Optical activity and chiral memory of thiol-capped CdTe nanocrystals

PARAFAC under non-negativity constraint is adapted to recover the underlying Beer-Lambert law of the excitation-emission fluorescence matrix measurements acquired from analyte-triggered semiconductor QDs photoluminescence modulation. When and why?

BACKGROUND

Analyte-triggered semiconductor quantum dots (QDs) modulation in the presence of non-consistently responsive fluorescent species represents a challenging analytical issue in concrete multi-way data handling. QDs with heterogeneous sizes and/or uneven distribution of functional moieties on their surfaces exhibit significant fluctuations in the fluorescent response components, known as chemical rank, across different excitation/emission modes. This phenomenon may lead to a substantial deviation from the proportionality prescribed by Beer-Lambert law. Nonetheless, even in the presence of such deviation, a multi-way model may be successfully selected after determining a proper chemical rank in a QDs system.

RESULTS

We show that in a valid PARAllel FACtor (PARAFAC) model under properly determined chemical rank, meaningfully resolved pure spectral profiles can be reached for each fluorescent responsive constituent in the original excitation-emission fluorescence matrix (EEFM) measurements. This was thoroughly illustrated by applying PARAFAC trilinear decomposition of a three-way data array of two distinct datasets acquired from semiconductor QDs sensing systems with low-rank trilinear assumption. The first dataset, presented here for the first time, comprises EEFM measurements of the ligand-driven quenching of thiomalic acid (TMA)-capped AgInS2 (AIS) QDs by vomitoxin. The second dataset, employed for illustrative purposes, comprises EEFM measurements of the quenching, via cation bridging, of glutathione (GSH)-capped CdTe QDs by Pb(II). The results of this study enabled the determination of vomitoxin at a ppb level in real samples of fish feeds, showcasing the efficacy of the PARAFAC model in resolving spectral signatures (loadings) and pure concentration profiles (scores).

SIGNIFICANCE

PARAFAC under a properly examined chemical rank can be easily adapted for retrieval the underlying Beer-Lambert law of the original EEFM measurements with a low-rank trilinear structure through the chemically meaningful information either when (i) no deviation of Beer-Lambert law was observed as deeply discussed in connection with the dataset acquired from vomitoxin-driven molecular sensing through TMA-capped AIS QDs, or when (ii) substantial deviations of the Beer-Lambert law are evident, as discussed in connection with the dataset collected from sensing ionic species through Pb(II) bridging of GSH-capped CdTe QDs.

Chiral inorganic nanomaterials in the tumor microenvironment: A new chapter in cancer therapy

Chirality plays a crucial function in the regulation of normal physiological processes and is widespread in organisms. Chirality can be imparted to nanomaterials, whether they are natural or manmade, through the process of asymmetric assembly and/or grafting of molecular chiral groups or linkers. Chiral inorganic nanomaterials possess unique physical and chemical features that set them apart from regular nanomaterials. They also have the ability to interact with cells and tissues in a specific manner, making them useful in various biomedical applications, particularly in the treatment of tumors. Despite the growing amount of research on chiral inorganic nanomaterials in the tumor microenvironment (TME) and their promising potential applications, there is a lack of literature that comprehensively summarizes the intricate interactions between chiral inorganic nanomaterials and TME. In this review, we introduce the fundamental concept, classification, synthesis methods, and physicochemical features of chiral inorganic nanomaterials. Next, we briefly outline the components of TME, such as T cells, macrophages, dendritic cells, and weak acids, and then discuss the anti-tumor effects of several chiral inorganic nanoparticles targeting these components and their potential for possible application during cancer therapy. Finally, the present challenges faced by chiral inorganic nanomaterials in cancer treatment and their future areas of investigation are disclosed.

Intrinsic Chiroptical Activity and Excitonic Properties of Group II-VI Magic-Size Clusters

Semiconductor magic-size clusters (MSCs), lying in the local minima of the potential landscape, are important intermediates that emerge during the synthesis of colloidal quantum dots. They have definite geometrical and electronic structures, thus serving as atomically precise building blocks for assembling supramolecular structures and devices with unprecedented functionalities. Here we report the intrinsic chiroptical activity in the magic-size cadmium and zinc chalcogenide clusters with magic numbers of 13, 33, and 34 possessing unique core-shell structures. They are responsive to circularly polarized light from the ultraviolet to visible region, with size-tunable energy gap, absorption wavelength, and excitonic characteristics. The origin of the chiroptical activity and the evolution of excitonic states with magic size are disclosed by time-dependent density functional theory calculations within a correlated electron-hole picture. This molecular-level understanding of the photophysical properties of group II-VI MSCs provides essential guidelines for utilizing them for chiral optoelectronics and photonics.

