Nanosized ferrite spherical particles, ∼30 nm in diameter as revealed by scanning electron microscopy, were synthesized from an aqueous Fe(OH)2 suspension (pH=7.6–8.0) at 25 °C by oxidizing it with H2O2. The nanoparticles were of a spinel structure of an intermediate between Fe3O4 and γ-Fe2O3, as revealed by x-ray diffraction. Compared to the nanoparticles synthesized by our previous method in which an aqueous solution of Fe2++Fe3+ was oxidized by air (oxygen), the nanoparticles increased in size, from ∼10 nm (previous method) to 30 nm. Also saturation magnetization increased, though slightly, from 76 emu/g (previous method) to 80 emu/g (present method). Therefore, the ferrite nanoparticles synthesized by this method will improve the efficiency of magnetic separation. Because synthesis is performed at room temperature and neutral conditions (pH=7.1–7.8), which are compatible with most bioactive molecules (e.g., antibodies and proteins), these molecules will be immobilized onto the surface of the nanoparticles during their syntheses.

FITC-avidin, a fluorescent substance, was successfully immobilized onto the surfaces of nanoparticles of ferrite of a mixture between Fe3O4 and γ-Fe2O3, during the synthesis of the nanoparticles an aqueous solution from containing Fe2+, Fe3+, and FITC-avidin. The particles were spherical in shape and ∼10 nm in size. The process was performed in open air, on near neutral conditions of pH 7–9, and at ∼4 °C. Utilizing the fluorescent magnetic particles, we successfully observed magnetic patterns (track pitch 187.5 μm) written on a floppy disk.

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