Chiral Shell Research Articles

Towards high-performance polarimeters with large-area uniform chiral shells: a comparative study on the polarization detection precision enabled by the Mueller matrix and deep learning algorithm

Polarization detection and imaging technologies have attracted significant attention for their extensive applications in remote sensing, biological diagnosis, and beyond. However, previously reported polarimeters heavily relied on polarization-sensitive materials and pre- established mapping relationships between the Stokes parameters and detected light intensities. This dependence, along with fabrication and detection errors, severely constrain the working waveband and detection precision. In this work, we demonstrated a highly precise, stable, and broadband full-Stokes polarimeter based on large-area uniform chiral shells and a post-established mapping relationship. By precisely controlling the geometry through the deposition of Ag on a large-area microsphere monolayer with a uniform lattice, the optical chirality and anisotropy of chiral shells can reach about 0.15 (circular dichroism, CD) and 1.7, respectively. The post-established mapping relationship between the Stokes parameters and detected light intensities is established through training a deep learning algorithm (DLA) or fitting the derived mapping-relationship formula based on the Mueller matrix theory with a large dataset collected from our home-built polarization system. For the detection precision with DLA, the mean squared errors (MSEs) at 710 nm can reach 0.10% (S1), 0.41% (S2), and 0.24% (S3), while for the Mueller matrix theory, the corresponding values are 0.14% (S1), 0.46% (S2), and 0.48% (S3). The in-depth comparative studies indicate that the DLA outperforms the Mueller matrix theory in terms of detection precision and robustness, especially for weak illumination, small optical anisotropy and chirality. The averaged MSEs over a broad waveband ranging from 500 nm to 750 nm are 0.16% (S1), 0.46% (S2), and 0.61% (S3), which are significantly smaller than those derived from the Mueller matrix theory (0.45% (S1), 1% (S2), and 39.8% (S3)). The optical properties of chiral shells, the theory and DLA enabled mapping-relationships, the combination modes of chiral shells, and the MSE spectra have been systematically investigated.

Engineering high-performance dielectric chiral shells with enhanced chiral fields for sensitive chiral biosensor

Engineering high-performance dielectric chiral shells with enhanced chiral fields for sensitive chiral biosensor

Highly Precise and Broadband Full-Stokes Polarimeter Based on a Deep Learning Algorithm

Recent developments in nanophotonics enable the practical realization of ultracompact full-Stokes polarimeters and imaging devices based on the well-defined polarization-sensitive structures of subwavelength size. However, the resonant feature of building blocks and the limited ability of the current processing technology greatly limit their detection accuracy and working waveband. Herein, we experimentally demonstrate a highly precise and broadband full-Stokes polarimeter based on the high-performance dielectric chiral shells (DCSs) and the deep learning (DL) algorithm. The large-area dielectric chiral metasurfaces (DCMs) fabricated by depositing Si on the self-assembled microsphere monolayer own a large transmittance, strong chirality, and anisotropy in the visible waveband, which enable the effective perception of the polarization state of light. The Stokes parameters are successfully detected by measuring several transmittances from DCSs with different rotation angles, i.e., Î, and then analyzing with the pre-established mapping relationship between the Stokes parameters Ŝ and the recorded transmittance Î based on the DL algorithm, i.e., Ŝ = f(Î). In contrast to the traditional polarimeters, the detection accuracy based on the DL approach seems insensitive to the fabrication errors. A mean square error (MSE) of smaller than 0.5% at 760.06 nm was recorded, and an averaged MSE of less than 4% for Stokes parameters over a broad waveband from 400 to 840 nm was obtained, although the optical anisotropy and chirality of DCMs own a strong dispersion feature. The small MSE in a broad waveband, together with the easily accessing DCMs, make our polarimeter as the most potential candidate for future applications, such as the color polarization imaging devices and the ultraviolent polarimeter.

Modulation of plasmonic chiral shell growth on gold nanorods via nonchiral surfactants.

Recently, in combination with seed-mediated growth, thiolated chiral molecule-guided growth has shown great promise in obtaining chiral plasmonic nanostructures. Previously, with the assistance of chiral cysteines (Cys), we realized helical growth of plasmonic shells on gold nanorod (AuNR) seeds dispersed in cetyltrimethylammonium bromide (CTAB) solution. Herein, we further studied the roles of non-chiral cationic surfactants in tuning the helical growth. Both the counter anion and the hydrocarbon chain length of the surfactants were found to affect the formation of helical shells greatly. In particular, we exhibited surfactant-modulated conversion of the chiral shell deposition mode between layer growth and island growth. By optimizing growth conditions, an obvious plasmonic circular dichroism (PCD) response could be achieved for the island helical shell. Our findings demonstrated promising potential of nanochemical synthesis in fabricating chiral plasmonic nanostructures with small structural sizes.

