In the present study Fe 3 O 4 magnetic nanoparticles were synthesized by coprecipitation of Fe 2+ and Fe 3+ from chlorides. In the next step magnetite–gold core–shell nanoparticles were synthesized from HAuCl 4 using an ethanol as a reducing agent. Finally, magnetic nanoparticles were functionalized by hexadecanethiol. The immobilization of biological molecules (trypsin and glucose oxidase) to the thiol-modified and unmodified magnetite–gold nanoparticles surface was tested. The resulting nanoparticles were characterized by infrared spectroscopy, differential scanning calorimetry, Mössbauer spectroscopy and transmission electron microscopy.