Chiral Assembly of Gold-Silver Core-Shell Plasmonic Nanorods on DNA Origami with Strong Optical Activity

Synthesis of Chiral Ag, Pd, and Pt Helicoids inside Chiral Silica Mold

Chiral inorganic nanomaterials hold significant promise for various applications, including enantioselective catalysis, polarization-controlling optical devices, metamaterials, and enantioselective molecular sensors. In our previous work, we presented a method for synthesizing chiral Au 432 helicoid III (Au helicoids) from peptides and amino acids, where helical gaps are intricately arranged with 432 symmetry within single cubic nanoparticles. In this study, we have achieved the fabrication of chiral silica molds through Au etching subsequent to the silica coating of Au helicoids. We demonstrate that these molds serve as geometrically confined reactors capable of producing chiral Ag, Pd, and Pt 432 helicoid III (Ag, Pd, and Pt helicoids). The morphology of the synthesized Ag, Pd, and Pt helicoids closely resembles that of the Au helicoids, exhibiting a superior g-factor compared to other reported chiral structures of each material. Notably, the Ag and Pd helicoids are found to be single-crystalline, with high-index planes exposed within the gaps. We believe that this silica mold-based approach can be generalized to synthesize chiral nanomaterials of various metal and even oxide materials.

Self-Matching Assembly of Chiral Gold Nanoparticles Leads to High Optical Asymmetry and Sensitive Detection of Adenosine Triphosphate

To achieve chiral amplification, life uses small chiral molecules as building blocks to construct hierarchical chiral architectures that can realize advanced physiological functions. Inspired by the chiral amplification strategy of nature, we herein demonstrate that the chiral assembly of chiral gold nanorods (GNRs) leads to enhanced optical asymmetry factors (g-factors), up to 0.24. The assembly of chiral GNRs, dictated by structural self-matching, leads to g-factors with over 100-fold higher values than those of individual chiral GNRs, as confirmed by numerical simulations. Moreover, the efficient optical asymmetry of chiral GNR assemblies enables their application as highly sensitive sensors of adenosine triphosphate (ATP detection limit of 1.0 μM), with selectivity against adenosine diphosphate and adenosine monophosphate.

Regulating superstructures of conjugated polymers towards enhanced and stable photocatalytic hydrogen evolution via covalent crosslinking and complementary supramolecular self-assembly

The modulation of microstructures in conjugated polymers represents a viable strategy for enhancing photocatalytic efficiency, albeit hampered by complex processing techniques. Here, we present an uncomplicated, template-free method to synthesize polymeric photocatalysts, namely BCN(x)@PPy, featuring a hollow nanotube-nanocluster core-shell superstructure. This configuration is realized through intramolecular covalent crosslinking and synergistic intermolecular donor-acceptor (D-A) interactions between phenylene pyrene (PPy, D) nanotubes and poly([1,1'-biphenyl]-3-carbonitrile) (PBCN, A) nanoclusters. Interestingly, the optimized BCN2@PPy composite demonstrates remarkably enhanced performance for photocatalytic hydrogen evolution, with an efficiency of 14.7-fold higher than that of unmodified PPy nanotubes. Experimental and density functional theory calculations revealed that BCN(x)@PPy composites are conducive to shortening photogenerated exciton migration, facilitating charge separation and transfer, reducing nanoclusters aggregation or re-stacking, and providing sufficient catalytically active sites, all contributing to the heightened efficiency in photocatalysis. These insights underscore the potential for precise molecular adjustments in conjugated polymers, advancing artificial photosynthesis.

Engineering AIEgens-Tethered Gold Nanoparticles with Enzymatic Dual Self-Assembly for Amplified Cancer-Specific Phototheranostics

Accurate imaging and precise treatment are critical to controlling the progression of pancreatic cancer. However, current approaches for pancreatic cancer theranostics suffer from limitations in tumor specificity and invasive surgery. Herein, a pancreatic cancer-specific phototheranostic modulator (AuHQ) dominated by aggregation-induced emission (AIE) luminogens-tethered gold nanoparticles is meticulously designed to facilitate prominent fluorescence-photoacoustic bimodal imaging-guided photothermal immunotherapy. Once reaching the pancreatic tumor microenvironment (TME), the peptide Ala-Gly-Phe-Ser-Leu-Pro-Ala-Gly-Cys (AGFSLPAGC) linkage within AuHQ can be specifically cleaved by the overexpressed enzyme Cathepsin E (CTSE), triggering the dual self-assembly of AuNPs and AIE luminogens. The aggregation of AuNPs mediated by enzymatic cleavage results in potentiated photothermal therapy (PTT) under near-infrared (NIR) laser irradiation, induced immunogenic cell death (ICD), and enhanced photoacoustic imaging. Simultaneously, AIE luminogen aggregates formed by hydrophobic interaction can generate AIE fluorescence, enabling real-time and specific fluorescence imaging of pancreatic cancer. Furthermore, coadministration of an indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor with AuHQ can address the limitations of PTT efficacy imposed by the immunosuppressive TME and leverage the synergistic potential to activate systemic antitumor immunity. Thus, this well-designed phototheranostic modulator AuHQ facilitates the intelligent enzymatic dual self-assembly of imaging and therapeutic agents, providing an efficient and precise approach for pancreatic cancer theranostics.

Preparation of DNA nanoflower-modified capillary silica monoliths for chiral separation

Innovative chiral capillary silica monoliths (CSMs) were developed based on DNA nanoflowers (DNFs). Baseline separation of enantiomers such as atenolol, tyrosine, histidine, and nefopam was achieved by using DNF-modified CSMs, and the obtained resolution value was higher than 1.78. To further explore the effect of DNFs on enantioseparation, different types of chiral columns including DNA strand containing the complementary sequence of the template (DCT)-modified CSMs, DNF2-modified CSMs, and DNF3-modified CSMs were prepared as well. It was observed that DNF-modified CSMs displayed better chiral separation ability compared with DCT-based columns. The intra-day and inter-day repeatability of model analytes' retention time and resolution kept desirable relative standard deviation values of less than 8.28%. DNF2/DNF3-modified CSMs were able to achieve baseline separation of atenolol, propranolol, 2'-deoxyadenosine, and nefopam enantiomers. Molecular docking simulations were performed to investigate enantioselectivity mechanisms of DNA sequences for enantiomers. To indicate the successful construction of DNFs and DNF-modified CSMs, various charaterization approaches including scanning electron microscopy, agarose gel electrophoresis, dynamic light scattering analysis, electroosmotic flow, and Fourier-transform infrared spectroscopy were utilized. Moreover, the enantioseparation performance of DNF-modified CSMs was characterized in terms of sample volume, applied voltage, and buffer concentration. This work paves the way to applying DNF-based capillary electrochromatography microsystems for chiral separation.

