Magnetic Plasmon Networks Programmed by Molecular Self-Assembly

Free-Standing DNA Origami Superlattice to Facilitate Cryo-EM Visualization of Membrane Vesicles

Technological breakthroughs in cryo-electron microscopy (cryo-EM) methods open new perspectives for highly detailed structural characterizations of extracellular vesicles (EVs) and synthetic liposome-protein assemblies. Structural characterizations of these vesicles in solution under a nearly native hydrated state are of great importance to decipher cell-to-cell communication and to improve EVs' application as markers in diagnosis and as drug carriers in disease therapy. However, difficulties in preparing holey carbon cryo-EM grids with low vesicle heterogeneities, at low concentration and with kinetic control of the chemical reactions or assembly processes, have limited cryo-EM use in the EV study. We report a straightforward membrane vesicle cryo-EM sample preparation method that assists in circumventing these limitations by using a free-standing DNA-affinity superlattice for covering holey carbon cryo-EM grids. Our approach uses DNA origami to self-assemble to a solution-stable and micrometer-sized ordered molecular template in which structure and functional properties can be rationally controlled. We engineered the template with cholesterol-binding sites to specifically trap membrane vesicles. The advantages of this DNA-cholesterol-affinity lattice (DCAL) include (1) local enrichment of artificial and biological vesicles at low concentration and (2) isolation of heterogeneous cell-derived membrane vesicles (exosomes) from a prepurified pellet of cell culture conditioned medium on the grid.

Magnetic-Plasmonic Nanocomposites as Versatile Substrates for Surface-enhanced Raman Scattering (SERS) Spectroscopy

Surface-enhanced Raman scattering (SERS) spectroscopy, a highly sensitive technique for detecting trace-level analytes, relies on plasmonic substrates. The choice of substrate, its morphology, and the excitation wavelength are crucial in SERS applications. To address advanced SERS requirements, the design and use of efficient nanocomposite substrates have become increasingly important. Notably, magnetic-plasmonic (MP) nanocomposites, which combine magnetic and plasmonic properties within a single particle system, stand out as promising nanoarchitectures with versatile applications in nanomedicine and SERS spectroscopy. In this review, we present an overview of MP nanocomposite fabrication methods, explore surface functionalization strategies, and evaluate their use in SERS. Our focus is on how different nanocomposite designs, magnetic and plasmonic properties, and surface modifications can significantly influence their SERS-related characteristics, thereby affecting their performance in specific applications such as separation, environmental monitoring, and biological applications. Reviewing recent studies highlights the multifaceted nature of these materials, which have great potential to transform SERS applications across a range of fields, from medical diagnostics to environmental monitoring. Finally, we discuss the prospects of MP nanocomposites, anticipating favorable developments that will make substantial contributions to various scientific and technological areas.

Colloidal Self-Assembly of Silver Nanoparticle Clusters for Optical Metasurfaces

Optical metasurfaces are two-dimensional assemblies of nanoscale optical resonators and could constitute the next generation of ultrathin optical components. The development of methods to manufacture these nanostructures on a large scale is still a challenge, while most performance demonstrations were obtained with lithographically fabricated metasurfaces that are restricted to small scales. Self-assembly fabrication routes are promising alternatives and have been used to produce original nanoresonators. Reports of self-assembled metasurface fabrication, however, are still scarce. Here, we show that an emulsion-based formulation approach can be used both for the fabrication of complex colloidal resonators, presenting a strong interaction with light, in particular due to simultaneous magnetic and electric modes of resonance, and for their deposition in homogeneous films. This fabrication technique involves emulsification of an aqueous suspension of silver nanoparticles in an oil phase, followed by controlled drying of the emulsion, and produces silver colloidal clusters. We show that the drying process can be controlled in a liquid emulsion, producing a metafluid, as well as in a sedimented emulsion, producing a metasurface. The structural control of the synthesized colloidal clusters is demonstrated with electron microscopy and X-ray scattering techniques. Using a polarization-resolved multiangle light scattering setup in the visible wavelength range, we conduct a comprehensive angular and spectroscopic study of the optical resonant scattering of the nanoresonators in a metafluid and show that they present strong optical magnetic resonances and directional forward-scattering patterns, with scattering efficiencies of up to 4. The metasurfaces consist of homogeneous films, of variable surface density, of colloidal clusters that have the same extinction properties on the surface and in the fluid. This experimental approach allows for large-scale production of metasurfaces.

