnetic field. The spectral peak significantly increases by more than 103 with the NaCl concentration in the range between 0.03 and 0.1 mol/l. Furthermore, a sensitive immunoassay by means of magnetic particles can be achieved in a short-time measurement without any complex procedures.