Morphological and Optical Transitions during Micelle-Seeded Chiral Growth on Gold Nanorods

Abstract

Chiral plasmonics is a rapidly developing field where breakthroughs and unsolved problems coexist. We have recently reported binary surfactant-assisted seeded growth of chiral gold nanorods (Au NRs) with high chiroptical activity. Such a seeded-growth process involves the use of a chiral cosurfactant that induces micellar helicity, in turn driving the transition from achiral to chiral Au NRs, from both the morphological and the optical points of view. We report herein a detailed study on both transitions, which reveals intermediate states that were hidden so far. The correlation between structure and optical response is carefully analyzed, including the (linear and CD) spectral evolution over time, electron tomography, the impact of NR dimensions on their optical response, the variation of the absorption-to-scattering ratio during the evolution from achiral to chiral Au NRs, and the near-field enhancement related to chiral plasmon modes. Our findings provide further understanding of the growth process of chiral Au NRs and the associated optical changes, which will facilitate further study and applications of chiral nanomaterials.

Coated Chiral Plasmonic Nanorods with Enhanced Structural Stability

“…In the particular case of plasmonic nanomaterials, chiral structures have been reported for both individual nanoparticles (NPs) and multi-NP assemblies, which result in the so-called plasmonic optical activity. In practice, the chiroptical response can be recorded as plasmonic circular dichroism (CD), i.e., different interactions with circularly polarized light of opposite handedness, through excitation of asymmetric localized surface plasmon resonances (LSPRs). − Since the demonstration of the colloidal synthesis of highly efficient chiral Au helicoids by Nam et al, the synthesis of intrinsically chiral plasmonic NPs has seen a rapid development of various chiral Au NPs with different structures, including chiral nanorods (NRs), − nanoprisms, , nanorings, nanobipyramids, , and other helicoids. , Some of these studies involve applications of such chiral NPs in circularly polarized luminescence, , surface-enhanced Raman scattering, enantiomer-dependent immunological response, , and biosensing, which reflect the great potential of chiral plasmonic NPs. Considering the widespread presence of chirality in biological systems, much room is left for many other biological and clinical applications of chiral plasmonic NPs …”

Practical Considerations for Simulating the Plasmonic Properties of Metal Nanoparticles

“…We particularly found this approach beneficial as there is also a need to untangle the chiroptical activity from near-field enhancement emanating from surface-bound chiral growth molecules . We anticipate that the application of tomographic reconstructions to create models for simulations will prove useful in many complex nanoparticle systems as shown similarly for Au nanostars, chiral Au nanorods, and chiral nanoparticle assemblies. ,,, …”

“…59 We anticipate that the application of tomographic reconstructions to create models for simulations will prove useful in many complex nanoparticle systems as shown similarly for Au nanostars, chiral Au nanorods, and chiral nanoparticle assemblies. 70,72,75,76 ■ CHALLENGE TO THE FIELD: ACCURATE…”

Structurally Induced Chirality of an Achiral Chromophore on Self-Assembled Nanofibers: A Twist Makes It Chiral

“…More intriguing is nature’s exclusive preference for a particular handedness which we call homochirality; for example, left-handedness in amino acids, right-handedness in sugars, right-handed helices of DNA, − and directionality in the growth of seashells, though with exceptions . While the origin of homochirality remains an open question, significant progress has been made on our understanding of the transfer of chirality onto achiral molecules/materials and the amplification of chiral signals. − Broadly, chiroptical properties of designed molecules/materials originate either from inherent chirality or induced chirality. While the former is primarily observed in systems with point and axial chirality, the latter originates through either off-resonance or on-resonance coupling of various transition dipoles. ,, Although the inherent chirality of molecules is well established, ,, our understanding on the induction of chirality from a chiral system to an achiral molecule/material has been a matter of investigation. ,,,,,,− Induced circular dichroism (ICD) is observed in molecular or supramolecular assemblies wherein an achiral guest molecule displays chiroptical signals while interacting with a nonracemic chiral host system such as cyclodextrins, ,, biomolecular systems, ,,−…”