Snowman-shaped Au-FeO nanoheterodimers were synthesized by thermal decomposition of iron oleate on presynthesized Au nanoparticles. Subsequently performed ligand exchange with nitrosyl tetrafluoroborate provided water solubility and enabled X-ray-induced NO release. These Au-FeO nanoheterodimers combine high- Z material with catalytically active FeO surfaces and, moreover, plasmonic properties with superparamagnetic performance. We could establish synergetic interactions between X-radiation and both the Au and FeO surfaces, which resulted in the simultaneous production of the nitric oxide radical at the FeO surface and the superoxide radical at the Au surface. The surface-confined reaction between these radicals generated peroxynitrite. This highly reactive species may cause nitration of mitochondrial proteins and lipid peroxidation and induce DNA strand breaks. Therefore, high concentrations of peroxynitrite are expected to give rise to severe cellular energetic derangements and thereupon entail rapid cell death. As providing a common platform for X-ray-induced formation of the highly reactive radical nitric oxide, superoxide, and peroxynitrite, nitrosyl tetrafluoroborate functionalized Au-FeO nanosnowmen were shown to exhibit excellent performance as X-ray-enhancing agents in radiation therapy.

Bifunctional Au–Fe3O4 nanoheterodimers were synthesized by thermally decomposing Fe­(III)­oleate on gold nanoparticles followed by functionalizing with tiron, 2,3-dihydroxybenzoic acid, or caffeic acid. These catechol derivatives are antioxidative and thus are predicted to function as superoxide scavengers. In particular, caffeic acid lost its antioxidant capacity, although it was covalently linked through its carboxyl moiety to the Fe3O4 surface. Tiron was shown to bind via its catechol group to the Au–Fe3O4 nanoheterodimers, and 2,3-dihydroxybenzoic was just physisorbed between the oleic acid surface structures. Caffeic-acid stabilized Au–Fe3O4 nanoheterodimers turned out to act as X-ray protector in healthy cells but as X-ray enhancing agents in cancer cells. Furthermore, these functionalized Au–Fe3O4 nanoheterodimers were found to inhibit the migratory capacity of the cancer cells.

A facile one-pot synthesis route for the preparation of water-soluble, biocompatible patchy Fe3O4-Au nanoparticles (Fe3O4-Au pNPs) was developed. Biocompatibility was attained through surface functionalization with 1-methyl-3-(dodecylphosphonic acid) imidazolium bromide. The morphology, composition, crystal structure and magnetic properties of the Fe3O4-Au pNPs were investigated by conducting experiments with transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and superconducting quantum interference device, respectively. Internalization of the Fe3O4-Au pNPs by MCF-7 cells occurred via endocytosis. The performance of the Fe3O4-Au pNPs as X-ray radiosensitizer in tumor cells was compared with that of gold nanocluster and Fe3O4 NPs. For this reason, MCF-7, A549 and MCF-10A cells were loaded with the respective kind of nanoparticles and treated with X-rays at doses of 1, 2 or 3 Gy. The nanoparticle-induced changes of the concentration of the reactive oxygen species (ROS) were detected using specific assays, and the cell survival under X-ray exposure was assessed employing the clonogenic assay. In comparison with the gold nanocluster and Fe3O4 NPs, the Fe3O4-Au pNPs exhibited the highest catalytic capacity for ROS generation in MCF-7 and A549 cells, whereas in the X-ray-induced ROS formation in healthy MCF-10A cells was hardly enhanced by the Fe3O4 NPs and Fe3O4-Au pNPs. Moreover, the excellent performance of Fe3O4-Au pNPs as X-ray radiosensitizers was verified by the quickly decaying radiation dose survival curve of the nanoparticle-loaded MCF-7 and A549 cells and corroborated by the small values of the associated dose-modifying factors.

Capability of TEM and XRD to reveal scale-bridging information about the microstructure of non-monodisperse quantum dots is illustrated on the CdSe quantum dots synthesized using an automated hot-injection method.

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