Competition of Chiroptical Effect Caused by Nanostructure and Chiral Molecules

TL;DR

This paper develops a T-matrix based theory to analyze the circular dichroism in chiral molecule-nanostructure systems, revealing how plasmonic effects and molecule placement influence optical activity for biosensing applications.

Contribution

It introduces a new theoretical framework to distinguish structure- and molecule-induced plasmonic CD effects in nanocomposites, aiding biosensor design.

Findings

Total CD is not additive when molecules are close in nanoparticle clusters.

Plasmonic CD from structure chirality depends on nanostructure geometry and orientation.

Molecule-induced CD can be spectrally distinguished from structure chirality effects.

Abstract

The theory to calculate circular dichroism (CD) of chiral molecules in a finite cluster with arbitrarily disposed objects has been developed by means of T-matrix method. The interactions between chiral molecules and nanostructures have been investigated. Our studies focus on the case of chiral molecules inserted into plasmonic hot spots of nanostructures. Our results show that the total CD of the system with two chiral molecules is not sum for two cases when two chiral molecules inserted respectively into the hot spots of nanoparticle clusters as the distances among nanoparticles are small, although the relationship is established at the case of large interparticle distances. The plasmonic CD arising from structure chirality of nanocomposites depends strongly on the relative positions and orientations of nanospheroids, and are much greater than that from molecule-induced chirality. However, the molecule-induced plasmonic CD effect from the molecule-NP nanocomposites with special chiral structures can be spectrally distinguishable from the structure chirality-based optical activity. Our results provide a new theoretical framework for understanding the two different aspects of plasmonic CD effect in molecule-NP nanocomposites, which would be helpful for the experimental design of novel biosensors to realize ultrasensitive probe of chiral information of molecules by plasmon-based nanotechnology.