Optically active chiral CuO "nanoflowers"

Homochiral layered indium phosphonates: solvent modulation of morphology and chiral discrimination adsorption

Assembling chiral coordination polymers into nano/microflower structures may improve their performance in applications such as chiral recognition and separation. In this study, we chose a chiral metal phosphonate system, i.e., In(NO3)3/R-, S-pempH2 [pempH2 = (1-phenylethylamino)methylphosphonic acid], and carried out systematic work on the self-assembly of this system in different alcohol/H2O mixed solvents under solvothermal conditions. Enantiomeric compounds R-, S-[In2(pempH)2(μ2-OH)2(H2O)2](NO3)2 (R-, S-1) were obtained showing dense layered structures, but their morphologies varied with alcohol solvent. We obtained crystals of R-, S-1C in triethylene glycol (TEG)/H2O mixed solvent and spiral microflowers of R-, S-1MF in isopropanol (IPA)/H2O mixed solvent. Adsorption isotherms using enantiopure R-2-butanol and S-2-butanol as probe molecules revealed that compounds R-1MF and S-1MF had higher adsorption capacity compared to the crystalline sample and displayed enantioselective adsorption behaviour.

Unveiling Chirality in MoS2 Nanosheets: A Breakthrough in Phase Engineering for Enhanced Chiroptical Properties

The development of new synthetic strategies to introduce and control chirality in inorganic nanostructures has been highly stimulated by the broad spectrum of potential applications of these exiting nanomaterials. Molybdenum disulfide is among the most investigated transition metal dichalcogenides due to its promising properties for applications that spread from optoelectronic to spintronic. Herein, we report a new two-step approach for the production of chiroptically active semiconductor 2H MoS2 nanosheets with chiral morphology based on the manipulation of their crystallographic structure. In the first step, metastable metallic 1T MoS2 nanosheets with chiral morphology were produced via hydrothermal synthesis. Then, thermal annealing was used to progressively tune the conversion of the metallic 1T phase into the thermodynamically stable semiconductor 2H phase while preserving the nanocrystals' chiral morphology. Our detailed study covers the evolution of the chiroptical properties of the material during the crystallographic phase transition, revealing critical insights into the formation of chiroptically active excitonic transitions. This study represents a unique approach to the production of high-quality chiral nanomaterials by exploiting phase engineering, and paves the way for the development of new synthetic methods to further expand the range and properties of chiral nanomaterials.

Solvent-free fabrication of ultrathin two-dimensional metal oxides/sulfides in a fixed interlayer by geometric confinement

Two-dimensional (2D) nanomaterials display unique characteristics owing to their ultrahigh surface-to-volume ratio and quantum confinement effects. Nonetheless, seeking a versatile and facile method to rationally shape ultrathin 2D frameworks is still an appealing challenge. Herein, a series of ultrathin 2D metal oxide crystals (2D MOs), including 3d transition metals (Ti, Cr, Mn, Fe, Co, Ni, Cu, Zr, W), lanthanide (Ce) and nontransition metal (In, Sn, Bi) oxides, were created through a confined interlayer growth strategy in combination with melt infiltration, in which no complicated chemistry or sophisticated equipment was needed. The 2D oxides presented lamellar constructions with high crystallinity, and the thickness was strictly limited to ~ 1 nm. The crystallization process, including the Frank-van der Merwe mode and the Volmer-Weber mode, was described. The defects and distortions of 2D TiO2 reduced the optical band gap and improved the sunlight utilization efficiency, thus accelerating the photocatalytic activity. This method could be extended to the preparation of 2D polymetallic oxides, metal sulfides etc., which enables the development of versatile systems for ultrathin 2D frameworks, especially for nonlayered structures originally.

Localized Oxidative Catalytic Reactions Triggered by Cavitation Bubbles Confinement on Copper Oxide Microstructured Particles

Efficient energy transfer management in catalytic processes is crucial for overcoming activation energy barriers while minimizing costs and CO2 emissions. We exploit here a concept of CuO particle design with multiple gas-stabilizing sites, engineered to function as cavitation nuclei and catalysts. This concept facilitates the selective and efficient acoustic energy transfer directly to the catalyst surface, avoiding the undesired dissipation of acoustic energy into the bulk solution while demonstrating superior cavitation properties at lower acoustic pressure amplitudes. Utilizing a chemical thermometric approach, we demonstrate that the local temperature on the surface of our CuO particles during cavitation bubble implosions can create an effective equivalent temperature of about 360 °C. This temperature effect facilitates the efficient catalysis of oxidative reactions using an organic pollutant probe molecule. Density functional theory (DFT) calculations were used to assess the decomposition of H2O2 and of pollutant probe molecule on CuO (111). Our work represents a significant advance in sonocatalytic systems, promising efficient energy use in catalytic reactions.

Chirality Engineering of Nanostructured Copper Oxide for Enhancing Oxygen Evolution from Water Electrolysis

The exploration of a new conceptual strategy for improving the oxygen evolution reaction (OER) of earth-abundant electrocatalysts is critical. In this study, chiral copper oxide nanoflower is explored by a self-assembly method. The characterization suggests the chiral structure originates from the crystal plane-level helical stack of the secondary nanosheets. Of note, the assembly illustrates a record-high degree of spin polarization of 96%, indicating the ideal alignment of electron spin. Moreover, density function theory calculations show the chiral structure reducing the reaction energy barrier (REB) while switching the potential-determining step from *O→*OOH to *OH→*O. Together with the enhanced electrochemical active surface area and accelerated charge transfer, the production of ground-state triplet O2 is improved via a spin-forbidden route that involves the singlet H2O/OH•. Consequently, the chiral nanoflower shows a overpotential of 308 mV at 10 mA cm-2 and a Tafel slope of 93.5 mV dec-1, which is even superior to the commercial RuO2 (310 mV, 101 mV dec-1). This study presents a new strategy for improving the OER activity by simultaneously enhancing electronic properties and lowering the REB of an non-noble electrocatalyst via chirality engineering.