Chirality-Induced Spin Selectivity in Composite Materials: A Device Perspective

ConspectusMagnetism is an area of immense fundamental and technological importance. At the atomic level, magnetism originates from electron "spin". The field of nanospintronics (or nanoscale spin-based electronics) aims to control spins in nanoscale systems, which has resulted in astronomical improvement in data storage and magnetic field sensing technologies over the past few decades, recognized by the 2007 Nobel Prize in Physics. Spins in nanoscale solid-state devices can also act as quantum bits or qubits for emerging quantum technologies, such as quantum computing and quantum sensing.Due to the fundamental connection between magnetism and spins, ferromagnets play a key role in many solid-state spintronic devices. This is because at the Fermi level, electron density of states is spin-polarized, which permits ferromagnets to act as electrical injectors and detectors of spins. Ferromagnets, however, have limitations in terms of low spin polarization at the Fermi level, stray magnetic fields, crosstalk, and thermal instability at the nanoscale. Therefore, new physics and new materials are needed to propel spintronic and quantum device technologies to the true atomic limit. Emerging new phenomena such as chirality induced spin selectivity or CISS, in which an intriguing correlation between carrier spin and medium chirality is observed, could therefore be instrumental in nanospintronics. This effect could allow molecular-scale, chirality controlled spin injection and detection without the need for any ferromagnet, thus opening a fundamentally new direction for device spintronics.While CISS finds a myriad of applications in diverse areas such as chiral separation, recognition, detection, and asymmetric catalysis, in this focused Account, we exclusively review spintronic device results of this effect due to its immense potential for future spintronics. The first generation of CISS-based spintronic devices have primarily used chiral bioorganic molecules; however, many practical limitations of these materials have also been identified. Therefore, our discussion revolves around the family of chiral composite materials, which may emerge as an ideal platform for CISS due to their ability to assimilate various desirable material properties on a single platform. This class of materials has been extensively studied by the organic chemistry community in the past decades, and we discuss the various chirality transfer mechanisms that have been identified, which play a central role in CISS. Next, we discuss CISS device studies performed on some of these chiral composite materials. Emphasis is given to the family of chiral organic-carbon allotrope composites, which have been extensively studied by the authors of this Account over the past several years. Interestingly, due to the presence of multiple materials, CISS signals from hybrid chiral systems sometimes differ from those observed in purely chiral systems. Given the sheer diversity of chiral composite materials, CISS device studies so far have been limited to only a few varieties, and this Account is expected to draw increased attention to the family of chiral composites and motivate further studies of their CISS applications.

Engineering copper plasmonic chirality via ligand-induced dissolution for enantioselective recognition of amino acids

The formation of chiral nanosystems and their subsequent enantioselective interaction with chiral amino acids are vital steps in many biological processes. Due to their potential to mimic biological systems, the synthesis of chiral nanomaterials has garnered significant attention over the years. Despite the emergence of diverse nanomaterials showcasing strong chiral responses, the in-depth understanding of the mechanism of plasmonic chirality in copper nanoparticles and their subsequent application in various fields are least explored. Herein, we demonstrate a facile approach for the synthesis of chiral copper nanoparticles using cysteine as a chiral precursor and capping ligand. Ligand-mediated chiral induction, established through experimental findings and a theoretical model, is ascribed as the major contributor to the origin of plasmonic chirality. The enantioselective recognition of chiral copper nanoparticles towards histidine, an amino acid with vast biological functions, was meticulously investigated by leveraging the strong copper-histidine binding ability. Ligand-induced dissolution, a unique phenomenon in nanoparticle reactions, was identified as the underlying mechanism for the nanoparticle-to-complex conversion. Understanding the mechanism of chiral induction in copper nanoparticles coupled with their enantioselective recognition of biomolecules not only holds promise in biomedical research but also sheds light on their potential as catalysts for asymmetric synthesis.

Chirality in Atomically Thin CdSe Nanoplatelets Capped with Thiol-Free Amino Acid Ligands: Circular Dichroism vs. Carboxylate Group Coordination

Chiral semiconductor nanostructures and nanoparticles are promising materials for applications in biological sensing, enantioselective separation, photonics, and spin-polarized devices. Here, we studied the induction of chirality in atomically thin only two-monolayer-thick CdSe nanoplatelets (NPLs) grown using a colloidal method and exchanged with L-alanine and L-phenylalanine as model thiol-free chiral ligands. We have developed a novel two-step approach to completely exchange the native oleic acid ligands for chiral amino acids at the basal planes of NPLs. We performed an analysis of the optical and chiroptical properties of the chiral CdSe nanoplatelets with amino acids, which was supplemented by an analysis of the composition and coordination of ligands. After the exchange, the nanoplatelets retained heavy-hole, light-hole, and spin-orbit split-off exciton absorbance and bright heavy-hole exciton luminescence. Capping with thiol-free enantiomer amino acid ligands induced the pronounced chirality of excitons in the nanoplatelets, as proven by circular dichroism spectroscopy, with a high dissymmetry g-factor of up to 3.4 × 10-3 achieved for heavy-hole excitons in the case of L-phenylalanine.

Ligand induced chirality in In2S3 nanoparticles

Chiral inorganic nanostructures have attracted a lot of attention over the last few years. Here we report the first observation of chirality in indium sulfide nanoparticles, which have been produced by a co-precipitation reaction in the presence of cysteine as a chiral agent. The process resulted in the production of spherical nanoparticles with an average diameter of around 3.6 nm. Circular dichroism spectroscopy of the nanoparticles showed an intense chiroptical signal corresponding to the indium sulfide excitonic transition, confirming the successful transfer of chirality to the In2S3 inorganic matrix. Nuclear magnetic resonance analysis of a colloidal solution of the nanoparticles demonstrated critical evidence of chemisorption of the chiral ligand on the surface of the nanoparticles and revealed a characteristic fast chemical exchange between the ligand chemisorbed on the surface of the nanoparticles and the free ligand in solution. Finally, the effect of the chiral ligand's structure on the transfer of chirality was investigated, with consideration of other amino acid ligands, and the critical role of the thiolate group in the optimisation of the chiral transfer was observed. This research is expected to stimulate further development and applications of new chiral semiconductor nanomaterials.