Core-Shell Three-Dimensional Perovskite Nanocrystals with Chiral-Induced Spin Selectivity for Room-Temperature Spin Light-Emitting Diodes.

We developed type-II core-shell nanocrystals (NCs) with a chiral low-dimensional perovskite shell and an achiral 3D MAPbBr3 core. The core-shell NCs exhibit spin-polarized luminescence at the first excitation band of the achiral core, which is due to the chiral-induced spin selectivity (CISS) effect-governed spin-dependent shell-to-core electron transportation and the subsequent electron-hole recombination in the core. The preferred spin state of the transferred electrons is determined by the handness of the chiral shell. For the core-shell NCs film, a photoluminescence quantum yield (PLQY) of 54% and a circularly polarized luminescence (CPL) with a maximum |glum| of 4.0 × 10-3 are obtained at room temperature. Finally, we achieved a spin-polarized light-emitting diode (spin-LED), affording a circularly polarized electroluminescence (CP-EL) with a |gCP-EL|of 6.0 × 10-3 under ambient conditions.

The Role of Polymer–AuNP Interaction in the Stimuli‐Response Properties of PPA–AuNP Nanocomposites

Back Cover: In article number 2100616 by Félix Freire and co-workers, dynamic helical polymers such as poly(phenylacetylene)s interact and respond to external stimuli such as metal ions, due to the formation of a helical polymer metal complex (HPMC), which can further be transformed into a hybrid material by reducing the metal ion. The resulting nano-composites combine the properties of the metal nanoparticles and the dynamic helical polymers and show stimuli-responsive properties towards different stimuli such as metal ions, temperature or solvents. Moreover, these nanocomposites can be nanostructured into nanospheres that show a dynamic chiral shell and encapsulation properties.

The physical basis of mollusk shell chiral coiling

Significance A theoretical model suggests that a mechanically induced twist of the soft body underlies the formation of helicospiral shells in snails and ammonites and also accounts for the startling and unique meandering shells observed in certain species. This theory addresses fundamental developmental issues of chirality and symmetry breaking: in the case of ammonites, how a bilaterally symmetric body can sometimes secrete a nonsymmetric shell; for gastropods, how an intrinsic twist possibly due to the asymmetric development of musculature can provide a mechanical motor for generating a chiral shell. Our model highlights the importance of physical forces in biological development and sheds light on shell coiling in snails, which have been used for a century as model organisms in genetic research.

Scattering from a multilayered chiral sphere: Internal and near fields

An iterative method is proposed for dealing with scattering from a multilayered chiral sphere in Lorenz-Mie regime in the authors’ previous work. In this paper the research is extended on the internal fields and near fields. By using four intermediate variables in each region of the multilayered chiral sphere, an iterative relationship of expansion coefficients for calculating internal fields is proposed. Numerical results of internal and near fields for plane wave and Gaussian beam incidence are calculated and analyzed. It is found that amplitudes and distributions of the electric field Eθ and Eφ inside the sphere are significantly affected by chirality parameter and size of each region inside the multilayered chiral sphere. Internal and near fields of a multilayered chiral spherical shell with 50 layers interacting with light wave are calculated and presented. The model could be used to explore the properties of graded index chiral shells or coatings.

Chiral Polymeric Nanocapsules and Their Use for Conformational Deracemization of Liquid Crystals

We present the first preparation and properties of chiral nanocapsules. The chiral shell, a polyurea derivative, was obtained by interfacial emulsion polymerization of l-lysine with polymethylene polyphenyl isocyanate. The chirality of these nanocapsules was manifested by its ability to induce conformational deracemization of a liquid crystal. This induced chirality was measured using the “Raynes’ experiment”, in which the boundary conditions of cells impose a ±90° rotation of the liquid crystal director from one surface to the other. Both left- and right-handed director twist domains appear on cooling from the isotropic to the nematic phase. Owing to the weak induced chirality of the liquid crystal, one sense of director rotation is energetically more favorable and its domain size expands, resulting in curvature of the domain walls. The curvature was measured as a function of capsule concentration and serves as a metric of the induction of chirality in the surrounding liquid crystal.

Chiral Shell Core-Satellite Nanostructures for Ultrasensitive Detection of Mycotoxin.

