Observation of Defocus Images of a Single Metal Nanorod

Abstract

We examined an emission of light from a single metallic nanoparticle based on surface plasmon (SP) resonance for determination of three-dimensional orientation of nanoparticles as well as their optical properties. The defocused image of individual Au nanorods (Au NRs) is recorded by changing the focus distance under total internal reflection microscopy (TIRM) observations. Numerical and statistical analysis revealed that the observed light distribution patterns of Au NRs defocused images were classified into two groups. One is explained by considering that a single dipole dominates its light emission property. The other is explained by assuming the presence of multidipoles. This result leads us to a consideration that the emission of light coupled with the transverse and the longitudinal SP modes was observed reflecting the optical characteristics of NRs. Additionally, unique multiple ring patterns were also observed by placing Au NRs at the vicinity of nanoscopic structure, reflecting the distance between NRs and the wall of the structure in the scale less than a few tens of nanometers. The inclusive SP measurement for both the transverse and longitudinal axes of these anisotropic metal NRs using a defocused imaging system brings us reliable optical and conformational information