Chiral Gold Nanocups with Large Magnetic Plasmonic Enhancement for Single-Particle Chiroptical Response

Abstract

Chiral plasmonic nanoparticles have recently attracted much attention owing to their strong chiroptical responses and wide applications. However, most chiral plasmonic nanoparticles exhibit electric plasmon resonance modes but lack magnetic plasmon resonance modes, the latter of which are crucial for achieving strong chiroptical responses. Herein we report on a type of chiral Au nanocup structure featuring an asymmetric hollow architecture with a side opening. The chiral Au nanocups are synthesized by the vertex-initiated overgrowth of Au on PbS nano-octahedra, which is templated by chiral glutathione molecules. The chiral extinction and scattering measurements are conducted at the ensemble and single-particle level, respectively. The scattering dissymmetry factors of individual nanocups supported on silica substrates exhibit a 50-fold enhancement compared to the extinction dissymmetry factor of the ensemble in solution. Numerical simulations indicate that this enhancement arises from strong enhancements of electric and magnetic fields, as well as synergistic coupling between the nanocup and the substrate. Experimentally, residual linear-polarization artifacts were identified through achiral nanocup controls and rotation measurements. They may contribute partially to the measured dissymmetry factors. Our study enriches chiral plasmonic nanoparticles and offers promising perspectives for the design of plasmonic nanoparticles with desired chiroptical properties.