Chiral nanotechnology

Chiral induction in the crystallization of KIO3 and LiIO3: the role of amino acids in controlling the chirality of inorganic crystals

Chiral induction in crystals has attracted significant attention due to its implications for developing chiral materials and understanding mechanisms of symmetry-breaking enantioselective crystallization of naturally occurring chiral minerals. Despite its potential use in chiral discrimination, this area remains largely unexplored. Here, we investigate chiral induction during crystallization of naturally occurring chiral KIO3 and LiIO3 minerals using arginine and alanine as chiral inducers. The chiral nature of the crystallization and the effect of the chiral inducers were examined using circular dichroism, polarimetry, and low-frequency Raman spectroscopy. The impact of chiral molecules on the rate and final crystal structure was studied by electron microscopy including SEM and TEM. We demonstrate that it is possible to control the chirality with chiral exogenous molecules, mainly amino acids. Understanding chiral induction in crystal growth may open avenues for controlled assembly of chiral materials and development of novel functional materials with unique properties.

Sensitive Detection of Hg2+ and l-Cysteine through Optical Asymmetry-Tuned Fluorescence Switch Off-On Behavior in N-Doped Chiral Carbon Dot

Blue-emissive nitrogen-doped chiral carbon dots (d-NCD230 and l-NCD230) exhibiting antipodal chiroptical activity, synthesized from the thermal pyrolysis of citric acid and d/l-aspartic acid in 1:2 molar ratios, have been explored as chirality-based fluorescent turn-off/on probes for the detection of Hg2+ and l-cysteine (l-Cys). Circular dichroism (CD) spectroscopy revealed that the chiroptical activity originates from a synergy among intrinsic chirality, chiral precursors on the NCD surface, and hybridization of lower energy levels within the embedded chiral chromophore. Quantitative analysis of optical asymmetry using the Kuhn asymmetry factor (g) at the CD signal of 312 nm showed a higher value for d-NCD230 (1.03 × 10-4) compared to l-NCD230 (1.13 × 10-5). Moreover, we have demonstrated chirality transfer and chiral inversion phenomena in d/l-NCDs by preparing carbon dots with different precursor ratios at different temperatures and probing them through CD spectroscopy. The NCDs exhibited selective fluorescence quenching in the presence of Hg2+, demonstrating linearity in the Stern-Volmer plot. Limits of detection (LODs) for Hg2+ were calculated to be 129 and 192 nM for d-NCD230 and l-NCD230, respectively, in the 0-150 μM concentration range. The quenching mechanism involves nonradiative electron transfer due to Hg2+ binding to oxygen-rich functional groups on the d/l-NCD230 surface. The slight variation in LOD values between d-NCD230 and l-NCD230 indicates the negligible effect of the chirality on Hg2+ sensing. Notably, the fluorescence intensity of d/l-NCD230 could be restored upon adding l-cysteine, with d-NCD230 showing a more pronounced enhancement than l-NCD230. This differential response is attributed to a preferential stereoselective interaction arising from the homochirality of d-NCD230/Hg2+ and l-cysteine. These findings demonstrate the potential of chiral nitrogen-doped carbon dots as sensitive and selective probes for Hg2+ and l-cysteine, with implications for environmental monitoring and biological sensing applications.

Self-Assembled Chiral Film Based on Melanin Polymers

Chirality plays a fundamental role in natural phenomena, yet its manifestation on solid surfaces remains relatively unexplored. In this study, we investigate the formation of chiroptical melanin-based self-assembled films on quartz substrates, leveraging mussel-inspired surface chemistry. Water-soluble porphyrins serve as molecular synthons, facilitating the spontaneous formation of hetero-aggregates in phosphate-buffered saline containing L- or D-DOPA. Spectroscopic analysis reveals chiral transfer from DOPA enantiomers to porphyrin hetero-aggregates, followed by the disruption of these latter and subsequent generation of chiral melanin structures in solution. Quartz substrates inserted into these solutions spontaneously accumulate homogeneous melanin-like films over days, demonstrating the feasibility of self-assembly. The resulting films exhibit characteristic UV/Vis and CD spectra, with distinct signals indicating successful chiral induction. Interestingly, the AFM characterizations reveal a distinct surface morphology, and in addition, some thermal and mechanical properties have been taken into account. Overall, this study sheds light on the formation, stability, and chiroptical properties of melanin-based films, paving the way for their application in various fields.