Chiral Inorganic Nanomaterials Characterized by Advanced TEM: A Qualitative and Quantitative Study

Chiral inorganic nanomaterials (CINMs) have garnered significant interest due to their exceptional optical, electronic, and catalytic properties, offering promising advancements in energy conversion, data storage, catalysis, and biomedicine. While traditional optical spectrophotometers reveal the chiroptical performance of CINMs on an ensemble level, the direct structural visualization for the qualitative and quantitative discernment of their chiral features has become increasingly distinct with the advancements of transmission electron microscopy (TEM) techniques. The need for reasonable and high-standard discrimination requirements of CINMs has driven the progress of chirality-based TEM technologies. Therefore, this review in the good season takes the initiative to summarize the current advancements in TEM technologies for CINMs characterization, emphasizing a qualitative analysis of chiral atomic-level features, 0D, 1D, and 2D nanocrystals, and assembled nanomaterials. Then, the quantitative methods for determining chirality is also highlighted, such as 3D electron tomography, and further address the evolution of chiral structures monitored by the Ex-situ and In-situ TEM technologies. By providing a roadmap for the current challenges and proposing future advancements in TEM technologies for the qualitative, quantitative, and real-time analysis of CINMs, it can drive innovations in the field of chiral nanomaterials as well as the development of TEM technologies.

Metal-ligand cross-link strategy engineered iron-doped dopamine-based superstructure as peroxidase-like nanozymes for detection of glucose

Nanozymes are nanomaterials with mimetic enzyme properties and the related research has attracted much attention. It is of great value to develop methods to construct nanozymes and to study their application in bioanalysis. Herein, the metal-ligand cross-linking strategy was developed to fabricate superstructure nanozymes. This strategy takes advantage of being easy to operate, adjustable, cheap, and universal. The fabricated superstructure nanozymes possess efficient peroxidase-like catalytic activity. The enzyme reaction kinetic tests demonstrated that for TMB and H2O2, the Km is 0.229 and 1.308 mM, respectively. Furthermore, these superstructure nanozymes are applied to highly efficient and sensitive detection of glucose. The linear range for detecting glucose is 20-2000 μM, and the limit of detection is 17.5 μM. Furthermore, mechanistic research illustrated that this integrated system oxidizes glucose to produce hydrogen peroxide and further catalyzes the production of ·OH and O2·-, which results in a chromogenic reaction of oxidized TMB for the detection of glucose. This work could not only contribute to the development of efficient nanozymes but also inspire research in the highly sensitive detection of other biomarkers.

First Cu-nanostar as a sustainable catalyst realized through synergistic effects of bowl-shaped features and surface activation of sporopollenin exine

Recently, nanostar-shaped structures, including gold nanostars (NS), have drawn much attention for their potential use in surface-enhanced Raman spectroscopy (SERS) and catalysis. Yet, very few studies have been conducted on Cu-Au hybrid NS, and there are none for Cu-based NS. Herein, we describe an effective method for controlling copper-oxide nanostar (ESP-PEI-CuI/IIO-NS) growth using sporopollenin as a sustainable template material. However, ESP-PEI-CuI/IIO-NS growth depends on sporopollenin surface functionalization. Sporopollenin surface activation was done by amine functionalization with polyethyleneimine (PEI), without which ESP-PEI-CuI/IIO-NS growth was not observed. The sporopollenin's exine (outer wall) has a bowl-like structure, which mediates the growth of Cu nanorods, resulting in an NS morphology. Furthermore, due to their increased surface area, ESP-PEI-CuI/IIO-NS showed excellent catalytic activity for Huisgen 1,3-dipolar cycloadditions even when used in H2O and without additives under green conditions. This approach utilising biomass as a sustainable template would pave the way for developing controlled growth of nanostructures for SERS-related and catalytic applications.

From individuals to families: design and application of self-similar chiral nanomaterials

Establishing an intimate relationship between similar individuals is the beginning of self-extension. Various self-similar chiral nanomaterials can be designed using an individual-to-family approach, accomplishing self-extension. This self-similarity facilitates chiral communication, transmission, and amplification of synthons. We focus on describing the marriage of discrete cages to develop self-similar extended frameworks. The advantages of utilizing cage-based frameworks for chiral recognition, enantioseparation, chiral catalysis and sensing are highlighted. To further promote self-extension, fractal chiral nanomaterials with self-similar and iterated architectures have attracted tremendous attention. The beauty of a fractal family tree lies in its ability to capture the complexity and interconnectedness of a family's lineage. As a type of fractal material, nanoflowers possess an overarching importance in chiral amplification due to their large surface-to-volume ratio. This review summarizes the design and application of state-of-the-art self-similar chiral nanomaterials including cage-based extended frameworks, fractal nanomaterials, and nanoflowers. We hope this formation process from individuals to families will inherit and broaden this great chirality.

Chiral Transfer and Evolution in Cysteine Induced Cobalt Superstructures

Chiral organic additives have unveiled the extraordinary capacity to form chiral inorganic superstructures, however, complex hierarchical structures have hindered the understanding of chiral transfer and growth mechanisms. This study introduces a simple hydrothermal synthesis method for constructing chiral cobalt superstructures with cysteine, demonstrating specific recognition of chiral molecules and outstanding electrocatalytic activity. The mild preparation conditions allow in situ tracking of chirality evolution in the chiral cobalt superstructure, offering unprecedented insights into the chiral transfer and amplification mechanism. The resulting superstructures exhibit a universal formation process applicable to other metal oxides, extending the understanding of chiral superstructure evolution. This work contributes not only to the fundamental understanding of chirality in self-assembled structures but also provides a versatile method for designing chiral inorganic nanomaterials with remarkable molecular recognition and electrocatalytic capabilities.

