Chiral Surface and Geometry of Metal Nanocrystals

Decoding Polarization in a Single Achiral Gold Nanostructure from Emitted Far-Field Radiation

The emergence of optical chirality in the light emitted from plasmonic nanostructures is commonly associated with their geometrical chirality. Although it has been demonstrated that even achiral structures can exhibit chiral near-fields, the existence of chiroptical far-field responses of such structures is widely neglected. In this paper, we present a detailed analysis of the polarization state in a single planar achiral plasmonic nanostructure that sustains more than one prominent plasmon mode. In consideration of the relative phase, the superposition of the fields associated with these modes determines the polarization state of the emitted light in the far-field. Supported by simulations of the surface charge distribution of the particle, we show that the polarization state of the emitted light is already determined in the near-field. The chiroptical far-field responses are analyzed by polarized single-particle dark-field scattering spectroscopy. We introduce an analytical model that enables us to obtain the polarization information from the spectra of structures with dipolar resonances taken under unpolarized illumination. The same principle is confirmed in polarimetric spectroscopy measurements on rhomboids with systematically varied angles, therefore, introducing increasing values of geometrical chirality to the structures. The agreement between the calculation and measurement demonstrates the general validity of our model for both chiral and achiral structures.

Chiral Mesostructured Inorganic Materials with Optical Chiral Response

Fabricating chiral inorganic materials and revealing their unique quantum confinement-determined optical chiral responses are crucial tasks in the multidisciplinary fields of chemistry, physics, and biology. The field of chiral mesostructured inorganic materials started from the synthesis of individual nanocrystals and evolved to include their assembly from metals, semiconductors, ceramics, and inorganic salts endowed with various chiral structures ranging from atomic to micron scales. This tutorial review highlights the recent research on chiral mesostructured inorganic materials, especially the novel expression of mesostructured chirality and endowed optical chiral response, and it may inspire us with new strategies for the design of chiral inorganic materials and new opportunities beyond the traditional applications of chirality. Fabrication methods for chiral mesostructured inorganic materials are classified according to chirality type, scale, and symmetry-breaking mechanism. Special attention is given to highlight systems with original discoveries, exceptional phenomena, or unique mechanisms of optical chiral response for left- and right-handedness.

Selective Chiral Recognition between Amino Acids and Growing Gypsum Crystals

In nature, selective chiral interactions between biomolecules and minerals provide insight into the mysterious origin of homochirality. Here, we show growing gypsum crystals in a nonequilibrium state can recognize chiral enantiomers of amino acids. The chiral selection for amino acids with different functional groups by growing minerals are distinct. For 11 amino acids, the d-isomer slows dynamic gypsum growth more than the l-isomer, whereas for another 7 amino acids, the opposite was observed. These differences in chiral recognition are attributed to the different stereochemical matching between the chiral amino acids and the dynamic steps of growing gypsum. These stereoselective interactions between amino acid enantiomers and dynamic growing crystals can be applied toward the fabrication of gypsum cements to regulate their structure and mechanical properties. These findings provide insight into understanding the mechanism of the origin of homochirality in nature and suggest a pathway for constructing advanced functional materials.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Geometric Control and Optical Properties of Intrinsically Chiral Plasmonic Nanomaterials

Intrinsically chiral plasmonic nanomaterials exhibit intriguing geometry-dependent chiroptical properties, which is due to the combination of plasmonic features with geometric chirality. Thus, chiral plasmonic nanomaterials have become promising candidates for applications in biosensing, asymmetric catalysis, biomedicine, photonics, etc. Recent advances in geometric control and optical tuning of intrinsically chiral plasmonic nanomaterials have further opened up a unique opportunity for their widespread applications in many emerging technological areas. Here, the recent developments in the geometric control of chiral plasmonic nanomaterials are reviewed with special attention given to the quantitative understanding of the chiroptical structure-property relationship. Several important optical spectroscopic tools for characterizing the optical chirality of plasmonic nanomaterials at both ensemble and single-particle levels are also discussed. Three emerging applications of chiral plasmonic nanomaterials, including enantioselective sensing, enantioselective catalysis, and biomedicine, are further highlighted. It is envisioned that these advanced studies in chiral plasmonic nanomaterials will pave the way toward the rational design of chiral nanomaterials with desired optical properties for diverse emerging technological applications.

