Fe3O4-protected gold nanoparticles: New plasmonic-magnetic nanomaterial for Raman analysis of surfaces

The first example of the application of core–shell nanoparticles with a plasmonic core and a magnetic shell for the shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) analysis of surfaces has been reported. Synthesized Au@Fe3O4 nanoparticles are efficient electromagnetic nanoresonators that induce a significant increase in the efficiency of Raman scattering for molecules in their close proximity. The formed shell layer of Fe3O4 is thin enough not to significantly dampen the electromagnetic enhancement generated by the plasmonic gold core, yet the amount of Fe3O4 is sufficient to allow the nanomaterial to be manipulated by a magnetic field. It is possible to form homogeneous layers of Au@Fe3O4 nanoresonators with different and controllable surface densities using a simple procedure: the deposition of a drop of a sol of Au@Fe3O4 nanoparticles and evaporation of the solvent while the sample is placed in a strong magnetic field. This method of homogeneous deposition of a layer of SHINERS nanoresonators could not be applied for the previously used SHINERS materials due to the socalled coffee ring effect. The possibility of an easily controllable homogeneous deposition of Au@Fe3O4 nanoparticles on the surface of a sample placed on a strong permanent magnet makes these nanoparticles a very promising material for SHINERS.