Surface-enhanced Raman spectroscopy on single Fe2O3@Au spindle nanoparticle: polarization dependence and FDTD simulation

The surface-enhanced Raman scattering (SERS) effect was critically dependent on the shape of the plasmonic nanostructures. It still remains a significant challenge in exploring the correlation between the SERS effect and the shape of nanostructures. Here, the polarized SERS combined with finite difference time domain (FDTD) calculation was developed to elucidate the origination of the SERS effect on an anisotropic spindle-shaped Fe2O3@Au nanoparticle. The surface enhancement factor for spindle-shaped Fe2O3@Au nanoparticles was estimated to be about six-orders by using pyridine as model molecules. A dramatic variation in SERS effect was observed by changing the excitation polarization direction. The maximum SERS intensity was detected when the excitation polarization was parallel to the long axes of Fe2O3@Au nanoparticles, while the minimum intensity was observed at the perpendicular orientation. The remarkable polarization-dependent SERS effects can be attributed to the local enhanced electric field that strongly depends on the polarization direction. The theoretical simulation based on the FDTD method was performed to evaluate the distribution of a local electromagnetic field on Fe2O3@Au single nanoparticles. It was in good agreement with the experimental results. This strategy provided deeper insight into the distribution of the SERS effect on a single anisotropic nanoparticle.