Photoluminescent ellipsometric circular dichroism

A novel spectroscopic technique, photoluminescent ellipsometric circular dichroism (PECD), which distinguishes all radiative electronic transitions related to molecular chiral centers. Additionally, it is proposed as complementary to the ellipsometric Raman spectroscopy (ERS) technique, thus establishing a relationship between vibrational modes and electronic transitions, associated with molecular chiral centers. In this way, PECD turns into a powerful technique for chiral material characterization. The PECD technique was performed on a chiral oligomer (1R,2R)-diiminocyclohexane, and its derivative polymer. A complete photophysical characterization in solution was performed to corroborate the new PECD technique.

Biomimetic mineralization based on self-assembling peptides

Biomimetic science has attracted great interest in the fields of chemistry, biology, materials science, and energy. Biomimetic mineralization is the process of synthesizing inorganic minerals under the control of organic molecules or biomolecules under mild conditions. Peptides are the motifs that constitute proteins, and can self-assemble into various hierarchical structures and show a high affinity for inorganic substances. Therefore, peptides can be used as building blocks for the synthesis of functional biomimetic materials. With the participation of peptides, the morphology, size, and composition of mineralized materials can be controlled precisely. Peptides not only provide well-defined templates for the nucleation and growth of inorganic nanomaterials but also have the potential to confer inorganic nanomaterials with high catalytic efficiency, selectivity, and biotherapeutic functions. In this review, we systematically summarize research progress in the formation mechanism, nanostructural manipulation, and applications of peptide-templated mineralized materials. These can further inspire researchers to design structurally complex and functionalized biomimetic materials with great promising applications.

Tunable Reversal of Circular Dichroism in the Seed-Mediated Growth of Bichiral Plasmonic Nanoparticles

Plasmonic nanoparticles with an intrinsic chiral structure have emerged as a promising chiral platform for applications in biosensing, medicine, catalysis, separation, and photonics. Quantitative understanding of the correlation between nanoparticle structure and optical chirality becomes increasingly important but still represents a significantly challenging task. Here we demonstrate that tunable signal reversal of circular dichroism in the seed-mediated chiral growth of plasmonic nanoparticles can be achieved through the hybridization of bichiral centers without inverting the geometric chirality. Both experimental and theoretical results demonstrated the opposite sign of circular dichroism of two different bichiral geometries. Chiral molecules were found to not only contribute to the chirality transfer from molecules to nanoparticles but also manipulate the structural evolution of nanoparticles that synergistically drive the formation of two different chiral centers. By deliberately adjusting the concentration of chiral molecules and other synthetic parameters, such as the reducing agent concentration, the capping surfactant concentration, and the amount of Au precursor, we have been able to fine-tune the circular dichroism reversal of bichiral Au nanoparticles. We further demonstrate that the structure of chiral molecules and the crystal structure of Au seeds play crucial roles in the formation of Au nanoparticles with bichiral centers. The insights gained from this work not only shed light on the underlying mechanisms dictating the intriguing geometric and chirality evolution of bichiral plasmonic nanoparticles but also provide an important knowledge framework that guides the rational design of bichiral plasmonic nanostructures toward chiroptical applications.

Chiral Porous Carbon Surfaces for Enantiospecific Synthesis

Chiral surfaces, developed in the last decade, serve as media for enantioselective chemical reactions. Until today, they have been based mostly on developments in silica templating, and are made mainly from imprints of silicate materials developed a long time ago. Here, a chiral porous activated carbon surface was developed based on a chiral ionic liquid, and the surface chemistry and pore structure were studied to lay a new course of action in the field. The enantioselectivities of surfaces are examined by using variety of methods such as circular dichroism, linear sweep voltammetry and catalysis. These techniques revealed a 28.1% preference for the D enantiomer of the amino acid proline, and linear sweep voltammetry confirmed chirality recognition by another probe. An aldol surface chiral catalytic reaction was devised and allowed to determine the root of the enantiomeric excess. These results affirm the path toward a new type of chiral surface.

