A Facile Approach to Monodisperse Au Nanoparticles on Fe3O4 Nanostructures with Surface Plasmon Resonance Amplification.

Composite magnetic nanoparticles, Fe3O4@Au, were synthesized in an aqueous phase via reducing gold chloride acid (HAuCl4) in-situ on (3-aminopropyl) triethoxysilane layer around Fe3O4 nanostructures. Connection between gold and Fe3O4 was confirmed by the magnetic separa- tion technique and X-ray diffraction (XRD). Transmission electron microscopy (TEM) observation revealed that the gold nanoparticles were dispersed on the surface of magnetic Fe3O4 nanoparticles. Significantly, aqueous dispersion of such composite nanoparticles exhibited surface plasmon of Au nanoparticles. The composite magnetic nanoparticles were then modified with 3-mercaptopropionic via an Au-S bond. These ligand-modified nanoparticles were facilely conjugated to anti-penicillin antibody. The resulting Fe3O4@Au-antibody conjugates were successfully used as a powerful sandwich element and an excellent amplification reagent for surface plasmon resonance based sandwich immunoassay. By the amplification effect of Fe3O4 @ Au-antibody conjugates, there was a nearly 30-fold increase in signal and penicillin in aqueous solution was detected at a lowest detection limit of 5 ng/ml. The biological properties of the Fe3O4@Au-antibody conjugates were investigated by Western Blotting. To our knowledge, this is the first report on the in-situ synthesis of monodisperse Au nanoparticles on Fe3O4 magnetic nanostructures in an aqueous solution with surface plasmon resonance amplification.