Synthesis and characterization of superparamagnetic nanoparticles coated with fluorescent gold nanoclusters

Multifunctional nanoparticles (NPs) combining the superparamagnetism of Mn-Zn-ferrite and the fluorescence property of gold nanoclusters have been prepared by wet chemistry. Magnetic NPs synthesized by coprecipitation method were coated several times with oppositely charged polyelectrolytes using the layer-by-layer technique. Common techniques (FTIR, electron microscopy, zeta potential…) indicated the monodispersity and the stability of the coated nanoparticles providing a positive charged surface. Fluorescent gold nanoclusters bound to a standard protein bovine serum albumin (BSA) were adsorbed on the surface of the magnetic NPs. Structural investigations prove the presence of small gold clusters (~ 2 nm) in a shell surrounding the magnetic nanomaterial. The stable nanocomposite kept the original fluorescence property of the metal clusters with 211-fold increase of the red emission (= 690 nm) compared to the uncoated NPs. These NPs can be moved with a permanent magnet despite a 72 wt% increase of the non magnetic fraction due to the polyelectrolyte coating and the protein absorption.