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.

Site-directed placement of three-dimensional DNA origami

The combination of lithographic methods with two-dimensional DNA origami self-assembly has led, among others, to the development of photonic crystal cavity arrays and the exploration of sensing nanoarrays where molecular devices are patterned on the sub-micrometre scale. Here we extend this concept to the third dimension by mounting three-dimensional DNA origami onto nanopatterned substrates, followed by silicification to provide hybrid DNA-silica structures exhibiting mechanical and chemical stability and achieving feature sizes in the sub-10-nm regime. Our versatile and scalable method relying on self-assembly at ambient temperatures offers the potential to three-dimensionally position any inorganic and organic components compatible with DNA origami nanoarchitecture, demonstrated here with gold nanoparticles. This way of nanotexturing could provide a route for the low-cost production of complex and three-dimensionally patterned surfaces and integrated devices designed on the molecular level and reaching macroscopic dimensions.

2D Plasmonic Molecules via Hydrogen Bond Interaction between Polymer-Grafted Nanoparticles

The use of macromolecular design features to regulate non-covalent bonding on the nanoscale is a young and emerging fabrication strategy for advanced nanostructures. For the first time, we describe a self-assembly method to create a series of 2D plasmonic molecules (PMs) using hydrogen-bond interaction between a pair of polymer-capped gold nanoparticles (hydrogen-bond donor and acceptor). Due to the nature of hydrogen-bond interaction, we found that polymer interaction and solvation compete with each other during the self-assembly process, which turns out to be the most important condition for controlling the coordination number of PMs. We have conducted an extensive study on the solvent effect, which has helped us to design and fabricate a series of precise PMs with high symmetry.

DNA-Based Gold Nanoparticle Assemblies: From Structure Constructions to Sensing Applications

Gold nanoparticles (Au NPs) have become one of the building blocks for superior assembly and device fabrication due to the intrinsic, tunable physical properties of nanoparticles. With the development of DNA nanotechnology, gold nanoparticles are organized in a highly precise and controllable way under the mediation of DNA, achieving programmability and specificity unmatched by other ligands. The successful construction of abundant gold nanoparticle assembly structures has also given rise to the fabrication of a wide range of sensors, which has greatly contributed to the development of the sensing field. In this review, we focus on the progress in the DNA-mediated assembly of Au NPs and their application in sensing in the past five years. Firstly, we highlight the strategies used for the orderly organization of Au NPs with DNA. Then, we describe the DNA-based assembly of Au NPs for sensing applications and representative research therein. Finally, we summarize the advantages of DNA nanotechnology in assembling complex Au NPs and outline the challenges and limitations in constructing complex gold nanoparticle assembly structures with tailored functionalities.

Chemical and Physical Properties of Photonic Noble-Metal Nanomaterials

Colloidal noble metal nanoparticles (NPs) are composed of metal cores and organic or inorganic ligand shells. These NPs support size- and shape-dependent plasmonic resonances. They can be assembled from dispersions into artificial metamolecules which have collective plasmonic resonances originating from coupled bright and dark optical electric and magnetic modes that form depending on the size and shape of the constituent NPs and their number, arrangement, and interparticle distance. NPs can also be assembled into extended 2D and 3D metamaterials that are glassy thin films or ordered thin films or crystals, also known as superlattices and supercrystals. The metamaterials have tunable optical properties that depend on the size, shape, and composition of the NPs, and on the number of NP layers and their interparticle distance. Interestingly, strong light-matter interactions in superlattices form plasmon polaritons. Tunable interparticle distances allow designer materials with dielectric functions tailorable from that characteristic of an insulator to that of a metal, and serve as strong optical absorbers or scatterers, respectively. In combination with lithography techniques, these extended assemblies can be patterned to create subwavelength NP superstructures and form large-area 2D and 3D metamaterials that manipulate the amplitude, phase, and polarization of transmitted or reflected light.

