Nanoparticle Superstructures Research Articles

A non-classical synthetic strategy for organic mesocrystals.

Mesocrystals are ordered nanoparticle superstructures, often with internal porosity, which receive much recent research interest in catalysis, energy storage, sensors, and biomedicine area. Understanding the mechanism of synthetic routes is essential for precise control of size and structure that affect the function of mesocrystals. The classical synthetic strategy of mesocrystal was formed via self-assembly of nanoparticles with a faceted inorganic core but a denser (or thicker) shell of organic molecules. However, the potential materials and synthetic handles still need to be explored to meet new applications. In this work, we develop a non-classical synthetic strategy for organic molecules, such as tetrakis (4-hydroxyphenyl) ethylene (TPE-4OH), tetrakis (4-bromophenyl) ethylene (TPE-4Br), and benzopinacole, to produce mesocrystals with composed of microrod arrays via co-solvent-induced crystal transformation. The aligned nanorods are grown epitaxially onto organic microplates, directed by small lattice mismatch between plates and rods. Thus, the present work offers general synthetic handle for establishing well-organized organic mesocrystals.

Enzyme-Programmed Self-Assembly of Nanoparticles.

Nanoparticles are a hot topic in the field of nanomaterial research due to their excellent physical and chemical properties. In recent years, DNA-directed nanoparticle self-assembly technology has been widely applied to the development of numerous complex nanoparticle superstructures. Due to the inherent stability and surface electric repulsion of nanoparticles, it is difficult to make nanoparticle superstructures respond to molecular signals in the external environment. In fact, enzyme-programmed molecular systems are developed to allow diverse functions, including logical operations, signal amplification, and dynamic assembly control. Therefore, combining enzyme-controlled DNA systems may endow nanoparticle assembly systems with more flexibility in program design, allowing them to respond to a variety of external signals. In this review, we summarize the basic principles of enzyme-controlled DNA/nanoparticle self-assembly and introduce its applications in heavy metal detection, gene expression, proteins inside living cells, cancer cell therapy, and drug delivery. With the continuous development of new nanoparticle materials and the increasing functionality of enzyme DNA circuits, enzyme-directed DNA/nanoparticle self-assembled probe technology is expected to see significant future development.

Supercrystal Engineering of Nanoarrows Enabled by Tailored Concavity.

Self-assembly of nanoparticles into supercrystals represents a powerful approach to create unique and complex superstructures with fascinating properties and novel functions, but the complexity in spatial configuration, and the tunability in lattice structure are still quite limited compared to the crystals formed by atoms and molecules. Herein, shallowly concave gold nanoarrows with a unique concave-convex geometry are synthesized and employed as novel building blocks for shape-directed self-assembly of a wealth of complex 3D supercrystals with unprecedented configurations. The obtained diverse superstructures including six Interlocking-type supercrystals and three Packing-type supercrystals exhibit four types of Bravais lattices (i.e., tP, oI, tI, and oF) and six types of crystallographic space groups (i.e., Pmmm, I222, Pnnm, Ibam, I4/mmm, and Fmmm), which have not been documented in the mesoscale self-assembled systems. It has been revealed that the relative yield of different supercrystal structures is mainly determined by the packing density and deformability of the supercrystals, which are closely related to the tailored concavity of the nanoparticles and is affected by the particle concentration, thus allowing for programmable self-assembly into specific supercrystals through particle shape modulation. The concavity-enabled supercrystal engineering may open a new avenue toward unconventional nanoparticle superstructures with expanded complexity, tunability, and functionality.

Three-Dimensionally Nanometallic Superstructure Synthesized via a Single-Particle Soft-Enveloping Strategy.