Enhancing Circularly Polarized Luminescence in Quantum Dots through Chiral Coordination-Mediated Growth at the Liquid/Liquid Interface

Here, we develop a novel methodology for synthesizing chiral CdSe@ZnS quantum dots (QDs) with enhanced circularly polarized luminescence (CPL) by incorporating l-/d-histidine (l-/d-His) ligands during ZnS shell growth at the water/oil interface. The resulting chiral QDs exhibit exceptional absolute photoluminescence quantum yield of up to 67.2%, surpassing the reported limits of 40.0% for chiral inorganic QDs, along with absorption dissymmetry factor (|gabs|) and luminescence dissymmetry factor (|glum|) values of 10-2, exceeding the range of 10-5-10-3 and 10-4-10-2, respectively. Detailed investigations of the synthetic pathway reveal that the interface, as a binary synthetic environment, facilitates the coordinated ligand exchange and shell growth mediated by chiral His-Zn2+ coordination complexes, leading to a maximum fluorescent brightness and chiroptical activities. The growth process, regulated by the His-Zn2+ coordination complex, not only reduces trap states on the CdSe surface, thereby enhancing the fluorescence intensity, but also significantly promotes the orbital hybridization between QDs and chiral ligands, effectively overcoming the shielding effect of the wide bandgap shell and imparting pronounced chirality. The proposed growth pathway elucidates the origin of chirality and provides insights into the regulation of the CPL intensity in chiral QDs. Furthermore, the application of CPL QDs in multilevel anticounterfeiting systems overcomes the limitations of replication in achiral fluorescence materials and enhances the system's resistance to counterfeiting, thus opening new opportunities for chiral QDs in optical anticounterfeiting and intelligent information encryption.

Chiral-induced spin selectivity in biomolecules, hybrid organic-inorganic perovskites and inorganic materials: a comprehensive review on recent progress

The two spin states of electrons are degenerate in nonmagnetic materials. The chiral-induced spin selectivity (CISS) effect provides a new strategy for manipulating electron's spin and a deeper understanding of spin selective processes in organisms. Here, we summarize the important discoveries and recent experiments performed during the development of the CISS effect, analyze the spin polarized transport in various types of materials and discuss the mechanisms, theoretical calculations, experimental techniques and biological significance of the CISS effect. The first part of this review concisely presents a general overview of the discoveries and importance of the CISS effect, laws and underlying mechanisms of which are discussed in the next section, where several classical experimental methods for detecting the CISS effect are also introduced. Based on the organic and inorganic properties of materials, the CISS effect of organic biomolecules, hybrid organic-inorganic perovskites and inorganic materials are reviewed in the third, fourth and fifth sections, especially the chiral transfer mechanism of hybrid materials and the relationship between the CISS effect and life science. In addition, conclusions and prospective future of the CISS effect are outlined at the end, where the development and applications of the CISS effect in spintronics are directly described, which is helpful for designing promising chiral spintronic devices and understanding the natural status of chirality from a new perspective.

Non-spherical gold nanoparticles enhanced fluorescence of carbon dots for norovirus-like particles detection

BACKGROUND

Norovirus is a common pathogen that causes foodborne outbreaks every year and the increasing number of deaths caused by it has become a substantial concern in both developed and underdeveloped countries. To date, no vaccines or drugs are able to control the outbreak, highlighting the importance of finding specific, and sensitive detection tools for the viral pathogen. Current diagnostic tests are limited to public health laboratories and/or clinical laboratories and are time-consuming. Hence, a rapid and on-site monitoring strategy for this disease is urgently needed to control, prevent and raise awareness among the general public.

RESULTS

The present study focuses on a nanohybridization technique to build a higher sensitivity and faster detection response to norovirus-like particles (NLPs). Firstly, the wet chemical-based green synthesis of fluorescent carbon quantum dots and gold nanoparticles (Au NPs) has been reported. Then, a series of characterization studies were conducted on the synthesized carbon dots and Au NPs, for example, high-resolution transmission emission microscopy, fluorescence spectroscopy, fluorescence life-lime measurement, UV-visible spectroscopy, and X-ray diffraction (XRD). The fluorescence emission of the as-synthesized carbon dots and the absorption of Au NPs were located at 440 nm and 590 nm, respectively. Then, the plasmonic properties of Au NPs were utilized to enhance the fluorescence emission of carbon dots in the presence of NLPs in human serum. Here, the enhanced fluorescence response was linearly correlated up to 1 μg mL^-1. A limit of detection (LOD) value was calculated to be 80.3 pg mL^-1 demonstrating that the sensitivity of the proposed study is 10 times greater than that of the commercial diagnostic kits.

CONCLUSIONS

The proposed exciton-plasmon interaction-based NLPs-sensing strategy was highly sensitive, specific, and suitable for controlling upcoming outbreaks. Most importantly, the overall finding in the article will take the technology a step further to applicable point-of-care (POC) devices.

Size-dependent chiro-optical properties of CsPbBr3 nanoparticles

Chiral metal halide perovskites have garnered substantial interest because of their promising properties for application in optoelectronics and spintronics. Understanding the mechanism of chiral imprinting is paramount for optimizing their utility. To elucidate the nature of the underlying chiral imprinting mechanism, we investigated how the circular dichroism (CD) intensity varies with nanoparticle size for quantum confined sizes of colloidal CsPbBr₃ perovskite nanoparticles (NPs) capped by chiral β-methylphenethylammonium bromide ligands. We find that the CD intensity decreases strongly with increasing NP size, which, along with the shape of the CD spectra, points to electronic interactions between ligand and NP as the dominant mechanism of chiral imprinting in smaller NPs. We observe that as the NP size increases and crosses the quantum confinement threshold, the dominant mechanism of chirality transfer switches and is dominated by surfaces effects, e.g., structural distortions. These findings provide a benchmark for quantitative models of chiral imprinting.

