Controlled growth and shape-directed self-assembly of gold nanoarrows

Engineering Anisotropy into Organized Nanoscale Matter

Programming the organization of discrete building blocks into periodic and quasi-periodic arrays is challenging. Methods for organizing materials are particularly important at the nanoscale, where the time required for organization processes is practically manageable in experiments, and the resulting structures are of interest for applications spanning catalysis, optics, and plasmonics. While the assembly of isotropic nanoscale objects has been extensively studied and described by empirical design rules, recent synthetic advances have allowed anisotropy to be programmed into macroscopic assemblies made from nanoscale building blocks, opening new opportunities to engineer periodic materials and even quasicrystals with unnatural properties. In this review, we define guidelines for leveraging anisotropy of individual building blocks to direct the organization of nanoscale matter. First, the nature and spatial distribution of local interactions are considered and three design rules that guide particle organization are derived. Subsequently, recent examples from the literature are examined in the context of these design rules. Within the discussion of each rule, we delineate the examples according to the dimensionality (0D-3D) of the building blocks. Finally, we use geometric considerations to propose a general inverse design-based construction strategy that will enable the engineering of colloidal crystals with unprecedented structural control.

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.

Nanopipette dynamic microscopy unveils nano coffee ring

Liquid-phase electron microscopy (LP-EM) imaging has revolutionized our understanding of nanosynthesis and assembly. However, the current closed geometry limits its application for open systems. The ubiquitous physical process of the coffee-ring phenomenon that underpins materials and engineering science remains elusive at the nanoscale due to the lack of experimental tools. We introduce a quartz nanopipette liquid cell with a tunable dimension that requires only standard microscopes. Depending on the imaging condition, the open geometry of the nanopipette allows the imaging of evaporation-induced pattern formation, but it can also function as an ordinary closed-geometry liquid cell where evaporation is negligible despite the nano opening. The nano coffee-ring phenomenon was observed by tracking individual nanoparticles in an evaporating nanodroplet created from a thin liquid film by interfacial instability. Nanoflows drive the assembly and disruption of a ring pattern with the absence of particle-particle correlations. With surface effects, nanoflows override thermal fluctuations at tens of nanometers, in which nanoparticles displayed a "drunken man trajectory" and performed work at a value much smaller than kBT.

Chiral Au-Pd Alloy Nanorods with Tunable Optical Chirality and Catalytically Active Surfaces

Integrating the plasmonic chirality with excellent catalytic activities in plasmonic hybrid nanostructures provides a promising strategy to realize the chiral nanocatalysis toward many chemical reactions. However, the controllable synthesis of catalytically active chiral plasmonic nanoparticles with tailored geometries and compositions remains a significant challenge. Here it is demonstrated that chiral Au-Pd alloy nanorods with tunable optical chirality and catalytically active surfaces can be achieved by a seed-mediated coreduction growth method. Through manipulating the chiral inducers, Au nanorods selectively transform into two different intrinsically chiral Au-Pd alloy nanorods with distinct geometric chirality and tunable optical chirality. By further adjusting several key synthetic parameters, the optical chirality, composition, and geometry of the chiral Au-Pd nanorods are fine-tailored. More importantly, the chiral Au-Pd alloy nanorods exhibit appealing chiral catalytic activities as well as polarization-dependent plasmon-enhanced nanozyme catalytic activity, which has great potential for chiral nanocatalysis and plasmon-induced chiral photochemistry.

Ready-to-Use Free-Standing Super-Powder Made with Complex Nanoparticles for SERS

This study presents a straightforward and efficient synthetic approach for producing high-yield, ready-to-use, free-standing super-powder. The synthesis protocol demonstrates versatility, enabling the creation of assemblies from various nanoparticle morphologies and compositions without the need for specific substrates. Au nanorings are employed as building blocks for fabricating the super-powder, which can be used in surface-enhanced Raman spectroscopy (SERS). The distinctive aspect ratio of the ring nanoframes allows the formation of densely packed columnar assemblies on the substrate, aligning the exposed gaps perpendicular to the laser beam. This arrangement significantly enhances the charge separation among nanorings, leading to a highly focused near-field that is applicable to SERS analysis. The SERS detection feasibility of this powder in both pre- and post-contamination conditions is demonstrated. Using a wide range of building blocks, encompassing various shapes (for instance, rods, hexagons, cubes, cuboctahedrons, elongated dodecahedrons, triangular rings, double-rings, elongated dodecahedra frames, cuboctahedra frames, and double-walled frames), the generalizability of the process for synthesizing super-powders with diverse morphologies is substantiated.

Open Cross-gap Gold Nanocubes with Strong, Large-Area, Symmetric Electromagnetic Field Enhancement for On-Particle Molecular-Fingerprint Raman Bioassays

Plasmonic nanoparticles with an externally open nanogap can localize the electromagnetic (EM) field inside the gap and directly detect the target via the open nanogap with surface-enhanced Raman scattering (SERS). It would be beneficial to design and synthesize the open gap nanoprobes in a high yield for obtaining uniform and quantitative signals from randomly oriented nanoparticles and utilizing these particles for direct SERS analysis. Here, we report a facile strategy to synthesize open cross-gap (X-gap) nanocubes (OXNCs) with size- and EM field-tunable gaps in a high yield. The site-specific growth of Au budding structures at the corners of the AuNC using the principle that the Au deposition rate is faster than the surface diffusion rate of the adatoms allows for a uniform X-gap formation. The average SERS enhancement factor (EF) for the OXNCs with 2.6 nm X-gaps was 1.2 × 109, and the EFs were narrowly distributed within 1 order of magnitude for ∼93% of the measured OXNCs. OXNCs consistently displayed strong EM field enhancement on large particle surfaces for widely varying incident light polarization directions, and this can be attributed to the symmetric X-gap geometry and the availability of these gaps on all 6 faces of a cube. Finally, the OXNC probes with varying X-gap sizes have been utilized in directly detecting biomolecules with varying sizes without Raman dyes. The concept, synthetic method, and biosensing results shown here with OXNCs pave the way for designing, synthesizing, and utilizing plasmonic nanoparticles for selective, quantitative molecular-fingerprint Raman sensing and imaging applications.