Open and Close-Packed, Shape-Engineered Polygonal Nanoparticle Metamolecules with Tailorable Fano Resonances

A top-down lithographic patterning and deposition process is reported for producing nanoparticles (NPs) with well-defined sizes, shapes, and compositions that are often not accessible by wet-chemical synthetic methods. These NPs are ligated and harvested from the substrate surface to prepare colloidal NP dispersions. Using a template-assisted assembly technique, fabricated NPs are driven by capillary forces to assemble into size- and shape-engineered templates and organize into open or close-packed multi-NP structures or NP metamolecules. The sizes and shapes of the NPs and of the templates control the NP number, coordination, interparticle gap size, disorder, and location of defects such as voids in the NP metamolecules. The plasmonic resonances of polygonal-shaped Au NPs are exploited to correlate the structure and optical properties of assembled NP metamolecules. Comparing open and close-packed architectures highlights that introduction of a center NP to form close-packed assemblies supports collective interactions, altering magnetic optical modes and multipolar interactions in Fano resonances. Decreasing the distance between NPs strengthens the plasmonic coupling, and the structural symmetries of the NP metamolecules determine the orientation-dependent scattering response.

Programming the morphology of DNA origami crystals by magnesium ion strength

Harnessing the programmable nature of DNA origami for controlling structural features in crystalline materials affords opportunities to bring crystal engineering to a remarkable level. However, the challenge of crystallizing a single type of DNA origami unit into varied structural outcomes remains, given the requirement for specific DNA designs for each targeted structure. Here, we show that crystals with distinct equilibrium phases and shapes can be realized using a single DNA origami morphology with an allosteric factor to modulate the binding coordination. As a result, origami crystals undergo phase transitions from a simple cubic lattice to a simple hexagonal (SH) lattice and eventually to a face-centered cubic (FCC) lattice. After selectively removing internal nanoparticles from DNA origami building blocks, the body-centered tetragonal and chalcopyrite lattice are derived from the SH and FCC lattices, respectively, revealing another phase transition involving crystal system conversions. The rich phase space was realized through the de novo synthesis of crystals under varying solution environments, followed by the individual characterizations of the resulting products. Such phase transitions can lead to associated transitions in the shape of the resulting products. Hexagonal prism crystals, crystals characterized by triangular facets, and twinned crystals are observed to form from SH and FCC systems, which have not previously been experimentally realized by DNA origami crystallization. These findings open a promising pathway toward accessing a rich phase space with a single type of building block and wielding other instructions as tools to develop crystalline materials with tunable properties.

Recent Advances in DNA Origami-Engineered Nanomaterials and Applications

DNA nanotechnology is a unique field, where physics, chemistry, biology, mathematics, engineering, and materials science can elegantly converge. Since the original proposal of Nadrian Seeman, significant advances have been achieved in the past four decades. During this glory time, the DNA origami technique developed by Paul Rothemund further pushed the field forward with a vigorous momentum, fostering a plethora of concepts, models, methodologies, and applications that were not thought of before. This review focuses on the recent progress in DNA origami-engineered nanomaterials in the past five years, outlining the exciting achievements as well as the unexplored research avenues. We believe that the spirit and assets that Seeman left for scientists will continue to bring interdisciplinary innovations and useful applications to this field in the next decade.

Ultralow-Loss Substrate for Nanophotonic Dark-Field Microscopy

For the colloidal nanophotonic structures, a transmission electron microscope (TEM) grid has been widely used as a substrate of dark-field microscopy because a nanometer-scale feature can be effectively determined by TEM imaging following dark-field microscopic studies. However, an optically lossy carbon layer has been implemented in conventional TEM grids. A broadband scattering from the edges of the TEM grid further restricted an accessible signal-to-noise ratio. Herein, we demonstrate that the freely suspended, ultrathin, and wide-scale transparent nanomembrane can address such challenges. We developed a 1 mm by 600 μm scale and 20 nm thick poly(vinyl formal) nanomembrane, whose area is around 180 times wider than a conventional TEM grid, so that the possible broadband scattering at the edges of the grid was effectively excluded. Also, such nanomembranes can be formed without the assistance of carbon support; allowing us to achieve the highest signal-to-background ratio of scattering among other substrates.

