Synthesis of Bifunctional Magneto-Plasmonic Fe₃O₄@SiO₂–Au Nanoparticles by an Ultrasound-Assisted Chemical Method

Abstract

Bifunctional magneto–plasmonic nanoparticles Fe₃O₄@SiO₂–Au (FSA) were successfully synthesized by an ultrasound-assisted chemical method with high pH conditions. Gold ions were absorbed on the surface of silica-coated magnetic nanoparticles and then reduced by sodium borohydride (NaBH₄) under the influence of a 200 W ultrasonic wave for 45 min. The magneto–plasmonic FSA exhibits superparamagnetism with a high saturation magnetization and simultaneously absorbs visible blue light with the surface plasmon resonant (SPR) peak at around 545 nm. When the amount of precursor gold ions increased from 16 µmol to 40 µmol, the relative atomic ratio of gold/iron increased from 0.84 to 3.35. In the consequence, the peak absorption positions increased from 540 nm to 550 nm, which can be explained by the increase in the Au crystal size. The controllable optical and magnetic properties of the nanoparticles show that they have high potential in biomedical applications, such as MR imaging, SERS-enhanced, computed tomography imaging, photothermal therapy, etc.