Step-by-Step Nanoscale Top-Down Blocking and Etching Lead to Nanohexapods with Cartesian Geometry

In this research, we designed a stepwise synthetic method for Au@Pt hexapods where six elongated Au pods are arranged in a pairwise perpendicular fashion, sharing a common point (the central origin in a Cartesian-coordinate-like hexapod shape), featured with tip-selectively decorated Pt square nanoplates. Au@Pt hexapods were successfully synthesized by applying three distinctive chemical reactions in a stepwise manner. The Pt adatoms formed discontinuous thin nanoplates that selectively covered six concave facets of a Au truncated octahedron and served as etching masks in the succeeding etching process, which prevented underlying Au atoms from being oxidized. The subsequent isotropic etching proceeded radially, starting from the bare Au surface, carving the central nanocrystal in a concave manner. By controlling the etching conditions, Au@Pt hexapods were successfully fabricated, wherein the core Au domain is connected to six protruding arms, which hold Pt nanoplates at the ends. Due to their morphology, Au@Pt hexapods feature distinctive optical properties in the near-infrared region, as a proof of concept, allowing for surface-enhanced Raman spectroscopy (SERS)-based monitoring of in situ CO electrooxidation. We further extended our synthetic library by tailoring the size of the Pt nanoplates and neck widths of Au branches, demonstrating the validity of selective blocking and etching-based colloidal synthesis.

Recent Advances of Seed-Mediated Growth of Metal Nanoparticles: from Growth to Applications

Unprecedented advances in metal nanoparticle synthesis have paved the way for broad applications in sensing, imaging, catalysis, diagnosis, and therapy by tuning the optical properties, enhancing catalytic performance, and improving chemical and biological properties of metal nanoparticles. The central guiding concept for regulating the size and morphology of metal nanoparticles is identified as the precise manipulation of nucleation and subsequent growth, often known as seed-mediated growth methods. However, since the growth process is sensitive not only to the metal seeds but also to capping agents, metal precursors, growth solution, growth/incubation time, reductants, and other influencing factors, the precise control of metal nanoparticle morphology is multifactorial. Further, multiple reaction parameters are entangled with each other, so it is necessary to clarify the mechanism by which each factor precisely regulates the morphology of metal nanoparticles. In this review, to exploit the generality and extendibility of metal nanoparticle synthesis, the mechanisms of growth influencing factors in seed-mediated growth methods are systematically summarized. Second, a variety of critical properties and applications enabled by grown metal nanoparticles are focused upon. Finally, the current progress and offer insights on the challenges, opportunities, and future directions for the growth and applications of grown metal nanoparticles are reviewed.

Nanoscale goldbeating: Solid-state transformation of 0D and 1D gold nanoparticles to anisotropic 2D morphologies

Goldbeating is the ancient craft of thinning bulk gold (Au) into gossamer leaves. Pioneered by ancient Egyptian craftsmen, modern mechanized iterations of this technique can fabricate sheets as thin as ∼100 nm. We take inspiration from this millennia-old craft and adapt it to the nanoscale regime, using colloidally synthesized 0D/1D Au nanoparticles (AuNPs) as highly ductile and malleable nanoscopic Au ingots and subjecting them to solid-state, uniaxial compression. The applied stress induces anisotropic morphological transformation of AuNPs into 2D leaf form and elucidates insights into metal nanocrystal deformation at the extreme length scales. The induced 2D morphology is found to be dependent on the precursor 0D/1D NP morphology, size (0D nanosphere diameter and 1D nanorod diameter and length), and their on-substrate arrangement (e.g., interparticle separation and packing order) prior to compression. Overall, this versatile and generalizable solid-state compression technique enables new pathways to synthesize and investigate the anisotropic morphological transformation of arbitrary NPs and their resultant emergent phenomena.

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

All forms of energy follow the law of conservation of energy, by which they can be neither created nor destroyed. Light-to-heat conversion as a traditional yet constantly evolving means of converting light into thermal energy has been of enduring appeal to researchers and the public. With the continuous development of advanced nanotechnologies, a variety of photothermal nanomaterials have been endowed with excellent light harvesting and photothermal conversion capabilities for exploring fascinating and prospective applications. Herein we review the latest progresses on photothermal nanomaterials, with a focus on their underlying mechanisms as powerful light-to-heat converters. We present an extensive catalogue of nanostructured photothermal materials, including metallic/semiconductor structures, carbon materials, organic polymers, and two-dimensional materials. The proper material selection and rational structural design for improving the photothermal performance are then discussed. We also provide a representative overview of the latest techniques for probing photothermally generated heat at the nanoscale. We finally review the recent significant developments of photothermal applications and give a brief outlook on the current challenges and future directions of photothermal nanomaterials.

Growth Reaction of Gold Nanorods in the Presence of Mutated Peptides and Amine-Modified Single-Stranded Nucleic Acids

Conformation of biomolecules like DNA, peptides and amino acids play vital role during nanoparticle growth. Herein, we have experimentally explored the effect of different noncovalent interaction between a 5'-amine modified DNA sequence (NH₂ -C₆ H₁₂ -5'-ACATCAGT-3', PMR) and arginine during the seed-mediated growth reaction of gold nanorods (GNRs). Amino acid-mediated growth reaction of GNRs results in a snowflake-like gold nanoarchitecture. However, in case of Arg, prior incubation of GNRs with PMR selectively produces sea urchin-like gold suprastructures, via strong hydrogen bonding and cation-π interaction between PMR and Arg. This distinctive structure formation strategy has been extended to study the structural modulation caused by two structurally close α-helical RRR (Ac-(AAAAR)₃ A-NH₂ ) peptide and the lysine mutated KKR (Ac-AAAAKAAAAKAAAARA-NH₂ ) peptide with partial helix at the amino terminus. Simulation studies confirm that a greater number of hydrogen bonding and cation-π interaction between the Arg residues and PMR resulted in the gold sea urchin structure for RRR peptide against KKR peptide.