From Short- to Long-Range Chiral Recognition on Surfaces: Chiral Assembly and Synthesis

Research on chiral behaviors of small organic molecules at solid surfaces, including chiral assembly and synthesis, can not only help unravel the origin of the chiral phenomenon in biological/chemical systems but also provide promising strategies to build up unprecedented chiral surfaces or nanoarchitectures with advanced applications in novel nanomaterials/nanodevices. Understanding how molecular chirality is recognized is considered to be a mandatory basis for such studies. In this review, a series of recent studies in chiral assembly and synthesis at well-defined metal surfaces under ultra-high vacuum conditions are outlined. More importantly, the intrinsic mechanisms of chiral recognition are highlighted, including short/long-range chiral recognition in chiral assembly and two main strategies to steer the reaction pathways and modulate selective synthesis of specific chiral products on surfaces.

Synthesis of novel fluorescence probes and their application in the enantioselective recognition of arginine

Arginine (Arg) plays a crucial and multifaceted role in various biological processes, encompassing cell division, wound healing, immune system modulation, and plant signaling. This study introduced a pair of novel chiral fluorescent probes, (R)-5 and (S)-5, constructed upon the BINOL framework, which exhibited enantiomeric selectivity and sensitivity to d-Arg/l-Arg in fluorescence experiments. These probes offered a simple, rapid, low-cost, and highly selective method for detecting Arg enantiomers, thereby providing a highly sensitive approach for their qualitative and quantitative analysis. The enantioselective fluorescence enhancement ratios {ef = [(I1 - I0)/(I2 - I0) = ΔI1/ΔI2]} of (R)-5 and (S)-5 to Arg were 1694 and 5163, respectively. Moreover, the probes demonstrated the capability to detect the concentration of d-Arg and l-Arg with a limit of detection of 4.84 × 10-7 M and 3.35 × 10-7 M, respectively, as well as determine the enantiomeric excess. These probes exhibited high chemical selectivity and enantioselectivity, enabling the identification of different configurations of Arg, quantification of Arg concentrations, and determination of the enantiomeric composition of Arg. This study provides valuable insights for the development of sensitive and selective chiral molecular detection methods, significantly advancing our comprehension of the relationship between Arg concentration and probe fluorescence response.

Knot Formation on DNA Pushed Inside Chiral Nanochannels

We performed coarse-grained molecular dynamics simulations of DNA polymers pushed inside infinite open chiral and achiral channels. We investigated the behavior of the polymer metrics in terms of span, monomer distributions and changes of topological state of the polymer in the channels. We also compared the regime of pushing a polymer inside the infinite channel to the case of polymer compression in finite channels of knot factories investigated in earlier works. We observed that the compression in the open channels affects the polymer metrics to different extents in chiral and achiral channels. We also observed that the chiral channels give rise to the formation of equichiral knots with the same handedness as the handedness of the chiral channels.

Polymeric Carbon Nitride with Chirality Inherited from Supramolecular Assemblies

The facile synthesis of chiral materials is of paramount importance for various applications. Supramolecular preorganization of monomers for thermal polymerization has been proven as an effective tool to synthesize carbon and carbon nitride-based (CN) materials with ordered morphology and controlled properties. However, the transfer of an intrinsic chemical property, such as chirality from supramolecular assemblies to the final material after thermal condensation, was not shown. Here, we report the large-scale synthesis of chiral CN materials capable of enantioselective recognition. To achieve this, we designed supramolecular assemblies with a chiral center that remains intact at elevated temperatures. The optimized chiral CN demonstrates an enantiomeric preference of ca. 14 %; CN electrodes were also prepared and show stereoselective interactions with enantiomeric probes in electrochemical measurements. By adding chirality to the properties transferrable from monomers to the final product of a thermal polymerization, this study confirms the potential of using supramolecular precursors to produce carbon and CN materials and electrodes with designed chemical properties.

Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Chiroptical-responsive nanoprobe for the optosensing of chiral amino acids

A supersensitive chiroptical-responsive system of enantioselectively recognizing L- and D-tryptophan (Trp) based on ( +)-diacetyl-L-tartaric anhydride-functionalized 1,3,5-triformylphloroglucinol (DTA-functionalized Tp) was constructed for the first time. With a high fluorescence quantum yield of 15.2% and fluorescence lifetime of 57.6 μs, DTA-functionalized Tp as both fluorescent and chiral recognition nanoprobe was used for the discrimination of L- and D-Trp with excitation/emission maxima at 330/490 nm within 3 min. The linear range of the fluorescence sensing was 0.002-0.15 μg mL^-1, and the detection limit achieved 1.4 ng mL^-1. Furthermore, a smartphone was employed as a detector and processor to couple with the chiroptical-responsive nanoprobe for establishing a novel and visual integration system for rapid and real-time detection of chiral amino acids with a detection limit of 13 ng mL^-1. The spiked recoveries of L-Trp in two commercially available functional beverages ranged from 86.00 to 118.33% in fluorescence and smartphone-based sensing system. Based on the excellent chiroptical-responsive effects, high stability, and biocompatibility, the chiroptical-responsive nanoprobe was successfully applied to visual optosensing and fluorescence imaging in response to L- and D-Trp in HeLa cells. This discrimination methodology with high sensitivity and enantioselectively shows great potential for in-site visually monitoring chiral amino acids in real food samples and tracking physiological processes.

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.

Locally superengineered cascade recognition–quantification zones in nanochannels for sensitive enantiomer identification

As an intriguing and intrinsic feature of life, chirality is highly associated with many significant biological processes. Simultaneous recognition and quantification of enantiomers remains a major challenge. Here, a sensitive enantiomer identification device is developed on TiO₂ nanochannels via the design of cascade recognition–quantification zones along the nanochannels. In this system, β-cyclodextrin (β-CD) is self-assembled on one side of the nanochannels for the selective recognition of enantiomers; CuMOFs are designed as the target-responsive partners on the other side of the nanochannels for the quantification of enantiomers that pass through the nanochannels. As a proof-of-principle of the cascade design, arginine (Arg) enantiomers are tested as the identification targets. The l-Arg molecules selectively bind in the recognition zone; d-Arg molecules pass through the recognition zone and then interact with the quantification zone via a specialized reduction reaction. As verified by nanofluidic simulations, because of the confinement effect of nanoscale channels combined with the condensation effect of porous structure, the in situ reaction in the quantification zone contributes to an unprecedented variation in transmembrane K⁺ flux, leading to an improved identification signal. This novel cascade-zone nanochannel membrane provides a smart strategy to design multifunctional nanofluidic devices.

A design of the cascade recognition–quantification zone is developed along TiO₂ nanochannels. The asymmetric nanochannels exhibit a predominant sensitivity and selectivity for enantiomer discrimination.

Channels with Helical Modulation Display Stereospecific Sensitivity for Chiral Superstructures

By means of coarse-grained molecular dynamics simulations, we explore chiral sensitivity of confining spaces modelled as helical channels to chiral superstructures represented by polymer knots. The simulations show that helical channels exhibit stereosensitivity to chiral knots localized on linear chains by effect of external pulling force and also to knots embedded on circular chains. The magnitude of the stereoselective effect is stronger for torus knots, the effect is weaker in the case of twist knots, and amphichiral knots do exhibit no chiral effects. The magnitude of the effect can be tuned by the so-far investigated radius of the helix, the pitch of the helix and the strength of the pulling force. The model is aimed to simulate and address a range of practical situations that may occur in experimental settings such as designing of nanotechnological devices for the detection of topological state of molecules, preparation of new gels with tailor made stereoselective properties, or diffusion of knotted DNA in biological conditions.