Induction of Chirality in Atomically Thin ZnSe and CdSe Nanoplatelets: Strengthening of Circular Dichroism via Different Coordination of Cysteine-Based Ligands on an Ultimate Thin Semiconductor Core

Chiral nanostructures exhibiting different absorption of right- and left-handed circularly polarized light are of rapidly growing interest due to their potential applications in various fields. Here, we have studied the induction of chirality in atomically thin (0.6-1.2 nm thick) ZnSe and CdSe nanoplatelets grown by a colloidal method and coated with L-cysteine and N-acetyl-L-cysteine ligands. We conducted an analysis of the optical and chiroptical properties of atomically thin ZnSe and CdSe nanoplatelets, which was supplemented by a detailed analysis of the composition and coordination of ligands. Different signs of circular dichroism were shown for L-cysteine and N-acetyl-L-cysteine ligands, confirmed by different coordination of these ligands on the basal planes of nanoplatelets. A maximum value of the dissymmetry factor of (2-3) × 10^-3 was found for N-acetyl-L-cysteine ligand in the case of the thinnest nanoplatelets.

Chiral non-stoichiometric ternary silver indium sulfide quantum dots: investigation on the chirality transfer by cysteine

Chiral semiconductor quantum dots have recently received broad attention due to their promising application in several fields such as sensing and photonics. The extensive work in the last few years was focused on the observation of the chiroptical properties in binary Cd based systems. Herein, we report on the first evidence of ligand-induced chirality in silver indium sulfide semiconductor quantum dots. Ternary disulfide quantum dots are of great interest due to their remarkable optical properties and low toxicity. Non-stoichiometric silver indium sulfide quantum dots were produced via a room temperature coprecipitation in water, in the presence of cysteine as a capping agent. The obtained nanocrystals show a notable photoluminescence quantum yield of 0.24 in water dispersions. Several critical aspects of the nanocrystal growth and chemico-physical characterization, and the optimisation of the surface passivation by the chiral ligand in order to optimize the nanoparticle chirality are thoroughly investigated. Optical spectroscopy methods such as circular dichroism and luminescence as well as nuclear magnetic resonance techniques are exploited to analyze the coordination processes leading to the formation of the ligand-nanocrystal chiral interface. This study highlights the dynamic nature of the interaction between the nanocrystal surface and the chiral ligand and clarifies some fundamental aspects for the transfer and optimization of the chiroptical properties.

Recent advances in chiral nanomaterials with unique electric and magnetic properties

Research on chiral nanomaterials (NMs) has grown radically with a rapid increase in the number of publications over the past decade. It has attracted a large number of scientists in various fields predominantly because of the emergence of unprecedented electric, optical, and magnetic properties when chirality arises in NMs. For applications, it is particularly informative and fascinating to investigate how chiral NMs interact with electromagnetic waves and magnetic fields, depending on their intrinsic composition properties, atomic distortions, and assembled structures. This review provides an overview of recent advances in chiral NMs, such as semiconducting, metallic, and magnetic nanostructures.

Electrostatically Directed Long-Range Self-Assembly of Nucleotides with Cationic Nanoparticles To Form Multifunctional Bioplasmonic Networks

Precise control over interparticle interactions is essential to retain the functions of individual components in a self-assembled superstructure. Here, we report the design of a multifunctional bioplasmonic network via an electrostatically directed self-assembly process involving adenosine 5'-triphosphate (ATP). The present study unveils the ability of ATP to undergo a long-range self-assembly in the presence of cations and gold nanoparticles (AuNP). Modelling and NMR studies gave a qualitative insight into the major interactions driving the bioplasmonic network formation. ATP-Ca²⁺ coordination helps in regulating the electrostatic interaction, which is crucial in transforming an uncontrolled precipitation into a kinetically controlled aggregation process. Remarkably, ATP and AuNP retained their inherent properties in the multifunctional bioplasmonic network. The generality of electrostatically directed self-assembly process was extended to different nucleotide-nanoparticle systems.

Chiral carbon dots: synthesis, optical properties, and emerging applications

Carbon dots are luminescent carbonaceous nanoparticles that can be endowed with chiral properties, making them particularly interesting for biomedical applications due to their low cytotoxicity and facile synthesis. In recent years, synthetic efforts leading to chiral carbon dots with other attractive optical properties such as two-photon absorption and circularly polarized light emission have flourished. We start this review by introducing examples of molecular chirality and its origins and providing a summary of chiroptical spectroscopy used for its characterization. Then approaches used to induce chirality in nanomaterials are reviewed. In the main part of this review we focus on chiral carbon dots, introducing their fabrication techniques such as bottom-up and top-down chemical syntheses, their morphology, and optical/chiroptical properties. We then consider emerging applications of chiral carbon dots in sensing, bioimaging, and catalysis, and conclude this review with a summary and future challenges.