Concave gold nano-arrows (AuCNAs) for efficient catalytic reduction of 4-nitrophenol

Anisotropic gold nanostructures have attracted great attention in different fields including catalysis. Thermodynamically driven selective surface growth offers a reliable and reproducible method for anisotropic gold nanoparticle synthesis with specific morphologies. Herein, monocrystalline concave gold nano-arrows (AuCNAs) are prepared by the over-growth method using Au nanorods (AuNRs) as seeds. The as-prepared AuCNAs consist of a biconical head and four concave structures. Interestingly, silver ions (Ag⁺) concentration significantly affects the product morphology by tuning the peak positions of surface plasmon resonance (SPR), aspect ratio, arrow, and concave morphology of AuCNAs. The position of longitudinal SPR peaks is observed at 810, 805 and 782 nm at [Ag⁺]/[Au³⁺] molar ratios of 1:2, 1:1, and 2:1, respectively. Diameters and lengths of AuCNAs varied from 25 nm to 36 nm; 104 nm, 78 nm, and 120 nm, respectively. Additionally, the AuCNAs are applied for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in presence of excess NaBH₄. Compared to gold nanorods (AuNRs), the prepared AuCNAs catalyst shows excellent catalytic activity, demonstrating that concave structures and sharp corners significantly enhance the catalytic activity. The value of pseudo-first-order reaction kinetic constants (k_app) increased from 0.0051 to 0.0195 s^-1 with increasing catalyst valume from 7.5 to 37.5 μL. The highest normalized reaction rate constant (K_nor) and turnover frequency (TOF) reach 5.84 × 10⁴ min^-1 mmol^-1 and 443.47 h^-1, respectively, at [Ag⁺]/[Au³⁺] ratio of 1:1 in AuCNAs catalyst. This study expands catalytic applications of anisotropic gold nanostructures and widens their potential application areas, such as surface plasmon exciton photonics, biomedical photonics, and photocatalysis.

Shape-Mediated Oriented Assembly of Concave Nanoparticles under Cylindrical Confinement

This contribution describes the self-assembly of colloidal nanodumbbells (NDs) with tunable shapes within cylindrical channels. We present that the intrinsic concave geometry of NDs endows them with peculiar packing and interlocking behaviors, which, in conjunction with the adjustable confinement constraint, leads to a variety of superstructures such as tilted-ladder chains and crossed-chain superlattices. A mechanistic investigation, corroborated by geometric calculations, reveals that the phase behavior of NDs under strong confinement can be rationalized by the entropy-driven maximization of the packing efficiency. Based on the experimental results, an empirical phase diagram is generated, which could provide general guidance in the design of intended superstructures from NDs. This study provides essential insight into how the interplay between the particle shape and confinement conditions can be exploited to direct the orientationally ordered assembly of concave nanoparticles into unusual superlattices.

Morphological and Optical Transitions during Micelle-Seeded Chiral Growth on Gold Nanorods

Chiral plasmonics is a rapidly developing field where breakthroughs and unsolved problems coexist. We have recently reported binary surfactant-assisted seeded growth of chiral gold nanorods (Au NRs) with high chiroptical activity. Such a seeded-growth process involves the use of a chiral cosurfactant that induces micellar helicity, in turn driving the transition from achiral to chiral Au NRs, from both the morphological and the optical points of view. We report herein a detailed study on both transitions, which reveals intermediate states that were hidden so far. The correlation between structure and optical response is carefully analyzed, including the (linear and CD) spectral evolution over time, electron tomography, the impact of NR dimensions on their optical response, the variation of the absorption-to-scattering ratio during the evolution from achiral to chiral Au NRs, and the near-field enhancement related to chiral plasmon modes. Our findings provide further understanding of the growth process of chiral Au NRs and the associated optical changes, which will facilitate further study and applications of chiral nanomaterials.

Atom Absorption Energy Directed Symmetry-Breaking Synthesis of Au-Ag Hierarchical Nanostructures and Their Efficient Photothermal Conversion

Asymmetric plasmonic hierarchical nanostructures (HNs) are of great significance in optics, catalysis, and sensors, but the complex growth kinetics and lack of fine structure design limit their practical applications. Herein, a new atom absorption energy strategy is developed to achieve a series of Au-Ag HNs with the continuously tuned contact area in Janus and Ag island number/size on Au seeds. Different from the traditional passive growth mode, this strategy endows seed with a hand to capture the hetero atoms in a proactive manner, which is beyond the size, shape, and assembles of Au seed. Density functional theory reveals ththe adsorption of PDDA on Au surface leads to lower formation energy of Au-Ag bonds (-3.96 eV) than FSDNA modified Au surface (-2.44 eV). The competitive adsorption of two ligands on Au seed is the decisive factor for the formation of diverse Au-Ag HNs. In particular, the Au-Ag₂ HNs exhibit outstanding photothermal conversion capability in the near-infrared window, and in vivo experiments verify them as superior photothermal therapy agents. This work highlights the importance of the atom absorption energy strategy in unlocking the diversity of HNs and may push the synthesis and application of superstructures to a higher level.

An artificial intelligence enabled chemical synthesis robot for exploration and optimization of nanomaterials

We present an autonomous chemical synthesis robot for the exploration, discovery, and optimization of nanostructures driven by real-time spectroscopic feedback, theory, and machine learning algorithms that control the reaction conditions and allow the selective templating of reactions. This approach allows the transfer of materials as seeds between cycles of exploration, opening the search space like gene transfer in biology. The open-ended exploration of the seed-mediated multistep synthesis of gold nanoparticles (AuNPs) via in-line ultraviolet-visible characterization led to the discovery of five categories of nanoparticles by only performing ca. 1000 experiments in three hierarchically linked chemical spaces. The platform optimized nanostructures with desired optical properties by combining experiments and extinction spectrum simulations to achieve a yield of up to 95%. The synthetic procedure is outputted in a universal format using the chemical description language (χDL) with analytical data to produce a unique digital signature to enable the reproducibility of the synthesis.

Advances in plasmonic-based MOF composites, their bio-applications and perspectives in this field

INTRODUCTION

Nanomaterials have been used for bio-applications since the late 20st century. In an attempt to tailor and optimize their properties, and by extension their efficiency, composites have attracted considerable attention. In this regard, recent studies on plasmonic nanoparticles and metal-organic framework (NP@MOF) composites suggested these materials show great promise in this field.

AREAS COVERED

This review focused on the more recent scientific advances in the synthetic strategies to optimize plasmonic MOF nanocomposites currently available, as well as their bio-application, particularly as biosensors and therapy.

EXPERT OPINION

Plasmonic MOF nanocomposites have shown great potential as they combine the properties of both materials with proven efficiency in bio-application. On the one hand, nanoMOFs have proven their potential particularly as drug nanocarriers, owing to their exceptional porosity and tunability. On the other hand, plasmonic nanoparticles have been an asset for imaging and phototherapy. Different strategies have been reported to develop these nanocomposites, mainly including core-shell, encapsulation, and in situ reduction. In addition, advanced composite structures should be considered, such as mixed metal nanoparticles, hollow structures or the combination of several approaches. Specifically, plasmonic MOF nanocomposites prove to be attractive stimuli responsive drug delivery systems, phototherapeutic agents as well as highly sensitive biosensors.