Surface-enhanced Raman scattering-based identification of breast cancer progression using extracellular vesicles-derived integrin α6β4

Detection of progression is of great importance to breast cancer treatment and can benefit patients. Limited by current detection technologies and biomarkers, early breast cancer progression diagnosis remains challenging. Researchers have found blood extracellular vesicles (EVs)-derived integrin α6β4 directly facilitate progression in breast cancer, enabling cancer detection. However, EVs size and heterogeneity hinder protein detection, masked by abundant background EVs. Hence, novel tools for efficient detection of EVs with high selectivity and low interference are significantly desired. Here, a new silver-coated gold nanorods SERS probe, termed as Au@Ag@IDA-B/4MSTP, based on DNA aptamer was established for the detection of integrin α6β4 derived from EVs. Validation of the Au@Ag@IDA-B/4MSTP probes using cell-culture-derived EVs revealed a LOD of 23 particles/μL for EVs detection. This tool was further confirmed to mimic the real state of cancer with subcutaneous tumor model and lung metastasis model in mice. With 10 μL of blood plasma and simple Raman analysis process, the test achieved 85.7 % sensitivity and 83.3 % specificity. Moreover, our method achieves a simplified approach that expedites the detection process. These results demonstrate the good detection performance of Au@Ag@IDA-B/4MSTP probes for EVs integrin α6β4, and suggest that this non-invasive approach could be a promising tool for early detection of breast cancer progression.

Dichroism of plasmonic chiral nanoalloys by rational design

Time-dependent density functional theory (TDDFT) simulations are conducted on a series of chiral gold/silver alloy nanowires to explore whether silver doping can produce an enhancement of circular dichroism at the plasmon resonance in these systems, and to identify the quantum-mechanical origin of the observed effects. We find a strong plasmonic dichroism when one or two helixes of gold atoms are substituted by silver in a linear chiral nanotube, whose pure gold counterpart does not display any plasmonic dichroism, and we rationalize this finding in terms of "decoupling" the destructive interference of excitations in the pure gold nanotube via alloying. However, further attempts to increase the plasmonic dichroism by considering multi-shell gold nanowires in which one entire shell is doped with silver did not produce the desired effect, but rather a decrease in circular dichroism. We show that this latter result is due to a more severe destructive interference in the dipole excitation contributions, and suggest that further amplification should be possible in principle by properly tuning simultaneously the nanowire structure and chemical ordering.

Universal Click-Chemistry Approach for the DNA Functionalization of Nanoparticles

Nanotechnology has revolutionized the fabrication of hybrid species with tailored functionalities. A milestone in this field is the deoxyribonucleic acid (DNA) conjugation of nanoparticles, introduced almost 30 years ago, which typically exploits the affinity between thiol groups and metallic surfaces. Over the last decades, developments in colloidal research have enabled the synthesis of an assortment of nonmetallic structures, such as high-index dielectric nanoparticles, with unique properties not previously accessible with traditional metallic nanoparticles. However, to stabilize, integrate, and provide further functionality to nonmetallic nanoparticles, reliable techniques for their functionalization with DNA will be crucial. Here, we combine well-established dibenzylcyclooctyne-azide click-chemistry with a simple freeze-thaw method to achieve the functionalization of silica and silicon nanoparticles, which form exceptionally stable colloids with a high DNA surface density of ∼0.2 molecules/nm2. Furthermore, we demonstrate that these functionalized colloids can be self-assembled into high-index dielectric dimers with a yield of over 50% via the use of DNA origami. Finally, we extend this method to functionalize other important nanomaterials, including oxides, polymers, core-shell, and metal nanostructures. Our results indicate that the method presented herein serves as a crucial complement to conventional thiol functionalization chemistry and thus greatly expands the toolbox of DNA-functionalized nanoparticles currently available.

The Mechanism of Manipulating Chirality and Chiral Sensing Based on Chiral Plexcitons in a Strong-Coupling Regime

Manipulating plasmonic chirality has shown promising applications in nanophotonics, stereochemistry, chirality sensing, and biomedicine. However, to reconfigure plasmonic chirality, the strategy of constructing chiral plasmonic systems with a tunable morphology is cumbersome and complicated to apply for integrated devices. Here, we present a simple and effective method that can also manipulate chirality and control chiral light-matter interactions only via strong coupling between chiral plasmonic nanoparticles and excitons. This paper presents a chiral plexcitonic system consisting of L-shaped nanorod dimers and achiral molecule excitons. The circular dichroism (CD) spectra in our strong-coupling system can be calculated by finite element method simulations. We found that the formation of the chiral plexcitons can significantly modulate the CD spectra, including the appearance of new hybridized peaks, double Rabi splitting, and bisignate anti-crossing behaviors. This phenomenon can be explained by our extended coupled-mode theory. Moreover, we explored the applications of this method in enantiomer ratio sensing by using the properties of the CD spectra. We found a strong linear dependence of the CD spectra on the enantiomer ratio. Our work provides a facile and efficient method to modulate the chirality of nanosystems, deepens our understanding of chiral plexcitons in nanosystems, and facilitates the development of chiral devices and chiral sensing.

