Development of methods for fabricating nanoparticles composed of magnetite, gold, and silica toward diagnostic imaging

Nontoxic nanoparticle contrast agents with multiple imaging functions are required for medical diagnostic imaging, and coating the nanoparticle contrast agents with less toxic materials meets this requirement. This work proposes a method for fabricating magnetite, gold (Au), and silica nanoparticles toward diagnostic imaging. The proposed method involved four steps: the synthesis of magnetite (Fe₃O₄) nanoparticles, synthesis of Au nanoparticles, formation of a composite of Fe₃O₄ and Au (Fe₃O₄/Au), and silica coating of Fe₃O₄/Au nanoparticles. The synthesis of 6.3 ± 1.2 nm-sized Fe₃O₄ nanoparticles was performed via a salt-based reaction in an aqueous solution containing FeCl₃, FeCl₂, citric acid, HCl, and NaOH. The synthesis of 2.2 ± 0.4 nm-sized Au nanoparticles was performed with a reduction of HAuCl₄ in an aqueous solution containing tetrakis (hydroxymethyl) phosphonium chloride, and NaOH. The silica coating of Fe₃O₄/Au nanoparticles was performed with a sol–gel reaction in ethanol containing Fe₃O₄ nanoparticles, Au nanoparticles, poly-diallyldimetheylammonium chloride, tetraethylorthosilicate, NaOH, and water under sonication. The Fe₃O₄/Au/SiO₂ nanoparticles were degraded in a fetal bovine serum/phosphate-buffered saline solution, PEGylated Fe₃O₄/Au/SiO₂ (Fe₃O₄/Au/SiO₂–PEG) nanoparticles adsorbed protein after PEGylation, and Fe₃O₄/Au/SiO₂–PEG nanoparticles had a magnetic property and an X-ray imaging ability, revealing that the composite nanoparticles were expected to function as a safe and excretable contrast agent of MRI and X-ray.