Bioinspired Solid-State Nanochannel Sensors: From Ionic Current Signals, Current, and Fluorescence Dual Signals to Faraday Current Signals

Inspired from bioprotein channels of living organisms, constructing "abiotic" analogues, solid-state nanochannels, to achieve "smart" sensing towards various targets, is highly seductive. When encountered with certain stimuli, dynamic switch of terminal modified probes in terms of surface charge, conformation, fluorescence property, electric potential as well as wettability can be monitored via transmembrane ionic current, fluorescence intensity, faraday current signals of nanochannels and so on. Herein, the modification methodologies of nanochannels and targets-detecting application are summarized in ions, small molecules, as well as biomolecules, and systematically reviewed are the nanochannel-based detection means including 1) by transmembrane current signals; 2) by the coordination of current- and fluorescence-dual signals; 3) by faraday current signals from nanochannel-based electrode. The coordination of current and fluorescence dual signals offers great benefits for synchronous temporal and spatial monitoring. Faraday signals enable the nanoelectrode to monitor both redox and non-redox components. Notably, by incorporation with confined effect of tip region of a needle-like nanopipette, glorious in-vivo monitoring is conferred on the nanopipette detector at high temporal-spatial resolution. In addition, some outlooks for future application in reliable practical samples analysis and leading research endeavors in the related fantastic fields are provided.

S-citalopram imprinted monolithic columns for capillary electrochromatography enantioseparations

In this study, the molecular imprinting method was used to separate enantiomeric forms of chiral antidepressant drug, R,S-citalopram (R,S-CIT) in aqueous solution by CEC system combining the advantages of capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). For that, an amino acid-based molecularly imprinted monolithic capillary column was designed and used as a stationary phase for selective separation of S-citalopram (S-CIT) for the first time. S-CIT was selectively separated from the aqueous solution containing the other enantiomeric form of R-CIT, which is the same in size and shape as the template molecule. Morphology of the molecularly imprinted (MIP S-CIT) and non-imprinted (NIP S-CIT) monolithic capillary columns was observed by scanning electron microscopy. Imprinting efficiency of MIP S-CIT monolithic capillary column used for selective S-CIT separation was verified by comparing with NIP S-CIT and calculated imprinting factor (I.F:1.81) proved the high selectivity of the MIP S-CIT for S-CIT. Cavities formed for S-CIT form enabled selective (α = 2.08) separation of the target molecule from the other enantiomeric R-CIT form. Separation was achieved in a short period of 10 min, with the electrophoretic mobility of 7.68 × 10^-6 m² /Vs for R,S-CIT at pH 7.0 10 mM PB and 50% ACN ratio. The performance of both MIP S-CIT and NIP S-CIT columns was estimated by repeating the R,S-CIT separations with intra-batch and inter-batch studies for reproducibility of retention times of R,S-CITs. Estimated RSD values that are lower than 2% suggest that the monolithic columns separate R,S-CIT enantiomers without losing separation efficiency.

Chiral carbon dots based on L/D-cysteine produced via room temperature surface modification and one-pot carbonization

Since chirality is one of the phenomena often occurring in nature, optically active chiral compounds are important for applications in the fields of biology, pharmacology, and medicine. With this in mind, chiral carbon dots (CDs), which are eco-friendly and easy-to-obtain light-emissive nanoparticles, offer great potential for sensing, bioimaging, enantioselective synthesis, and development of emitters of circularly polarized light. Herein, chiral CDs have been produced via two synthetic approaches using a chiral amino acid precursor l/d-cysteine: (i) surface modification treatment of achiral CDs at room temperature and (ii) one-pot carbonization in the presence of chiral precursor. The chiral signal in the absorption spectra of synthesized CDs originates not only from the chiral precursor but from the optical transitions attributed to the core and surface states of CDs. The use of chiral amino acid molecules in the CD synthesis through carbonization results in a substantial (up to 8 times) increase in their emission quantum yield. Moreover, the synthesized CDs show two-photon absorption which is an attractive feature for their potential bioimaging and sensing applications.

Enantioselection and chiral sorting of single microspheres using optical pulling forces

We put forward a novel, twofold scheme that enables, at the same time, all-optical enantioselection and sorting of single multipolar chiral microspheres based on optical pulling forces exerted by two non-collinear, non-structured, circularly polarized light sources. Our chiral resolution method can be externally controlled by varying the angle between their incident wavevectors, allowing for fine-tuning of the range of chiral indices for enantioselection. Enantioselectivity is achieved by choosing angles such that only particles with the same handedness of the light sources are pulled. This proposal allows one to achieve all-optical sorting of chiral microspheres with arbitrarily small chiral parameters, thus outperforming current optical methods.