Three-dimensionally (3D) integrated metallic nanomaterials composed of two or more different types of nanostructures make up a class of advanced materials due to the multidimensional and synergistic effects between different components. However, designing and synthesizing intricate, well-defined metallic 3D nanomaterials remain great challenges. Here, a novel single-particle soft-enveloping strategy using a core-shell Au NP@mSiO2 particle as a template was proposed to synthesize 3D nanomaterials, namely, a Au nanoparticle@center-radial nanorod-Au-Pt nanoparticle (Au NP@NR-NP-Pt NP) superstructure. Taking advantage of the excellent plasmonic properties of Au NP@NR-NP by the synergistic plasmonic coupling of the outer Au NPs and inner Au nanorods, we can enhance the catalytic performance for 4-nitrophenol hydrogenation using Au NP@NR-NP-Pt NP as a photocatalyst with plasmon-excited hot electrons from Au NP@NR-NP under light irradiation, which is 2.76 times higher than in the dark. This process opens a door for the design of a new generation of 3D metallic nanomaterials for different fields.

Free-Standing Hierarchically Porous Silica Nanoparticle Superstructures: Bridging the Nano- to Microscale for Tailorable Delivery of Small and Large Therapeutics.

Nanoscale colloidal self-assembly is an exciting approach to yield superstructures with properties distinct from those of individual nanoparticles. However, the bottom-up self-assembly of 3D nanoparticle superstructures typically requires extensive chemical functionalization, harsh conditions, and a long preparation time, which are undesirable for biomedical applications. Here, we report the directional freezing of porous silica nanoparticles (PSiNPs) as a simple and versatile technique to create anisotropic 3D superstructures with hierarchical porosity afforded by microporous PSiNPs and newly generated meso- and macropores between the PSiNPs. By varying the PSiNP building block size, the interparticle pore sizes can be readily tuned. The newly created hierarchical pores greatly augment the loading of a small molecule-anticancer drug, doxorubicin (Dox), and a large macromolecule, lysozyme (Lyz). Importantly, Dox loading into both the micro- and meso/macropores of the nanoparticle assemblies not only gave a pore size-dependent drug release but also significantly extended the drug release to 25 days compared to a much shorter 7 or 11 day drug release from Dox loaded into either the micro- or meso/macropores only. Moreover, a unique temporal drug release profile, with a higher and faster release of Lyz from the larger interparticle macropores than Dox from the smaller PSiNP micropores, was observed. Finally, the formulation of the Dox-loaded superstructures within a composite hydrogel induces prolonged growth inhibition in a 3D spheroid model of pancreatic ductal adenocarcinoma. This study presents a facile modular approach for the rapid assembly of drug-loaded superstructures in fully aqueous environments and demonstrates their potential as highly tailorable and sustained delivery systems for diverse therapeutics.

Ordered hierarchical superlattice amplifies coated-CeO2 nanoparticles luminescence

Achieving a controlled preparation of nanoparticle superstructures with spatially periodic arrangement, also called superlattices, is one of the most intriguing and open questions in soft matter science. The interest in such regular superlattices originates from the potentialities in tailoring the physicochemical properties of the individual constituent nanoparticles, eventually leading to emerging behaviors and/or functionalities that are not exhibited by the initial building blocks. Despite progress, it is currently difficult to obtain such ordered structures; the influence of parameters, such as size, softness, interaction potentials, and entropy, are neither fully understood yet and not sufficiently studied for 3D systems. In this work, we describe the synthesis and characterization of spatially ordered hierarchical structures of coated cerium oxide nanoparticles in water suspension prepared by a bottom-up approach. Covering the CeO2 surface with amphiphilic molecules having chains of appropriate length makes it possible to form ordered structures in which the particles occupy well-defined positions. In the present case superlattice arrangement is accompanied by an improvement in photoluminescence (PL) efficiency, as an increase in PL intensity of the superlattice structure of up to 400 % compared with that of randomly dispersed nanoparticles was observed. To the best of our knowledge, this is one of the first works in the literature in which the coexistence of 3D structures in solution, such as face-centered cubic (FCC) and Frank-Kasper (FK) phases, of semiconductor nanoparticles have been related to their optical properties.

Catalytic Gold Nanoparticle Assembly Programmed by DNAzyme Circuits.

