Plasmon Hybridization Mediated Structure-Specific Refractive Index Sensitivity of Hollow Gold Nanoprism in the Vis-NIR Region

The refractive index sensitivity of plasmonic nanoantennas depends on the plasmon field strength and its distribution (sensing volume). As a result, the sensitivity factors can be larger for hollow nanoparticles than for solid ones of comparable dimensions due to their larger sensing volume and the strong local electric fields resulting from the plasmon hybridization between the external and internal surfaces. The plasmonic field strength of a hollow nanostructure is further enhanced when it has anisotropic shape. In the present paper, the plasmon resonances along with the associated local electric fields and the RI sensitivity factors of an anisotropic hollow nanostructure, namely, hollow gold nanoprism (HGN, an equilateral triangular gold nanoprism with a circular cavity) of different cavity size and thickness have been determined by finite-difference time-domain simulation. The dependence of the RI sensitivity factors on the prism thickness, the size, and the position of the cavity, and shape defects such as corner-rounding or snipping has been determined and discussed. The RI sensitivity increases linearly with the aspect ratio of the HGN. The RI sensitivity is especially sensitive to the position of the cavity of the HGNs. We show that properly designed HGNs have RI sensitivity values that are more than several hundred units higher than those of solid gold nanoprisms and even gold nanoframes of comparable size. Moreover, the loss in sensitivity factor due to shape defects such as corner rounding or snipping is much less in HGNs than their solid analogues. All these properties of HGNs make them a superior material for chemical and biosensing applications than any other plasmonic nanostructure of similar dimension

Magnetic Dipolar Interactions in Solid Gold Nanosphere Dimers

We report the first observation of a magnetic dipolar contribution to the nonlinear optical (NLO) response of colloidal metal nanostructures. Second-order NLO responses from several individual solid gold nanosphere (SGN) dimers, which we prepared by a bottom-up approach, were examined using polarization-resolved second harmonic generation (SHG) spectroscopy at the single-particle level. Unambiguous circular dichroism in the SH signal was observed for most of the dimeric colloids, indicating that the plasmon field located within the interparticle gap was chiral. Detailed analysis of the polarization line shapes of the SH intensities obtained by continuous polarization variation suggested that the effect resulted from strong magnetic-dipole contributions to the nanostructure’s optical properties

Three-Dimensional Interfacial Structure Determination of Hollow Gold Nanosphere Aggregates

The boundary regions between hollow gold nanospheres (HGNs) comprising an extended aggregate were examined using 3-D electron tomography. The images obtained from these experiments allowed for precise determination of the 3-D arrangement of the HGNs within the aggregate and revealed structural heterogeneities that were not resolvable with traditional two-dimensional techniques. These features included particle necking, point contacts, lattice pinholes, and HGN cavities that were joined by pores. The theoretical influence of these interfacial substructures on nanoscale plasmon properties was assessed using finite difference time domain (FDTD) numerical simulations. These results demonstrated the prospective impact of 3-D imaging techniques on the development of complete-structure descriptions of nanoscale optical properties