Dispersion of Fe₃O₄Nanoparticle Beads Driven by Femtosecond Laser Pulses for Quantitative Magnetic Immunoassay Measurements

Magnetic nanoparticles (MNPs) are widely employed in various medical applications. The magnetic immunoassay (MIA) has good potential for pathological diagnosis to detect biomaterials in the human body. However, MIA signals are generally affected by the aggregation of MNPs; therefore, the dispersion of MNPs during measurements is important for the quantitative measurement of immune reactions. In this study, we proposed a process for the nonthermal dispersion of MNPs using femtosecond pulse laser irradiation. To evaluate the disparity of the MNPs in the solution, the change in the magnetic signals of MNPs was measured using the developed MIA systems. Only magnetic signals of MNPs were detected by the third-harmonic measurement. Nano-sized ferrites made of magnetite (Fe3O4) coated with polyglycidyl methacrylate in pure water were used as MNP samples, and a recovery rate of 15.8% in the magnetic signals was observed before and after femtosecond pulse laser irradiation. The laser had an average power of 150 mW and a pulse width of 150 fs with a full-width at half maximum of peak intensity. This result indicates that femtosecond pulse laser irradiation is a good candidate for the dispersion of MNPs in MIA systems.