Tunable circular dichroism of bilayer b-type chiral nanostructures

Abstract

Circular dichroism (CD) of chiral molecules are key to medicine detection, optoelectronic devices and chiral biosensors. However, the CD effects of natural chiral molecules are weak that prevents their wide applications. Chiral plasmonic nanostructures have been demonstrated as an effective way to enhance CD effects of natural molecules due to the localized enhanced electromagnetic field and the high contrast in chiroptical response to left- and right-handed circular polarized light. Here we proposed a 3D plasmonic chiral platform consisting of bilayer b-shape nanoelements and investigated their tunable CD effects through rotating the upper layer b-elements. Near-field analysis based on Born–Kuhn model had been proposed to explain the mechanism of the tunable CD effects. Results demonstrated that a maximum CD signal was achieved with the 3D chiral nanostructure supporting bonding and antibonding plasmonic modes under left- and right-handed circular polarized light, respectively. While the smallest CD was for the nanostructure only supporting one mode (antibonding mode) under circular polarized light. The tunable CD effects of the bilayer b-type nanostructures is beneficial for chiral optical switches and high-sensitivity chiral biosensors.