Structural and Electronic Chirality in Inorganic Crystals: from Construction to Application

Chirality represents a fundamental characteristic inherent in nature, playing a pivotal role in the emergence of homochirality and the origin of life. While the principles of chirality in organic chemistry are well-documented, the exploration of chirality within inorganic crystal structures continues to evolve. This ongoing development is primarily due to the diverse nature of crystal/amorphous structures in inorganic materials, along with the intricate symmetrical and asymmetrical relationships in the geometry of their constituent atoms. In this review, we commence with a summary of the foundational concept of chirality in molecules and solid states matters. This is followed by an introduction of structural chirality and electronic chirality in three-dimensional and two-dimensional inorganic materials. The construction of chirality in inorganic materials is classified into physical photolithography, wet-chemistry method, self-assembly, and chiral imprinting. Highlighting the significance of this field, we also summarize the research progress of chiral inorganic materials for applications in optical activity, enantiomeric recognition and chiral sensing, selective adsorption and enantioselective separation, asymmetric synthesis and catalysis, and chirality-induced spin polarization. This review aims to provide a reference for ongoing research in chiral inorganic materials and potentially stimulate innovative strategies and novel applications in the realm of chirality.

Chiral MoS2@BC fibrous membranes selectively promote peripheral nerve regeneration

BACKGROUND

Molybdenum disulfide (MoS2) has excellent physical and chemical properties. Further, chiral MoS2 (CMS) exhibits excellent chiroptical and enantioselective effects, and the enantioselective properties of CMS have been studied for the treatment of neurodegenerative diseases. Intriguingly, left- and right-handed materials have different effects on promoting the differentiation of neural stem cells into neurons. However, the effect of the enantioselectivity of chiral materials on peripheral nerve regeneration remains unclear.

METHODS

In this study, CMS@bacterial cellulose (BC) scaffolds were fabricated using a hydrothermal approach. The CMS@BC films synthesized with L-2-amino-3-phenyl-1-propanol was defined as L-CMS. The CMS@BC films synthesized with D-2-amino-3-phenyl-1-propanol was defined as D-CMS. The biocompatibility of CMS@BC scaffolds and their effect on Schwann cells (SCs) were validated by cellular experiments. In addition, these scaffolds were implanted in rat sciatic nerve defect sites for three months.

RESULTS

These chiral scaffolds displayed high hydrophilicity, good mechanical properties, and low cytotoxicity. Further, we found that the L-CMS scaffolds were superior to the D-CMS scaffolds in promoting SCs proliferation. After three months, the scaffolds showed good biocompatibility in vivo, and the nerve conducting velocities of the L-CMS and D-CMS scaffolds were 51.2 m/s and 26.8 m/s, respectively. The L-CMS scaffolds showed a better regenerative effect than the D-CMS scaffolds. Similarly, the sciatic nerve function index and effects on the motor and electrophysiological functions were higher for the L-CMS scaffolds than the D-CMS scaffolds. Finally, the axon diameter and myelin sheath thickness of the regenerated nerves were improved in the L-CMS group.

CONCLUSION

We found that the CMS@BC can promote peripheral nerve regeneration, and in general, the L-CMS group exhibited superior repair performance. Overall, the findings of this study reveal that CMS@BC can be used as a chiral nanomaterial nerve scaffold for peripheral nerve repair.

Enhanced Replenishment of Active Lattice Oxygen Using Chiral Copper Oxide

Effective catalytic performance of the transition metal oxide is attributed to high specific surface areas, abundant surface oxygen atoms, and balanced valence ratios. Although the chirality of the transition metal has attracted attention, most studies have focused on optical application. A few chiral transition metal oxides were used as electrocatalysts and photocatalysts. The influence of the chiral catalysts on the thermal catalysis process has been less explored. In this study, Mn-loaded chiral (M/l-CuO and M/d-CuO) and achiral CuO (M/a-CuO) were synthesized and compared in the catalytic oxidization of toluene. Spectrally analyzed Mn was well-dispersed on both chiral and achiral CuO. l-CuO and d-CuO showed nanoflower-like chirality. The angles between each (001) plane of CuO were the source of chirality. The toluene turnover frequency (TOF) of the samples was in the order of Mn/d-CuO (5.6 × 10-5 s-1) > Mn/l-CuO (4.4 × 10-5 s-1) > Mn/a-CuO (3.2 × 10-5 s-1) at 240 °C, consistent with the order of the oxygen replenishment rate. The as-prepared catalysts had similar ratios of lattice oxygen/surface adsorbed oxygen, Mn3+/Mn4+, and Cu+/Cu2+. A higher TOF was attributed to chirality, which increased the lattice oxygen replenishment speed from the gaseous phase to the solid surface. Our study indicates gas-solid catalysis from a structure-activity viewpoint.

Circularly polarized light emission and detection by chiral inorganic semiconductors

Chiral inorganic semiconductors with high dissymmetric factor are highly desirable, but it is generally difficult to induce chiral structure in inorganic semiconductors because of their structure rigidity and symmetry. In this study, we introduced chiral ZnO film as hard template to transfer chirality to CsPbBr3 film and PbS quantum dots (QDs) for circularly polarized light (CPL) emission and detection, respectively. The prepared CsPbBr3/ZnO thin film exhibited CPL emission at 520 nm and the PbS QDs/ZnO film realized CPL detection at 780 nm, featuring high dissymmetric factor up to around 0.4. The electron transition based mechanism is responsible for chirality transfer.