Recent Advances in the 3D Chiral Plasmonic Nanomaterials

From the view of geometry, chirality is that an object cannot overlap with its mirror image, which has been a fundamental scientific problem in biology and chemistry since the 19th century. Chiral inorganic nanomaterials serve as ideal templates for investigating chiral transfer and amplification mechanisms between molecule and bulk materials, garnering widespread attentions. The chiroptical property of chiral plasmonic nanomaterials is enhanced through localized surface plasmon resonance effects, which exhibits distinctive circular dichroism (CD) response across a wide wavelength range. Recently, 3D chiral plasmonic nanomaterials are becoming a focal research point due to their unique characteristics and planar-independence. This review provides an overview of recent progresses in 3D chiral plasmonic nanomaterials studies. It begins by discussing the mechanisms of plasmonic enhancement of molecular CD response, following by a detailed presentation of novel classifications of 3D chiral plasmonic nanomaterials. Finally, the applications of 3D chiral nanomaterials such as biology, sensing, chiral catalysis, photology, and other fields have been discussed and prospected. It is hoped that this review will contribute to the flourishing development of 3D chiral nanomaterials.

Controlling Chiroptical Responses via Chemo-Mechanical Deformation of DNA Origami Structures

DNA origami-based templates have been widely used to fabricate chiral plasmonic metamaterials due to their precise control of the placement of nanoparticles (NPs) in a desired configuration. However, achieving various chiroptical responses inevitably requires a change in the structure of DNA origami-based templates or binding sites on them, leading to the use of significantly different sets of DNA strands. Here, we propose an approach to controlling various chiroptical responses with a single DNA origami design using its chemo-mechanical deformation induced by DNA intercalators. The chiroptical response could be finely tuned by altering the concentration of intercalators only. The silver (Ag) enhancement was used to amplify the chiroptical signal by enlarging NPs and to maintain it by stiffening the template DNA structure. Furthermore, the sensitivity in the chiroptical signal change to the concentration of intercalators could be modulated by the type of intercalator, the mixture of two intercalators, and the stiffness of DNA origami structures. This approach would be useful in a variety of optical applications that require programmed spatial modification of chiroptical responses.

Reshaping and induction of optical activity in gold@silver nanocuboids by chiral glutathione molecules

Core-shell gold-silver cuboidal nanoparticles were produced, with either concave or straight facets. Their incubation with a low concentration of chiral l-glutathione (GSH) biomolecules was found to produce near UV plasmonic extinction and induced circular dichroism (CD) peaks. The effect is sensitive to the silver shell thickness. The GSH molecules were found to cause redistribution of silver in the shell, removing silver atoms from edges/corners and re-depositing them at the nanocuboid facets, probably through some redox and complexation processes between the silver and thiol group of the GSH. Other thiolated chiral biomolecules (and drug molecules) did not show this effect. The emerging near UV surface plasmon resonance is a silver slab resonance, which might also possess some multipolar resonance nature. The concave-shaped nanocuboids exhibited stronger induced plasmonic CD relative to the nanocuboids with straight facets.

Nanophotonic Enhanced Chiral Sensing and Its Biomedical Applications

Chiral sensing is crucial in the fields of biology and the pharmaceutical industry. Many naturally occurring biomolecules, i.e., amino acids, sugars, and nucleotides, are inherently chiral. Their enantiomers are strongly associated with the pharmacological effects of chiral drugs. Owing to the extremely weak chiral light-matter interactions, chiral sensing at an optical frequency is challenging, especially when trace amounts of molecules are involved. The nanophotonic platform allows for a stronger interaction between the chiral molecules and light to enhance chiral sensing. Here, we review the recent progress in nanophotonic-enhanced chiral sensing, with a focus on the superchiral near-field and enhanced circular dichroism (CD) spectroscopy generated in both the dielectric and in plasmonic structures. In addition, the recent applications of chiral sensing in biomedical fields are discussed, including the detection and treatment of difficult diseases, i.e., Alzheimer's disease, diabetes, and cancer.

Recent advances in surface modified gold nanorods and their improved sensing performance

Gold nanorods (AuNRs) have received tremendous attention recently in the fields of sensing and detection applications due to their unique characteristic of surface plasmon resonance. Surface modification of the AuNRs is a necessary path to effectively utilize their properties for these applications. In this Article, we have focused both on demonstrating the recent advances in methods for surface functionalization of AuNRs as well as their use for improved sensing performance using various techniques. The main surface modification methods discussed include ligand exchange with the assistance of a thiol-group, the layer by layer assembly method, and depositing inorganic materials with the desired surface and morphology. Covered techniques that can then be applied for using these functionalized AuNRs include colourimetric sensing, refractive index sensing and surface enhance Raman scattering sensing. Finally, the outlook on the future development of surface modified AuNRs for improved sensing performance is considered.

Chiral Plasmonic Hybrid Nanostructures: A Gateway to Advanced Chiroptical Materials

Chirality introduces a new dimension of functionality to materials, unlocking new possibilities across various fields. When integrated with plasmonic hybrid nanostructures, this attribute synergizes with plasmonic and other functionalities, resulting in unprecedented chiroptical materials that push the boundaries of the system's capabilities. Recent advancements have illuminated the remarkable chiral light-matter interactions within chiral plasmonic hybrid nanomaterials, allowing for the harnessing of their tunable optical activity and hybrid components. These advancements have led to applications in areas such as chiral sensing, catalysis, and spin optics. Despite these promising developments, there remains a need for a comprehensive synthesis of the current state-of-the-art knowledge, as well as a thorough understanding of the construction techniques and practical applications in this field. This review begins with an exploration of the origins of plasmonic chirality and an overview of the latest advancements in the synthesis of chiral plasmonic hybrid nanostructures. Furthermore, representative emerging categories of hybrid nanomaterials are classified and summarized, elucidating their versatile applications. Finally, the review engages with the fundamental challenges associated with chiral plasmonic hybrid nanostructures and offer insights into the future prospects of this advanced field.

Tuning the Plexcitonic Optical Chirality Using Discrete Structurally Chiral Plasmonic Nanoparticles

Constructing chiral plexcitonic systems with tunable plasmon-exciton coupling may advance the scientific exploitation of strong light-matter interactions. Because of their intriguing chiroptical properties, chiral plasmonic materials have shown promising applications in photonics, sensing, and biomedicine. However, the strong coupling of chiral plasmonic nanoparticles with excitons remains largely unexplored. Here we demonstrate the construction of a chiral plasmon-exciton system using chiral AuAg nanorods and J aggregates for tuning the plexcitonic optical chirality. Circular dichroism spectroscopy was employed to characterize chiral plasmon-exciton coupling, in which Rabi splitting and anticrossing behaviors were observed, whereas the extinction spectra exhibited less prominent phenomena. By controlling the number of molecular excitons and the energy detuning between plasmons and excitons, we have been able to fine-tune the plexcitonic optical chirality. The ability to fine-tune the plexcitonic optical chirality opens up unique opportunities for exploring chiral light-matter interactions and boosting the development of emerging chiroptical devices.

