Novel Aqueous Fabrication and Characterization of Gold Coated Cobalt Nanoparticles

Background: Biological applications such as imaging and targeted drug delivery and many others require non-toxic, stable, inert and biocompatible nanoparticles. Coating the nanoparticles with inert materials is one of the ways that is used to enhance the stability and biocompatibility of nanoparticles. In particular, gold coating is very attractive as it reduces the toxicity of the magnetic nanoparticles, enhances their stability in biological systems and provides stable and inert platforms for further functionalization. However, current methods for the fabrication of gold-coated magnetic nanoparticles are carried out in non-aqueous media with toxic organic solvents at very high temperatures. In this article, we demonstrate a novel procedure for the fabrication of gold-coated cobalt nanoparticles. Unlike previous procedures that are performed in nonaqueous conditions at elevated temperatures, this method can be carried out exclusively in aqueous media at ambient conditions. Methods: Cobalt nanoparticles were prepared by the reduction of a cobalt precursor and subsequently coated with gold by an electroless plating procedure. The Co NPs and the gold-coated Co NPs were characterized by ultraviolet-visible (UVVis) spectroscopy, X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometry, scanning electron (SEM) and transmission electron (TEM) microscopy. Results: Results from SEM and TEM imaging indicated that the resulting gold-coated Co NPs had a Co core and an Au shell, were well dispersed and within the nanoscale range in terms of size (45 ± 8 nm in diameter). EDX confirmed the presence of both Co and Au in the coated sample. XRD data demonstrated a pattern with diffraction peaks indicating presence of gold and cobalt. SQUID results indicated that the magnetic properties of the nanoparticles were maintained even after coating with gold. Conclusion: All these results confirmed the fabrication of stable, well dispersed magnetic gold-coated Co NPs in aqueous media making them potentially ideal for downstream applications such as in vivo imaging, therapeutics and biological applications.