Assembled gold nanoparticle (AuNP) superstructures can generate unique physicochemical characteristics and be used in various applications, thus becoming an attractive research field. Recently, several DNA-assisted gold nanoparticle assembly methods have been rigorously developed that typically require a non-catalytic equimolar molecular assembly to guarantee the designed assembly. Although efficient and accurate, exploring such non-catalytic nanoparticle assemblies in the complex cellular milieu under low trigger concentrations remains challenging. Therefore, developing a catalytic method that facilitates gold nanoparticle assemblies with relatively low DNA trigger concentrations is desirable. In this report, a catalytic method to program gold nanoparticle assemblies by DNAzyme circuits is presented, where only a small number of DNA triggers are able to induce the production of a large number of the desired nanoparticle assemblies. The feasibility of using logic DNAzyme circuits to control catalytic nanoparticle assemblies is experimentally verified. Additionally, catalytic AuNP assembly systems are established with cascading and feedback functions. The work provides an alternative research direction to enrich the tool library of nanoparticle assembly and their application in biosensing and nanomedicine.

Nanoparticle assembly by transient topography induced by applying soft lithography to block copolymer films.

We present a simple approach for patterning metal nanoparticles into periodic superstructures on flat films spanning centimeter-square areas. Our approach is based on capillary force lithography, a soft lithography method that is used to impart topography to molten polymer films, and applies it to block copolymer films to obtain substrates featuring both topographic and chemical contrasts that can serve as templates for the selective deposition of nanoparticles. Here we show that flattening the films by exposure to solvent vapour prior to nanoparticle deposition not only retains chemical heterogeneity but also provides access to unique hierarchically-organized nanoparticle superstructures that are unattainable by other methods. Such structures could be useful for optical, sensor, and catalytic applications.

A Spatially Programmable DNA Nanorobot Arm to Modulate Anisotropic Gold Nanoparticle Assembly by Enzymatic Excision.

Programmable assembly of gold nanoparticle superstructures with precise spatial arrangement has drawn much attention for their unique characteristics in plasmonics and biomedicine. Bio-inspired methods have already provided programmable, molecular approaches to direct AuNP assemblies using biopolymers. The existing methods, however, predominantly use DNA as scaffolds to directly guide the AuNP interactions to produce intended superstructures. New paradigms for regulating AuNP assembly will greatly enrich the toolbox for DNA-directed AuNP manipulation and fabrication. Here, we developed a strategy of using a spatially programmable enzymatic nanorobot arm to modulate anisotropic DNA surface modifications and assembly of AuNPs. Through spatial controls of the proximity of the reactants, the locations of the modifications were precisely regulated. We demonstrated the control of the modifications on a single 15 nm AuNP, as well as on a rectangular DNA origami platform, to direct unique anisotropic AuNP assemblies. This method adds an alternative enzymatic manipulation to DNA-directed AuNP superstructure assembly.

A Spatially Programmable DNA Nanorobot Arm to Modulate Anisotropic Gold Nanoparticle Assembly by Enzymatic Excision

AbstractProgrammable assembly of gold nanoparticle superstructures with precise spatial arrangement has drawn much attention for their unique characteristics in plasmonics and biomedicine. Bio‐inspired methods have already provided programmable, molecular approaches to direct AuNP assemblies using biopolymers. The existing methods, however, predominantly use DNA as scaffolds to directly guide the AuNP interactions to produce intended superstructures. New paradigms for regulating AuNP assembly will greatly enrich the toolbox for DNA‐directed AuNP manipulation and fabrication. Here, we developed a strategy of using a spatially programmable enzymatic nanorobot arm to modulate anisotropic DNA surface modifications and assembly of AuNPs. Through spatial controls of the proximity of the reactants, the locations of the modifications were precisely regulated. We demonstrated the control of the modifications on a single 15 nm AuNP, as well as on a rectangular DNA origami platform, to direct unique anisotropic AuNP assemblies. This method adds an alternative enzymatic manipulation to DNA‐directed AuNP superstructure assembly.