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 Supramolecular Systems: Helical Assemblies, Structure Designs, and Functions

Chirality, as one of the most striking characteristics, exists at various scales in nature. Originating from the interactions of host and guest molecules, supramolecular chirality possesses huge potential in the design of functional materials. Here, an overview of the recent progress in structure designs and functions of chiral supramolecular materials is present. First, three design routes of the chiral supramolecular structure are summarized. Compared with the template-induced and chemical synthesis strategies that depend on accurate molecular identification, the twisted-assembly technique creates chiral materials through the ordered stacking of the nanowire or films. Next, chirality inversion and amplification are reviewed to explain the chirality transfer from the molecular level to the macroscopic scale, where the available external stimuli on the chirality inversion are also given. Lastly, owing to the optical activity and the characteristics of the layer-by-layer stacking structure, the supramolecular chirality materials display various excellent performances, including smart response, shape-memorization, superior mechanical performance, and applications in biomedical fields. To sum up, this work provides a systematic review of the helical assemblies, structure design, and applications of supramolecular chirality systems.

Chirality Engineering of Colloidal Copper Oxide Nanostructures for Tailored Spin-Polarized Catalysis

The combination of the chiral concept and inorganic nanostructures holds great potential for significantly impacting catalytic processes and products. However, the synthesis of inorganic nanomaterials with engineered chiroptical activity and identical structure and size presents a substantial challenge, impeding exploration of the relationship between chirality (optical activity) and catalytic efficiency. Here, we present a facile wet-chemical synthesis for achieving intrinsic and tunable chiroptical activity within colloidal copper oxide nanostructures. These nanostructures exhibit strong spin-polarization selectivity compared with their achiral counterparts. More importantly, the ability to engineer chiroptical activity within the same type of chiral nanostructures allows for the manipulation of spin-dependent catalysis, facilitating a study of the connection between the chiroptical magnitude (asymmetric factor) and catalytic performance in inorganic nanostructures. Specifically, using these materials as model catalysts in a proof-of-concept catalytic reaction, we reveal a linear correlation between the asymmetric factor of chiral nanomaterials and the efficiency of the catalytic reaction. This work paves the way for the development of chiral inorganic nanosystems and their application in catalysis through chiroptical engineering.

Chiral Mesostructured Inorganic Materials with Optical Chiral Response

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

Nonlinear optical properties in chiral copper oxide nanosheets

Chiral transition metal oxides (TMOs) are in the forefront of research as potential active materials in various optoelectronic applications. However, the nonlinear optical (NLO) properties of the chiral TMOs have not been fully understood. Here, several kinds of copper oxide nanosheets capped with different chiral amino acids are synthesized. Notably, we investigate the NLO activities of these materials, including broadband second harmonic generation and transformation of nonlinear optical properties from saturable absorption to reverse saturable absorption. This work will broaden the use of chiral TMO materials in nonlinear photonic devices.

Optical Asymmetry and Structural Complexity in Hierarchically Organized Chiral CuO Nanostructures: Insight into the Geometric and Crystallographic Effects on Cooperative Chirality

Optical asymmetry and structural complexity across different length scales were realized in flower-shaped CuO nanostructures, prepared through refluxing an aqueous solution of copper acetate, sodium hydroxide, and D-tartaric acid, as well as in their toroid-like forms obtained on calcination at 600 °C. Atomic scale chirality in the flower morphology could be visualized as putative Boerdijk-Coexter-Bernal like tetrahelical fragments, while that in the toroid form could be identified as screw dislocation-driven helicity. The fraction of asymmetry in the nanostructures has been evaluated from their chiroptical responses based on Kuhn asymmetry factor (g) from circular dichroism (CD) spectroscopy in the entire UV-vis range. The origin of chirality in the two CuO nanostructures has been assigned to the helical arrangement of the Cu-O-Cu network in accordance with their microscopic and spectroscopic observations. Attempts have been made to interpret the crystallographic and geometric chiralities in the two CuO nanostructures based on the redshift and augmented intensity of the CD signal along with an increase in their corresponding anisotropic factor on calcination. Further, the diverse interaction of the toroid-shaped CuO nanostructures with enantiomeric tryptophan moieties has been illustrated from the measurement of their corresponding thermodynamic parameters.

Sr2+-Doped CuO Nanoribbons with the Hydrophobic Surface Enabling CO2 Electroreduction to Ethane

Electrochemical reduction of carbon dioxide to value-added multicarbon (C2+) products is a promising way to obtain renewable fuels of high energy densities and chemicals and close the carbon cycle. However, the difficulty of C-C coupling and complexity of the proton-coupled electron transfer process greatly hinder CO2 electroreduction into specific C2+ products with high selectivity. Here, we design an electrocatalyst of Sr-doped CuO nanoribbons with a hydrophobic surface for CO2 electroreduction to ethane with high selectivity. Sr doping enhances the chemical adsorption and activation of CO2 by inducing oxygen vacancies and increasing *CO coverage by stabilizing Cu2+ active sites, thus further boosting subsequent C-C coupling. The hydrophobic surface with dodecyl sulfate anions (DS-) adsorption increases the oxophilicity of the catalyst surface, enhancing the conversion of the *OCH2CH3 intermediate to ethane. As a result, the optimized Sr1.97%-CuO exhibits a Faradaic efficiency of 53.4% and a partial current density of 13.5 mA cm-2 for ethane under a potential of -0.8 V. This study provides a strategy to design a Cu-based catalyst by alkaline earth metal ions doping with the hydrophobic surface to engineer the evolution of the intermediates for a desired product during CO2RR.

Geometric Control and Optical Properties of Intrinsically Chiral Plasmonic Nanomaterials

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

Chiral Perovskite Nanocrystal Growth inside Helical Hollow Silica Nanoribbons

Helical perovskite nanocrystals (H-PNCs) were prepared using nanometric silica helical ribbons as platforms for the in situ growth of the crystals using the supersaturated recrystallization method. The H-PNCs grow inside nanometric helical porous silica, and their handedness is determined by the handedness of porous silica templates. They show both strong induced circular dichroism (CD) and strong induced circularly polarized luminescence (CPL) signals, with high dissymmetry g-factors. Right-handed and left-handed PNCs show respectively positive and negative CD and CPL signals, with a dissymmetry g-factor (abs and lum) of ∼±2 × 10^-2. Simulations based on the boundary element method demonstrate that the circular dichroism originates from the chiral shape of H-PNCs.

