Wide-spread applications of nanoparticles require large-scale fabrication techniques. Being intrinsically scalable, bottom-up nanoparticle synthesis shows an ever-growing control over particle morphology, enabling even chirally selective shapes. Significant efforts have been undertaken to refine the synthesis in order to decrease the structural spread of the particles and to purify and maximize the resulting handedness. So far, imaging technologies such as electron microscopy are mostly used to investigate the quality of the synthesis. However, for nanophotonic and plasmonic applications, the optical properties are, in fact, key. In this work, we show that single particle chiral scatterometry holds great potential as a feedback to characterize the (chir-)­optical quality of chemically synthesized nanoparticles. The spectra of single helicoid nanoparticles reveal a diverse set of chiroptical responses with hugely varying absolute chiral asymmetry in spite of the well-controlled morphology of the particles. Averaging over the single nanoparticles reproduces the solution ensemble measurement remarkably well. This demonstrates that the single particles, despite their morphological and consequently chiroptical differences, exhibit a clearly pronounced chiral spectral and structural feature. We find that the g-factor, that is, the degree of asymmetry of chiral light scattering of single nanoparticles can be up to 4 times larger than that for the ensemble. This proves that chiral scatterometry can be a highly important optical feedback for bottom-up nanoparticle synthesis as it reveals that the asymmetry of the ensemble solution can be further increased and maximized by appropriate refinement methods or by postfabrication purification.

Synthesis of chiral plasmonic materials has been highlighted for the last decades with their optical properties and versatile potential applications. Recently reported aqueous-based amino acid- and peptide-directed synthesis of chiral plasmonic gold nanoparticles with 432 point-group symmetry shows exceptionally high chiroptic response within 100 nm scales. Despite its already excellent chiroptic response, a single-nanoparticle dark field scattering study revealed that full chiroptic potential of chiral gold nanoparticle is limited with its overall synthetic uniformity. Based on this knowledge, we present a multi-chirality-evolution step synthesis method for the enhancement of chiroptic response through an increase in particle uniformity. Detailed time variant study and interrelationship study of reaction parameters allowed the systematic construction of design principles for chiral nanoparticles with exceptional chiroptic response. With the application of precisely controlled growth kinetic to two distinct growth regimes, modified chiral gold nanoparticles showed significantly improved uniformity, achieving an improved dissymmetry factor of g = 0.31. We expect that our strategy will aid in precise morphology and property control for chiral nanomaterials, which can be used in various plasmonic metamaterial applications.

and their microscopic assembling and folding gradually give rise to chirality and left-right asymmetry from supramolecules to organelles, cells, and macroscopic organisms. Although the origin of homochirality is still unexplained and opens to arguments, investigating the chirality of matter and its origination is a central part of understanding asymmetric physical and chemical phenomena. The importance of chirality in chemistry lies in the asymmetric biochemical reactions with different physiological effect, which has paramount importance in biochemistry and pharmaceutical industry. [3,14,15] A mirror image of chiral objects can be determined into one of the left-handed or right-handed forms of geometry, called enantiomer or enantiomorph. Both enantiomers of a chiral object consist of identical chemical compositions but indeed are significantly different in their light-matter interaction, catalysis, and biological functions. The enantioselective signaling and enzymatic reaction are attributed to the homochirality of the living organism and its biological receptors, which are only composed of l-form amino acids and d-form sugars in nature. [7,14,15] Thalidomide is often referred to as a representative but also the most tragic example. The R-form of this drug is harmless to the body and was released as a painkiller for pregnant women, but its enantiomer causes severe malformation in the limbs of infants. [15,16] Since then, it has been a requirement for drugs to be characterized as a single enantiomer to be approved. 3D chirality is a unique characteristic of life, and the stereochemical aspect of molecular materials has come to fore of modern chemistry and biology. The optical property of chiral compounds, the so-called chiroptical effect, is highly effective for observing chirality in a nondestructive manner. [17] Chiroptical effects can be used for determination of the absolute configuration and enantiomeric excess of chiral molecules and as an optical probe for estimating the 3D structure of biomacromolecules such as proteins and DNA. [18] However, in most chiral organic molecules and biomolecules, chiroptical effects are typically very weak due to the much smaller size of molecules than the wavelength of exciting light. Integration of inorganic nanomaterials is one promising method for increasing the chiroptical signal of molecules; it focuses the light into nanoscale area to maximize the lightmatter interaction. [19-22] For example, a complex spatial profile Chirality is a basic property of nature and has great importance in photonics, biochemistry, medicine, and catalysis. This importance has led to the emergence of the chiral inorganic nanostructure field in the last two decades, providing opportunities to control the chirality of light and biochemical reactions. While the facile production of 3D nanostructures has remained a major challenge, recent advances in nanocrystal synthesis have provided a new pathway for efficient control of chirality at the nanoscale by transferring molecular chirality to the geo...

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Chiral optical metamaterials with delicate structures are in high demand in various fields because of their strong light–matter interactions. Recently, a scalable strategy for the synthesis of chiral plasmonic nanoparticles (NPs) using amino acids and peptides has been reported. Reported herein, 3D chiral gold NPs were synthesized using dipeptide γ‐Glu‐Cys and Cys‐Gly and analyzed crystallographically. The γ‐Glu‐Cys‐directed NPs present a cube‐like outline with a protruding chiral wing. In comparison, the NPs synthesized with Cys‐Gly exhibited a rhombic dodecahedron‐like outline with curved edges and elliptical cavities on each face. Morphology analysis of intermediates indicated that γ‐Glu‐Cys generated an intermediate concave hexoctahedron morphology, while Cys‐Gly formed a concave rhombic dodecahedron. NPs synthesized with Cys‐Gly are named 432 helicoid V because of their unique morphology and growth pathway.