Chiral Seeded Growth of Gold Nanorods Into Fourfold Twisted Nanoparticles with Plasmonic Optical Activity

Abstract

A robust and reproducible methodology to prepare stable inorganic nanoparticles with chiral morphology may hold the key to the practical utilization of these materials. An optimized chiral growth method to prepare fourfold twisted gold nanorods is described herein, where the amino acid cysteine is used as a dissymmetry inducer. Four tilted ridges are found to develop on the surface of single‐crystal nanorods upon repeated reduction of HAuCl4, in the presence of cysteine as the chiral inducer and ascorbic acid as a reducing agent. From detailed electron microscopy analysis of the crystallographic structures, it is proposed that the dissymmetry results from the development of chiral facets in the form of protrusions (tilted ridges) on the initial nanorods, eventually leading to a twisted shape. The role of cysteine is attributed to assisting enantioselective facet evolution, which is supported by density functional theory simulations of the surface energies, modified upon adsorption of the chiral molecule. The development of R‐type and S‐type chiral structures (small facets, terraces, or kinks) would thus be non‐equal, removing the mirror symmetry of the Au NR and in turn resulting in a markedly chiral morphology with high plasmonic optical activity.

Green room temperature synthesis of silver–gold alloy nanoparticles

“…5 In this context, targeted product design strategies of any type of NPs require an iterative approach and multiple optimization steps. 6 In particular, the NPs' composition, size and shape 7,8 have to be precisely controlled both in the lab and during scale-up. Therefore, methods to determine those quantities are imperative for the development of promising synthesis routes.…”

A Facile and Rational Method to Tailor the Symmetry of Au@Ag Nanoparticles

“…[ 43 ] When the amounts of the enantiomeric chiral facets within a particle are not equal (the amount of R‐type facets ≠ S‐type facets), the particle should be dissymmetric. [ 21 ] It has been confirmed that l ‐cys could enantioselectively assist the formation of chiral facets during the growth of Au NPs, [ 18,23,44,45 ] resulting in the controlled growth of chiral NPs. The l ‐cys in our case might function similarly as the chiral inducer to control the chirality, resulting in reproducible chiral NPs.…”

“…[5] Furthermore, Ag is a key catalytic material for Au@Ag chiral NPs, [16,17] inspired by the impressive progress on the chiral Au NPs. [18][19][20][21] Nonetheless, the chiral shapes have not been well illustrated and the measured optical activities remained at the level of chiral small molecules. Plasmonic chirality has been a hot topic recently, [22] and different chiral forms of Au NPs including clusters, discrete helical NPs, and assembling structures, have been found, and subjected to different applications, respectively.…”

Advances in Enantiomer-Dependent Nanotherapeutics

“…Chiral peptides such as cysteine, glutathione, and some dipeptides have gained attention as effective ligands in chiral therapeutics owing to their biocompatibility, small size, and ease of functionalization. , These naturally occurring compounds in cells, such as sulfhydryl groups in cysteine or glutathione, and hydrophobic side chains in phenylalanine or dipeptides, are capable of forming strong and stable covalent or hydrophobic bonds with the surfaces of NPs . The presence of these functional groups also confers stability in biological environments and reduces oxidative stress .…”