Liquid-crystalline behavior on dumbbell-shaped colloids and the observation of chiral blue phases

Colloidal liquid crystals are an emerging class of soft materials that naturally combine the unique properties of both liquid crystal molecules and colloidal particles. Chiral liquid crystal blue phases are attractive for use in fast optical displays and electrooptical devices, but the construction of blue phases is limited to a few chiral building blocks and the formation of blue phases from achiral ones is often counterintuitive. Herein we demonstrate that achiral dumbbell-shaped colloids can assemble into a rich variety of characteristic liquid crystal phases, including nematic phases with lock structures, smectic phase, and particularly experimental observation of blue phase III with double-twisted chiral columns. Phase diagrams from experiments and simulations show that the existence and stable regions of different liquid crystal phases are strongly dependent on the geometrical parameters of dumbbell-shaped colloids. This work paves a new route to the design and construction of blue phases for photonic applications.

Colloidal liquid crystals account for various applications due to the combination of characteristics relevant for liquid crystals and colloids. The authors elaborate the impact of concave geometry on the properties of colloidal liquid crystals for development of functional materials.

Shape controlled synthesis of concave octahedral Au@AuAg nanoparticles to improve their surface-enhanced Raman scattering performance

In this work, a seed mediated strategy has been proposed to design and fabricate uniform octahedral shaped gold@gold-silver nanoparticles (Au@AuAg NPs) with unique concave structure and an AuAg alloy shell. The morphology and Au/Ag ratio of the Au@AuAg nanostructures can be delicately controlled by varying the concentration of reagents, namely the Au nanorod (NR) seeds, HAuCl₄ and AgNO₃ precursor. Besides, the investigation of the growth mechanism revealed that the morphology of the product also can be controlled by tuning the growth time. Furthermore, uniformly arranged assemblies of concave octahedral Au@AuAg NPs were prepared through a solvent evaporation self-assembly strategy and employed as surface-enhanced Raman scattering (SERS) substrates, effectively applied to the analysis of R6G for the examination of SERS performance. Satisfyingly, owing to the synergistic effect between the Au and Ag elements and concave structure, concave octahedral Au@AuAg NPs exhibit significantly higher SERS enhancement compared with traditional octahedral Au NPs, which have an enhancement factor of ∼1.3 × 10⁷ and a detection limit as low as 10⁻¹⁰ M. Meanwhile, the SERS substrate reveals an excellent uniformity and reproducibility of the SERS performance. This work opens a new avenue toward bimetallic NPs with concave structure, which have broad application prospects in optics, SERS detection and other fields.

In this work, a seed mediated strategy has been proposed to design and fabricate uniform octahedral shaped gold@gold-silver nanoparticles (Au@AuAg NPs) with unique concave structure and an AuAg alloy shell.

Methionine-Controlled Impediment of Secondary Nucleation Leading to Nonclassical Growth within Self-Assembled De Novo Gold Nanoparticles

The conventional key steps for seed-mediated growth of noble metal nanostructures involve classical and nonclassical nucleation. Furthermore, the surface of the seed catalytically enhances the secondary nucleation involving Au⁺ to Au⁰ reduction, thus providing in-plane growth of the seed. In contrast to this well-established growth mechanism, herein, we report the unique case of a methionine (Met)-controlled seed-mediated growth reaction, which rather proceeds via impeding secondary nucleation in the presence of citrate-stabilized gold nanoparticles (AuNPs). The interaction between the freshly generated Au⁺ and the thioether group of Met in the medium restricts the secondary nucleation process of further seed-catalyzed Au⁺ reduction to Au⁰. This incomplete conversion of Au⁺, as confirmed by X-ray photoelectron spectroscopy, results in a significant enhancement of the zeta (ζ) potential even at low Met concentrations. Nucleation of in situ generated small-sized particles (nAuNPs) takes place on the parent seed surface followed by their segregation from the seed. The self-assembly process of these nAuNPs arises from the aurophilic interaction among the Au⁺. Furthermore, the time-dependent growth of smaller particles to larger-sized particles through assembly and merging within the same self-assembly validates the nonclassical growth. This strategy has been successfully extended toward the seed-mediated growth reaction of AuNPs in the presence of three bio-inspired decameric peptides having varying numbers of Met residues. The study confirms the nucleation strategy even in the presence of a single Met residue in the peptide and also the self-assembly of nucleated particles with increasing Met residues within the peptide.

Tunable Assembly of Organic-Inorganic Molecules into Hierarchical Superstructures as Ligase Mimics for Enhancing Tumor Photothermal Therapy

The assembly of molecules into hierarchical superstructures is ubiquitous in the construction of novel geometrically complex hierarchical superstructures, attracting great attention. Herein, a metal-ligand cross-linking strategy is developed for the fabrication of ferric ion-dopamine coordination hierarchical superstructures. A range of superstructures with highly complex morphologies, such as flower-like, octopus-like, and hedgehog-like superstructures, are synthesized. The mechanism for formation of hierarchical superstructures involves the pre-cross-linking of ferric ion with dopamine molecules, the fabrication of iron-dopamine precursors aggregated into the spherical aggregates, the nanoscale aggregates sintering and ordering themselves upon equilibration, the nanodots polymerizing into nanorods, and finally the nanorods self-assembling into hierarchical superstructures. In-depth research illustrates that as the permittivity (ξ) of the reaction system increases, the resulting hierarchical superstructures tend to converge into spherical shape. As a proof of concept, the 0D nanospheres, 1D nanorods, and 3D hierarchical superstructures are fabricated through adjusting system permittivity. The hierarchical superstructure is utilized as peroxidase-like ligase mimics to enhance the effect of tumor photothermal treatment. Further in vitro and in vivo assays demonstrate that the hierarchical superstructure can effectively ablate tumor cells. This work opens new horizons in hierarchical superstructures with complex architectures, and has great potential in nanozymology, biomedical science, and catalysis.