Plasmonic Cyclic Au Nanosphere Hexamers

Rational design of plasmonic colloidal assemblies via bottom-up synthesis is challenging but would show unprecedented optical properties that strongly relate to the assembly's shape and spatial arrangement. Herein, the synthesis of plasmonic cyclic Au nanosphere hexamers (PCHs) is reported, wherein six Au nanospheres (Au NSs) are connected via thin metal ligaments. By tuning Au reduction, six dangling Au NSs are interconnected with a core hexagon nanoplate (NPL). Then, Pt atoms are selectively deposited on the edges of the spheres. After etching of the core, necklace-like nanostructures of Pt framework are obtained. Deposition of Au is followed, leading to PCHs in high yield (≈90%). Notably, PCHs exhibit the combinatorial plasmonic characteristics of individual Au NSs and the in-plane coupling of the six linked Au NSs. They yield highly uniform, reproducible, and polarization-independent single-particle surface-enhanced Raman scattering signals, which are attributed to the 2-dimensional isotropic alignment of the Au NSs. Those are applied to a SERS-based immunoassay as quantitative and qualitative single particle SERS nanoprobes. This assay shows a low limit-of-detection, down to 100 pm, which is orders of magnitude lower than those based on Au NSs, and one order of magnitude lower than an assay using analogous particles of smooth Au nanorings.

DNA Tetrahedron Framework Guided Conjugation and Assembly of Gold Nanoparticles

Au nanoparticles (AuNPs) have been extensively used to assemble programmable structures that feature various functions. One central challenge of precisely directed assembly is to make valence-programmable building blocks. Herein, we use the DNA tetrahedron framework to stoichiometrically conjugate to Au nanoparticles, which results in monovalent building blocks at nanometer scale. We further fabricated high-order Au-tetrahedron structures to verify the ability of the blocks for building assemblies. These structures represent an exploration of an avenue to monovalent AuNPs, and provide the feasibility of precisely manipulating nanoparticles into prescribed assemblies.

Gold nanoparticle ring arrays from core-satellite nanostructures made to order by hydrogen bond interactions

Polyethylene glycol-grafted gold nanoparticles are attached to silica nanoparticle cores via hydrogen bonding in a controlled fashion, forming well-defined core-satellite structures in colloidal solution. For separating these complex structures effectively from the parental nanoparticles, a straightforward and easy protocol using glass beads has been developed. The attached gold nanoparticles show unique surface mobility on the silica core surface, which allows for nanoparticle rearrangement into a 2D ring pattern surrounding the silica nanoparticle template when the core-satellite structures are cast to a planar surface. When etching away the silica core under conditions in which the polymer shell fixes the satellites to the substrate, highly ordered ring-shaped patterns of gold nanoparticles are formed. By variation of the size of the parental particles - 13 to 28 nm for gold nanoparticles and 39 to 62 nm for silica nanoparticles - a great library of different ring-structures regarding size and particle number is accessible with relative ease. The proposed protocol is low-cost and can easily be scaled up. It moreover demonstrates the power of hydrogen bonds in polymers as a dynamic anchoring tool for creating nanoclusters with rearrangement ability. We believe that this concept constitutes a powerful strategy for the development of new and innovative nanostructures.

Patch formation on diblock copolymer micelles confined in templates for inducing patch orientation and cyclic colloidal molecules

HYPOTHESIS

Chemically or physically distinct patches can be induced on the micelles of amphiphilic block copolymers, which facilitate directional binding for the creation of hierarchical structures. Hence, control over the direction of patches on the micelles is a crucial factor to attain the directionality on the interactions between the micelles, particularly for generating colloidal molecules mimicking the symmetry of molecular structures. We hypothesized that direction and combination of the patches could be controlled by physical confinement of the micelles.

