An efficient strategy to synthesize a multifunctional ferroferric oxide core@dye/SiO₂@Au shell nanocomposite and its...

Magnetic nanoparticles with superparamagnetic properties have provided a versatile platform for constructing multifunctional nanostructures, which show great promise in tumor-targeted multimodal imaging and non-invasive therapy. Herein, we first systematically investigated the effect of crystalline water in the reactants on the assembly of primary Fe₃O₄ nanocrystals prepared by a solvothermal method. The presence of water would hinder the formation of monodisperse Fe₃O₄ nanocrystals. The regular spheric Fe₃O₄ nanoclusters with high saturated magnetization values and superparamagnetism can be synthesized with anhydrous reactants and sodium citrate as a stabilizer. Furthermore, the monodisperse Fe₃O₄ nanoclusters were used as cores and coated with fluorescent dye molecule covalently-doped silica layers, on which carbohydrate-stabilized gold nanoparticles could be assembled. Fe₃O₄ core@dye/SiO₂@Au shell nanocomposites were gradually formed by several cycles of a reduction process in the growth solution. The resultant ferroferric oxide@dye/silica@Au nanoshells exhibited good biocompatibility, an excellent T₂-weighted relaxation rate, a strong fluorescence signal and tunable near IR surface plasmon resonance (SPR) spectra. Finally, colorectal cancer cell SW620-specific phage fusion proteins (fusion-pVIII) were conjugated onto the surface of gold nanoshells, which exhibited a maximal SPR peak of 774 nm and effectively achieved the photothermal ablation of tumor cells selectively with 808 nm laser irradiation for 10 min in a light intensity of 3 W cm^-2. Additionally, the prepared bio-nanocomposite showed good T₂-weighted magnetic resonance imaging (MRI). Therefore, the Fe₃O₄@dye/SiO₂@Au@fusion-pVIII nanocomposites were successfully prepared and applied for targeted optical imaging and the targeted photothermal therapy of cancer cells. The prepared bio-nanocomposites can be potentially applied as ideal contrast agents for tumors in MRI.