Rothe, M.; Zhao, Y.; Müller, J.; Kewes, G.; Koch, C.T.; Lu, Y.; Benson, O.: Self-Assembly of Plasmonic Nanoantenna–Waveguide Structures for Subdiffractional Chiral Sensing. ACS Nano 15 (2021), p. 351–361
10.1021/acsnano.0c05240

Abstract:
Spin-momentum locking is a peculiar effect in thenear-field of guided optical or plasmonic modes. It can beutilized to map the spinning or handedness of electromagneticfields onto the propagation direction. This motivates a methodto probe the circular dichroism of an illuminated chiral object.In this work, we demonstrate local, subdiffraction limited chiralcoupling of light and propagating surface plasmon polaritons ina self-assembled system of a gold nanoantenna and a silvernanowire. A thin silica shell around the nanowire providesprecise distance control and also serves as a host forfluorescentmolecules, which indicate the direction of plasmon propaga-tion. We characterize our nanoantenna−nanowire systems comprehensively through correlated electron microscopy, energy-dispersive X-ray spectroscopy, dark-field, andfluorescence imaging. Three-dimensional numerical simulations support theexperimentalfindings. Besides our measurement of far-field polarization, we estimate sensing capabilities and derive not only asensitivity of 1 mdeg for the ellipticity of the lightfield, but alsofind 103deg cm2/dmol for the circular dichroism of an analytelocally introduced in the hot spot of the antenna−wire system. Thorough modeling of a prototypical design predicts on-chipsensing of chiral analytes. This introduces our system as an ultracompact sensor for chiral response far below the diffraction