EXPERIMENTS

We first confined spherical micelles of diblock copolymers in topographic templates fabricated from nanopatterns of block copolymers by adjusting the coating conditions. Then, patch formation was conducted on the confined micelles by exposing them with a core-favorable solvent. Microscopic techniques of SEM, TEM, and AFM were employed to investigate directions of patches and structures of combined micelles in the template.

FINDINGS

The orientation of the patches on the micelles was guided by the physical confinement of the micelles in linear trenches. In addition, by confining the micelles in a circular hole, we obtained a specific polygon arrangement of the micelles depending on the number of micelles in the hole, which enabled the formation of cyclic colloidal molecules consisting of micelles.

Gold-Nanoparticle-Mediated Assembly of High-Order DNA Nano-Architectures

Constructing high-order DNA nano-architectures in large sizes is of critical significance for the application of DNA nanotechnology. Robust and flexible design strategies together with easy protocols to construct high-order large-size DNA nano-architectures remain highly desirable. In this work, the authors report a simple and versatile one-pot strategy to fabricate DNA architectures with the assistance of spherical gold nanoparticles modified with thiolated oligonucleotide strands (SH-DNA-AuNPs), which serve as "power strips" to connect various DNA nanostructures carrying complementary ssDNA strands as "plugs". By modulating the plug numbers and positions on each DNA nanostructure and the ratios between DNA nanostructures and AuNPs, the desired architectures are formed via the stochastic co-assembly of different modules. This SH-DNA-AuNP-mediated plug-in assembly (SAMPA) strategy offers new opportunities to drive macroscopic self-assembly to meet the demand of the fabrication of well-defined nanomaterials and nanodevices.

Suppressing high-dimensional crystallographic defects for ultra-scaled DNA arrays

While DNA-directed nano-fabrication enables the high-resolution patterning for conventional electronic materials and devices, the intrinsic self-assembly defects of DNA structures present challenges for further scaling into sub-1 nm technology nodes. The high-dimensional crystallographic defects, including line dislocations and grain boundaries, typically lead to the pattern defects of the DNA lattices. Using periodic line arrays as model systems, we discover that the sequence periodicity mainly determines the formation of line defects, and the defect rate reaches 74% at 8.2-nm line pitch. To suppress high-dimensional defects rate, we develop an effective approach by assigning the orthogonal sequence sets into neighboring unit cells, reducing line defect rate by two orders of magnitude at 7.5-nm line pitch. We further demonstrate densely aligned metal nano-line arrays by depositing metal layers onto the assembled DNA templates. The ultra-scaled critical pitches in the defect-free DNA arrays may further promote the dimension-dependent properties of DNA-templated materials.

1D Colloidal chains: recent progress from formation to emergent properties and applications

Integrating nanoscale building blocks of low dimensionality (0D; i.e., spheres) into higher dimensional structures endows them and their corresponding materials with emergent properties non-existent or only weakly existent in the individual building blocks. Constructing 1D chains, 2D arrays and 3D superlattices using nanoparticles and colloids therefore continues to be one of the grand goals in colloid and nanomaterial science. Amongst these higher order structures, 1D colloidal chains are of particular interest, as they possess unique anisotropic properties. In recent years, the most relevant advances in 1D colloidal chain research have been made in novel synthetic methodologies and applications. In this review, we first address a comprehensive description of the research progress concerning various synthetic strategies developed to construct 1D colloidal chains. Following this, we highlight the amplified and emergent properties of the resulting materials, originating from the assembly of the individual building blocks and their collective behavior, and discuss relevant applications in advanced materials. In the discussion of synthetic strategies, properties, and applications, particular attention will be paid to overarching concepts, fresh trends, and potential areas of future research. We believe that this comprehensive review will be a driver to guide the interdisciplinary field of 1D colloidal chains, where nanomaterial synthesis, self-assembly, physical property studies, and material applications meet, to a higher level, and open up new research opportunities at the interface of classical disciplines.

