In this study, we report a method to synthesize core–satellite structured Fe₃O₄/polydopamine/Au composite nanoparticles (NPs). Firstly, the Fe₃O₄/polydopamine composite NPs with a well-defined core–shell structure are obtained using dopamine self-polymerization to form thin, surface-adherent polydopamine films onto the surface of a Fe₃O₄ “core”. The polydopamine shell could be adjusted by controlling the experimental parameters such as reaction time and the reactant concentrations. Then, numerous “satellites” of gold nanoparticles were assembled on the surface of Fe₃O₄/polydopamine by reducing Au³⁺ between the Fe₃O₄/polydopamine solid and HAuCl₄ solution. Next, 11-mercaptoundecanoic acid (11-MUA) forms a self-assembled monolayer of MUA on the surface of the Au NPs and polydopamine layer. Finally, IDA-Cu functionalized Fe₃O₄/polydopamine/Au composite NPs are obtained by the carboxyl groups of MUA reacting with iminodiacetic acid (IDA), charged with Cu²⁺. The IDA-Cu groups, acting as an “anchor”, are attached on the gold and the polydopamine surface is designed for capturing target molecules. The morphology, structure and composition of the nanocomposites are characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectrometry (XPS). The resulting Fe₃O₄/polydopamine/Au composite NPs show not only a strong magnetic response to an externally applied magnetic field, but are also highly specific to protein bovine hemoglobin (BHb), and removal of abundant protein BHb in the bovine blood as well. This opens a novel route for future application in removing abundant protein in proteomic analysis.