Block Copolymer Enabled Synthesis and Assembly of Chiral Metal Oxide Nanoparticle

Chiral metal oxide nanostructures have received tremendous attention in nanotechnological applications owing to their intriguing chiroptical and magnetic properties. Current synthetic methods mostly rely on the use of amino acids or peptides as chiral inducers. Here, we report a general approach to fabricate chiral metal oxide nanostructures with tunable magneto-chiral effects, using block copolymer (BCP) inverse micelle and R/S-mandelic acid (MA). Diverse chiral metal oxide nanostructures are prepared by the selective incorporation of precursors within micellar cores followed by the oxidation process, exhibiting intense chiroptical properties with a g-factor up to 7.0 × 10^-3 in the visible-NIR range for the Cr₂O₃ nanoparticle multilayer. The BCP inverse micelle is found to inhibit the racemization of MA, allowing MA to act as a chiral dopant that imparts chirality to nanostructures via hierarchical chirality transfer. Notably, for paramagnetic nanostructures, magneto-chiroptical modulation is realized by regulating the direction of the external magnetic field. This BCP-driven approach can be extended to the mass production of chiral nanostructures with tunable architectures and optical activities, which may provide insights into the development of chiroptical functional materials.

Histidine-Mediated Synthesis of Chiral Cobalt Oxide Nanoparticles for Enantiomeric Discrimination and Quantification

Chiral transition metal oxide nanoparticles (CTMOs) are attracting a lot of attention due to their fascinating properties. Nevertheless, elucidating the chirality induction mechanism often remains a major challenge. Herein, the synthesis of chiral cobalt oxide nanoparticles mediated by histidine (Co₃ O₄ @L-His and Co₃ O₄ @D-His for nanoparticles synthesized in the presence of L- and D-histidine, respectively) is investigated. Interestingly, these CTMOs exhibit remarkable and tunable chiroptical properties. Their analysis by x-ray photoelectron, Fourier transform infrared, and ultraviolet-visible absorption spectroscopy indicates that the ratio of Co²⁺ /Co³⁺ and their interactions with the imidazole groups of histidine are behind their chiral properties. In addition, the use of chiral Co₃ O₄ nanoparticles for the development of sensitive, rapid, and enantioselective circular dichroism-based sensors is demonstrated, allowing direct molecular detection and discrimination between cysteine or penicillamine enantiomers. The circular dichroism response of the chiral Co₃ O₄ exhibits a limit of detection and discrimination of cysteine and penicillamine enantiomers as low as 10 µm. Theoretical calculations suggest that the ligand exchange and the coexistence of both species adsorbed on the oxide surface are responsible for the enantiomeric discrimination. This research will enrich the synthetic approaches to obtain CTMOs and enable the extension of the applications and the discovery of new chiroptical properties.

Bioinspired crowding directs supramolecular polymerisation

Crowding effects are crucial to maintaining functionality in biological systems, but little is known about their role in analogous artificial counterparts. Within the growing field of supramolecular polymer science, crowding effects have hitherto remained underappreciated. Herein, we show that crowding effects exhibit strong and distinct control over the kinetics, accessible pathways and final outcomes of supramolecular polymerisation processes. In the presence of a pre-formed supramolecular polymer as crowding agent, a model supramolecular polymer dramatically changes its self-assembly behaviour and undergoes a morphological transformation from bundled fibres into flower-like hierarchical assemblies, despite no co-assembly taking place. Notably, this new pathway can only be accessed in crowded environments and when the crowding agent exhibits a one-dimensional morphology. These results allow accessing diverse morphologies and properties in supramolecular polymers and pave the way towards a better understanding of high-precision self-assembly in nature.

Extracting Pure Circular Dichroism from Hierarchically Structured CdS Magic Cluster Films

Chiroptically active, hierarchically structured materials are difficult to accurately characterize due to linear anisotropic contributions (i.e., linear dichroism (LD) and linear birefringence (LB)) and parasitic ellipticities that produce artifactual circular dichroism (CD) signals, in addition to chiral analyte contributions ranging from molecular-scale clusters to micron-sized assemblies. Recently, we have shown that CdS magic-sized clusters (MSC) can self-assemble into ordered films that have a hierarchical structure spanning seven orders of length-scale. These films have a strong CD response, but the chiral origins are obfuscated by the hierarchical architecture and LDLB contributions. Here, we derive and demonstrate a method for extracting the "pure" CD signal (CD generated by structural dissymmetry) from hierarchical MSC films and identified the chiral origin. The theory behind the method is derived using Mueller matrix and Stokes vector conventions and verified experimentally before being applied to hierarchical MSC and nanoparticle films with varying macroscopic orderings. Each film's extracted "true CD" shares a bisignate profile aligned with the exciton peak, indicating the assemblies adopt a chiral arrangement and form an exciton coupled system. Interestingly, the linearly aligned MSC film possesses one of the highest g-factors (0.05) among semiconducting nanostructures reported. Additionally, we find that films with similar electronic transition dipole alignment can possess greatly different g-factors, indicating chirality change rather than anisotropy is the cause of the difference in the CD signal. The difference in g-factor is controllable via film evaporation geometry. This study provides a simple means to measure "true" CD and presents an example of experimentally understanding chiroptic interactions in hierarchical nanostructures.