Recent Progress of Magnetically Actuated DNA Micro/Nanorobots

In the past few decades, the field of DNA origami-based micro/nanotechnology has developed dramatically and spawned attention increasingly, as its high integrality, rigid structure, and excellent resistance ability to enzyme digestion. Many two-dimensional and three-dimensional DNA nanostructures coordinated with optical, chemical, or magnetic triggers have been designed and assembled, extensively used as versatile templates for molecular robots, nanosensors, and intracellular drug delivery. The magnetic field has been widely regarded as an ideal driving and operating system for micro/nanomaterials, as it does not require high-intensity lasers like light control, nor does it need to change the chemical composition similar to chemical activation. Herein, we review the recent achievements in the induction and actuation of DNA origami-based nanodevices that respond to magnetic fields. These magnetic actuation-based DNA nanodevices were regularly combined with magnetic beads or gold nanoparticles and applied to generate single-stranded scaffolds, assemble various DNA nanostructures, and purify specific DNA nanostructures. Moreover, they also produced artificial magnetism or moved regularly driven by external magnetic fields to explain deeper scientific issues.

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.

Strong Light-Matter Interactions in Chiral Plasmonic-Excitonic Systems Assembled on DNA Origami

The exploitation of strong light-matter interactions in chiral plasmonic nanocavities may enable exceptional physical phenomena and lead to potential applications in nanophotonics, information communication, etc. Therefore, a deep understanding of strong light-matter interactions in chiral plasmonic-excitonic (plexcitonic) systems constructed by a chiral plasmonic nanocavity and molecular excitons is urgently needed. Herein, we systematically studied the strong light-matter interactions in gold nanorod-based chiral plexcitonic systems assembled on DNA origami. Rabi splitting and anticrossing behavior were observed in circular dichroism spectra, manifesting chiroptical characteristic hybridization. The bisignate line shape of the circular dichroism (CD) signal allows the accurate discrimination of hybrid modes. A large Rabi splitting of ∼205/∼199 meV for left-handed/right-handed plexcitonic nanosystems meets the criterion of strong coupling. Our work deepens the understanding of light-matter interactions in chiral plexcitonic nanosystems and will facilitate the development of chiral quantum optics and chiroptical devices.

DNA Origami Guided Self-Assembly of Plasmonic Polymers with Robust Long-Range Plasmonic Resonance

Plasmonic polymers consisting of metallic nanoparticles (NPs) are able to squeeze light into the deep-subwavelength space and transfer along a highly confined nanoscale path in long range. DNA nanotechnology, particularly benefiting from the molecular programmability of DNA origami, has provided otherwise nearly impossible platforms for constructing plasmonic nanoparticle polymers with designer configurations and nanoscale gaps. Here, we design and assemble a DNA origami hashtag tile that is able to polymerize into one-dimensional chains with high rigidity. The DNA origami hashtag chains are used as frames to enable robust, versatile, and precise arrangement of metallic NPs into micrometer-long chiral and magnetic plasmonic polymers, which are capable of efficiently transporting plasmonic angular momentum and magnetic surface plasmonic polaritons at the deep-subwavelength scale. Our work provides a molecular platform for the fabrication of long, straight, and structurally complex nanoparticle polymers with emerging plasmonic properties that are appealing to a variety of fields.

Exploiting Colloidal Metamaterials for Achieving Unnatural Optical Refractions

The scaling down of meta-atoms or metamolecules (collectively denoted as metaunits) is a long-lasting issue from the time when the concept of metamaterials was first suggested. According to the effective medium theory, which is the foundational concept of metamaterials, the structural sizes of meta-units should be much smaller than the working wavelengths (e.g., << 1/5 wavelength). At relatively low frequency regimes (e.g., microwave and terahertz), the conventional monolithic lithography can readily address the materialization of metamaterials. However, it is still challenging to fabricate optical metamaterials (metamaterials working at optical frequencies such as the visible and near-infrared regimes) through the lithographic approaches. This serves as the rationale for using colloidal self-assembly as a strategy for the realization of optical metamaterials. Colloidal self-assembly can address various critical issues associated with the materialization of optical metamaterials, such as achieving nanogaps over a large area, increasing true 3D structural complexities, and cost-effective processing, which all are difficult to attain through monolithic lithography. Nevertheless, colloidal self-assembly is still a toolset underutilized by optical engineers. Here, the design principle of the colloidally self-assembled optical metamaterials exhibiting unnatural refractions, the practical challenge of relevant experiments, and the future opportunities are critically reviewed.