Chiral Confined Unimolecular Micelles for Controlled In Situ Fabrication of Optically Active Hybrid Nanostructures

Functional nanomaterials made by chiral induction have attracted extensive attention because of their intriguing characteristics and potential applications. However, the precise and controllable fabrication of chiral nanomaterials still remains challenging but is highly desired. In this study, chiral unimolecular micelles with different molecular weights and chiroptical activities were prepared by photoinduced atom transfer radical polymerization (photoATRP). Through nanoconfined growth, the chiral plasmonic nanoparticle assemblies with predesigned size and morphology were prepared using chiral unimolecular micelles as nanoreactors. The controllability over chiral assemblies and the size effect on chiroptical properties were also investigated. Furthermore, chiral complexes with absorption asymmetry and circularly polarized luminescence (glum = 4.25 × 10-4) were easily constructed via mixing of organic fluorescent molecules and chiral templates based on intermolecular hydrogen bonds. Such results indicated that our unimolecular-micelle-based templates enable the controllable preparation of both inorganic and organic chiral nanostructures with tailored dimensions, sizes, compositions, and optical activities.

Bioinspired Multifunctional Silver Nanoparticles for Optical Sensing Applications: A Sustainable Approach

Silver nanoparticles developed via biosynthesis are the most fascinating nanosized particles and encompassed with excellent physicochemical properties. The bioinspired nanoparticles with different shapes and sizes have attracted huge attention due to their stability, low cost, environmental friendliness, and use of less hazardous chemicals. This is an ideal method for synthesizing a range of nanosized metal particles from plants and biomolecules. Optical biosensors are progressively being fabricated for the attainment of sustainability by using opportunities offered by nanotechnology. This review focuses mainly on tuning the optical properties of the metal nanoparticles for optical sensing to explore the importance and applications of bioinspired silver nanoparticles. Further, this review deliberates the role of bioinspired silver nanoparticles (Ag NPs) in biomedical, agricultural, environmental, and energy applications. Profound insight into the antimicrobial properties of these nanoparticles is also appreciated. Tailor-made bioinspired nanoparticles with effectuating characteristics can unsurprisingly target tumor cells and distribute enwrapped payloads intensively. Existing challenges and prospects of bioinspired Ag NPs are also summarized. This review is expected to deliver perceptions about the progress of the next generation of bioinspired Ag NPs and their outstanding performances in various fields by promoting sustainable practices for fabricating optical sensing devices.

A cooperation tale of biomolecules and nanomaterials in nanoscale chiral sensing and separation

The cooperative relationship between biomolecules and nanomaterials makes up a beautiful tale about nanoscale chiral sensing and separation. Biomolecules are considered a fabulous chirality 'donor' to develop chiral sensors and separation systems. Nature has endowed biomolecules with mysterious chirality. Various nanomaterials with specific physicochemical attributes can realize the transmission and amplification of this chirality. We focus on highlighting the advantages of combining biomolecules and nanomaterials in nanoscale chirality. To enhance the sensors' detection sensitivity, novel cooperation approaches between nanomaterials and biomolecules have attracted tremendous attention. Moreover, innovative biomolecule-based nanocomposites possess great importance in developing chiral separation systems with improved assay performance. This review describes the formation of a network based on nanomaterials and biomolecules mainly including DNA, proteins, peptides, amino acids, and polysaccharides. We hope this tale will record the perpetual relation between biomolecules and nanomaterials in nanoscale chirality.

DNA-Guided Metallization of Nanomaterials and Their Biomedical Applications

Precise control of the structure of metallic nanomaterials is critical for the advancement of nanobiotechnology. As DNA (deoxyribonucleic acid) can readily modify various moieties, such as sulfhydryl, carboxyl, and amino groups, using DNA as a directing ligand to modulate the morphology of nanomaterials is a promising strategy. In this review, we focus on the use of DNA as a template to control the morphology of metallic nanoparticles and their biomedical applications, discuss the use of DNA for the metallization of gold and silver, explore the factors that influence the process, and outline its biomedical applications. This review aims to provide valuable insights into the DNA-guided growth of nanomaterials. The challenges and future directions are also discussed.

Tracking the Growth of Chiral Plasmonic Nanocrystals at Molybdenum Disulfide Heterostructural Interfaces

The way of accurately regulating the growth of chiral plasmonics is of great importance for exploring the chirality information and improving its potential values. Herein, cysteine enantiomers modulate the anisotropic and epitaxial growth of gold nanoplasmonics on seeds of exfoliated MoS₂ nanosheets. The heterostructural Au and MoS₂ hybrids induced by enantiomeric cysteine are presented with chiroptical characteristics, dendritic morphologies, and plasmonic performances. Moreover, the synthesis, condition optimization, formation mechanism, and plasmonic properties of Au and MoS₂ dendritic nanostructures are studied. The chirality characteristics are identified using the circular dichroism spectra and scanning electron microscopy. Time-resolved transmission electron microscopy and UV-vis spectra of the intermediate products captured are analyzed to confirm the formation mechanism of dendritic plasmonic nanostructures at heterostructural surfaces. The specific dendritic morphologies originate from the synergistic impacts of heterostructural MoS₂ interfaces and enantiomeric cysteine-induced anisotropic manipulation. Significantly, the developed synthesis strategy of chiral nanostructures at heterostructural interfaces is highly promising in promoting the understanding of the plasmonic function and crucial chirality bioinformation.