Ligand-Induced Ground- and Excited-State Chirality in Silicon Nanoparticles: Surface Interactions Matter

Silicon-based light-emitting materials have emerged as a favorable substitute to various organic and inorganic systems due to silicon's high natural abundance, low toxicity, and excellent biocompatibility. However, efforts on the design of free-standing silicon nanoparticles with chiral non-racemic absorption and emission attributes are rather scare. Herein, we unravel the structural requirements for ligand-induced chirality in silicon-based nanomaterials by functionalizing with D- and L-isomers of a bifunctional ligand, namely, tryptophan. The structural aspects of these systems are established using high-resolution high-angle annular dark-field imaging in the scanning transmission electron microscopy mode, solid-state nuclear magnetic resonance, Fourier transform infrared, and X-ray photoelectron spectroscopy. Silicon nanoparticles capped with L- and D-isomers of tryptophan displayed positive and negative monosignated circular dichroic signals and circularly polarized luminescence indicating their ground- and excited-state chirality. Various studies supported by density functional theory calculations signify that the functionalization of indole ring nitrogen on the silicon surface plays a decisive role in modifying the chiroptical characteristics by generating emissive charge-transfer states. The chiroptical responses originate from the multipoint interactions of tryptophan with the nanoparticle surface through the indole nitrogen and -CO₂^- groups that can transmit an enantiomeric structural imprint on the silicon surface. However, chiroptical properties are not observed in phenylalanine- and alanine-capped silicon nanoparticles, which are devoid of Si-N bonds and chiral footprints. Thus, the ground- and excited-state chiroptics in tryptophan-capped silicon nanoparticles originates from the collective effect of ligand-bound emissive charge-transfer states and chiral footprints. Being the first report on the circularly polarized luminescence in silicon nanoparticles, this work will open newer possibilities in the field of chirality.

Mechanism of diastereoisomer-induced chirality of BiOBr

Chiral molecule-driven asymmetric structures are known to be elusive because of the intriguing chirality transfer from chiral molecules to achiral species. Here, we found that the chiral assembly of BiOBr is independent of the chirality of the organic molecular inducer but dependent on geometric structural matching between the inducer and inorganic species. Diastereoisomeric sugar alcohols (DSAs) with identical numbers of carbon chiral centers and functional groups but with different R/S configurations and optical activities (OAs) were chosen as symmetry-breaking agents for inducing chiral mesostructured BiOBr films (CMBFs) under hydrothermal conditions. Multiple levels of chirality with different handedness were identified in the CMBFs. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations suggest that asymmetric defects in the Br–Bi tetragonal cone caused by physically adsorbed DSAs on the surfaces of the BiOBr crystals are the geometric basis for triggering the chiral twist in the BiOBr monolayer. Our findings provide new insights for understanding the origin of chirality and the chiral transfer mechanism underlying the assembly of achiral species.

The chirality transfer is dependent on geometrical matching between the chiral inducer and inorganic species.

Recent Advances in Inorganic Chiral Nanomaterials

Inorganic nanoparticles offer a multifunctional platform for biomedical applications in drug delivery, biosensing, bioimaging, disease diagnosis, screening, and therapies. Homochirality prevalently exists in biological systems composed of asymmetric biochemical activities and processes, so biomedical applications essentially favor the usage of inorganic chiral nanomaterials, which have been widely studied in the past two decades. Here, the latest investigations are summarized including the characterization of 3D stereochirality, the bionic fabrication of hierarchical chirality, extension of the compositional space to poly-elements, studying optical activities with the (sub-)single-particle resolution, and the experimental demonstration in biomedical applications. These advanced studies pave the way toward fully understanding the two important chiral effects (i.e., the chiroptical and enantioselective effects), and prospectively promote the flexible design and fabrication of inorganic chiral nanoparticles with engineerable functionalities to solve diverse practical problems closely associated with environment and public health.

Chiral Perovskites for Next-Generation Photonics: From Chirality Transfer to Chiroptical Activity

Organic-inorganic hybrid halide perovskites (OIHPs) are commonly used as prototypical materials for various applications, including photovoltaics, photodetectors, and light-emitting devices. Since the chiroptical properties of OIHPs are deciphered in 2017, chiral OIHPs have been rediscovered as new hybrid systems comprising chiral organic molecules and achiral inorganic octahedral layers. Owing to their exceptional optoelectrical properties and structural flexibility, chiral OIHPs have received a considerable amount of attention in chiral photonics, chiroptoelectronics, spintronics, and ferroelectrics. Despite their intriguing chiral properties, the transfer mechanism from chiral molecules to achiral semiconductors has not been extensively investigated. Furthermore, an in-depth understanding of the origin of chiroptical activity is still elusive. In this review article, recent advances in the chiroptical activities of chiral OIHPs and polarization-based devices adopting chiral OIHPs are comprehensively discussed, and insight into the underlying chirality transfer mechanism based on theoretical considerations is provided. This comprehensive survey, with an emphasis on the chirality transfer mechanism, will help readers understand the chiroptical properties of OIHPs, which are crucial for the development of spin-based photonic and optoelectronic devices. Additionally, promising strategies to exploit the potential of chiral OIHPs are also discussed.

Chirality Induction to CdSe Nanocrystals Self-Organized on Silica Nanohelices: Tuning Chiroptical Properties

CdSe nanocrystals (NCs) were grafted on chiral silica nanoribbons, and the mechanism of resulting chirality induction was investigated. Because of their chiral organization, these NCs show optically active properties that depend strongly on their grafting densities and sizes of the NCs. The effect of the morphology of the chiral silica templates between helical (cylindrical curvature) vs twisted (saddle like curvature) ribbons was investigated. The g-factor of NCs-silica helical ribbons is larger than that of the NCs-silica twisted ribbons. Finally, rod-like NCs (QR) with different lengths were grafted on the twisted silica ribbons. Interestingly, their grafting direction with respect to the helix surface changed from side-grafting for short QR to tip-grafting for long rods and the corresponding CD spectra switched signs.