Enantioselective Crystallization of Chiral Inorganic Crystals of ϵ-Zn(OH)2 with Amino Acids

Many inorganic materials can form crystals, but little is known about their enantioselective crystallization. Herein, we report on the enantioselective crystallization of ϵ-Zn(OH)₂ (Wulfingite) chiral crystals by using amino acids. Crystals of ϵ-Zn(OH)₂ were crystallized from supersaturated sodium hydroxide and zinc nitrate aqueous solutions in the presence of l- or d-arginine. All of the chiral measurements, such as selective chiral adsorption by circular dichroism (CD), chiral chromatography, and polarimetry measurements, clearly show chiral discrimination during the crystallization of ϵ-Zn(OH)₂ . In addition, a new method has been developed for identifying chirality in crystals by using electron paramagnetic resonance (EPR). Although the values of chiral induction of the ϵ-Zn(OH)₂ crystals obtained are somewhat low, these values are still significant because they demonstrate that enantioselectivity during the crystallization of chiral inorganic crystals with chiral additives can be achieved. The method can be applied to many chiral inorganic systems. Understanding and controlling the crystallization of chiral inorganic crystals is important for gaining knowledge on the interaction of chiral molecules with inorganic surfaces. This knowledge can lead to an understanding of basic scientific questions such as the evolution of homochirality in biomolecules and the development of chiral inorganic crystals for a variety of purposes such as asymmetric catalysis and optical applications.

Enantioselective manipulation of single chiral nanoparticles using optical tweezers

We put forward an enantioselective method for chiral nanoparticles using optical tweezers. We demonstrate that the optical trapping force in a typical, realistic optical tweezing setup with circularly-polarized trapping beams is sensitive to the chirality of core-shell nanoparticles, allowing for efficient enantioselection. It turns out that the handedness of the trapped particles can be selected by choosing the appropriate circular polarization of the trapping beam. The chirality of each individual trapped nanoparticle can be characterized by measuring the rotation of the equilibrium position under the effect of a transverse Stokes drag force. We show that the chirality of the shell gives rise to an additional twist, leading to a strong enhancement of the optical torque driving the rotation. Both methods are shown to be robust against variations of size and material parameters, demonstrating that they are particularly useful in (but not restricted to) several situations of practical interest in chiral plasmonics, where enantioselection and characterization of single chiral nanoparticles, each and every one with its unique handedness and optical properties, are in order. In particular, our method could be employed to unveil the chiral response arising from disorder in individual plasmonic raspberries, synthesized by close-packing a large number of metallic nanospheres around a dielectric core.

Amino acid-based ionic liquids as precursors for the synthesis of chiral nanoporous carbons

The synthesis of chiral nanoporous carbons based on chiral ionic liquids (CILs) of amino acids as precursors is described. Such unique precursors for the carbonization of CILs yield chiral carbonaceous materials with high surface area (≈620 m2 g-1). The enantioselectivities of the porous carbons are examined by advanced techniques such as selective adsorption of enantiomers using cyclic voltammetry, isothermal titration calorimetry, and mass spectrometry. These techniques demonstrate the chiral nature and high enantioselectivity of the chiral carbon materials. Overall, we believe that the novel approach presented here can contribute significantly to the development of new chiral carbon materials that will find important applications in chiral chemistry, such as in chiral catalysis and separation and in chiral sensors. From a scientific point of view, the approach and results reported here can significantly deepen our understanding of chirality at the nanoscale and of the structure and nature of chiral nonporous materials and surfaces.

Ab Initio Study of Circular Dichroism and Circularly Polarized Luminescence of Spin-Allowed and Spin-Forbidden Transitions: From Organic Ketones to Lanthanide Complexes

Complete and restricted active space self-consistent field (CAS-/RAS-SCF) wave function methods are applied for the calculation of circular dichroism (CD) and circularly polarized luminescence (CPL) of a series of molecules comprising four organic ketones, the chiral cobalt(III) complex [Co(en)₃]³⁺, and the europium(III) complex [Eu(DPA)₃]^3-. The ab initio results are in good agreement with the experimental data and previous results obtained with Kohn-Sham density functional theory in the case of the spin-allowed transitions. CD and CPL properties are calculated ab initio for the spin-forbidden transitions of both a transition metal and a lanthanide complex.

