Self-Assembly of Plasmonic Nanoantenna–Waveguide Structures for Subdiffractional Chiral Sensing

作者：Martin Rothe, Yuhang Zhao, Johannes Müller, Günter Kewes, Christoph T. Koch, Yan Lü, Oliver Benson · 发表于：ACS Nano · 年份：2020 · DOI：10.1021/acsnano.0c05240 · 被引用次数：29 · 研究领域：Metamaterials and Metasurfaces Applications、Plasmonic and Surface Plasmon Research、Orbital Angular Momentum in Optics

Spin-momentum locking is a peculiar effect in the near-field of guided optical or plasmonic modes. It can be utilized to map the spinning or handedness of electromagnetic fields onto the propagation direction. This motivates a method to probe the circular dichroism of an illuminated chiral object. In this work, we demonstrate local, subdiffraction limited chiral coupling of light and propagating surface plasmon polaritons in a self-assembled system of a gold nanoantenna and a silver nanowire. A thin silica shell around the nanowire provides precise distance control and also serves as a host for fluorescent molecules, which indicate the direction of plasmon propagation. We characterize our nanoantenna–nanowire systems comprehensively through correlated electron microscopy, energy-dispersive X-ray spectroscopy, dark-field, and fluorescence imaging. Three-dimensional numerical simulations support the experimental findings. Besides our measurement of far-field polarization, we estimate sensing capabilities and derive not only a sensitivity of 1 mdeg for the ellipticity of the light field, but also find 10 3 deg cm 2 /dmol for the circular dichroism of an analyte locally introduced in the hot spot of the antenna–wire system. Thorough modeling of a prototypical design predicts on-chip sensing of chiral analytes. This introduces our system as an ultracompact sensor for chiral response far below the diffraction limit.