We prepared an amino-substituted nanoparticle by means of the amino-silane coupling procedure. The original magnetic particles were γ-Fe2O3, which ranged in size from 1.3 to 34 nm, surrounded by amorphous SiO2. The modification of the magnetic particle by the addition of an amino group was confirmed using a Fourier transform infrared spectrophotometer (FT-IR). The X-ray diffraction patterns showed a spinel structure both before and after modification of the amino group. The magnetization curve indicated paramagnetic behavior for the 3 nm particles, superparamagnetic behavior for the 7 nm particles, and ferromagnetic behavior for 9 nm particles at room temperature. A fluorescent reagent was applied to the particle, and the particle was introduced into a cell. The magnetic particles in the cell were localized using an external magnetic field.