## 3 Results and Discussion  
### Characteristics of Fe\({}_{3}\)O\({}_{4}\)/Au Gold Magnetic Nanoparticles by TEM and EDX  
TEM images of Fe\({}_{3}\)O\({}_{4}\) nanoparticles, Au nanoparticles and Fe\({}_{3}\)O\({}_{4}\)/Au gold magnetic nanoparticles at various resolutions are shown in Figure 2 and the corresponding EDX spectrum of Fe\({}_{3}\)O\({}_{4}\)/Au is presented in Figure 3. The Fe\({}_{3}\)O\({}_{4}\) nanoparticles were in cubic shape and the particle size was in the range of 100-200 nm (Figure 2a) and the spherical or oval Au nanoparticles had a relatively narrow size distribution with a diameter ranging from 10 to 20 nm (Figure 2b). Figure 2c demonstrates the structure of Fe\({}_{3}\)O\({}_{4}\)/Au gold magnetic nanoparticles. Obviously, the cubic Fe\({}_{3}\)O\({}_{4}\) nanoparticles were densely covered by a layer of spherical Au nanoparticles. At higher resolutions, the Au nanoparticles were found to closely attach on the surface of Fe\({}_{3}\)O\({}_{4}\) nanoparticle (Figure 2d,e). Figure 2f clearly shows the crystal lattice fringes of Au nanoparticles and Fe\({}_{3}\)O\({}_{4}\) nanoparticles. The EDX spectrum (Figure 3) of the gold magnetic nanoparticles shows Au signal peaks and Fe signal peaks from Au nanoparticles and Fe\({}_{3}\)O\({}_{4}\) nanoparticles, respectively, as well as C peaks and Cu peaks from the ultrathin carbon-coated copper grids. These results indicated the formation of Fe\({}_{3}\)O\({}_{4}\)/Au gold magnetic nanoparticles.  
Figure 2: _Cont._  
Characterization of AOA-Coated Gold Magnetic Nanoparticles (Fe\({}_{3}\)O\({}_{4}\)/Au\(-\)AOA) by FTIR  
Figure 4a presents the FTIR spectrum of Fe\({}_{3}\)O\({}_{4}\)/Au. The broad double peaks at 1110 cm\({}^{-1}\) and 1014 cm\({}^{-1}\) are due to the stretching vibration of Si-O-Si. Au, as a simple metal substance, has no obvious absorption peaks. Figure 4b clearly shows characteristic double peaks of the amino group of 5-aminoorotic acid (AOA) at 3470 cm\({}^{-1}\) and 3343 cm\({}^{-1}\), as well as a strong carbonyl C=O stretching vibration at 1696 cm\({}^{-1}\), respectively. Figure 4c indicates the spectrum of AOA-coated gold magnetic nanoparticles synthesized by the connection of AOA to Fe\({}_{3}\)O\({}_{4}\)/Au nanoparticles through polyethylene glycolthiol (NHS-PEG-SH). As the -SH group was firmly attached to the surface of Fe\({}_{3}\)O\({}_{4}\)/Au via  
Figure 3: Energy dispersive X-ray (EDX) spectrum of Fe\({}_{3}\)O\({}_{4}\)/Au gold magnetic nanoparticles.  
Figure 2: Transmission electron microscope (TEM) images of Fe\({}_{3}\)O\({}_{4}\) nanoparticles (**a**), Au nanoparticles (**b**), Fe\({}_{3}\)O\({}_{4}\)/Au nanoparticles at normal resolution (**c–e**), and high resolution (**f**).  
a stable Au-S bond, the -NHS reacted with the amino group of AOA to form an amide bond by amidation reaction. As can be seen from Figure 4c, the disappearance of the amino double peaks and the appearance of a broad amide peaks between 3100 cm\({}^{-1}\) and 3200 cm\({}^{-1}\) in addition to the carbonyl C=O peak at 1696 cm\({}^{-1}\) unambiguously proved that the AOA had been coated on the surface of Fe\({}_{3}\)O\({}_{4}\)/Au via the polyethylene glycolthiol linkage.