Molecular Modulator Approach for Controlling the Length of Chiral 1D Single-Helical Gold Nanoparticle Superstructures.

Peptide-based methods have proven useful for constructing helical gold nanoparticle superstructures that exhibit strong plasmonic chiroptical activity. Superstructure syntheses using the amphiphilic peptide conjugate C16-(AYSSGAPPMoxPPF)2 typically yield 1D helices with a broad length distribution. In this study, we introduce a molecular modulator approach for controlling helix length. It represents a first step toward achieving narrowly disperse populations of single helices fabricated using peptide-based methods. Varying amounts of modulator, C16-(AYSSGA)2, were added to C16-(AYSSGAPPMoxPPF)2-based single-helix syntheses, resulting in decreased helix length and narrowing of the helix length distribution. Kinetic studies of fiber assembly were performed to investigate the mechanism by which the modulator affects helix length. It was found that the modulator leads to rapid peptide conjugate nucleation and fiber growth, which in turn results in large amounts of short fibers that serve as the underlying scaffold for the single-helix superstructures. These results constitute important advances toward generating monodisperse samples of plasmonic helical colloids.

Designing two-dimensional FeP@C nanoparticle superstructures for efficient hydrogen evolution

Hydrogen evolution reaction (HER) is a promising technology for the production of clean and renewable energy. Iron phosphide (FeP) has attracted significant attention as HER catalysts due to its excellent catalytic activity and low cost. We report herein a new method to construct two-dimensional (2D) superstructures composed of close-packed FeP@C nanoparticles. Such rationally designed FeP@C superstructures, benefiting from their 2D geometry and highly accessible active sites, show excellent activity and stability as HER electrocatalysts.

Single Amino Acid Modifications for Controlling the Helicity of Peptide-Based Chiral Gold Nanoparticle Superstructures.

Assembling nanoparticles (NPs) into well-defined superstructures can lead to emergent collective properties that depend on their 3-D structural arrangement. Peptide conjugate molecules designed to both bind to NP surfaces and direct NP assembly have proven useful for constructing NP superstructures, and atomic- and molecular-level alterations to these conjugates have been shown to manifest in observable changes to nanoscale structure and properties. The divalent peptide conjugate, C16-(PEPAu)2 (PEPAu = AYSSGAPPMPPF), directs the formation of one-dimensional helical Au NP superstructures. This study examines how variation of the ninth amino acid residue (M), which is known to be a key Au anchoring residue, affects the structure of the helical assemblies. A series of conjugates of differential Au binding affinities based on variation of the ninth residue were designed, and Replica Exchange with Solute Tempering (REST) Molecular Dynamics simulations of the peptides on an Au(111) surface were performed to determine the approximate surface contact and to assign a binding score for each new peptide. A helical structure transition from double helices to single helices is observed as the peptide binding affinity to the Au(111) surface decreases. Accompanying this distinct structural transition is the emergence of a plasmonic chiroptical signal. REST-MD simulations were also used to predict new peptide conjugate molecules that would preferentially direct the formation of single-helical AuNP superstructures. Significantly, these findings demonstrate how small modifications to peptide precursors can be leveraged to precisely direct inorganic NP structure and assembly at the nano- and microscale, further expanding and enriching the peptide-based molecular toolkit for controlling NP superstructure assembly and properties.

Crystallization-driven Nanoparticle Crystalsomes.

Nanoparticle (NP) assembly has been extensively studied, and a library of NP superstructures has been synthesized. These intricate structures show unique collective optical, electronic, and magnetic properties. In this work, we report a bottom-up approach for fabricating spherical gold nanoparticle (AuNP) assemblies that mimic colloidosomes. Co-crystallization of lipoic acid-end-functionalized poly(ethylene oxide) (PEO) and AuNPs in solution via a self-seeding method led to the formation of hollow spherical NP assemblies named nanoparticle crystalsomes (NPCs). Due to the spherical shape, the translational symmetry of PEO crystals is broken in NPCs, which can be attributed to the competition between NP close packing and polymer crystallization. This was confirmed by tuning the NPC morphology via varying the self-seeding temperature, crystallization temperature, and PEO molecular weight. We envisage that this strategy paves the way to attaining exquisite morphological control of NP assemblies with broken translational symmetry.