DNA-assembled superconducting 3D nanoscale architectures

Studies of nanoscale superconducting structures have revealed various physical phenomena and led to the development of a wide range of applications. Most of these studies concentrated on one- and two-dimensional structures due to the lack of approaches for creation of fully engineered three-dimensional (3D) nanostructures. Here, we present a 'bottom-up' method to create 3D superconducting nanostructures with prescribed multiscale organization using DNA-based self-assembly methods. We assemble 3D DNA superlattices from octahedral DNA frames with incorporated nanoparticles, through connecting frames at their vertices, which result in cubic superlattices with a 48 nm unit cell. The superconductive superlattice is formed by converting a DNA superlattice first into highly-structured 3D silica scaffold, to turn it from a soft and liquid-environment dependent macromolecular construction into a solid structure, following by its coating with superconducting niobium (Nb). Through low-temperature electrical characterization we demonstrate that this process creates 3D arrays of Josephson junctions. This approach may be utilized in development of a variety of applications such as 3D Superconducting Quantum interference Devices (SQUIDs) for measurement of the magnetic field vector, highly sensitive Superconducting Quantum Interference Filters (SQIFs), and parametric amplifiers for quantum information systems.

Programmable assembly of gold nanoparticle nanoclusters and lattices

Deterministic assembly of metallic nanoparticles (e.g. gold nanoparticles) into prescribed configurations has promising applications in many fields such as biosensing and drug delivery. DNA-directed bottom-up assembly has demonstrated unparalleled capability to precisely organize metallic nanoparticles into assemblies of designer configurations. However, the fabrication of assemblies comprising delicate nanoparticle arrangements, especially across large dimensions (e.g. micron size), has remained challenging. In this report, we have designed DNA origami hexagon tiles that are capable of assembling into higher-order networks of honeycomb arrays or tubes with dimensions up to several microns. The versatile addressability of the unit tile enables precise and periodic positioning of nanoparticles onto these higher-order DNA origami frame structures. Overall, we have constructed a series of 9 gold nanoparticle architectures with programmable configurations ranging from nanometer-sized clusters to micrometer-sized lattices. We believe these architectures shall hold great application potential in numerous biomedical fields.

Characterisation and Manipulation of Polarisation Response in Plasmonic and Magneto-Plasmonic Nanostructures and Metamaterials

Optical properties of metal nanostructures, governed by the so-called localised surface plasmon resonance (LSPR) effects, have invoked intensive investigations in recent times owing to their fundamental nature and potential applications. LSPR scattering from metal nanostructures is expected to show the symmetry of the oscillation mode and the particle shape. Therefore, information on the polarisation properties of the LSPR scattering is crucial for identifying different oscillation modes within one particle and to distinguish differently shaped particles within one sample. On the contrary, the polarisation state of light itself can be arbitrarily manipulated by the inverse designed sample, known as metamaterials. Apart from polarisation state, external stimulus, e.g., magnetic field also controls the LSPR scattering from plasmonic nanostructures, giving rise to a new field of magneto-plasmonics. In this review, we pay special attention to polarisation and its effect in three contrasting aspects. First, tailoring between LSPR scattering and symmetry of plasmonic nanostructures, secondly, manipulating polarisation state through metamaterials and lastly, polarisation modulation in magneto-plasmonics. Finally, we will review recent progress in applications of plasmonic and magneto-plasmonic nanostructures and metamaterials in various fields.