Tunable optical activities in chiral transition metal oxide nanoparticles

Chiral transition metal oxides (TMOs) are widely used in various optoelectronic devices. However, the currently poor understanding of how the optical activities of TMOs can be regulated considerably hinders their applications. We have synthesized a series of chiral TMO nanoparticles (NPs), i.e., MoO_x (x = 2, 2.4 and 2.5) and Co₃O₄. Compared with TMO NPs with L-/D-cysteine molecules as the capping ligand, L-/D-histidine-capped TMO NPs possess larger anisotropic factors (g_abs), which are as high as ∼0.01 and ∼0.02 for L-/D-histidine-capped MoO_2.5 and Co₃O₄ NPs, respectively. A nondegenerate coupled oscillator (NDCO) theoretical calculation confirms that L-/D-histidine molecules can generate a smaller electric dipole moment and thus induce higher optical activity than L-/D-cysteine molecules. Impressively, the chiral NPs exhibit broadband second harmonic generation. This work indicates that chiral TMO NPs have potential for application in nonlinear optical devices.

Biomimetic Self-Assembled Chiral Inorganic Nanomaterials: A New Strategy for Solving Medical Problems

The rapid expansion of the study of chiral inorganic structures has led to the extension of the functional boundaries of inorganic materials. Nature-inspired self-assembled chiral inorganic structures exhibit diverse morphologies due to their high assembly efficiency and controlled assembly process, and they exhibit superior inherent properties such as mechanical properties, chiral optical activity, and chiral fluorescence. Although chiral self-assembled inorganic structures are becoming more mature in chiral catalysis and chiral optical regulation, biomedical research is still in its infancy. In this paper, various forms of chiral self-assembled inorganic structures are summarized, which provides a structural starting point for various applications of chiral self-assembly inorganic structures in biomedical fields. Based on the few existing research statuses and mechanism discussions on the chiral self-assembled materials-mediated regulation of cell behavior, molecular probes, and tumor therapy, this paper provides guidance for future chiral self-assembled structures to solve the same or similar medical problems. In the field of chiral photonics, chiral self-assembled structures exhibit a chirality-induced selection effect, while selectivity is exhibited by chiral isomers in the medical field. It is worth considering whether there is some correspondence or juxtaposition between these phenomena. Future chiral self-assembled structures in medicine will focus on the precise treatment of tumors, induction of soft and hard tissue regeneration, explanation of the biochemical mechanisms and processes of its medical effects, and improvement of related theories.

Chiral-Solvent-Mediated Manganese-Based Hierarchical Supraparticles with Chiroptical Activity

In this study, manganese-based multiply hierarchical chiral supraparticles (SPs), with an anisotropy factor (g-factor) of 0.102 and circular dichroism (CD) intensity of 260 mdeg at 530 nm, are successfully synthesized with polar-solvent-mediated strategies. Notably, the g-factor of the SPs is further enhanced to 0.121 by the addition of an external chiral solvent, generating a chiral biased environment, which increases their CD intensity to 320 mdeg at 500 nm. The mechanism underlying the different chirality is proposed to be a difference in the angle of tilt of ±33° between the two enantiomers of the chiral SPs, which involves a difference of ±7° between the orientation of individual nanoplatelets. Chiral solvents induce the angle between adjacent nanoplatelets to get smaller than the original structure that leads to their higher anisotropic value. These findings potentially provide a practical method for the construction of complex chiral superstructures and the regulation of chiroptical activity.

Inorganic Nanoflowers—Synthetic Strategies and Physicochemical Properties for Biomedical Applications: A Review

Nanoflowers, which are flower-shaped nanomaterials, have attracted significant attention from scientists due to their unique morphologies, facile synthetic methods, and physicochemical properties such as a high surface-to-volume ratio, enhanced charge transfer and carrier immobility, and an increased surface reaction efficiency. Nanoflowers can be synthesized using inorganic or organic materials, or a combination of both (called a hybrid), and are mainly used for biomedical applications. Thus far, researchers have focused on hybrid nanoflowers and only a few studies on inorganic nanoflowers have been reported. For the first time in the literature, we have consolidated all the reports on the biomedical applications of inorganic nanoflowers in this review. Herein, we review some important inorganic nanoflowers, which have applications in antibacterial treatment, wound healing, combinatorial cancer therapy, drug delivery, and biosensors to detect diseased conditions such as diabetes, amyloidosis, and hydrogen peroxide poisoning. In addition, we discuss the recent advances in their biomedical applications and preparation methods. Finally, we provide a perspective on the current trends and potential future directions in nanoflower research. The development of inorganic nanoflowers for biomedical applications has been limited to date. Therefore, a diverse range of nanoflowers comprising inorganic elements and materials with composite structures must be synthesized using ecofriendly synthetic strategies.

Six-Pointed Star Chiral Cobalt Superstructures with Strong Antibacterial Activity

Chiral inorganic nanomaterials have shown promise as a potential means of combating bacteria due to their high levels of biocompatibility, easy surface modification, and excellent optical properties. In this study, a diverse range of chiral hierarchical nanomaterials are prepared from Co²⁺ and L/D-Tartaric acid (Tar) ligands. By combining the ligands in different ratios, chiral Co superstructures (Co SS) are obtained with different morphologies, including chiral nanoflowers, chiral nanohanamaki, a chiral six-pointed star, a chiral fan shape, and a chiral fusiform shape. It is found that the chiral six-pointed star structures exhibit chiroptical activity across a broad range of wavelengths from 300 to 1300 nm and that the g-factor is as high as 0.033 with superparamagnetic properties. Under the action of electromagnetic fields, the chiral six-pointed star Co SS shows excellent killing ability against Gram-positive Staphylococcus aureus (ATCC 25923). Compared to L-Co SS, D-Co SS shows stronger levels of antibacterial ability. It is found that the levels of reactive oxygen species generated by D-Co SS are 1.59-fold higher than L-Co SS which is attributed to chiral-induced spin selectivity effects. These findings are of significance for the further development of chiral materials with antibacterial properties.

