Chiral Bioinspired Plasmonics: A Paradigm Shift for Optical Activity and Photochemistry

Abstract

This Perspective concerns the latest developments in the field of chiral nanocrystals (NCs) and metastructures, focusing primarily on plasmonic nanostructures. Such nanomaterials exhibit unusually strong near-field and electromagnetic responses that enable efficient biosensing and light manipulation. Herein we share our thoughts on the latest trends that mark what we call a paradigm shift for the vast and dynamic field of chiroptical materials. The topics to be considered include polarization-sensitive photocatalysis with chiral plasmonic NCs, chiral bioconjugates, DNA-based assemblies, chiral growth, and we also describe the fundamental challenges for optical induction of chirality, transfer of chirality between different scales, and theoretical issues that nanoscience is facing.

Onset of Chirality in Plasmonic Meta-Molecules and Dielectric Coupling

“…This orientation averaging is of fundamental importance in measuring the intrinsic chiral property, as was demonstrated theoretically by Rosenfeld . Another kind of chiroptical effect, called extrinsic chirality, appears for oriented nanostructures, which can be either chiral or achiral. ,, However, our study records intrinsic chirality of the DNA–gold nanoparticle complexes in the solution setting.…”

“…52 Another kind of chiroptical effect, called extrinsic chirality, appears for oriented nanostructures, which can be either chiral or achiral. 45,53,54 However, our study records intrinsic chirality of the DNA−gold nanoparticle complexes in the solution setting.…”

Optically Probing the Chirality of Single Plasmonic Nanostructures and of Single Molecules: Potential and Obstacles

“…Such experimental parameters are typically averaged out in measurements on solutions or suspensions. A full characterization of a nanoparticle’s chiral properties requires sampling of its orientations or at least an average over three ( x , y , z ) or better six (± x , ± y , ± z ) orientations to reproduce the ensemble-averaged result. The intensity of light scattered away from the incident light beam is negligible for small molecules, but the (dark-field) scattering cross-section of a plasmonic nanoparticle scales quadratically with its volume. Therefore, nanoparticles with sizes larger than typically 30 nm in diameter scatter a significant amount of light, so that extinction can no longer be assimilated to pure absorption.…”

“…Such experimental parameters are typically averaged out in measurements on solutions or suspensions. A full characterization of a nanoparticle’s chiral properties requires sampling of its orientations or at least an average over three ( x , y , z ) or better six (± x , ± y , ± z ) orientations to reproduce the ensemble-averaged result.…”

“…The optical effects of chirality in organic molecules are generally weak, not only because molecules are small compared to the light wavelength, but because of the low electronic velocities ( v ) compared to light velocity ( c ). The circular dichroism (CD) cross section of a transition scales as a scalar product of its electronic and magnetic dipole moments: , σ CD ∝ μ 12 · m 21 …”