A graphene-interlayered magnetic composite as a multifunctional SERS substrate

Investigations in the combination of graphene with noble-metal nanostructures mostly focus on the fabrication of stacked hybrid films or nanoparticle (Au or Ag NPs) decorated graphene sheets, while few are carried out in graphene built-in monodispersed microspheres. Herein, we propose a novel hierarchical composite with a silver-shelled Fe₃O₄ microsphere as the initial core and graphene oxide (GO) as the multifunctional inserted layer. The flexible GO provides abundant nucleation sites for further in situ growth of Au nanoparticles. Moreover, it introduces considerable chemical enhancement and enhances surface adsorption toward aromatic molecules. Considering the synergistic properties of versatile GO with noble-metal nanostructures, the synthesized Fe₃O₄@Ag-rGO-Au microspheres were expected to have excellent surface-enhanced Raman scattering (SERS) activity, which was verified by the detection of the sulfhydryl-contained PATP and aromatic DTTC, with respective detection limits of 10^-11 M and 10^-10 M. The enhancement factor (EF) was calculated to be 2.83 × 10⁶ for totally symmetric (a1) vibrations located at 1077 cm^-1 of PATP. Additionally, its fast magnetic response enables rapid separation from solution, which is a key factor for many practical applications. Therefore, the well-dispersed hybrid microspheres have enormous potential in sensing applications as well as in effective immobilization and enrichment of biomolecules and aromatic pollution.