Advancements in cell membrane camouflaged nanoparticles: A bioinspired platform for cancer therapy

The idea of employing natural cell membranes as a coating medium for nanoparticles (NPs) endows man-made vectors with natural capabilities and benefits. In addition to retaining the physicochemical characteristics of the NPs, the biomimetic NPs also have the functionality of source cell membranes. It has emerged as a promising approach to enhancing the properties of NPs for drug delivery, immune evasion, imaging, cancer-targeting, and phototherapy sensitivity. Several studies have been reported with a multitude of approaches to reengineering the surface of NPs using biological membranes. Owing to their low immunogenicity and intriguing biomimetic properties, cell-membrane-based biohybrid delivery systems have recently gained a lot of interest as therapeutic delivery systems. This review summarises different kinds of biomimetic NPs reported so far, their fabrication aspects, and their application in the biomedical field. Finally, it briefs on the latest advances available in this biohybrid concept.

Three-dimensional artificial chirality towards low-cost and ultra-sensitive enantioselective sensing

Artificial chiral structures have potential applications in the field of enantioselective signal sensing. Advanced nanofabrication methods enable a large diversity in geometric structures and broad selectivity of materials, which can be exploited to manufacture artificial three-dimensional chiral structures. Various chiroptical phenomena exploiting spin and orbital angular momentum at the nanoscale have been continuously exploited as a way to effectively detect enantiomers. This review introduces precisely controlled bottom-up and large-area top-down metamaterial fabrication methods to solve the limitations of high manufacturing cost and low production speed. Particle synthesis, self-assembly, glanced angled vapor deposition, and three-dimensional plasmonic nanostructure printing are introduced. Furthermore, emerging sensitive chiral sensing methods such as cavity-enhanced chirality, photothermal circular dichroism, and helical dichroism of single particles are discussed. The continuous progress of nanofabrication technology presents the strong potential for developing artificial chiral structures for applications in biomedical, pharmaceutical, nanophotonic systems.

Effect of calcination temperature on the morphology and catalytic properties of ZnO nanostructures fabricated from a chiral precursor for photodegradation of both cationic and anionic dyes

A chiral Zn MOF is fabricated into ZnO microflowers, polyhedrons and nanorods at three different temperatures and these are utilized for the photodegradation of methylene blue and Congo red.

Design of surface nanostructures for chirality sensing based on quartz crystal microbalance

Quartz crystal microbalance (QCM) has been widely used for various sensing applications, including chirality detection due to the high sensitivity to nanogram or picogram mass changes, fast response, real-time detection, easy operation, suitability in different media, and low experimental cost. The sensing performance of QCM is dependent on the surface design of the recognition layers. Various strategies have been employed for studying the relationship between the structural features and the specific detection of chiral isomers. This review provides an overview of the construction of chiral sensing layers by various nanostructures and materials in the QCM system, which include organic molecules, supermolecular assemblies, inorganic nanostructures, and metal surfaces. The sensing mechanisms based on these surface nanostructures and the related potentials for chiral detection by the QCM system are also summarized.

Nanobioremediation: A sustainable approach towards the degradation of sodium dodecyl sulfate in the environment and simulated conditions

Nanotechnology has gained huge importance in the field of environmental clean-up today. Due to their remarkable and unique properties, it has shown potential application for the remediation of several pesticides and textile dyes. Recently it has shown positive results for the remediation of sodium dodecyl sulfate (SDS). One of the highly exploited surfactants in detergent preparation is anionic surfactants. The SDS selected for the present study is an example of anionic linear alkyl sulfate. It is utilized extensively in industrial washing, which results in the high effluent level of this contaminant and ubiquitously toxic to the environment. The present review is based on the research depicting the adverse effects of SDS in general and possible strategies to minimizing its effects by bacterial degradation which are capable of exploiting the SDS as an only source of carbon. Moreover, it has also highlighted that how nanotechnology can play a role in the remediation of such recalcitrant pesticides.