Chiral inorganic nanomaterials for biological applications

Chiral nanomaterials in biology play indispensable roles in maintaining numerous physiological processes, such as signaling, site-specific catalysis, transport, protection, and synthesis. Like natural chiral nanomaterials, chiral inorganic nanomaterials can also be established with similar size, charge, surface properties, and morphology. However, chiral inorganic nanomaterials usually exhibit extraordinary properties that are different from those of organic materials, such as high g-factor values, broad distribution range, and symmetrical mirror configurations. Because of these unique characteristics, there is great potential for application in the fields of biosensing, drug delivery, early diagnosis, bio-imaging, and disease therapy. Related research is summarized and discussed in this review to showcase the bio-functions and bio-applications of chiral inorganic nanomaterials, including the construction methods, classification and properties, and biological applications of chiral inorganic nanomaterials. Moreover, the deficiencies in existing studies are noted, and future development is prospected. This review will provide helpful guidance for constructing chiral inorganic nanomaterials with specific bio-functions for problem solving in living systems.

Large Optical Asymmetry in Silver Nanoparticle Assemblies Enabled by CH-π Interaction-Mediated Chirality Transfer

Transfer of asymmetry from the molecular system to the other distinct system requires appropriate chemical interactions. Here, we show how the CH-π interaction, one of the weakest hydrogen bonds, can be applied to transfer the asymmetry from π-conjugated chiral molecules to the assemblies of plasmonic Ag nanoparticles, where the aliphatic chains of chiral molecules and the polystyrene chains grafted on Ag nanoparticles are served as the hydrogen donor and acceptor, respectively. The optical asymmetry g-factor of the chiral assemblies of plasmonic nanoparticles is strongly dependent on the molecular weight of the polystyrene ligand, the core structure of the molecule, and the aliphatic chain length of the chiral molecule. Importantly, we explore a molecular mixing strategy to enhance the asymmetry g-factor of chiral molecular assemblies, which consequently promotes the g-factor of chiral plasmonics efficiently, reaching a high value of ∼0.05 under optimal conditions. Overall, we rationalize the chirality transfer from chiral molecules to inorganic nanoparticles, providing the guidance for structural design of chiral nanocomposites with a high g-factor.

Chiral Au Nanorods: Synthesis, Chirality Origin, and Applications

Chiral Au nanorods (c-Au NRs) with diverse architectures constitute an interesting nanospecies in the field of chiral nanophotonics. The numerous possible plasmonic behaviors of Au NRs can be coupled with chirality to initiate, tune, and amplify their chiroptical response. Interdisciplinary technologies have boosted the development of fabrication and applications of c-Au NRs. Herein, we have focused on the role of chirality in c-Au NRs which helps to manipulate the light-matter interaction in nontraditional ways. A broad overview on the chirality origin, chirality transfer, chiroptical activities, artificially synthetic methodologies, and circularly polarized applications of c-Au NRs will be summarized and discussed. A deeper understanding of light-matter interaction in c-Au NRs will help to manipulate the chirality at the nanoscale, reveal the natural evolution process taking place, and set up a series of circularly polarized applications.

Soluble porous organic cages as homogenizers and electron-acceptors for homogenization of heterogeneous alloy nanoparticle catalysts with enhanced catalytic activity

The creation of ultrafine alloy nanoparticles (<5 nm) that can maintain surface activity and avoid aggregation for heterogeneous catalysis has received much attention and is extremely challenging. Here, ultrafine PtRh alloy nanoparticles imprisoned by the cavities of reduced chiral covalent imine cage (PtRh@RCC3) are prepared successfully by an organic molecular cage (OMC) confinement strategy, while the soluble RCC3 can act as a homogenizer to homogenize the heterogeneous PtRh alloy in solution. Moreover, the X-ray absorption near-edge structure (XANES) results show that the RCC3 can act as an electron-acceptor to withdraw electrons from Pt, leading to the formation of higher valence Pt atoms, which is beneficial to improving the catalytic activity for the reduction of 4-nitrophenol. Attributed to the synergistic effect of Pt/Rh atoms and the unique function of the RCC3, the reaction rate constants of Pt₁Rh₁₆@RCC3 are 49.6, 8.2, and 5.5 times than those of the Pt₁Rh₁₆ bulk, Pt@RCC3 and Rh@RCC3, respectively. This work provides a feasible strategy to homogenize heterogeneous alloy nanoparticle catalysts in solution, showing huge potential for advanced catalytic application.

Gold-Nanoparticle-Based Chiral Plasmonic Nanostructures and Their Biomedical Applications

As chiral antennas, plasmonic nanoparticles (NPs) can enhance chiral responses of chiral materials by forming hybrid structures and improving their own chirality preference as well. Chirality-dependent properties of plasmonic NPs broaden application potentials of chiral nanostructures in the biomedical field. Herein, we review the wet-chemical synthesis and self-assembly fabrication of gold-NP-based chiral nanostructures. Discrete chiral NPs are mainly obtained via the seed-mediated growth of achiral gold NPs under the guide of chiral molecules during growth. Irradiation with chiral light during growth is demonstrated to be a promising method for chirality control. Chiral assemblies are fabricated via the bottom-up assembly of achiral gold NPs using chiral linkers or guided by chiral templates, which exhibit large chiroplasmonic activities. In describing recent advances, emphasis is placed on the design and synthesis of chiral nanostructures with the tuning and amplification of plasmonic circular dichroism responses. In addition, the review discusses the most recent or even emerging trends in biomedical fields from biosensing and imaging to disease diagnosis and therapy.

DNA-mediated dynamic plasmonic nanostructures: assembly, actuation, optical properties, and biological applications

Recent advances in DNA technology have made it possible to combine with the plasmonics to fabricate reconfigurable dynamic nanodevices with extraordinary property and function. These DNA-mediated plasmonic nanostructures have been investigated for a variety of unique and beneficial physicochemical properties and their dynamic behavior has been controlled by endogenous or exogenous stimuli for a variety of interesting biological applications. In this perspective, the recent efforts to use the DNA nanostructures as molecular linkers for fabricating dynamic plasmonic nanostructures are reviewed. Next, the actuation media for triggering the dynamic behavior of plasmonic nanostructures and the dynamic response in optical features are summarized. Finally, the applications, remaining challenges and perspectives of the DNA-mediated dynamic plasmonic nanostructures are discussed.

