## 3 Results
the image phase-contrast variation across the Fe\({}_{3}\)O\({}_{4}\)-Au pNP, which reveals 6 diffraction spots for the (111) planes of the Au nanopatch and 2 spots for the (511) planes of the Fe\({}_{3}\)O\({}_{4}\) NP (Figure 3d). The magnetic properties of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs were examined by measuring magnetization curves as a function of the applied magnetic field H and in dependence on the temperature T. The magnetization curve in Figure 4a measured at 300 K reflects the superparamagnetic character of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. The magnetization saturation (M\({}_{\rm S}\)) value of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs is 43.6 emu/g. This value is significantly smaller than that (i.e., 66.1 emu/g) derived from the magnetization curves of nearly equally sized Fe\({}_{3}\)O\({}_{4}\) NPs [30]. The smaller M\({}_{\rm S}\) value can be explained by the magnetically inactive gold surface layer. In addition, the interface communication between the Au nanopatches and the Fe\({}_{3}\)O\({}_{4}\) core may also partially destroy the magnetization properties of the Fe\({}_{3}\)O\({}_{4}\) NPs. The superparamagnetic behavior of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs is confirmed by the temperature dependence of the zero-field cooled-field cooled (ZFC-FC) magnetization under an applied magnetic field of 0.01 T (Figure 4b). The ZFC curve exhibits a broad maximum indicating the superparamagnetic blocking temperature at 80 K. The broadness of the ZFC curve indicates the existence of a dipolar coupling between nanoparticles due to their proximal distance. Figure 3: (**a**) HRTEM image of a Fe\({}_{3}\)O\({}_{4}\)@Au pNP (**b,c**) with magnified sections, and (**d**) the fast Fourier transform (FFT) image. The UV-Vis absorption spectrum of an aqueous solution of MPA-stabilized Fe\({}_{3}\)O\({}_{4}\)@Au pNPs (Figure 5) exhibits a broad shoulder between 320 and 420 nm, and a smaller one between 480 and 500 nm. The spectral feature around 490 nm is assigned to the partially masked plasmon resonance band of larger gold nanopatches, whereas the broad shoulder presumably arises from charge transfer across the Au-Fe\({}_{3}\)O\({}_{4}\) interface. To improve the water solubility, the MPA-terminated Fe\({}_{3}\)O\({}_{4}\)@Au pNPs were subsequently coated with 1-methyl-3-(dodecylphosphonic acid) imidazolium (Imidazolium-PA). This amphiphilic surfactant was recently shown to form a self-assembled monolayer on a nanoparticle surface [31]. The FTIR transmission spectra of the MPA-terminated Fe\({}_{3}\)O\({}_{4}\)@Au pNPs (black line) and the Imidazolium-PA-terminated Fe\({}_{3}\)O\({}_{4}\)@Au pNPs (red line) are depicted in Figure 6. For MPA-terminated Fe\({}_{3}\)O\({}_{4}\)@Au pNPs, the two peaks at 1645 and 1532 cm\({}^{-1}\), which are ascribed to the symmetric and asymmetric carboxylate (COO\({}^{-}\)) stretch, respectively, substantiate that MPA was covalently bound to the Fe\({}_{3}\)O\({}_{4}\) nanoparticle surface [32]. The absence of the characteristic peak at 2575 cm\({}^{-1}\) for the S-H stretching represents an indirect evidence for the formation of the covalent Au-S bond at the gold surface. MPA was very likely bound to both, the Fe\({}_{3}\)O\({}_{4}\) and Au surface. In case of the surfactant Imidazolium-Pa, the predominant peaks at 991 and 1395 cm\({}^{-1}\) are assigned to the symmetric P-O and P=O stretching vibration, respectively. Furthermore, the CH\({}_{2}\)/CH\({}_{3}\)-stretching vibrational bands peaking at 2849 and 2920 cm\({}^{-1}\) indicate the surface binding of Imidazolium-PA for Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. Figure 4: (a) Magnetization curve at 300 K and, (b) the temperature dependence of the ZFC/FC magnetization of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. Figure 5: UV-Vis absorption spectrum of an aqueous solution of MPA-stabilized Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. The cellular uptake of Imidazolium-PA-terminated Fe\({}_{3}\)O\({}_{4}\)@Au pNPs by human breast adenocarcinoma cells (MCF-7 cells) was examined using TEM (Figure 7).