Magnetic Fe₃O₄‐Au core‐shell nanostructures for surface enhanced Raman scattering

Abstract

Abstract The synthesis, structural and optical characterization, and application of superparamagnetic and water‐dispersed Fe 3 O 4 ‐Au core‐shell nanoparticles for surface enhanced Raman scattering (SERS) is reported. The structure of the nanoparticles was determined by scanning transmission electron microscopy (STEM) and high‐resolution transmission electron microscopy (HRTEM). STEM images of the Fe 3 O 4 ‐Au core‐shell nanoparticles reveal an average diameter of 120 nm and a high degree of surface roughness. The nanoparticles, which display superparamagnetic properties due to the core Fe 3 O 4 material, exhibit a visible surface plasmon resonance (SPR) peaked at 580 nm due to the outer gold shell. The nanoparticles are used as a substrate for surface enhanced Raman scattering (SERS) with rhodamine 6G (R6G) as a Raman reporter molecule. The SERS enhancement factor is estimated to be on the order of 10 6 , which is ∼ 2 times larger than that of conventional gold nanoparticles (AuNPs) under similar conditions. Significantly, magnetically‐induced aggregation of the Fe 3 O 4 ‐Au core‐shell nanoparticles substantially enhanced SERS activity compared to non‐magnetically‐aggregated Fe 3 O 4 ‐Au nanoparticles. This is attributed to both increased scattering from the aggregates as well as “hot spots” due to more junction sites in the magnetically‐induced aggregates. The magnetic properties of the Fe 3 O 4 core, coupled with the optical properties of the Au shell, make the Fe 3 O 4 ‐Au nanoparticles unique for various potential applications including biological sensing and therapy.