Selenocystine and Photo-Irradiation Directed Growth of Helically Grooved Gold Nanoarrows

The fabrication of discrete nanostructures with both plasmonic circular dichroism (PCD) and chiral features is still a challenge. Here, gold nanoarrows (GNAs) with both chiroptical responses and chiral morphologies are achieved by using L-selenocystine (L-SeCys₂ ) as a chiral inducer. While L-SeCys₂ generates GNAs with a weak PCD signal, the irradiated L-SeCys₂ (irr-L-SeCys₂ ) leads to GNAs with featured helical grooves (HeliGNAs) accompanying with a strong PCD signal. It is revealed that when L-SeCys₂ is photo-irradiated, the emergence of selenyl radicals plays an important role in the formation of HeliGNAs and enhancement of the chiroptical signal. In comparison with L-SeCys₂ and the other kinds of sulfur-containing amino acids, the formation mechanism of helical grooves on the surface of GNAs is proposed. Both HeliGNAs and GNAs are used to discriminate amino acids by utilizing surface enhanced Raman scattering (SERS) effect. In the presence of either GNAs or HeliGNAs as the substrate, Fmoc-L-Phe shows more significant SERS than Fmoc-D-Phe. This study may advance the design of discrete plasmonic nanomaterials with both chiral morphology and potential applications in discrimination of chiral molecules.

Polyhedral Micromotors of Metal-Organic Frameworks: Symmetry Breaking and Propulsion

Colloidal micromotors can autonomously propel due to their broken symmetry that leads to unbalanced local mechanical forces. Most commonly, micromotors are synthesized to possess a Janus structure or its variants, having two components distinct in shape, composition, or surface joined together on opposite sides. Here, we report on an alternative approach for creating micromotors, where microcrystals of metal-organic frameworks (MOFs) with various polyhedral shapes are propelled under an AC electric field. In these cases, symmetry breaking is realized by orienting the polyhedral particles in a unique direction to generate uneven electrohydrodynamic flow. The particle orientations are controlled by a delicate competition between the electric and gravitational forces exerted on the particle, which we rationalize using experiments and a theoretical model. Furthermore, by leveraging the MOF types and shapes, or surface properties, we show that the propulsion of MOF motors can be tuned or reversed. Because of the flexibility in designing MOFs and their one-step scalable synthesis, our strategy is simple yet versatile for making well-defined functional micromotors.

Surface lattice engineering for fine-tuned spatial configuration of nanocrystals

Hybrid nanocrystals combining different properties together are important multifunctional materials that underpin further development in catalysis, energy storage, et al., and they are often constructed using heterogeneous seeded growth. Their spatial configuration (shape, composition, and dimension) is primarily determined by the heterogeneous deposition process which depends on the lattice mismatch between deposited material and seed. Precise control of nanocrystals spatial configuration is crucial to applications, but suffers from the limited tunability of lattice mismatch. Here, we demonstrate that surface lattice engineering can be used to break this bottleneck. Surface lattices of various Au nanocrystal seeds are fine-tuned using this strategy regardless of their shape, size, and crystalline structure, creating adjustable lattice mismatch for subsequent growth of other metals; hence, diverse hybrid nanocrystals with fine-tuned spatial configuration can be synthesized. This study may pave a general approach for rationally designing and constructing target nanocrystals including metal, semiconductor, and oxide.

Programmable Self-Assembly of Gold Nanoarrows via Regioselective Adsorption

Programing the self-assembly of colloidal nanoparticles into predetermined superstructures represents an attractive strategy to realize functional assemblies and novel nanodevices, but it remains a challenge. Herein, gold nanoarrows (GNAs) showing a distinct convex-concave structure were employed as unique building blocks for programmable self-assembly involving multiple assembly modes. Regioselective adsorption of 1,10-decanedithiol on the vertexes, edges, and facets of GNAs allowed for programmable self-assembly of GNAs with five distinct assembly modes, and regioselective blocking with 1-dodecanethiol followed by adsorption of 1,10-decanedithiol gave rise to programmable self-assembly with six assembly modes including three novel wing-engaged modes. The assembly mode was essentially determined by regioselective adsorption of the dithiol linker dictated by the local curvature together with the shape complementarity of GNAs. This approach reveals how the geometric morphology of nanoparticles affects their regioselective functionalization and drives their self-assembly.

Engineering Electromagnetic Hot-Spots in Nanoparticle Cluster Arrays on Reflective Substrates for Highly Sensitive Detection of (Bio)molecular Analytes

Intense electromagnetic (EM) hot-spots arising at the junctions or gaps in plasmonic nanoparticle assemblies can drive ultrahigh sensitivity in molecular detection by surface-enhanced spectroscopies. Harnessing this potential however requires access to the confined physical space at the EM hot-spots, which is a challenge for larger analytes such as biomolecules. Here, we demonstrate self-assembly derived gold nanoparticle cluster arrays (NCAs) on gold substrates exhibiting controlled interparticle (<1 nm wide) and intercluster (<10 nm wide) hot-spots as highly promising in this direction. Sensitivity of the NCAs toward detection of small (<1 nm) or large (protein-receptor interactions) analytes in surface-enhanced Raman and metal-enhanced fluorescence assays is found to be strongly impacted by the size of the cluster and the presence of reflective substrates. Experiments supported by numerical simulations attribute the higher sensitivity to higher EM field enhancements at the hot-spots, as well as greater analyte leverage over EM hot-spots. The best-performing arrays could push the sensitivity down to picomolar detection limits for sub-nanometric organic analytes as well as large protein analytes. The investigation paves the way for rational design of plasmonic biosensors and highlights the unique capabilities of a molecular self-assembly approach toward catering to this objective.

Bespoke nanostars: synthetic strategies, tactics, and uses of tailored branched gold nanoparticles

Interest in branched colloidal gold nanosystems has gained increased traction due to the structures' outstanding optical and plasmonic properties, resulting in utilization in techniques such as surface-enhanced spectroscopy and bioimaging, as well as plasmon photocatalysis and photothermal therapy. The unique morphologies of nanostars, multipods, urchins, and other highly branched nanomaterials exhibit selective optical and crystallographic features accessible by alterations in the respective wet-chemical syntheses, opening a vast array of useful applications. Examination of discriminatory reaction conditions, such as seeded growth (e.g., single-crystalline vs. multiply twinned seeds), underpotential deposition of Ag(i), galvanic replacement, and the dual use of competing reducing and capping agents, is shown to reveal conditions necessary for the genesis of assorted branched nanoscale gold frameworks. By observing diverse approaches, including template-directed, microwave-mediated, and aggregation-based methods, among others, a schema of synthetic pathways can be constructed to provide a guiding roadmap for obtaining the full range of desired branched gold nanocrystals. This review presents a comprehensive summary of such advances and these nuances of the underlying procedures, as well as offering mechanistic insights into the directed nanoscale growth. We conclude the review by discussing various applications for these fascinating nanomaterials, particularly surface-enhanced Raman spectroscopy, photothermal and photodynamic therapy, catalysis, drug delivery, and biosensing.

