Exploiting the localized surface plasmon modes in gold triangular nanoparticles for sensing applications

Abstract

In this study we investigate and exploit, for optical sensing, the surface plasmon excitation in gold triangular nanoparticles with high aspect ratios (i.e., the ratio of the edge length of the triangles with the height) prepared by nanosphere lithography. As shown previously, the shape and size of these nanoparticles were used to tune their optical properties, monitored by far field extinction spectroscopy. Interestingly, several localized surface plasmon resonances were detected in the visible and near infrared regions and were attributed to dipole and quadrupole modes. These modes, identified from numerical simulations, “red-shift” as the aspect ratio of the particles increases. The plasmon modes observed for larger triangles exhibit unexpected sensitivity with a change in the refractive index. From experiments and numerical simulations, this higher sensitivity has been attributed to an increase of the local field enhancement for sharper tips. This new effect can provide important information for the design of particles as building blocks for sensing applications.