Chiral detection by induced surface-enhanced Raman optical activity

Combination of optical activity with surface-enhanced Raman scattering has been a dream of physical chemists for a long time. We report a measurement protocol based on silver colloids and aromatic linkers where chiral acids could be detected in concentrations of about 10-5 M. We explain the mechanism by binding and self-assembly of the linkers into chiral aggregates on the silver surface. Following the "sergeants-and-soldiers" principle, the chirality is determined by the relatively minor acidic component. Such detection of biologically relevant molecules may be useful when other methods, such as electronic circular dichroism, are not sensitive enough. In the future, variations of the chemical structure of the linker or other conditions are needed to provide a more specific signal allowing one to better discriminate among the optically active molecules.

Polarimetric Measurements of Surface Chirality Based on Linear and Nonlinear Light Scattering

A molecule, molecular aggregate, or protein that cannot be superimposed on its mirror image presents chirality. Most living systems are organized by chiral building blocks, such as amino acids, peptides, and carbohydrates, and any change in their molecular structure (i.e., handedness or helicity) alters the biochemical and pharmacological functions of the molecules, many of which take place at surfaces. Therefore, studying surface chirogenesis at the nanoscale is fundamentally important and derives various applications. For example, since proteins contain highly ordered secondary structures, the intrinsic chirality can be served as a signature to measure the dynamics of protein adsorption and protein conformational changes at biological surfaces. Furthermore, a better understanding of chiral recognition and separation at bio-nanointerfaces is helpful to standardize chiral drugs and monitor the synthesis of adsorbents with high precision. Thus, exploring the changes in surface chirality with polarized excitations would provide structural and biochemical information of the adsorbed molecules, which has led to the development of label-free and noninvasive measurement tools based on linear and nonlinear optical effects. In this review, the principles and selected applications of linear and nonlinear optical methods for quantifying surface chirality are introduced and compared, aiming to conceptualize new ideas to address critical issues in surface biochemistry.

Biomolecule-mediated chiral nanostructures: a review of chiral mechanism and application

The chirality of biomolecules is vital importance in biosensing and biomedicine. However, most biomolecules only have a chiral response in the ultraviolet region, and the corresponding chiral signal is weak. In recent years, inorganic nanomaterials can adjust chiral light signals to the visible and near-infrared regions and enhance optical signals due to their high polarizability and adjustable morphology-dependent optical properties. Nonetheless, inorganic nanomaterials usually lack specificity to identify targets, and have strong toxicity when applied in organisms. The combination of chiral biomolecules and inorganic nanomaterials offers a way to solve these problems. Because chiral biomolecules, such as DNA, amino acids, and peptides, have programmability, specific recognition, excellent biocompatibility, and strong binding force to inorganic nanomaterials. Biomolecule-mediated chiral nanostructures show specific recognition of targets, extremely low biological toxicity and adjustable optical activity by regulating, assembling and inducing inorganic nanomaterials. Therefore, biomolecule-mediated chiral nanostructures have received widespread attention, including chiral biosensing, enantiomers recognition and separation, biological diagnosis and treatment, chiral catalysis, and circular polarization of chiral metamaterials. This review mainly introduces the three chiral mechanisms of biomolecule-mediated chiral nanostructures, lists some important applications at present, and discusses the development prospects of biomolecule-mediated chiral nanostructures.

Tyrosyltyrosylcysteine-Directed Synthesis of Chiral Cobalt Oxide Nanoparticles and Peptide Conformation Analysis

Chiral inorganic nanomaterials have revealed opportunities in various fields owing to their strong light-matter interactions. In particular, chiral metal oxide nanomaterials that can control light and biochemical reactions have been highlighted due to their catalytic activity and biocompatibility. In this study, we present the synthesis of chiral cobalt oxide nanoparticles with a g-factor of 0.01 in the UV-visible region using l- and d-Tyr-Tyr-Cys ligands. The conformation of the Tyr-Tyr-Cys peptide on the nanoparticle surfaces was identified by 2D NMR spectroscopy analysis. In addition, the sequence effect of Tyr-Tyr-Cys developing chiral nanoparticles was analyzed. The revealed peptide structure, along with the experimental results, demonstrate the important role of the thiol group and carboxyl group of the Tyr-Tyr-Cys ligand in chirality evolution. Importantly, due to the magnetic properties of chiral cobalt oxide nanoparticles and their strong absorption in the UV region, the circular dichroism (CD) responses can be dramatically modulated under an external magnetic field.