Enantiomeric Recognition and Separation by Chiral Nanoparticles

Chiral molecules are stereoselective with regard to specific biological functions. Enantiomers differ considerably in their physiological reactions with the human body. Safeguarding the quality and safety of drugs requires an efficient analytical platform by which to selectively probe chiral compounds to ensure the extraction of single enantiomers. Asymmetric synthesis is a mature approach to the production of single enantiomers; however, it is poorly suited to mass production and allows for only specific enantioselective reactions. Furthermore, it is too expensive and time-consuming for the evaluation of therapeutic drugs in the early stages of development. These limitations have prompted the development of surface-modified nanoparticles using amino acids, chiral organic ligands, or functional groups as chiral selectors applicable to a racemic mixture of chiral molecules. The fact that these combinations can be optimized in terms of sensitivity, specificity, and enantioselectivity makes them ideal for enantiomeric recognition and separation. In chiral resolution, molecules bond selectively to particle surfaces according to homochiral interactions, whereupon an enantiopure compound is extracted from the solution through a simple filtration process. In this review article, we discuss the fabrication of chiral nanoparticles and look at the ways their distinctive surface properties have been adopted in enantiomeric recognition and separation.

Chiral Optical Stern-Gerlach Newtonian Experiment

We report on a chiral optical Stern-Gerlach experiment where chiral liquid crystal microspheres are selectively displaced by means of optical forces arising from optical helicity gradients. The present Newtonian experimental demonstration of an effect predicted at molecular scale [New J. Phys. 16, 013020 (2014)NJOPFM1367-263010.1088/1367-2630/16/1/013020] is a first instrumental step in an area restricted so far to theoretical discussions. Extending the Stern-Gerlach experiment legacy to chiral light-matter interactions should foster further studies, for instance towards the elaboration of chirality-enabled quantum technologies or spin-based optoelectronics.

Chirality Inversion on the Carbon Dot Surface via Covalent Surface Conjugation of Cyclic α-Amino Acid Capping Agents

Manipulating the chiroptical properties at the nanoscale is of great importance in stereoselective reactions, enantioseparation, self-assembly, and biological phenomena. In recent years, carbon dots have garnered great attention because of their favorable properties such as tunable fluorescence, high biocompatibility, and facile, scalable synthetic procedures. Herein, we report for the first time the unusual behavior of cyclic amino acids on the surface of carbon dots prepared via microwave-based carbonization. Various amino acids were introduced on the surface of carbon dots via EDC/NHS conjugation at room temperature. Circular dichroism results revealed that although most of the surface conjugated amino acids can preserve their chirality on negatively charged, "bare" carbon dots, the "handedness" of cyclic α-amino acids can be flipped when covalently attached on carbon dots. Moreover, these chiroptical carbon dots were found to interact with the cellular membrane or its mimic in a highly selective manner due to their acquired asymmetric selectivity. A comprehensive inhibitor study was conducted to investigate the pathway of cellular trafficking of these carbon dots. Overall, it was concluded that the chirality of the amino acid on the surface of carbon dots could regulate many of the cellular processes.

Scanning Techniques for Nanobioconjugates of Carbon Nanotubes

Nanobioconjugates using carbon nanotubes (CNTs) are attractive and promising hybrid materials. Various biological applications using the CNT nanobioconjugates, for example, drug delivery systems and nanobiosensors, have been proposed by many authors. Scanning techniques such as scanning electron microscopy (SEM) and scanning probe microscopy (SPM) have advantages to characterize the CNT nanobioconjugates under various conditions, for example, isolated conjugates, conjugates in thin films, and conjugates in living cells. In this review article, almost 300 papers are categorized based on types of CNT applications, and various scanning data are introduced to illuminate merits of scanning techniques.

A new nanosensor for the chiral recognition of cysteine enantiomers based on gold nanorods

A schematic illustration of the chiral recognition of d-Cys and l-Cys using GNRs in the presence of Cu²⁺ (0.125 mM).