Self-Assembled Nanodot Actuator with Changeable Fluorescence by π-π Stacking Force Based on a Four-Armed Foldable Phthalocyanine Molecule and Its Supersensitive Molecular Recognition

Designing intelligent molecules and smart nanomaterials as molecular machines is becoming increasingly important in the nanoscience fields. Herein, we report a nanodot actuator with changeable fluorescence by π-π stacking force based on a four-armed foldable phthalocyanine molecule. The assembled nanodot possessed a three-dimensional molecular space structure and multiple supramolecular interactions. The arms of the nanodot could fold and open intelligently in response to environmental molecular stimuli such as natural plant mimosa, which could lead to multiple variable fluorescence emissions. The nanodot was highly sensitive to the biomolecule thyroxine at the molecular level. The accurate molecular recognition and the changeable fluorescence conversion of the nanodot were attributed to multiple supramolecular interactions, including photoinduced electron transfer (PET), intramolecular fluorescence resonance energy transfer (FRET), and π-π stacking of the nanodots, resulting in an intelligent "nanodot machine with folding arms". The self-assembled nanodot actuators with changeable fluorescence have potential applications in advanced intelligent material fields.

Visible wavelength spectral tuning of absorption and circular dichroism of DNA-assembled Au/Ag core-shell nanorod assemblies

Plasmonic nanoparticles have unique properties which can be harnessed to manipulate light at the nanoscale. With recent advances in synthesis protocols that increase their stability, gold-silver core-shell nanoparticles have become suitable building blocks for plasmonic nanostructures to expand the range of attainable optical properties. Here we tune the plasmonic response of gold-silver core-shell nanorods over the visible spectrum by varying the thickness of the silver shell. Through the chiral arrangement of the nanorods with the help of various DNA origami designs, the spectral tunability of the plasmon resonance frequencies is transferred into circular dichroism signals covering the spectrum from 400 nm to 700 nm. Our approach could aid in the construction of better sensors as well as metamaterials with a tunable optical response in the visible region.

DNAzyme signal amplification based on Au@Ag core-shell nanorods for highly sensitive SERS sensing miRNA-21

Here, we developed a surface-enhanced Raman scattering (SERS) sensor based on functionalized Au@Ag core-shell nanorods (Au@Ag NRs) and cascade DNAzyme amplifier (CSA) for sensitive and accurate determination of microRNA-21 (miRNA-21). The as-prepared SERS nanoprobes were composed of a thiol-modification hairpin probe (HP2)-functionalized Au@Ag NRs and hairpin DNAzyme (HP1-Dz). Compared with original gold nanorods, the silver shell caused an enhancement of plasmonic properties, resulting in a significant enhancement of Raman signals. In the presence of target miRNAs, the hairpin construction of HP1-Dz changed due to DNA/RNA hybridization; subsequently, the DNAzyme-catalyzed cleaving process changed, and the Raman signals of the SERS nanoprobes gradually "turned off" with time elapse because of the dissociation of the Raman reporter from the surface of Au@Ag NRs. Hence, based on this principle, the proposed SERS sensor exhibited good linearity in the range 0.5 fM to 10 nM for miRNA-21 detection with a detection limit (LOD) of 0.5 fM. The proposed SERS platform has potential application in quantitative and precise detection of miRNA-21 in human serum.

Surface-Enhanced Raman Scattering Bioimaging with an Ultrahigh Signal-to-Background Ratio under Ambient Light

Surface-enhanced Raman scattering (SERS) nanoprobes have attracted particular interests in the field of bioimaging owing to their high sensitivity and specificity of the fingerprint spectrum. However, the limited signal-to-background ratio (SBR) in SERS imaging and the requirement to perform imaging in a dark environment have largely hindered its biomedical application. To circumvent this, we have developed a type of bio-orthogonal nanoprobes for SERS imaging with an ultrahigh SBR and ambient light anti-interference ability. The core-shell nanoprobes exhibit strongly enhanced Raman signals and depress the background from photoluminescence of metallic nanoparticles by off-resonance excitation and from the Raman scattering and auto-fluorescence of tissues by near-infrared laser excitation. Such nanoprobes have achieved an SBR of over 100 in SERS bioimaging, 5 times higher than the traditional on-resonant nanoprobes, and their bio-orthogonal signal in the Raman-silent region renders the anti-interference capability under ambient light. The development of these SERS probes opens up a new era for the future applications of Raman imaging in clinical medicine.

Multiple Wavelength Photopolymerization of Stable Poly(Catecholamines)-DNA Origami Nanostructures

The synthesis of multicomponent polymer hybrids with nanometer precision is chemically challenging in the bottom-up synthesis of complex nanostructures. Here, we leverage the fidelity of the DNA origami technique to install a multiple wavelength responsive photopolymerization system with nanometer resolution. By precisely immobilizing various photosensitizers on the origami template, which are only activated at their respective maximum wavelength, we can control sequential polymerization processes. In particular, the triggered photosensitizers generate reactive oxygen species that in turn initiate the polymerization of the catecholamines dopamine and norepinephrine. We imprint polymeric layers at designated positions on DNA origami, which modifies the polyanionic nature of the DNA objects, thus promoting their uptake into living cells while preserving their integrity. Our herein proposed method provides a rapid platform to access complex 3D nanostructures by customizing material and biological interfaces.

Self-assembled inorganic chiral superstructures

Controlled assembly of inorganic nanoparticles with different compositions, sizes and shapes into higher-order structures of collective functionalities is a central pursued objective in chemistry, physics, materials science and nanotechnology. The emerging chiral superstructures, which break spatial symmetries at the nanoscale, have attracted particular attention, owing to their unique chiroptical properties and potential applications in optics, catalysis, biology and so on. Various bottom-up strategies have been developed to build inorganic chiral superstructures based on the intrinsic configurational preference of the building blocks, external fields or chiral templates. Self-assembled inorganic chiral superstructures have demonstrated significant superior optical activity from the strong electric/magnetic coupling between the building blocks, as compared with the organic counterparts. In this Review, we discuss recent progress in preparing self-assembled inorganic chiral superstructures, with an emphasis on the driving forces that enable symmetry breaking during the assembly process. The chiroptical properties and applications are highlighted and a forward-looking trajectory of where research efforts should be focused is discussed.

