The end group of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer brush on ferric oxide (Fe3O4) nanoparticles was converted from bromine (Br) to amine (NH2) by "staudinger reduction". At first, poly(MPC) was grafted by atom transfer radical polymerization (ATRP) from surface initiator fixed on Fe3O4 nanoparticles. Br element located in MPC polymer brush was converted to azide (N3). Consequently, N3 was converted to NH2 using triphenyl phosphine (PPh3) and H2O. Characterization at each step was confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) measurements. As an example aiming for diagnostic material, fluorescein isothiocyanate (FITC) was able to immobilize via reaction between NH2 group located on the end of poly(MPC) chain and isothiocyanate. The surface structure own ability of capture biomolecular throw condensation between amine in polymer brush and carboxyl group in biomolecular.