Role of Surface Oxygen Vacancies and Oxygen Species on CuO Nanostructured Surfaces in Model Catalytic Oxidation and Reductions: Insight into the Structure-Activity Relationship Toward the Performance

Defect engineering, such as modification of oxygen vacancy density, has been considered as an effective approach to tailor the catalytic performance on transition-metal oxide nanostructured surfaces. The role of oxygen vacancies (O_V) on the surface of the as-prepared, zinnia-shaped morphology of CuO nanostructures and their marigold forms on calcination at 800 °C has been investigated through the study of model catalytic reactions of reduction of 4-nitrophenol and aerobic oxidation of benzyl alcohol. The O_V on the surfaces of different morphologies of CuO have been identified and quantified through Rietveld analysis and HRTEM, EPR, and XPS studies. The structure-activity relationships between surface oxygen vacancies (O_V) and catalytic performance have been systematically investigated. The enhanced catalytic performance of the cubic CuO nanostructures compared to their as-prepared forms has been attributed to the formation of surface oxygen species on the reactive and dominant (110) surface that has low oxygen vacancy formation energy. The mechanistic role of surface oxygen species in the studied reactions has been quantitatively correlated with the catalytic activity of the different morphological forms of the CuO nanostructures.

Geometric Engineering of Porous PtCu Nanotubes with Ultrahigh Methanol Oxidation and Oxygen Reduction Capability

Platinum (Pt), as a commonly used electrocatalyst in direct methanol fuel cells (DMFCs), suffers from sluggish kinetics of both the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). Geometric engineering has been proven effective for improving the MOR and ORR activities. Thus, by modulating the Pt precursor and poly(vinylpyrrolidone) (PVP) dosages, different porous PtCu nanotubes constructed by hollow nanospheres, solid alloy, and Pt-rich skinned nanoparticles, respectively, are successfully synthesized. Among them, the solid PtCu alloy nanoparticle coherent nanotubes exhibit the specific activity 9.42 times higher than Pt/C toward MOR, while the hollow PtCu alloy nanosphere coherent nanotubes show the specific activity 4.85 times higher than Pt/C toward ORR. The different Pt:Cu ratios of hollow nanospheres, solid alloy, and Pt-rich skinned nanoparticles cause the differences in electron transfer from Cu to Pt as well as electronic structures of Pt. As a result, the binding energies of intermediates can be regulated, leading to the enhancement in MOR and ORR.

Chiral CuS nanoparticles and their photothermal properties

Chiral CuS NPs were prepared through a ligand-exchange process and CPL-controlled photothermal performance was realized.

Inorganic Chiral Hybrid Nanostructures for Tailored Chiroptics and Chirality-Dependent Photocatalysis

Inorganic chiral hybrid nanostructures embedding chirality within distinct material compositions can create novel chiral properties and functionalities absent from achiral ones, but remain largely unexplored. We report for the first time a class of chiral plasmonic metal-semiconductor core-shell nanostructures by employing structurally chiral nanoparticles as chirality inducing templates to grow functional shell materials, which allows us to independently control material parameters including core geometry and shell thickness, as well as handedness of the system. We experimentally and theoretically achieve enhanced and tunable chiroptical activity of the hetero-structures as a result of the core-shell strong coupling effect. As a proof-of-concept demonstration, we show the chiral hybrid nanostructures can drive chirality-dependent photocatalytic hydrogen generation under circularly polarized light. This study enables rational design and functionalization of chiral hybrid nanomaterials towards enhanced chiral light-matter interactions and chiral device applications.

The Role of Surface Curvature in Electrocatalysts

Excessive consumption of fossil fuels has caused unavoidable environmental problems. The development of renewable and clean alternatives is essential for the sustainable and green development of human society. Electrocatalysts are most important parts in these energy-related devices. Recently, scientists found that the surface curvature of electrocatalysts could play an important role for the improvement of catalytic performance and the optimization of intrinsic catalytic activity during electrocatalytic process. The role of surface curvature in electrocatalysts is still under investigating. In this minireview, we summarized the latest progress of electrocatalysts with different surface curvatures and their applications in energy-related applications. This review mainly involves the strategies for preparation of electrocatalysts with different surface curvatures, three typical electrocatalysts with different surface curvatures (curled surface, onion-like structure, and spiral structure), and the potential mechanisms that surface curvature in electrocatalysts affects activities.

Tuning Sugar-Based Chiral and Flower-Like Microparticles

Unique supermolecular structures as chiral and flower-like microparticles and the precise tuning of the morphologies hold immense promise for a variety of applications. Examples of such structures deriving from monosaccharides are still rare, and a general understanding is also lacking. Herein, it is shown that chiral, flower-like, or solid microparticles can be tuned by only using monosaccharide esters without external stimuli. Chiral "left-handed" (counterclockwise) and "right-handed" (clockwise) morphologies can be induced by d- and l-glucose stearoyl esters. In comparison, other monosaccharides, i.e., galactose, mannose, and xylose, cannot formed chiral particles and generated diverse other morphologies of the supermolecular microparticles based on their distinct molecular configurations. Due to the numbers of side chains and the bond orientations, microparticles with solid and porous flower-like morphologies can be obtained. While glucose and xylose esters only lead to solid microparticles, mannose and galactose generate porous flower-like particles. These findings suggest a general method to design and control the superstructures by using monosaccharide backbones with diverse molecular configurations.

Metal Oxide-Related Dendritic Structures: Self-Assembly and Applications for Sensor, Catalysis, Energy Conversion and Beyond

In the past two decades, we have learned a great deal about self-assembly of dendritic metal oxide structures, partially inspired by the nanostructures mimicking the aesthetic hierarchical structures of ferns and corals. The self-assembly process involves either anisotropic polycondensation or molecular recognition mechanisms. The major driving force for research in this field is due to the wide variety of applications in addition to the unique structures and properties of these dendritic nanostructures. Our purpose of this minireview is twofold: (1) to showcase what we have learned so far about how the self-assembly process occurs; and (2) to encourage people to use this type of material for drug delivery, renewable energy conversion and storage, biomaterials, and electronic noses.

