Bifunctional Au–Fe₃O₄ Nanoheterodimers Acting as X‑ray Protector in Healthy Cells and as X‑ray Enhancer in Tumor Cells

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.