Probing the electrostatic aggregation of nanoparticles with oppositely charged molecular ions

AbstractThe co‐assembly of charged nanoparticles with oppositely charged molecular ions has emerged as a promising technique in the fabrication of nanoparticle superstructures. However, the underlying mechanism behind these molecular ions in mediating the repulsion between these charged nanoparticles remains elusive. Herein, coarse‐grained molecular dynamics simulations are used to elucidate the effects of valency, shape, and size of molecular anions on their co‐assembly with gold nanoparticles coated with positively charged ligands. The findings suggest that the valency, shape, and size of molecular anions significantly influence the repulsion and aggregating dynamics among these positively charged nanoparticles. Moreover, the free energy calculations reveal that ring‐shaped molecular anions with higher valences and larger sizes are more effective at reducing the repulsion between these gold nanoparticles and thus enhance the stability of the aggregate. This study contributes to a better understanding of the critical roles of valence, shape, and size of ions in mediating the electrostatic co‐assembly of nanoparticles with oppositely charged ions, and it also guides the future design of DNA templates and DNA origami in co‐assembly with oppositely charged nanoparticles.

Regulation of Chirality Transfer and Amplification from Chiral Cysteine to Gold Nanorod Assemblies using Nonchiral Surface Ligands

AbstractOwing to large chiroptical activity and high tunability, dynamic chiral superstructures of plasmonic nanoparticles have attracted great attention. A useful strategy has been developed to obtain strong plasmonic chiroptical responses (plasmonic circular dichroism, PCD) by adding small chiral thiols on achiral side‐by‐side assemblies of gold nanorods (AuNRs). Despite the critical role of chiral thiols, the impact of achiral surface ligands is yet to be revealed. Herein, the effects of achiral surface ligands are systematically investigated from the viewpoints of counter ion, hydrocarbon chain length, and head group of surfactants. A well‐packed ligand shell is found to be beneficial for the chirality transfer and amplification from adsorbed chiral thiols to rod assemblies. The PCD temperature amplification effect is observed by using different surfactant ligands and reflects the energy cost of rod‐twisting in the assemblies. This study deepens the understanding of chiral plasmonic assemblies driven by small chiral molecules and provides rational design to fabricate such assembly structures.

Unraveling the Complex Chirality Evolution in DNA‐Assembled High‐Order, Hybrid Chiroplasmonic Superstructures from Multi‐Scale Chirality Mechanisms

AbstractHierarchical, chiral hybrid superstructures of chromophores and nanoparticles are expected to give rise to intriguing unveiled chiroptical responses originating from the complex chiral interactions among the components. Herein, DNA origami cavity that could self‐assemble into one‐dimensional (1D) DNA tubes was employed as a scaffold to accurately organize metal nanoparticles and chromophores. The chiral interactions were studied at the level of individual hybrid particles and their 1D hybrid superstructures. Complex chirality mechanisms involving global structural chirality, plasmon‐induced circular dichroism (PICD) and exciton‐coupled circular dichroism (ECCD) were disentangled. The multiplexed CD spectrum superposition revealed the chirality evolution at different length scales. These results can offer a model for boosting the theoretical understanding of classical‐quantum hybrid systems, and would inspire the future design of optically‐active substances across length scales.

Unraveling the Complex Chirality Evolution in DNA-Assembled High-Order, Hybrid Chiroplasmonic Superstructures from Multi-Scale Chirality Mechanisms.

