Hybrid Plasmonic-Superparamagnetic Nanoparticle Clusters: Facile Synthesis and Characterization.

In this paper, a general method for making nanoscale Au–Fe3O4 clusters in an oil-in-water emulsion is reported, which involves thermolytic decomposition of Fe(acac)3 and reduction of AuCl3 in a hot oleyl amine–oleic acid mixture. A detailed investigation by transmission electron microscopy (TEM), X-ray diffraction, UV-vis, and vibrating-sample magnetometry was done in order to study the morphology and properties of the hybrid nanoparticulate clusters (NPCs). The NPCs are all spherical and their building blocks are individual Au and Fe3O4 nanoparticles (NPs) with an average diameter of 9.6 and 7.1 nm, respectively. TEM images show that these clusters have a flower-like morphology with controllable size. It is found that the cetyltrimethylammonium bromide concentration, the time, and the temperature of reaction are three important parameters that significantly affect the shape, size, and magnetic properties of these clusters. Magnetic measurements reveal the superparamagnetic behavior of individual NPs of Fe3O4 with a blocking $T_{\mathrm {B}}= 80.2$ K. The blocking temperature is significantly shifted to higher temperatures in the case of the clusters. The Au–Fe3O4 NPCs show a plasmonic peak at 530 nm and have a much higher magnetization than the individual NPs, making them better suited for biomedical applications. [ABSTRACT FROM AUTHOR]