Anisotropic nanocrystal shape and ligand design for co-assembly

The use of nanocrystal (NC) building blocks to create metamaterials is a powerful approach to access emergent materials. Given the immense library of materials choices, progress in this area for anisotropic NCs is limited by the lack of co-assembly design principles. Here, we use a rational design approach to guide the co-assembly of two such anisotropic systems. We modulate the removal of geometrical incompatibilities between NCs by tuning the ligand shell, taking advantage of the lock-and-key motifs between emergent shapes of the ligand coating to subvert phase separation. Using a combination of theory, simulation, and experiments, we use our strategy to achieve co-assembly of a binary system of cubes and triangular plates and a secondary system involving two two-dimensional (2D) nanoplates. This theory-guided approach to NC assembly has the potential to direct materials choices for targeted binary co-assembly.

Unconventional-Phase Crystalline Materials Constructed from Multiscale Building Blocks

Crystal phase, an intrinsic characteristic of crystalline materials, is one of the key parameters to determine their physicochemical properties. Recently, great progress has been made in the synthesis of nanomaterials with unconventional phases that are different from their thermodynamically stable bulk counterparts via various synthetic methods. A nanocrystalline material can also be viewed as an assembly of atoms with long-range order. When larger entities, such as nanoclusters, nanoparticles, and microparticles, are used as building blocks, supercrystalline materials with rich phases are obtained, some of which even have no analogues in the atomic and molecular crystals. The unconventional phases of nanocrystalline and supercrystalline materials endow them with distinctive properties as compared to their conventional counterparts. This Review highlights the state-of-the-art progress of nanocrystalline and supercrystalline materials with unconventional phases constructed from multiscale building blocks, including atoms, nanoclusters, spherical and anisotropic nanoparticles, and microparticles. Emerging strategies for engineering their crystal phases are introduced, with highlights on the governing parameters that are essential for the formation of unconventional phases. Phase-dependent properties and applications of nanocrystalline and supercrystalline materials are summarized. Finally, major challenges and opportunities in future research directions are proposed.

Rationally Programming Nanomaterials with DNA for Biomedical Applications

DNA is not only a carrier of genetic information, but also a versatile structural tool for the engineering and self-assembling of nanostructures. In this regard, the DNA template has dramatically enhanced the scalability, programmability, and functionality of the self-assembled DNA nanostructures. These capabilities provide opportunities for a wide range of biomedical applications in biosensing, bioimaging, drug delivery, and disease therapy. In this review, the importance and advantages of DNA for programming and fabricating of DNA nanostructures are first highlighted. The recent progress in design and construction of DNA nanostructures are then summarized, including DNA conjugated nanoparticle systems, DNA-based clusters and extended organizations, and DNA origami-templated assemblies. An overview on biomedical applications of the self-assembled DNA nanostructures is provided. Finally, the conclusion and perspectives on the self-assembled DNA nanostructures are presented.

Supramolecular Paradigm for Capture and Co-Precipitation of Gold(III) Coordination Complexes

A new supramolecular paradigm is presented for reliable capture and co-precipitation of haloauric acids (HAuX₄ ) from organic solvents or water. Two classes of acyclic organic compounds act as complementary receptors (tectons) by forming two sets of directional non-covalent interactions, (a) hydrogen bonding between amide (or amidinium) NH residues and the electronegative X ligands on the AuX₄ ^- , and (b) electrostatic stacking of the electron deficient Au center against the face of an aromatic surface. X-ray diffraction analysis of four co-crystal structures reveals the additional common feature of proton bridged carbonyls as a new and predictable supramolecular design element that creates one-dimensional polymers linked by very short hydrogen bonds (CO⋅⋅⋅OC distance <2.5 Å). Two other co-crystal structures show that the amidinium-π⋅⋅⋅XAu interaction will reliably engage AuX₄ ^- with high directionality. These acyclic compounds are very attractive as co-precipitation agents within new "green" gold recovery processes. They also have high potential as tectons for controlled self-assembly or co-crystal engineering of haloaurate composites. More generally, the supramolecular paradigm will facilitate the design of next-generation receptors or tectons with high affinity for precious metal square planar coordination complexes for use in advanced materials, nanotechnology, or medicine.

Tetragonal Superlattice of Elongated Rhombic Dodecahedra for Sensitive SERS Determination of Pesticide Residues in Fruit

The self-assembly of plasmonic nanoparticles into highly ordered superlattices could pave the way toward novel nanomaterials for surface-enhanced Raman scattering (SERS). Here, we propose the formation of large-area superlattices of elongated rhombic dodecahedra in a vertical orientation via a controlled droplet evaporation process. Expectedly, the constant humidity of the experimental condition could control the evaporation speed of droplets and this procedure promotes the balance between driven depletion attraction and electrostatic repulsion in the system, leading to the generation of well-organized three-dimensional (3D) superlattices. The unique geometry of elongated rhombic dodecahedra could establish the tetragonal superlattices, which breaks the conventional hexagonal symmetry of gold nanorods. Specifically, the influence of the type and concentration of surfactants, the concentration of nanoparticles, and the amount of droplets on the preparation results were systematically investigated to find the optimal assembly parameters. Remarkably, such close-packed tetragonal arrays of vertically aligned elongated rhombic dodecahedra exhibit more excellent SERS performance compared with the traditional hexagonal superstructure of gold nanorods. Benefiting from the high sensitivity and reproducibility of elongated rhombic dodecahedron superlattices, their applications in the determination of pesticide residues in apple and grape peels were successfully demonstrated. As a result, this study may advance the production of innovative plasmonic nanomaterials for a broad range of fields.