Hierarchical, chiral hybrid superstructures of chromophores and nanoparticles are expected to give rise to intriguing unveiled chiroptical responses originating from the complex chiral interactions among the components. Herein, DNA origami cavity that could self-assemble into one-dimensional (1D) DNA tubes was employed as a scaffold to accurately organize metal nanoparticles and chromophores. The chiral interactions were studied at the level of individual hybrid particles and their 1D hybrid superstructures. Complex chirality mechanisms involving global structural chirality, plasmon-induced circular dichroism (PICD) and exciton-coupled circular dichroism (ECCD) were disentangled. The multiplexed CD spectrum superposition revealed the chirality evolution at different length scales. These results can offer a model for boosting the theoretical understanding of classical-quantum hybrid systems, and would inspire the future design of optically-active substances across length scales.

Two-Dimensional Metal-Organic Framework Superstructures from Ice-Templated Self-Assembly.

Here, we report the synthesis of two-dimensional (2D) layered metal-organic framework (MOF) nanoparticle (NP) superstructures via an ice-templating strategy. MOF NP monolayers and bilayers can be obtained by regulating the concentration of colloidal MOF NPs without any external fields during self-assembly. Adjacent polyhedral MOF NPs are packed and aligned through crystalline facets, resulting in the formation of a quasi-ordered array superstructure. The morphology of the MOF layers is well preserved when subjected to pyrolysis, and the obtained carbon NPs have hollow interiors driven by the outward contraction of MOF precursors during pyrolysis. With the advantages of large surface areas, hierarchical porosity, high exposure of active sites, and fast electron transport of the 2D layered structure, the mono- and bilayered carbon NP superstructures show better oxygen reduction activity than isolated carbon particles in alkaline media. Our work demonstrates that ice-templating is a powerful strategy to fabricate superstructures of various MOFs and their derivatives.

Modulation of Nano-superstructures and Their Optical Properties.

Self-assembly, which enables spontaneous arrangement of objects, is of particular importance for nanomaterials in both fundamental and applied research fields. Multiple types of nanoparticle superstructures have been successfully built in highly controllable and efficient manners through balancing the nanoscale interactions. Uniform and proper arrangement of nanoparticles inside the assembled superstructures is essential to exhibit their constant, reliable, and homogeneous functionalities. To be specific, the long-range ordered superlattices not only succeed with their building blocks' intrinsic property, but also, more importantly, can display collective properties that are absent both in individual nanoparticles and in their bulk states. One of the most attractive aspects of nanomaterials is their exceptional optical properties that have tremendous application potential in multidisciplinary fields. In this regard, constructing the superstructures from optical nano units like noble metal nanostructures, semiconductor nanoparticles, or hybrid nanomaterials is critical for attaining the unique optical properties and exploring their practical applications in multiple fields including photonics, optoelectronics, optical sensing, photocatalysis, etc. In this Account, we provide guidelines for self-assembly strategies to fabricate the superstructures and discuss the optical properties that the superstructures display. In the first part, we categorize and discuss the key factors that strongly affect the self-assembly process and determine the configurational and integral quality of the superstructures. On one hand, the diversity and designability of nanoparticles offer the intrinsic complexity of the building blocks, including geometry, size, composition, and surface ligand, which efficiently tailors the assembly process and superstructure configuration. On the other hand, multiple factors originating from the introduction of extrinsic features are recognized to facilitate the metastable or dynamic self-assembly process. Such extrinsic features include both matter like DNA origami, peptides, small molecules, etc. and nonmatter involved with electric fields, magnetic fields, light, temperature, etc. In the second part, we introduce the state-of the art progress on the collective optical performances of the assembled superstructures, including (1) chiral optics, such as circular dichroism and circularly polarized luminescence, (2) plasmonic properties and related applications, and (3) luminescence related optics and their applications. Finally, we summarize the existing problems and main challenges briefly, and some future directions of this field are proposed. We envision that, with deep understanding of the assembly mechanism and development of the synthetic and surface chemistry, rational modulation of nanoassemblies will be the trend of this field, which is beneficial to achieve the emerging collective performances and create new generation devices with advanced functions.