Nanomaterials extensively studied by nanotechnology scientists have been extensively applied in biomedicine, chemistry, physics and other fields nowadays. Magnetic nanoparticles, surpassing nano applications, are found to possess many advantages over nonmagnetic nanomaterials. Graphene oxide (GO), in particular, draws growing scholarly attention due to its large surface area, good water solubility and biocompatibility, rich surface functional group and easy-to-modify property. In this paper, we modify the Polyethylene mide (PEI) molecule on the surface of GO to increase its biocompatibility. The Au-Fe₃O₄ nanoparticles and folic acid molecules on the ligand make the resulting composite applicable both in magnetic resonance imaging and in cancer cell targeting. In addition, the π-π accumulation of doxorubicin used to load the anticancer drug can release the drug under the acid condition of the cancer cells, detect the cancer cells by fluorescence and realize the multi-mode detection of cancer cells.