Analytical van der Waals interaction potential for faceted nanoparticles

Our ability to synthesize faceted nanoparticles of tunable shapes and sizes has opened up many intriguing applications of such particles. However, our progress in understanding, modeling, and simulating their collective rheology, phase behavior, and self-assembly has been hindered by the lack of analytical interparticle interaction potentials. Here, we present one of the first analytical models for the van der Waals interaction energy between faceted nanoparticles. The model was derived through various approximations that reduce the usual six-dimensional integral over particle volumes to a series of two-dimensional integrals over particle interaction areas with closed-form solutions. Comparison and analyses of energies obtained from the analytical model with those computed from exact atomistic calculations show that the model approximations lead to insignificant errors in predicted energies across all relevant particle configurations. We demonstrate that the model yields accurate energies for diverse particle shapes including nanocubes, triangular prisms, faceted rods, and square pyramids, while yielding many orders of magnitude improvement in computational efficiency compared to atomistic calculations. To make the model more accessible and to demonstrate its applicability, an open-source graphical user interface application implementing the model for nanocubes in arbitrary configurations has been developed. We expect that the analytical model will accelerate future investigations of faceted nanoparticles that require accurate calculation of interparticle interactions.

Self-Assembly of Surface-Acylated Cellulose Nanowhiskers and Graphene Oxide for Multiresponsive Janus-Like Films with Time-Dependent Dry-State Structures

For the first time Janus-like films of surface-acylated cellulose nanowhiskers (CNWs) with or without graphene oxide (GO) via one-step evaporation-driven self-assembly process are reported, which have reconstructible time-dependent micro-/nanostructures and asymmetric wettability. The heterogeneous aggregation of CNWs on rough Teflon substrates favors the formation of uniform films, leading to hydrophobic smooth bottom surface. The homogeneous nucleation of residual CNWs in bulk suspensions promotes the growth of patchy microspheres with an average diameter of 22.7 ± 2.1 µm, which precipitate on the top surface leading to enhanced hydrophobicity. These patchy microspheres are thermoresponsive and vanish after heating at 60 °C within 1 min, while they are reconstructed at room temperature with time-dependent evolving micro-/nanostructures in dry state within 2 d. The thermoresponsive transition of patchy microparticles leads to accompanied switchable change between transparency and opacity of Janus-like films. Furthermore, the incorporation of GO generates more patchy microspheres with an average diameter of 13.5 ± 1.3 µm on the top surface of hybrid Janus-like films. Different distributions of CNWs and GO in Janus-like films and the solvent-responsive self-assembled patchy microparticles of CNWs facilitate their reversible actuation by showing fast curling in THF within 6 s and flattening in water for at least 25 cycles.

Self-assembly of anisotropic nanoparticles into functional superstructures

Self-assembly of colloidal nanoparticles (NPs) into superstructures offers a flexible and promising pathway to manipulate the nanometer-sized particles and thus make full use of their unique properties. This bottom-up strategy builds a bridge between the NP regime and a new class of transformative materials across multiple length scales for technological applications. In this field, anisotropic NPs with size- and shape-dependent physical properties as self-assembly building blocks have long fascinated scientists. Self-assembly of anisotropic NPs not only opens up exciting opportunities to engineer a variety of intriguing and complex superlattice architectures, but also provides access to discover emergent collective properties that stem from their ordered arrangement. Thus, this has stimulated enormous research interests in both fundamental science and technological applications. This present review comprehensively summarizes the latest advances in this area, and highlights their rich packing behaviors from the viewpoint of NP shape. We provide the basics of the experimental techniques to produce NP superstructures and structural characterization tools, and detail the delicate assembled structures. Then the current understanding of the assembly dynamics is discussed with the assistance of in situ studies, followed by emergent collective properties from these NP assemblies. Finally, we end this article with the remaining challenges and outlook, hoping to encourage further research in this field.

"Colloid-Atom Duality" in the Assembly Dynamics of Concave Gold Nanoarrows

We use liquid-phase transmission electron microscopy (TEM) to study self-assembly dynamics of charged gold nanoarrows (GNAs), which reveal an unexpected "colloid-atom duality". On one hand, they assemble following the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for colloids when van der Waals attraction overruns slightly screened electrostatic repulsion. Due to concaveness in shape, GNAs adopt zipper motifs with lateral offset in their assembly matching with our modeling of inter-GNA interaction, which form into unconventional structures resembling degenerate crystals. On the other hand, further screening of electrostatic repulsion leads to merging of clusters assembled from GNAs, reminiscent of the coalescence growth mode in atomic crystals driven by minimization of surface energy, as we measure from the surface fluctuation of clusters. Liquid-phase TEM captures the initial formation of highly curved necks bridging the two clusters. Analysis of the real-time evolution of neck width illustrates the first-time observation of coalescence in colloidal assemblies facilitated by rapid surface diffusion of GNAs. We attribute the duality to the confluence of factors (e.g., nanoscale colloidal interaction, diffusional dynamics) that we access by liquid-phase TEM, taking turns to dominate at different conditions, which is potentially generic to the nanoscale. The atom aspect, in particular, can inspire utilization of atomic crystal synthesis strategies to encode structure and dynamics in nanoscale assembly.

Hydrochromic Smart Windows to Remove Harmful Substances by Mimicking Medieval European Stained Glasses

Medieval European stained glass windows are known to display various splendid colors and remove harmful airborne substances. At present, the functions of medieval stained glass windows are imperative, from the environment, health, and energy perspectives, to develop multi-functional windows that report/control environmental conditions and remove harmful substances by utilizing visible-near-infrared light sources. Here, we suggest a strategy to mimic medieval European stained glasses for devising plasmonic-based multi-functional smart stained glass windows. The stained glass windows are prepared from the deposition of gold nanoparticles on a glass that is preliminarily coated with a responsive colloidal nanosheet. The temperature responsiveness of the nanosheet enables the effective control the gold nanoparticle density of the stained glasses. Therefore, the windows can display blue, violet, and cranberry colors. The colors become iridescent by introducing a photonic crystal monolayer. The stained glass windows are hydrochromic: they switch the colors (blue ↔ cranberry) and modulate light transmittance depending on humidity conditions. Moreover, they can remove formaldehyde under the illumination of a low-power indoor light. These functions provide a new platform for the futuristic smart windows that clean indoor air for the human health and save energy.

