One-pot solvothermal synthesis of Fe3O4–PEI composite and its further modification with Au nanoparticles

A one-step strategy for the facile synthesis of polyethyleneimine-functionalized Fe3O4 (Fe3O4-PEI) composite is presented in this study. We also investigated the effects of reaction time and NaAc on the composite sizes. The composite with good dispersion, wonderful crystallization, and excellent magnetism was obtained through one-pot solvothermal reaction. In the sequential presence of PEI and colloidal gold (Au) solution, plentiful Au nanoparticles with a diameter of 5 nm were assembled on the surface of Fe3O4–PEI to get Fe3O4–PEI–Au1–PEI–Au2 (Fe3O4/Au) composite. In-depth characterization of the composite formation process was performed using transmission electron microscopy, scanning electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer, and UV–Visible spectroscopy. The Fe3O4/Au composite was obtained with an average diameter of 150 nm, and the absorption peak was red-shifted to 580 nm. The synthesized Fe3O4/Au composite, the saturation magnetization of which was 40.4 emu/g, presented good magnetic property. Moreover, the composite could easily combine with up to 890 μg antibodies per mg, and the antibodies still kept good immunocompetence after immobilization. These advantages suggest its great potential for applications in vitro, such as separation and immunoassay.