Soft optical metamaterials

Optical metamaterials consist of artificially engineered structures exhibiting unprecedented optical properties beyond natural materials. Optical metamaterials offer many novel functionalities, such as super-resolution imaging, negative refraction and invisibility cloaking. However, most optical metamaterials are comprised of rigid materials that lack tunability and flexibility, which hinder their practical applications. This limitation can be overcome by integrating soft matters within the metamaterials or designing responsive metamaterial structures. In addition, soft metamaterials can be reconfigured via optical, electrical, thermal and mechanical stimuli, thus enabling new optical properties and functionalities. This paper reviews different types of soft and reconfigurable optical metamaterials and their fabrication methods, highlighting their exotic properties. Future directions to employ soft optical metamaterials in next-generation metamaterial devices are identified.

Programming Surface-Enhanced Raman Scattering of DNA Origami-templated Metamolecules

DNA origami holds an unprecedented capability on assembling metallic nanoparticles into designer plasmonic metamolecules of emerging properties, including surface-enhanced Raman scattering (SERS). SERS metamolecules were produced by positioning nanoparticles in close proximity to each other on a DNA origami template for Raman enhancement. In earlier reports, SERS metamolecules were generally assembled into clusters containing small number of nanoparticles (2, 3, or 4) and thus had limited programmability over SERS. Herein, we expanded the structural complexity of SERS metamolecules by increasing the number of nanoparticles and by arranging them into sophisticated configurations. DNA origami hexagon tile was used as the assembling template to fabricate clusters consisting of 6, 7, 12, 18, and 30+ metallic nanoparticles. Programmable SERS was realized via controlling the size, number, or spatial arrangement of nanoparticles. We believe this method offers a general platform for fabricating sophisticated nanodevices with programmable SERS that may be applied to a variety of fields including plasmonics, nanophotonics, and sensing.

Bioinspired Toolkit Based on Intermolecular Encoder toward Evolutionary 4D Chiral Plasmonic Materials

Over the last two decades, nanophotonics, including plasmonics and metamaterials, have promised compelling opportunities for exotic control over light-matter interactions. The strong chiral light-matter interaction is a representative example. Three-dimensional (3D) chirality has existed naturally only in organic molecules and bio-organisms, but a negligible chiroptic effect was attained with these naturally occurring materials because of their small absorption cross sections. However, inspired by biological chirality, nanophotonic chiral materials have greatly expanded the design space of accessible chiroptic effects (e.g., pushing the chiral light-matter interaction to an exceptional regime, such as a broad-band circular polarizer, negative refractive index, and sensitive chiral sensing). Nevertheless, it is still a challenge to achieve precisely defined and dynamically reconfigurable chiral morphologies that further increase the chiroptic effect. Biological systems continue to inspire approaches to the design and synthesis of precisely defined 3D nanostructures. In particular, a living organism can program the evolutionary pathway of highly complexed 3D chiral morphology precisely from the molecular scale to the macroscopic scale while simultaneously enabling dynamic reconfiguration of their chirality. What if we could harness the power of biological selectivity and evolutionary capability in synthesizing chiral plasmonic materials? We envisioned that platform technology mimicking biological principles would enable control of 3D chiral structures for effective plasmonic interactions with polarized light and further impart the concept of time-dependent evolution (3D + 1D = 4D) to bring about responsive and dynamic changes in chiral plasmonics. In this Account, we review our efforts to develop the biomolecule-based synthesis of 3D chiral plasmonic materials and share the vision that as in biological systems, chirality can be programmed at the molecular level and hierarchically transferred at multiple scales to develop macroscopic chirality. Accompanied by a biomimetic time-dependent chirality of singular plasmonic nanometals, we also summarize recent achievements in the chemistry and nanophotonics communities pursuing 4D plasmonics that are closely related to our research. The biomimetic and bioinspired approaches discussed in this Account will provide new synthetic insights into implementing chiral nanomaterials and extend the range of accessible nanophotonic design. We hope that the molecular encoding approach will be useful to achieve dynamic light-matter interactions at unprecedented dimensions, time scales, and chirality.