Influence of Geometrical Parameters on the Optical Activity of Chiral Gold Nanorods

Abstract

Chiral metal nanoparticles (NPs) offer a powerful means of inducing and harnessing optical activity. However, due to the incomplete knowledge of the underlying growth mechanisms, there is still limited control over the achievable morphological detail and, consequently, over the resulting optical activity. Therefore, theoretical modeling is needed to guide experimental development toward optimizing the plasmonic chiroptical response. Toward filling this gap, herein an extensive parametric analysis is presented, via computer‐aided‐design (CAD) models and full‐wave electrodynamic simulations, which aims at systematically analyzing the influence of structural changes on the plasmonic circular dichroism (CD) spectra of rod‐shaped gold NPs comprising helical indentations on achiral nanorod cores. From this analysis, interesting patterns in the plasmon‐mediated resonant behavior are identified and cause–effect relationships are drawn that may serve as a go‐to recipe for the understanding and fabrication of these NPs and their applications, such as spectroscopic (bio)detection including CD spectral shifts and surface‐enhanced Raman optical activity.

Tuning the Growth of Chiral Gold Nanoparticles Through Rational Design of a Chiral Molecular Inducer

“…The simulated CD spectra (Figure C) were found to agree with the experimental trend in terms of both wavelength and relative intensity of the plasmonic CD bands. The increased and red-shifted g- factor bands observed for increasing LipoCYS concentrations are related to the formation of well-defined wrinkles, in agreement with a detailed computational analysis reported elsewhere . The effect of disorder in the wrinkled structure (for the highest LipoCYS concentrations) was also accounted for in the simulations, indeed revealing a loss of CD signal when the surface features are disordered (Figure S5).…”

Coated Chiral Plasmonic Nanorods with Enhanced Structural Stability

“…It is the helical wrinkles on the surface of Au NRs that lead to the plasmonic optical activity. Since the plasmonic optical activity of such chiral Au NRs is highly dependent on their morphological details, 29 any deformation hindering the helical morphology can be directly monitored through the corresponding loss of optical activity. Therefore, we first assessed the long-term stability of chiral Au NRs by storing them under different conditions and monitoring their spectral evolution over time, up to 1 month after synthesis (Figure 1).…”

Circular Polarization-Resolved Raman Optical Activity: A Perspective on Chiral Spectroscopies of Vibrational States

“…Based on atomistic electrodynamics−quantum mechanical models simulating SEROA for the two enantiomers of 2-bromohexahelicene, SEROA intensity could be maximized by manipulating the local electric field and field gradient, the orientation of the molecule, and the surface plasmon frequency width (Figure 1c). 30 Chiral plasmonic metal nanostructures have recently demonstrated chiral electromagnetic field enhancement and strong interaction with chiral materials, 8,31 which is highly beneficial in SEROA. Moreover, the local asymmetric sites (chiral component) exposed on chiral NPs induce stereospecific molecular interactions, enabling direct label-free chiral differentiation.…”

“…Chiral plasmonic metal nanostructures have recently demonstrated chiral electromagnetic field enhancement and strong interaction with chiral materials, , which is highly beneficial in SEROA. Moreover, the local asymmetric sites (chiral component) exposed on chiral NPs induce stereospecific molecular interactions, enabling direct label-free chiral differentiation. − The so-called superchiral fields (i.e., those whose chiral dissymmetry exceeds that of the fully circularly polarized light) generated by chiral Shuriken metamaterials (Figure a) have been utilized to discriminate between globular proteins with high α-helical content and more structurally anisotropic proteins with high β-sheet content .…”