Magneto-plasmonic Au-Coated Co nanoparticles synthesized via hot-injection method

A synthetic procedure is described to obtain superparamagnetic Co nanoparticles (NPs) via hot-injection method in the presence of sodium borohydride. The Co NPs obtained have an average diameter of 5.3 nm and saturation magnetization of 115 emu glsupg-1l/supg. A modified Langevin equation is fitted to the magnetization curves using a lognormal distribution for the particles diameter and an effective field to account for dipolar interactions. The calculated magnetic diameter of the Co NPs is 0.6 nm smaller than TEM-derived values, implying a magnetic dead layer of 0.3 nm. The magnetic core is coated with Au to prevent oxidation, resulting in water-stable magneto-plasmonic Co/Au core/shell NPs with saturation of 71.6 emu glsupg-1l/supg. The coating adds a localized surface plasmon resonance property with absorbance in the so-called "therapeutic window" (690-900nm), suitable for biomedical applications. It is suggested that these multifunctional NPs are distinguished as a potential platform for applied and fundamental research.