Chiral Near-Fields Induced by Plasmonic Chiral Conic Nanoshell Metallic Nanostructure for Sensitive Biomolecule Detection

Abstract

The complexity of lithography methods and other methods utilizing chiral templates to produce three-dimensional structures restricts further research on chiral plasmonics. Herein, a plasmonic nanostructure with a strong chiroptical response and enhanced near-fields generated on a large and highly ordered achiral tapered nanopore anodic aluminum oxide template is proposed and fabricated via a low-cost and efficient glancing angle deposition method. The plasmonic chiral conic nanoshell metallic nanostructure (CCNM), which is composed of three nanoshells of different heights, is obtained by varying the incidence and orientation angles of deposition to achieve symmetry breaking. Such a conic nanoshell nanostructure can couple incident light into the nanostructure, thus reducing the reflection and localizing the electromagnetic energy inside the nanoshell. The experimental circular dichroism spectra of the CCNM in the visible range shows that the chiroptical response is amplified with an increased height difference of the three nanoshells and period of the nanopore. The dissymmetry factor of the CCNM is up to 0.45, which results from the helix-like electron oscillation characteristics on the surface of the three nanoshells. The simulation result shows that the enhancement of the chiral near-fields of the CCNM reaches 155 times with respect to the circularly polarized light due to the small angle between electric and magnetic fields. The chiral signal is enhanced by about 2 orders of magnitude using the CCNM to detect chiral molecules. This study offers a concise and large-area regular method for fabricating plasmonic chiral nanostructures with a tunable chiroptical response and provides an effective and convenient idea to control the chiral near-fields for sensitive biomolecule detection.

Topics & Concepts