Excitons in gyrotropic quantum-dot supercrystals

We use quantum theory of molecular crystals to study collective excitations (excitons) of gyrotropic quantum-dot (QD) supercrystals with complex lattices consisting of two or more sublattices of semiconductor QDs. We illustrate the potentials of our approach by applying it to analytically calculate the linear permittivity tensor of supercrystals with two QDs per unit cell. The spatial dispersions of exciton energy bands and permittivity tensor components are examined in detail for two-dimensional supercrystals with a square lattice, which are relatively easy to fabricate in practice. Our results provide a systematic and versatile framework for the engineering of dispersion properties of gyrotropic QD supercrystals and for the analysis of their absorption and circular dichroism spectra.

Chiral Metal-Oxide Nanofilms by Cellulose Template Using Atomic Layer Deposition Process

In this article, we describe an advance approach for the fabrication of chiral metal-oxide nanofilms. Our approach is based on the atomic layer deposition of titania and alumina nanofilms onto cellulose microfibers, used as chiral templates, leading to the formation of chiral nanofilms with a spatial fibrous structure. The chiral nanofilms were extensively characterized by X-ray photoelectron spectroscopy and high-resolution electron microscopy. The chiral property of the produced titania nanofilms was studied by enantioselective adsorption experiments using circular-dichroism spectroscopy and chiral high-performance liquid chromatography. We demonstrate the application of the titania chiral nanofilms for enantioselective crystallization. Overall, the basic principle for the preparation of chiral nanofilms by atomic layer deposition is demonstrated, as well as their uses for several enantioselective applications.

Optically active quantum-dot molecules

Chiral molecules made of coupled achiral semiconductor nanocrystals, also known as quantum dots, show great promise for photonic applications owing to their prospective uses as configurable building blocks for optically active structures, materials, and devices. Here we present a simple model of optically active quantum-dot molecules, in which each of the quantum dots is assigned a dipole moment associated with the fundamental interband transition between the size-quantized states of its confined charge carriers. This model is used to analytically calculate the rotatory strengths of optical transitions occurring upon the excitation of chiral dimers, trimers, and tetramers of general configurations. The rotatory strengths of such quantum-dot molecules are found to exceed the typical rotatory strengths of chiral molecules by five to six orders of magnitude. We also study how the optical activity of quantum-dot molecules shows up in their circular dichroism spectra when the energy gap between the molecular states is much smaller than the states' lifetime, and maximize the strengths of the circular dichroism peaks by optimizing orientations of the quantum dots in the molecules. Our analytical results provide clear design guidelines for quantum-dot molecules and can prove useful in engineering optically active quantum-dot supercrystals and photonic devices.

A universal strategy for visual chiral recognition of α-amino acids with L-tartaric acid-capped gold nanoparticles as colorimetric probes

The ability to recognize and quantify the chirality of alpha-amino acids constitutes the basis of many critical areas for specific targeting in drug development and metabolite probing. It is still challenging to conveniently distinguish the enantiomer of amino acids largely due to the lack of a universal and simple strategy. In this work, we report a strategy for the visual recognition of α-amino acids. It is based on the chirality of L-tartaric acid-capped gold nanoparticles (L-TA-capped AuNPs, ca. 13 nm in diameter). All of 19 right-handed α-amino acids can induce a red-to-blue color change of L-TA-capped AuNP solution, whereas all of the left-handed amino acids (except cysteine) cannot. The chiral recognition can be achieved by the naked eye and a simple spectrophotometer. This method does not require complicated chiral modification, and excels through its low-cost, good availability of materials and its simplicity. Another notable feature of this method is its high generality, and this method can discriminate almost all native α-amino acid enantiomers. This versatile method could be potentially used for high-throughput chiral recognition of amino acids.

Mixing of quantum states: A new route to creating optical activity

The ability to induce optical activity in nanoparticles and dynamically control its strength is of great practical importance due to potential applications in various areas, including biochemistry, toxicology, and pharmaceutical science. Here we propose a new method of creating optical activity in originally achiral quantum nanostructures based on the mixing of their energy states of different parities. The mixing can be achieved by selective excitation of specific states or via perturbing all the states in a controllable fashion. We analyze the general features of the so produced optical activity and elucidate the conditions required to realize the total dissymmetry of optical response. The proposed approach is applicable to a broad variety of real systems that can be used to advance chiroptical devices and methods.