Herein, the design of a DNA-based chiral biosensor is described utilizing the self-assembly of shell core-gold (Au) satellite nanostructures for the detection of mycotoxin, ochratoxin A (OTA). The assembly of core-satellite nanostructures based on OTA-aptamer binding exhibits a strong chiral signal with an intense circular dichroism (CD) peak. The integrity of the assembly of core-satellite nanostructures is limited to some extent in the presence of different levels of OTA. Correspondingly, the chiral intensity of assembly is weakened with increasing OTA concentrations, allowing quantitative determination of the target. The developed chiral sensor shows an excellent linear relationship between the CD signal and concentrations of OTA in the range of 0.1-5 pg mL-1 with a limit of detection as low as 0.037 pg mL-1 . The effectiveness of the biosensor in a sample of red wine is verified and a good recovery rate is obtained. These results suggest that the strategy has great potential for practical application.

Engineering thiophene-based nanoparticles to induce phototransduction in live cells under illumination.

We report that nanoparticles prepared from appropriately functionalized polythiophenes once administered to live cells can acquire phototransduction properties under illumination, becoming photoactive sites able to absorb visible light and convert it to an electrical signal through cell membrane polarization. Amine-reactive fluorescent nanoparticles with pendant N-succinimidyl-ester groups (NPs-NHS) are prepared from polythiophenes alternating unsubstituted and 3-(2,5-dioxopyrrolidin-1-yl-8-octanoate)-substituted thiophenes by a nanoprecipitation method. By 1H NMR of nanoparticles prepared using THF-d8/D2O (solvent/non-solvent) we demonstrate that the hydrolysis of the N-succinimidyl-ester group to free N-hydroxysuccinimide takes place slowly over several hours. NPs-NHS reactivity towards primary amine groups is tested towards the NH2 of d- and l-enantiomers of tryptophan. We show that the formation of a tryptophan-nanoparticle amidic bond creates a chiral shell displaying opposite CD signals for the nanoparticles bound to d or l enantiomers. The interaction of NPs-NHS with live HEK-293 cells is monitored via LSCM. We show that the NPs-NHS are not internalized but remain docked on the cell membrane. We assume that this is mainly the result of the reaction of the NHS groups in the external layer with NH2 groups present in cell membrane proteins, although the contribution of alternative mechanisms cannot be excluded. To support this assumption LSCM experiments show that nanoparticles of comparable size obtained from poly(3-hexylthiophene), NPs-P3HT, are rapidly internalized by live HEK-293 cells. Finally, using the whole-cell current clamp technique under light illumination we demonstrate that NPs-NHS can polarize the cell membrane upon light irradiation while NPs-P3HT cannot.

Structure and thermal stability of AgCu chiral nanoparticles

The structure and thermal stability of AgCu core-shell chiral nanoparticles is investigated by means of global optimization searches and molecular-dynamics simulations within an atomistic model. The most energetically stable structures are searched for depending on the number N Ag of Ag atoms in the outer shell. Both icosahedral and C5 symmetry structures are considered. The thermal stability of the structures is studied for magic sizes and compositions by analyzing the melting transition. It is found that chiral shells are the most favourable in a wide range of N Ag and that the structures present a notable thermal stability.

Theory of Chiral Plasmonic Nanostructures Comprising Metal Nanocrystals and Chiral Molecular Media

Plasmonic nanocrystals strongly interact with chiral molecular shells through electric and magnetic fields and in this way acquire new chiro-optical properties. Transfer of chirality from biomolecules to the plasmonic resonances is a collective phenomenon and strongly depends on the geometry of nanostructure. Collective effects in a molecular chiral shell may suppress or enhance plasmonic circular dichroism (CD) depending on the geometry of hybrid nanocrystal. In large chiral plasmonic structures, we identify a new electrodynamic mechanism of plasmonic CD that is qualitatively different to the near-field, dipolar mechanism of the plasmonic chirality described by us previously. Our models also show that anisotropic nanocrystals, such as nanorods or oriented molecular shells, have strongly enhanced CD at the plasmonic frequency. A family of chiral plasmonic nanostructures proposed and modeled here can be used for designing new optical media and chiral sensors.