Chiral nanomaterials for tumor therapy: autophagy, apoptosis, and photothermal ablation

Chirality is a fundamental characteristic of natural molecules and a crucial factor in the biochemical reactions of living cells and organisms. Recently, researchers have successfully introduced chiral molecules to the surfaces of nanomaterials, creating chiral nanomaterials that exhibit an upscaling of chiral behavior from the molecular scale to the nanoscale. These chiral nanomaterials can selectively induce autophagy, apoptosis, and photothermal ablation in tumor cells based on their chirality, making them promising for application in anti-tumor therapy. However, these interesting and important phenomena have hitherto received little attention. Accordingly, we herein present a review of recent research progress in the field of chiral nanomaterials for tumor therapy along with brief looks at the mechanistic details of their actions. Finally, the current challenges and future perspectives of chiral nanomaterials in terms of maximizing their potential in tumor therapy are discussed. Thus, this review provides a helpful introduction to the design of chiral nanomaterials and will hopefully highlight the importance of chirality in tumor therapy.

Effect ofα-substitute group on the chirality of monocarboxylic acid stabilized CdSe nanocrystals

The effect ofα-substitute groups at the asymmetric carbon of chiral monocarboxylic acid ligand, on the chirality of CdSe nanocrystals (NCs) was studied. When the substitution groups have strong electron-withdrawing capability, the CdSe NCs displayed an enhanced chirality where theg-factors were comparable to those with dicarboxylic chiral ligands. In addition, adding ethanol was demonstrated as an effective way to stabilize NCs, however, completely oppositeg-factor evolution behavior was found for NCs with differentα-substituted ligands. Specifically, theg-factor has increased/decreased with strong/weak electron-withdrawingα-substitute groups probably due to the different intermolecular hydrogen bonding between carboxylic acids and ethanol.

Recent advances in colorimetry/fluorimetry-based dual-modal sensing technologies

Tailored to the increasing demands for sensing technologies, the fabrication of dual-modal sensing technologies through combining two signal transduction channels into one method has been proposed and drawn considerable attention. The integration of two sensing signals not only promotes the analytical efficiency with reduced assumption, but also improves the analytical performances with enlarged detection linear range, enhanced accuracy, and boosted application flexibility. The two top-rated output signals for developing dual-modal sensors are colorimetric and fluorescent signals because of their outstanding merits for point of care applications and real-time sensitive sensing. Given the rapid development of material chemistry and nanotechnology, the recent decade has witnessed great advance in colorimetric/fluorimetric signal based dual-modal sensing technologies. The new sensing strategy leads to a broad avenue for various applications in disease diagnosis, environmental monitoring and food safety because of the complementary and synergistic effects of the two output signals. In this state-of-the-art review, we comprehensively summarize different types of colorimetric/fluorimetric dual-modal sensing methods by highlighting representative research in the last 5 years, digging into their sensing methodologies, particularly the working principles of the signal transduction systems. Then, the challenges and future prospects for boosting further development of this research field are discussed.

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.

Chiral Surface and Geometry of Metal Nanocrystals

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 geometry of nanocrystals. Interestingly, this discovery stems from a purely crystallographic outcome: chirality can be generated on high-Miller-index surfaces, even for highly symmetric metal crystals. This is the starting point herein, with an overview of the scientific history and a summary of the crystallographic definition. With the advance of nanomaterial synthesis technology, high-Miller-index planes can be selectively exposed on metallic nanoparticles. The enantioselective interaction of chiral molecules and high-Miller-index facets can break the mirror symmetry of the metal nanocrystals. Herein, the fundamental principle of chirality evolution is emphasized and it is shown how chiral surfaces can be directly correlated with chiral morphologies, thus serving as a guide for researchers in chiral catalysts, chiral plasmonics, chiral metamaterials, and photonic devices.

Circularly Polarized Luminescence in Nanoassemblies: Generation, Amplification, and Application

Currently, the development of circularly polarized luminescent (CPL) materials has drawn extensive attention due to the numerous potential applications in optical data storage, displays, backlights in 3D displays, and so on. While the fabrication of CPL-active materials generally requires chiral luminescent molecules, the introduction of the "self-assembly" concept offers a new perspective in obtaining the CPL-active materials. Following this approach, various self-assembled materials, including organic-, inorganic-, and hybrid systems can be endowed with CPL properties. Benefiting from the advantages of self-assembly, not only chiral molecules, but also achiral species, as well as inorganic nanoparticles have potential to be self-assembled into chiral nanoassemblies showing CPL activity. In addition, the dissymmetry factor, an important parameter of CPL materials, can be enhanced through various pathways of self-assembly. Here, the present status and progress of self-assembled nanomaterials with CPL activity are reviewed. An overview of the key factors in regulating chiral emission materials at the supramolecular level will largely boost their application in multidisciplinary fields.

Chiral Surface and Geometry of Metal Nanocrystals

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 geometry of nanocrystals. Interestingly, this discovery stems from a purely crystallographic outcome: chirality can be generated on high-Miller-index surfaces, even for highly symmetric metal crystals. This is the starting point herein, with an overview of the scientific history and a summary of the crystallographic definition. With the advance of nanomaterial synthesis technology, high-Miller-index planes can be selectively exposed on metallic nanoparticles. The enantioselective interaction of chiral molecules and high-Miller-index facets can break the mirror symmetry of the metal nanocrystals. Herein, the fundamental principle of chirality evolution is emphasized and it is shown how chiral surfaces can be directly correlated with chiral morphologies, thus serving as a guide for researchers in chiral catalysts, chiral plasmonics, chiral metamaterials, and photonic devices.

