The synthesis and characterization of polymer-coated FeAu multifunctional nanoparticles.

We report the one-pot nanoemulsion synthesis of FeAu magnetic-optical multifunctional nanoparticles coated by the biocompatible triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO). The FTIR study confirms the PEO-PPO-PEO molecules on the surface of the resulting nanoparticles. The structural characterization identifies the crystallographic parameter 4.072 A of the cubic phase and the morphology analysis gives the nanoparticle shape, size and size distribution, showing the high crystallinity of the FeAu nanoparticles and an average particle size of approximately 6.5 nm. In addition there is direct confirmation of the alloying by elemental point probing of an individual nanoparticle. Following the visual demonstration of a rapid, efficient and reversible dispersion-collection process of the nanoparticles in solution, the magnetic measurement manifests a soft ferromagnetic behavior of the nanoparticles with a small coercivity of approximately 60 Oe at room temperature. The corresponding magnetic hysteresis curves were effectively assessed by modified bi-phase Langevin equations, which were satisfactorily explained in terms of a bimodal particle size distribution. The UV-vis studies display the broadband absorption of the PEO-PPO-PEO-coated nanoparticles with the maximum surface plasmon resonance around 585 nm. The characterization and analysis, therefore, shows the unification of iron and gold into one alloy nanostructure entity covered by the biocompatible triblock copolymer thin film, preserving the optical and magnetic properties of the individual constituents. This gives the prospect of enhanced performance in applications.