Chiral Nanoceramics

The study of different chiral inorganic nanomaterials has been experiencing rapid growth during the past decade, with its primary focus on metals and semiconductors. Ceramic materials can substantially expand the range of mechanical, optical, chemical, electrical, magnetic, and biological properties of chiral nanostructures, further stimulating theoretical, synthetic, and applied research in this area. An ever-expanding toolbox of nanoscale engineering and self-organization provides a chirality-based methodology for engineering of hierarchically organized ceramic materials. However, fundamental discoveries and technological translations of chiral nanoceramics have received substantially smaller attention than counterparts from metals and semiconductors. Findings in this research area are scattered over a variety of sources and subfields. Here, the diversity of chemistries, geometries, and properties found in chiral ceramic nanostructures are summarized. They represent a compelling materials platform for realization of chirality transfer through multiple scales that can result in new forms of ceramic materials. Multiscale chiral geometries and the structural versatility of nanoceramics are complemented by their high chiroptical activity, enantioselectivity, catalytic activity, and biocompatibility. Future development in this field is likely to encompass chiral synthesis, biomedical applications, and optical/electronic devices. The implementation of computationally designed chiral nanoceramics for biomimetic catalysts and quantum information devices may also be expected.

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 Transition Metal Oxides: Synthesis, Chiral Origins, and Perspectives

Transition metal oxides (TMOs) consist of a series of solid materials, exhibiting a wide variety of structures with tunability and versatile physicochemical properties. Such a statement is undeniably true for chiral TMOs since the introduction of chirality brings in not only active optical activities but also geometrical anisotropy due to the symmetry-breaking effect. Although progressive investigations have been made for accurately controlled synthesis and relevant explanations on the chirality origin of such materials, the overall field of chiral TMOs is still in its infancy with adequate space for interdisciplinary communications and development. Herein, therefore, recent advances in both experimental phenomena and theoretical calculations in this area are reviewed, to elucidate the underlying chiral origin with respect to their fabrications process, triggering new insights for further evolution of this field.

Enantioselective Recognition of Chiral Tryptophan with Achiral Glycine through the Strategy of Chirality Transfer

Glycine (Gly), an achiral amino acid, has never been reported for enantioselective recognition owing to the absence of chiral sites. Herein, a facile strategy of chirality transfer is proposed to endow Gly with chirality. Optically active CuO, L-CuO, is first prepared, which can be used for the decoration of Gly through the formation of the Cu(Gly)₂ complex. Successful chirality transfer from L-CuO to Gly is confirmed by circular dichroism (CD) spectra. The formation of the Cu(Gly)₂ complex is further confirmed by Fourier transform infrared spectra and X-ray photoelectron spectroscopy. Next, the resultant L-CuO-Gly is used for chiral analysis of the isomers of tryptophan (Trp). Because of the higher affinity of L-CuO-Gly toward L-Trp than its isomer, the Trp isomers exhibit significant differences in their oxidation peak currents at the L-CuO-Gly-modified glassy carbon electrode (GCE) (I_L-Trp/I_D-Trp = 5.24). Finally, the practicability of the developed L-CuO-Gly/GCE is assessed, and the results indicate that it could be a reliable chiral sensor for the quantitative analysis of Trp isomers in nonracemic mixtures.

Synthesis of chiral mesostructured titanium dioxide films

Chiral mesostructured TiO2 films (CMTFs) were synthesized by a hydrothermal method using l/d-mannitol as the symmetry-breaking agent and titanium foil as both the substrate and inorganic precursor. Five levels of hierarchical chirality exist in the CMTFs, exhibiting optical activity (OA) at ∼350 nm attributed to the electronic transitions in a dissymmetric electric field.

Multifarious Chiral Nanoarchitectures Serving as Handed-Selective Fluorescence Filters for Generating Full-Color Circularly Polarized Luminescence

A series of full-color circularly polarized luminescence (CPL)-active materials are fabricated by judiciously combining multifarious chiral nanoarchitectures with achiral fluorescence dyes. The investigated nanoarchitectures include organic polymer nanofibers, organic-inorganic hybrid nanoflowers, and inorganic nanoflowers. The as-prepared chiral nanoarchitectures all can act as handed-selective fluorescence filters to powerfully transform unpolarized fluorescent light into circularly polarized luminescence. Also notable, no interaction is required between chiral and fluorescent components for achieving CPL emission. The present study provides a convenient and universal approach for preparing full-color CPL materials. Following the strategy, numerous chiroptical materials with CPL performance can be expected due to the abundant chiral matters and achiral fluorophores.

Tuning the Superhydrophobic Properties of Hierarchical Nano-microstructural Silica Biomorph Arrays Grown at Triphasic Interfaces

The three-dimensional hierarchical morphology of surfaces greatly affects the wettability, absorption and microfabrication properties of their hybrid materials, however few scalable methods exist that controls simultaneously complex geometric shape and spatial scattered location and their physical properties tuned. Consequently, this report describes a synthetic strategy that enables the position of well-ordered biomorph nano-microstructures on hydrophobic surfaces to be precisely controlled. The hierarchical architecture can be accurately positioned on polydimethylsiloxane (PDMS) surfaces in an unprecedented level by leveraging a solid/liquid/gas triphase dynamic reaction diffusion system strategy. The effect of salt concentrations, pH, CO₂ levels, temperature and substrate patterning on this self-assembly process has been investigated, enabling protocols to be devised that enables the hydrophobic properties of the hierarchically assembled multiscale microstructures to be tuned as required. This combined top-down/bottom-up approach can be used to produce composites with outstanding hydrophobicity properties, affording superhydrophobic materials that are capable of retaining water droplets on their surfaces, even when the material is inverted by 180°, with a wide range of potential applications in oil/water separation technology and for selective cell recognition in biological systems.