In situ formation of chiral core–shell nanostructures with raspberry-like gold cores and dense organic shells using catechin and their catalytic application

Chiral core–shell nanostructures containing raspberry-like gold cores and well-defined dense organic shells are synthesized by an in situ method using a natural antioxidant catechin as the reducing agent. This method is flexible and enables control over the shell thickness by adjusting the molar ratio of catechin to HAuCl4. Transmission electron microscopic analysis shows the formation of core–shell nanostructures with somewhat raspberry-shaped gold cores. The proposed mechanism explains that catechin reduces Au3+ to metallic Au to gold nanostructures and gets oxidized to different oligomeric products that are adsorbed in situ and assembled through H-bonding and form a thick organic shell around the generated gold nanostructures. Each of these oxidized forms of catechin is well-characterized by FTIR, ESI-MS, and MALDI-TOF-MS spectroscopies. This reaction follows a radical pathway as confirmed by electron paramagnetic resonance spectroscopy. Due to the presence of a compact and dense shell, the rate of gold core dissolution sharply decreases compared to that of the dissolution of monolayer protected Au nanoparticles when etched with KCN solution. The optical activity of the core–shell nanostructure is the result of the interaction between chiral shells and gold cores as observed by circular dichroism (CD) spectroscopy. The chiral core–shell Au nanostructures exhibit a CD band at the plasmon resonance frequency (∼596 nm). Finally, these chiral core–shell nanostructures are used as an effective catalyst in the borohydride reduction of p-nitrophenol.

Size-Dependent Transition to High-Symmetry Chiral Structures in AgCu, AgCo, AgNi, and AuNi Nanoalloys

A class of nanomaterials possessing the highest degree of chiral symmetry, the chiral icosahedral symmetry, is found by a combination of global optimization searches and first-principle calculations. These nanomaterials are core-shell nanoalloys with a Cu, Ni, or Co core and a chiral Ag or Au shell of monatomic thickness. The chiral shell is obtained by a transformation of an anti-Mackay icosahedral shell by a concerted rotation of triangular atomic islands which breaks all mirror symmetries. This transformation becomes energetically favorable as the cluster size increases. Other chiral nanoalloys, belonging to a different structural family of C(5) group symmetry, are found in the size range between 100 and 200 atoms. High-symmetry chiral nanoalloys associate strong energetic stability with potential for applications in optics, catalysis, and magnetism.

Chiral Shells and Achiral Cores in CdS Quantum Dots

We report and explain circular dichroism in semiconductor quantum dots. CdS nanocrystals capped with penicillamine enantiomers were prepared and found to be both highly luminescent and optically active. No new features in circular dichroism were observed as the nanocrystal grew larger. Density functional calculations reveal that penicillamine strongly distorts surface Cd, transmitting an enantiomeric structure to the surface layers and associated electronic states. The quantum dot core is found to remain undistorted and achiral.

Behavior of an Optically Active Ferrocene Chiral Shell Located within Phosphorus-Containing Dendrimers

Three families of phosphorus-containing dendrimers having chiral ferrocenic subunits precisely placed at one individual shell within their skeleton are synthesized. The influence of the progressive “burying” of the chiral ferrocene derivatives upon their electrochemical and chiroptical properties is reported. It is shown that both properties depend mainly on the chemical environment of the chiral organometallic centers. However, they differ in the sensitivity to the “burying”; the chiroptical properties do not appear to be sensitive to where the chiral units are positioned within the dendrimer, whereas the electrochemical properties are.

Synthesis and Chiroptical Analysis of Optically Active Chiral Shell Dendrons

We have prepared a series of chiral dendrons (1-4) in which chiral subunits are placed in individual generational shells at varying distances from the focal point. The optical activity of these chiral dendritic structures is successfully modeled using structurally similar low-molecular weight model compounds. In dendrons 1a and 1b a chiral subunit is directly adjacent to the focal point, whereas in dendrons 2, 3, and 4a,b the chiral subunits are incorporated in the interior of the dendron. A marked difference in optical activity between the former 1a and 1b) and latter (2, 3, 4a,b) dendrons is mirrored in the optical activities of model compounds 12a, 12b, 19a, and 19b. These model compounds directly mimic the surrounding constitution of the chiral subunits in the dendrons. This successful analysis of the chiroptical data using low-molecular weight model compounds suggests that these dendrons do not possess conformational order in solution.

Diffraction and propagation of electromagnetic waves in the presence of chiral media

The propagation of electromagnetic waves in infinite, semiinfinite, and laminar chiral structures is investigated, along with the diffraction of electromagnetic waves on semiinfinite objects in a chiral medium and three-dimensional objects consisting entirely or partially of chiral materials. Particular attention is paid to diffraction on three-dimensional uniform chiral bodies and ideally conducting bodies covered by chiral shells.

Synthesis of optically active chiral shell dendrons

We present the preparation of a series of chiral dendrons, in which chiral subunits are placed in individual generational shells at increasing distances from the focal point, by a combination of convergent and divergent dendrimer synthesis methods. Analysis of chiroptical data suggests that these dendrons do not possess conformational order in solution.