Completely Chiral Optical Force for Enantioseparation

Fast and reliable separation of enantiomers of chiral nanoparticles requires elimination of all the forces that are independent of the nanoparticle handedness and creation of a sufficiently strong force that either pushes different enantiomers in opposite directions or delays the diffusion of one of them with respect to the other. Here we show how to construct such a completely chiral optical force using two counterpropagating circularly polarized plane waves of opposite helicities. We then explore capabilities of the related enantioseparation method by analytically solving the problem of the force-induced diffusion of chiral nanoparticles in a confined region, and reveal that it results in exponential spatial dependencies of the quantities measuring the purity of chiral substances. The proposed concept of a completely chiral optical force can potentially advance enantioseparation and enantiopurification techniques for all kinds of chiral nanoparticles that strongly interact with light.

Shape-induced optical activity of chiral nanocrystals

We present a general approach to analyzing the optical activity of semiconductor nanocrystals of chiral shapes. By using a coordinate transformation that turns a chiral nanocrystal into a nanocuboid, we calculate the rotatory strengths, dissymmetry factors, and peak values of the circular dichroism (CD) signal upon intraband transitions inside the nanocrystal. It is shown that the atomic roughness of the nanocrystal surface can result in rotatory strengths as high as 10^-36  erg×cm³ and in peak CD signals of about 0.1  cm^-1 for typical nanocrystal densities of 10¹⁶  cm^-3. The developed approach may prove useful for other nanocrystal shapes whereas the derived expressions apply directly for the modeling and interpretation of experimental CD spectra of quantum dots, nanorods, and nanoplatelets.

Optically active multi-helical erythrocyte-like Ln(OH)CO3 (Ln = La, Ce, Pr and Sm)

Hierarchical erythrocyte-like Ln(OH)CO₃ with nanosized chiral structure-induced circular dichroism responses, assigned to valence to conduction band transitions and coupling effects between the left-handed-assembled Ln(OH)CO₃ nanorods in the multi-helical RBC-like architecture.

Vortexes tune the chirality of graphene oxide and its non-covalent hosts

The ability of vortexes to tune the chirality of graphene oxide in water sheds light on its complex supramolecular organization allowing for selective noncovalent deposition of a predetermined handedness on a solid surface.

One-step synthesis of chiral carbon quantum dots and their enantioselective recognition

Chiral carbon quantum dots (l-carbon quantum dots, l-CQDs; and d-carbon quantum dots, d-CQDs) were synthesized through the facile hydrothermal treatment of carbonated citric acid and l-cysteine (or d-cysteine).

Modulation of helix stability of indolocarbazole–pyridine hybrid foldamers

The kinetic stabilities of the helical conformations of indolocarbazole–pyridine hybrid foldamers were modulated through single site modification.

Chiral recognition of l-tryptophan with beta-cyclodextrin-modified biomimetic single nanochannel

We realized the chiral recognition of an essential amino acid with a biomimetic nanochannel system for the first time.

Two-photon absorption and two-photon circular dichroism of hexahelicene derivatives: a study of the effect of the nature of intramolecular charge transfer

Effect of the strength and nature of the extension of the π-electronic delocalization on TPA and TPCD of helicenes derivatives.

RNA nucleosides as chiral sensing agents in NMR spectroscopy

The study reports chiral sensing properties of RNA nucleosides. A three component derivitazation protocol has been adopted to differentiate chiral amines. All RNA nucleosides exhibit chiral sensing property.

Far-red/near-infrared fluorescent conjugated polymer nanoparticles with size-dependent chirality and cell imaging applications

We prepared a series of novel chiral far-red/near-infrared fluorescent CPNs with different nanoparticle sizes, which show size-dependent chirality and are successfully employed for cell imaging.

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, reviews, edited volumes and monographs from this period are included, along with recently identified uncited materials from prior to 2004, which were omitted in the first instalment of this series covering the years 1930-2003. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by sections describing fundamental aspects of molecular imprinting including the development of novel polymer formats. Thereafter, literature describing efforts to apply these polymeric materials to a range of application areas is presented. Current trends and areas of rapid development are discussed.