Synthesis of colloidal gold nanobones with tunable negative curvatures at end surface and their application in SERS

In this work, gold nanobones with the length from 50 to 70 nm were synthesized by a seed-mediated method. The plasmonic optical properties and the roles of gold seed amount in regulating the negative curvatures of the end surfaces of the gold nanobones have also been studied. Compared with the gold nanorods, a new middle surface plasmon resonance (SPR) peak appears in the absorption spectra due to the negative curvatures on the end surfaces of the gold nanobones. What is more, the surface enhanced Raman scattering (SERS) activities of gold nanobones are much stronger than that of gold nanorods. By controlling the amount of the gold seed, the wavelength of the middle SPR peak can be adjusted between 560 and 650 nm, and the corresponding negative curvature of the end surfaces could also be fine tuned. When the amount of gold seed reaches saturation, the end surfaces of nanobones have the strongest negative curvature, which results in the greatest SERS activity. This improved SERS has been attributed to the negative curvature-induced formation of the antenna dimers. The orientation of plasmon coupling between the antenna dimers is perpendicular to the nanobones. Thus, the hot spots at the ends of nanobones could always be created when the excitation beam polarization is either parallel or perpendicular to the nanobones. This negative curvature-dependent SERS enhancement lays the foundation for the extensive application of gold nanobones in SERS.