Chiral Mesoporous Silica Materials: A Review on Synthetic Strategies and Applications

Because of its tunable textural properties and chirality feature, chiral mesoporous silica (CMS) gained significant consideration in many fields and has been developed rapidly in recent years. In this review, we provide an overview of synthesis strategies for fabricating CMS together with its main applications. The properties of CMS, including morphology and mesostructures and enantiomer excess (ee), can be altered according to the synthetic conditions during the synthesis process. Despite its primary stage, CMS has attracted extensive attention in many fields. In particular, CMS nanoparticles are widely used for enantioselective resolution and adsorption of chiral compounds with desirable separation capability. Also, CMS acts as a promising candidate for the effective delivery of chiral or achiral drugs to produce a chiral-responsive manner. Moreover, CMS also plays an important role in chromatographic separations and asymmetric catalysis. There has been an in-depth review of the synthetic methods and mechanisms of CMS. And this review aims to give a deep insight into the synthesis and application of CMS, especially in recent years, and highlights the significance that it may have in the future.

Tuning residual chirality in carbon dots with anti-microbial properties

Chirality remains a critical consideration in drug development and design, as well as in applications of enantioselective recognition and sensing. However, the preparation of chiral nanomaterials requires extensive post synthetic modifications with a chiral agent, coupled with extensive purification. This limits the use and application of chiral nanomaterials. Herein, we report a facile, one-step microwave-assisted synthesis of chiral carbon dots through the reaction of l- and d-cysteine amino acid precursors and citric acid. We modulated the synthetic parameters to preserve and tune the residual chiral properties of the dots and demonstrate that the reaction conditions play a critical role in dictating the chiral behaviour of the dots. Finally, in a proof of concept application we demonstrated that the synthesized carbon dots, particularly d-carbon dots inhibit bacterial growth at a lower concentration than l-carbon dots. By varying bacterial strains and chirality of the carbon dots, concentrations ranging from 0.25-4 mg mL-1 of the nanoparticles were required to inhibit microbial growth. The ability to preserve and tune chirality during synthesis can open up novel avenues and research directions for the development of enantioselective materials, as well as antibacterial films and surfaces.

Chiral Self-Assembly of Porphyrins Induced by Chiral Carbon Dots

Chirality plays a key role in many fields ranging from life to natural sciences. For a long time, chiral materials have been developed and used to interact with chiral environments. In recent years, fluorescent carbon dots (CDots) are a new class of carbon nanomaterials exhibit excellent optical properties, good biocompatibility, excellent water solubility, and low cost. However, chirality transfer between semiconductor CDots and organics remains a challenge. Herein, a facile one-step hydrothermal method was used to synthesize chiral CDs from cysteine (cys). The obtained chiral CDots can act as chiral templates to induce porphyrins to form chiral supramolecular assemblies. The successful transmission of chiral information provides more options for the development of various chiral composite materials and the preservation of chiral information in the future.

Chiral Ligand-Free, Optically Active Nanoparticles Inherently Composed of Chiral Lattices at the Atomic Scale

Bulk metals lack chirality. Recently, metals have been sculptured with metastable chirality varying from the micro- to nano-scale. The manipulation of molecular chirality could be novelly performed using metals composed of chiral lattices at atomic scales (i.e., chiral nanoparticles or CNPs) if one could fundamentally understand the interactions between molecules and the chiral metal lattices. The incorporation of chiral ligands has been generally adapted to form metal CNPs. However, post-fabrication removal of chiral ligands usually causes relaxation of the metastable chiral lattices to thermodynamically stable achiral structures, and thus the coexisting chiral ligands will unavoidably disturb or screen the interactions of interest. Herein, a concept of metal CNPs that are free of chiral ligands and consist of atomically chiral lattices is introduced. Without chiral ligands, shear forces applied by substrate rotation along with the translation of incident atoms lead to imposing the metastable chiral lattices onto metals. Metal CNPs show not only the chiroptical effect but the enantiospecific interactions of chiral lattices and molecules. These two unique chiral effects have resulted in the applications of enantiodifferentiation and asymmetric synthesis. Prospectively, the extension in composition space and constituent engineering will apply alloy CNPs to enantiodiscrimination, enantioseperation, bio-imaging, bio-sensing, and asymmetric catalysis.

Bulk Chiral Halide Perovskite Single Crystals for Active Circular Dichroism and Circularly Polarized Luminescence

Motivated by the chirality research of the hybrid halide perovskite, we reported the controllable growth of single crystals of (R)-, (S)-, and (R,S)-C₆H₅CH(CH₃)NH₃ (MBA)-based lead (Pb) halide perovskites. The crystal structures were redetermined and further refined to clarify the previously ambiguous crystal structure problems. We further investigated the chiral optical properties of these single crystals including nonlinear optical (NLO) properties and photoluminescence (PL) properties. The as-fabricated (R)- and (S)-MBAPbBr₃ single crystals not only show notable circular dichroism (CD) signals in the absorption spectra but also exhibit obvious circularly polarized luminescence (CPL) characteristics. The available chiral hybrid perovskite single crystals open up the possibility to study these intrinsic chirality properties for optoelectronic applications.

