The surface plasmon resonance( SPR) of gold( Au) nanorod can be tuned in a large visible-near infrared( Vis-NIR) region by changing the aspect ratio of nanorod. Compared with the SPR of isolated Au nanorod,assembly of Au nanorods exhibits strong coupling effect in the nanogap and wealthy changes in the optical spectra. The SPR coupling effects and localized electronic fields for end-to-end( E-E) and side-by-side( S-S) assembled Au nanorods dimers are studied through finite-difference time-domain( FDTD) simulation. With decreasing the gap spacing,the longitudinal SPR( SPRL) red-shifts for the E-E orients Au nanorods dimer and blue-shifts for S-S orientes Au nanorods dimer. The transverse SPR( SPRT) has slight red-shifting for S-S assembly and no shifting for the E-E assembly. Moreover,a new coupling SPR appears for the E-E assembly in a long wavelength in the NIR region,blue-shifting and enhancing with decreasing the gap spacing. Based on the spring oscillator model and the polarization of nanoparticles with incident electric field,the SPR shifting and the appearance of new coupling SPR of assembled Au nanorods are proposed.
Through anisotropic Ag overgrowth on the surface of Au nanobipyramids(Au NBPs), high-purity and sizecontrolled Ag nanorods(Au/Ag NRs) are obtained by a simplified purification process. The diameters of the Au/Ag NRs are determined by the size of the as-prepared Au NBPs, and the lengths of the Au/Ag NRs are tunable using different amounts of Ag precursor in the growth solution. Surface-enhanced Raman scattering(SERS) studies using Rhodamine-6G(R6G) as a test molecule indicate that the Au/Ag NRs have excellent sensing potential. The tunable optical properties and strong electromagnetic effect of the Au/Ag NRs, along with their superior SERS signal enhancement, show that Au/Ag NRs are promising for further applications in plasmon sensing and biomolecular detection.
Haiying XuCaixia KanChangzong MiaoChangshun WangJingjing WeiYuan NiBeibei LuDaning Shi
