Galvanic Displacement Synthesis of Monodisperse Janus- and Satellite-Like Plasmonic–Magnetic Ag–Fe@Fe₃O₄ Heterostructures with Reduced Cytotoxicity

The unique physicochemical properties of silver nanoparticles offer a large potential for biomedical application, however, the serious biotoxicity restricts their usage. Herein, nanogalvanic couple Ag–Fe@Fe₃O₄ heterostructures (AFHs) are designed to prevent Ag⁺ release from the cathodic Ag by sacrificial anodic Fe, which can reduce the cytotoxicity of Ag. AFHs are synthesized with modified galvanic displacement strategy in nonaqueous solution. To eliminate the restriction of lattice mismatch between Fe and Ag, amorphous Fe@Fe₃O₄ nanoparticles (NPs) are selected as seeds, meanwhile, reductive Fe can reduce Ag precursor directly even at as low as 20 °C without additional reductant. The thickness of the Fe₃O₄ shell can influence the amorphous properties of AFHs, and a series of Janus- and satellite-like AFHs are synthesized. A “cut-off thickness” effect is proposed based on the abnormal phenomenon that with the increase of reaction temperature, the diameter of Ag in AFHs decreases. Because of the interphase interaction and the coupling effect of Ag and Fe@Fe₃O₄, the AFHs exhibit unique optical and magnetic properties. This strategy for synthesis of monodisperse heterostructures can be extended for other metals, such as Au and Cu.