Hysteresis Nanoarchitectonics with Chiral Gel Fibers and Achiral Gold Nanospheres for Reversible Chiral Inversion

Intelligent control over the handedness of circular dichroism (CD) is of special significance in self-organized biological and artificial systems. Herein, we report a chiral organic molecule (R1) containing a disulfide unit self-assembles into M-type helical fibers gels, which undergoes chirality inversion by incorporating gold nanospheres due to the formation of Au-S bonds between R1 and gold nanospheres. Upon heating at 80oC, the aggregation of gold nanospheres results in a disappearance of the Au-S bond, allowing the reversible switching back to M-type helical fibers. The original chirality of M-type fibers could also be retained by adding anisotropic gold nanorods. A series of characterization methods, involving CD, Raman, Infrared spectroscopy, electric microscopy, and small-angle X-ray scattering (SAXS) measurements were used to investigate the mechanism of chiral evolutions. Our results provide a facile way of fabricating hysteresis nanoarchitectonics to achieve dynamic supramolecular chirality using inorganic metallic nanoparticles.

Plasmonic Circular Dichroism in Chiral Gold Nanowire Dimers

We report a computational study at the time-dependent density functional theory (TDDFT) level of the chiro-optical spectra of chiral gold nanowires coupled in dimers. Our goal is to explore whether it is possible to overcome destructive interference in single nanowires that damp chiral response in these systems and to achieve intense plasmonic circular dichroism (CD) through a coupling between the nanostructures. We predict a huge enhancement of circular dichroism at the plasmon resonance when two chiral nanowires are intimately coupled in an achiral relative arrangement. Such an effect is even more pronounced when two chiral nanowires are coupled in a chiral relative arrangement. Individual component maps of rotator strength, partial contributions according to the magnetic dipole component, and induced densities allow us to fully rationalize these findings, thus opening the way to the field of plasmonic CD and its rational design.

Controlling the polarization of chiral dipolar emission with a spherical dielectric nanoantenna

Circularly polarized light (CPL) carrying spin angular momentum is crucial to many applications, such as quantum computing, optical communication, novel displays, and biosensing. Nonetheless, the emission from chiral molecules contains comparable CPL components with opposite handedness, resulting in low levels of CPL overall with a small dissymmetry factor and fixed handedness consistent with the handedness of the molecules. Nanoantennas have proved to be useful tools for controlling the emission properties of quantum emitters. In particular, dielectric resonators support electric and magnetic modes, which implies unparalleled opportunities to interact with chiral molecules whose emission originates from both electric and magnetic dipole transitions. In this work, we theoretically study the effects of a spherical dielectric nanoantenna on the directionality and polarization of emission from a chiral molecule. With exact analytical solutions based on generalized Mie theory, we show that directional chiral light emission and nontrivial polarization modulation, such as handedness reversal or chirality enhancement, can be achieved simultaneously for a chiral dipole tangentially coupled with a silicon nanosphere. The influence of the relative strength and orientation between the electric and magnetic dipole moments is also discussed. Our results suggest a new approach to controlling chiral dipolar emission and could benefit the development of chiral light sources.

Recent developments in the chiroptical properties of chiral plasmonic gold nanostructures: bioanalytical applications

The presence of excess L-amino acid in the Murchison meteorite, circular polarization effect in the genesis of stars and existence of chirality in interstellar molecules contribute to the origin of life on earth. Chiral-sensitive techniques have been employed to untangle the secret of the symmetries of the universe, designing of effective secure drugs and investigation of chiral biomolecules. The relationship between light and chiral molecules was employed to probe and explore such molecules using spectroscopy techniques. The mutual interaction between electromagnetic spectrum and chirality of matter give rise to distinct optical response, which advances vital information contents in chiroptical spectroscopy. Chiral plasmonic gold nanoparticle exhibits distinctive circular dichroism peaks in broad wavelength range thereby crossing the limits of its characterization. The emergence of strong optical activity of gold nanosystem is related to its high polarizability, resulting in plasmonic and excitonic effects on incident photons. Inspired by the development of advanced chiral plasmonic nanomaterials and exploring its properties, this review gives an overview of various chiral gold nanostructures and the mechanism behind its chiroptical properties. Finally, we highlight the application of different chiral gold nanomaterials in the field of catalysis and medical applications with special emphasis to biosensing and biodetection.

Programmable and Site-Specific Patterning on DNA Origami Templates with Heterogeneous Condensation of Silver and Silica

DNA origami has been widely used as a modular platform for condensation of functional molecules to assemble optical, electronic, and biological components. However, the heterogeneous condensation with greater diversities in chemical composition templated with DNA origami is still challenging. Herein, a programmable deposition method is developed to precisely condense silver-silica nanohybrids on DNA origami templates. First, the site-specific metallization of Ag is achieved by thiol group-initiated silver reduction at the designed areas of DNA origami. Next, cysteamine is used to selectively modify the condensed Ag surface with positively charged amino groups for creating an electronically different environment for site-specific placement of silica by a modified Stöber method. Using these strategies, customized patterning of both silver and silica on tubular and rectangular DNA origami nanostructures is successfully achieved with nanoscale spatial resolution. These findings will greatly facilitate the development of DNA nanotechnology-based bottom-up nanofabrication.

Controlled Assembly of Plasmonic Nanoparticles: From Static to Dynamic Nanostructures

The spatial arrangement of plasmonic nanoparticles can dramatically affect their interaction with electromagnetic waves, which offers an effective approach to systematically control their optical properties and manifest new phenomena. To this end, significant efforts were made to develop methodologies by which the assembly structure of metal nanoparticles can be controlled with high precision. Herein, recent advances in bottom-up chemical strategies toward the well-controlled assembly of plasmonic nanoparticles, including multicomponent and multifunctional systems are reviewed. Further, it is discussed how the progress in this area has paved the way toward the construction of smart dynamic nanostructures capable of on-demand, reversible structural changes that alter their properties in a predictable and reproducible manner. Finally, this review provides insight into the challenges, future directions, and perspectives in the field of controlled plasmonic assemblies.