Optical nanoprobes for chiral discrimination

Chiral recognition can be achieved by exploiting chiral properties of nanoparticles within various colorimetric and luminescent sensing systems.

Tuning optical properties and optical rotation of 3-mercaptopropionic acid capped organic-inorganic hybrid perovskites

The emission wavelength of organic-inorganic hybrid perovskite quantum dots (QDs) can be tuned by controlling reaction time relevant to the halide exchange. It is because halide exchange with different time would lead to different molar ratio of halides in perovskite QDs such as Cl and Br. Here, to research the ligand's effect on the halide exchange, this work synthesized 3-mercaptopropionic acid (MPA)-capped CH₃ NH₃ PbBr_x Cl_3-x QDs. It was found that SH^- of MPA appeared to inhibit the halide exchange during the reation. Moreover, although the MPA-capped CH₃ NH₃ PbBr_x Cl_3-x QDs did not contain the chiral centre, they exhibit the optical rotation. This may provide a method for chirality manipulation of perovskite.

Chiral CdSe nanoplatelets as an ultrasensitive probe for lead ion sensing

As opposed to traditional photoluminescence and ultra-violet based optical sensing, we present here a sensing system based on resolved optically active polarization with promising applications. It is based on the ultrathin CdSe nanoplatelets (NPLs) when modified with either l or d-cysteine molecules (l/d-cys) as bio-to-nano ligands. The chiral ligand transfers its chiroptical activity to the achiral nanoplatelets with an anisotropy factor of ∼10-4, which unlocks the chiral excitonic transitions and allows lead ion detection with a limit of detection (LOD) as low as 4.9 nM. Simulations and modelling based on time-dependent density functional theory (TD-DFT) reveal the chiral mechanism of l/d-cys capped CdSe NPLs. The presented CD-based sensing system illustrates an alternative possibility of using chiral CdSe NPLs as competitive chiral sensors for heavy metal ion detection.

Chiral Plasmons: Au Nanoparticle Assemblies on Thermoresponsive Organic Templates

Template-assisted strategies are widely used to fabricate nanostructured materials. By taking these strategies a step forward, herein we report the design of two chiral plasmonic nanostructures based on Au nanoparticle (NP) assemblies organized in clockwise and anticlockwise directions, having opposite response to circularly polarized light. The chiral plasmonic nanostructures are obtained by growing Au NPs on chiral templates based on d- and l-forms of alanine functionalized phenyleneethynylenes. Interestingly, Au NP assemblies show mirror symmetrical electronic circular dichroism (ECD) bands at their surface plasmon frequency originating through their asymmetric organization. Upon increasing the temperature, the chiral templates dissociate as evident from the disappearance of their ECD signal. The profound advantage of the thermoresponsive nature of the templates is employed to obtain free-standing chiral plasmonic nanostructures. The tilt angle high-resolution transmission electron microscopic measurements indicate that the NP assemblies, grown on a template based on the d-isomer, organize in clockwise direction ( P-form) and on l-isomer in anticlockwise direction ( M-form). The inherent chirality prevailing on the surface of the template drives the helical growth of the Au NPs in opposite directions. Experimental results are rationalized by a model which accounts for the large polarizability of Au NPs. The large polarizability leads to large oscillating dipole moments whose effects become prominent when interparticle distances are comparable to the particle size.

Self-Assembled Chiral Nanoparticle Superstructures and Identification of Their Collective Optical Activity from Ligand Asymmetry

The spontaneous self-assembly of chiral nanoparticles (NPs) into stationary fabrication has garnered great interest in technique investigation and science advancement due to its expected apparent properties via orderly collective behaviors. However, this kind of characterization of assembled nanoparticles superstructure (NPS) is rarely reported and is distinguished with monodispersed chiral NPs. In this work, we used l-cysteine (Cys) as the chiral molecule in the form of functional surfactant, which had capped CdS/CdTe NPs and was treated as a linkage bridge for constructing orderly assembled NPS. Among the circular dichrosim (CD) phenomenon, Cys ligands exhibit related changes in CD absorption, while whole-molecule solution was used for treatment in different pH-controlling procedures. Synthesized chiral NPs are organized into ordered rod-shaped NPS during the spontaneous self-assembly process, and the CD response of NPS is monitored in different cultivating times; it showed a persuasive response appears in sum frequency generation (SFG) spectroscopy. Both experimental works and theory calculation convey that the ordered stacking of chiral stabilizer and the chirality of NPS, which are identified from chiral molecular status and their collective optical activity, originated from ligand asymmetry.

Helicoidal Patterning of Nanorods with Polymer Ligands

Chiral packing of ligands on the surface of nanoparticles (NPs) is of fundamental and practical importance, as it determines how NPs interact with each other and with the molecular world. Herein, for gold nanorods (NRs) capped with end-grafted nonchiral polymer ligands, we show a new mechanism of chiral surface patterning. Under poor solvency conditions, a smooth polymer layer segregates into helicoidally organized surface-pinned micelles (patches). The helicoidal morphology is dictated by the polymer grafting density and the ratio of the polymer ligand length to nanorod radius. Outside this specific parameter space, a range of polymer surface structures was observed, including random, shish-kebab, and hybrid patches, as well as a smooth polymer layer. We characterize polymer surface morphology by theoretical and experimental state diagrams. The helicoidally organized polymer patches on the NR surface can be used as a template for the helicoidal organization of other NPs, masked synthesis on the NR surface, as well as the exploration of new NP self-assembly modes.