Magneto-Optical Characteristics of Streptavidin Coated Core–Shell Fe3O4-Au Nanoparticles for Faraday Bioassay
Jian-Ming Chen1*, Chiu-Hsien Wu1,2, Kuen-Lin Chen2
1Institute of NanoScience, National Chung Hsing University, Taichung, Taiwan
2Department of Physics, National Chung Hsing University, Taichung, Taiwan
* presenting author:Jian-Ming Chen,
Recently, the gold coated magnetic nanoparticles (Fe3O4@Au NPs) are of interest to researchers because of their unique magnetoplasmonic characteristics. It had been reported that the Faraday effect of the Fe3O4@Au can be effectively enhanced because of the surface plasmon resonance from the gold shell. Besides, the Fe3O4@Au are ideal material for biomedical applications because of their high stability and good biocompatibility. In this study, iron oxide nanoparticles were prepared by co-precipitation of Fe(II) and Fe(III) and then the synthesized magnetic nanoparticles (Fe3O4) were dispersed in 0.1 M Tetramethylammonium hydroxide (TMAOH) solution. Next, the Fe3O4 were stirred with sodium citrate to replace the surface hydroxide ions with citrate ions. Afterward HAuCl4 solution and hydroxylamine hydrochloride (NH2OH·HCl) were added to the colloid to reduce the gold shell on the surface of Fe3O4. Furthermore, surface modification was used to bind streptavidin (STA) onto gold surface. 11-Mercaptoundecanoicacid (11-MUA) modifies gold shell to carboxylate Fe3O4@Au. For activating the surface of the gold prior to covalent coupling, N-(3-Dimethylaminopropyl)-N’-ethylcarbodiimidehydrochloride (EDC) was added to enable the reaction of carboxyl groups on the gold surface with the amino groups of STA molecules to form the bioconjugation of STA-Fe3O4@Au. The products was characterized by powder X-ray diffraction (XRD)﹐transmission electron microscopy (TEM), superconducting quantum interference device (SQUID), Raman spectrum and UV-visible spectrum (UV-vis). In addition, we measured the Faraday rotation of the Fe3O4@Au by our home made ac magneto-optical Faraday system and compared the results with MNPs’. Finally, we expect to apply the Fe3O4@Au to magneto-optical Faraday bioassay.

Keywords: magneto-optical, magnetic nanoparticles, Faraday bioassay, Core–Shell