Chiral Photomelting of DNA-Nanocrystal Assemblies Utilizing Plasmonic Photoheating

Chiral plasmonic nanostructures exhibit anomalously strong chiroptical signals and offer the possibility to realize asymmetric photophysical and photochemical processes controlled by circularly polarized light. Here, we use a chiral DNA-assembled nanorod pair as a model system for chiral plasmonic photomelting. We show that both the enantiomeric excess and consequent circular dichroism can be controlled with chiral light. The nonlinear chiroptical response of our plasmonic system results from the chiral photothermal effect leading to selective melting of the DNA linker strands. Our study describes both the single-complex and collective heating regimes, which should be treated with different models. The chiral asymmetry factors of the calculated photothermal and photomelting effects exceed the values typical for the chiral molecular photochemistry at least 10-fold. Our proposed mechanism can be used to develop chiral photoresponsive systems controllable with circularly polarized light.

Reconfigurable Chirality of DNA-Bridged Nanorod Dimers

Gold nanorods assembled in a side-by-side chiral configuration have potential applications in sensing due to their strong chiroptical surface plasmon resonances. Recent experiments have shown that dimers of gold nanorods bridged by double-stranded DNA exhibit variable chiral configurations depending on the chemical and ionic properties of the solvent medium. Here, we uncover the underlying physics governing this intriguing chiral behavior of such DNA-bridged nanorods by theoretically evaluating their configurational free energy landscape. Our results reveal how chiral configurations emerge from an interplay between the twist-stretch coupling of the intervening DNA and the intermolecular interactions between the nanorods, with dimers exhibiting left-handed chirality when the interparticle interactions are dominated by attractive depletion or van der Waals forces and right-handed chirality when dominated by repulsive electrostatic or steric forces. We demonstrate how changes in the depletant or ion concentration of the solvent medium lead to different classes of configurational responses by the dimers, including chirality-switching behavior, in good agreement with experimental observations. Based on extensive analyses of how material properties like nanorod aspect ratio, DNA length, and graft height modulate the free energy landscape, we propose strategies for tuning the environmentally responsive reconfigurability of the nanorod dimers. Overall, this work should help control the chirality and related optical activity of nanoparticle dimers and higher-order assemblies for various applications.

Circularly Polarized Plasmons in Chiral Gold Nanowires via Quantum-Mechanical Design

Time-dependent density functional theory (TDDFT) simulations are conducted on a series of chiral gold nanowires to explore whether an enhancement of circular dichroism at the plasmon resonance is possible and identify its quantum-mechanical origin. We find that in linear two-dimensional chiral nanowires the dichroic response is suppressed by destructive interference of nearly degenerate components with opposite signs, pointing to this phenomenon as a common and likely origin of the difficulty encountered so far in achieving a plasmonic CD response in experiment and suggesting nevertheless that these opposite components could be "decoupled" by using multiwall arrangements. In contrast, we predict a giant dichroic response for nanowires with three-dimensional helical coiling. We rationalize this finding via an electronic structure analysis of longitudinal and transversal plasmonic excitations and their coupling into chiral components, and we propose a simple formula for the chiral response as a function of structural parameters (nanowire length and coiling number).

Constructing chiral gold nanorod oligomers using a spatially separated sergeants-and-soldiers effect

A sergeants-and-soldiers (S&S) effect is very useful to the fabrication of supramolecular chirality. This strategy has not yet been explored in the construction of chiral plasmonic superstructures. Herein, we demonstrate a spatially separated S&S effect in fabricating plasmonic superstructures and modulating their chiroptical responses. Specifically, chiral cysteine (Cys) molecules, acting as sergeants, are sandwiched between a gold nanorod (AuNR) core and a Au shell via AuNR-templated Au overgrowth. Cationic surfactants, CTAB (cetyltrimethylammonium bromide) or CPC (cetylpyridinium chloride), are modified on the AuNR@Cys@Au shell surface, thus spatially separating from the chiral sergeants. During the assembly process, the surfactants act as soldiers which could transfer and amplify the local chirality induced by the adsorbed chiral molecules from the plasmonic monomers to the oligomers. Huge PCD signals could be achieved in the plasmonic oligomers by finely tuning chiral sergeants and achiral soldiers, indicating the feasibility of the S&S effect in fabricating chiral plasmonic superstructures.

Effect of aspect ratio on the chirality of gold nanorods prepared through conventional seed-mediated growth method

In this work, three kinds of gold nanorods (AuNRs) with different aspect ratios were synthesized through conventional seed-mediated growth method, and the chirality of these AuNRs were characterized by circular dichroism (CD) spectroscopy. The results showed that the AuNRs with bigger aspect ratio had larger chirality. The AuNRs with different aspect ratios were applied to distinguish the enantiomers of 19 kinds of α-amino acids. It was found that AuNRs with bigger aspect ratio exhibited the stronger chiral recognition ability. As a proof-of-principle, the AuNRs with the aspect ratio of 4.8 were used to quantitatively recognize enantiomers of valine. Furthermore, the microcalorimetry was applied to study the interaction of AuNRs with amino acid enantiomers. This work provides one method to improve the chiral recognition ability of AuNRs by optimizing the aspect ratio of AuNRs, and helps people better understand the intrinsic chirality of nanostructures.

DNA Origami-Enabled Plasmonic Sensing

The reliable programmability of DNA origami makes it an extremely attractive tool for bottom-up self-assembly of complex nanostructures. Utilizing this property for the tuned arrangement of plasmonic nanoparticles holds great promise particularly in the field of biosensing. Plasmonic particles are beneficial for sensing in multiple ways, from enhancing fluorescence to enabling a visualization of the nanoscale dynamic actuation via chiral rearrangements. In this Perspective, we discuss the recent developments and possible future directions of DNA origami-enabled plasmonic sensing systems. We start by discussing recent advancements in the area of fluorescence-based plasmonic sensing using DNA origami. We then move on to surface-enhanced Raman spectroscopy sensors followed by chiral sensing, both utilizing DNA origami nanostructures. We conclude by providing our own views on the future prospects for plasmonic biosensors enabled using DNA origami.