Shape-directed self-assembly of nanodumbbells into superstructure polymorphs

Self-assembly of colloidal nanoparticles into ordered superstructures provides a promising route to create novel/enhanced functional materials. Much progress has been made in self-assembly of anisotropic nanoparticles, but the complexity and tunability of superstructures remain restricted by their available geometries. Here we report the controlled packing of nanodumbbells (NDs) with two spherical lobes connected by one rod-like middle bar into varied superstructure polymorphs. When assembled into two-dimensional (2D) monolayer assemblies, such NDs with specific shape parameters could form orientationally ordered degenerate crystals with a 6-fold symmetry, in which these NDs possess no translational order but three allowed orientations with a rotational symmetry of 120 degrees. Detailed analyses identify the distinct roles of subunits in the ND assembly: the spherical lobes direct NDs to closely assemble together into a hexagonal pattern, and the rod-like connection between the lobes endows NDs with this specific orientational order. Such intralayer assembly features are well maintained in the two-layer superstructures of NDs; however, the interlayer stackings could be adjusted to produce stable bilayer superstructures and a series of metastable moiré patterns. Moreover, in addition to horizontal alignment, these NDs could gradually stand up to form tilted or even vertical packing based on the delicate control over the liquid-liquid interface and ND dimensions. This study provides novel insights into creating superstructures by controlling geometric features of nanoscale building blocks and may spur their novel applications.

Controllable synthesis of hierarchical Au/PdAg heterostructures consisting of nanosheets on nanorods with plasmon-enhanced electrocatalytic properties

Hierarchical Au/PdAg heterostructures consisting of PdAg nanosheets epitaxially grown on Au nanorods are synthesized in the presence of mixed surfactants and exhibit remarkable plasmon-enhanced electrocatalytic activity toward hydrogen evolution.

Directed Self-Assembly of Patchy Microgels into Anisotropic Nanostructures

Multi-geometry nanostructures with high-order, complex, and controllable geometries have attracted extensive attention in the development of functional nanomaterials. A simple and versatile strategy is proposed to construct various anisotropic nanostructures through the directed self-assembly (DSA) of patchy microgels. A general criterion for interaction parameters is developed by the variance analysis method to achieve the formation of 1D nanorods by the single directional DSA process, and 2D or 3D polymorphs including V/T/h/cross shapes, multiple arms, multi-directional bending, single/multiple rings, nanocages, etc., by the multi-directional DSA process of binary microgel blends. At the optimum interaction parameters, the nanorods exhibit the quickest formation process and the most thermodynamically stable geometry, while the various 2D or 3D assemblies exhibit controlled jointing behaviors for versatile assembly geometries. The number of recognition sites on the patchy microgel surface guides the aggregation modes of microgels during the DSA process. These assemblies can bear large curvature variance with the increase of shear rates due to the high flexibility and the ability of adjusting orientation spontaneously. The DSA behavior of patchy microgels differs from the traditional self-assembly process of block copolymers, which may open a new route for guiding the formation of controllable nanoparticle architectures.

Hollow Structures Based on Prussian Blue and Its Analogs for Electrochemical Energy Storage and Conversion

Due to their special structural characteristics, hollow structures grant fascinating physicochemical properties and widespread applications, especially in electrochemical energy storage and conversion. Recently, the research of Prussian blue (PB) and its analog (PBA) related nanomaterials has emerged and has drawn considerable attention because of their low cost, facile preparation, intrinsic open framework, and tunable composition. Here, the recent progress in the study of PB- and PBA-based hollow structures for electrochemical energy storage and conversion are summarized and discussed. First, some remarkable examples in the synthesis of hollow structures from PB- and PBA-based materials are illustrated in terms of the structural architectures, i.e., closed single-shelled hollow structures, open hollow structures, and complex hollow structures. Thereafter, their applications as potential electrode materials for lithium-/sodium-ion batteries, hybrid supercapacitors, and electrocatalysis are demonstrated. Finally, the current achievements in this field together with the limits and urgent challenges are summarized. Some perspectives on the potential solutions and possible future trends are also provided.

Directing Gold Nanoparticles into Free-Standing Honeycomb-Like Ordered Mesoporous Superstructures

2D mesoporous materials fabricated via the assembly of nanoparticles (NPs) not only possess the unique properties of nanoscale building blocks but also manifest additional collective properties due to the interactions between NPs. In this work, reported is a facile and designable way to prepare free-standing 2D mesoporous gold (Au) superstructures with a honeycomb-like configuration. During the fabrication process, Au NPs with an average diameter of 5.0 nm are assembled into a superlattice film on a diethylene glycol substrate. Then, a subsequent thermal treatment at 180 °C induces NP attachment, forming the honeycomb-like ordered mesoporous Au superstructures. Each individual NP connects with three neighboring NPs in the adjacent layer to form a tetrahedron-based framework. Mesopores confined in the superstructure have a uniform size of 3.5 nm and are arranged in an ordered hexagonal array. The metallic bonding between Au NPs increases the structural stability of architected superstructures, allowing them to be easily transferred to various substrates. In addition, electron energy-loss spectroscopy experiments and 3D finite-difference time-domain simulations reveal that electric field enhancement occurs at the confined mesopores when the superstructures are excited by light, showing their potential in nano-plasmonic applications.

Evolution of Co3O4 Nanocubes through Stepwise Oriented Attachment

Uniformly sized building units are generally required to construct highly elaborate architectures over a wide range. Defined nanocubes of Co₃O₄ evolved from deformed precursor nanograins 2-5 nm in diameter through direct oriented attachment in a nonpolar medium. Uniformly sized primary nanocubes ∼8 nm on a side with {100} faces were formed by adjusting the coverage of the oxide nanograins with oleic acid. Larger nanocubes 20-40 nm on a side were produced with further direct oriented attachment of the primary nanocubes. Ordered arrays, such as superlattices, were found to be constructed by the indirect oriented attachment of the primary and larger nanocubes covered with organic molecules.

In-Situ Growth of Au on KTaO3 Sub-Micron Cubes via Wet Chemical Approach for Enhanced Photodegradation of p-Nitrophenol

KTaO₃/Au hetero-nanostructures were synthesized by in-situ reduction of HAuCl₄ on the surface of hydrothermally-grown KTaO₃ sub-micron cubes. The concentration of Au source was found to be a critical factor in controlling the hetero-nucleation of Au nanoparticles on the surface of KTaO₃ sub-micron cubes. Loading of Au particles on KTaO₃ nanocrystals enriched KTaO₃ additional UV-vis absorption in the visible light region. Both KTaO₃ and KTaO₃/Au nanocrystals were shown to be active in the photo-degradation of p-nitrophenol, while the loading of Au on KTaO₃ clearly improved the photo-degradation efficiency of p-nitrophenol compared to that on bare KTaO₃ nanocrystals, probably due to the improved light absorption and charge separation.

Seed-Mediated Electroless Deposition of Gold Nanoparticles for Highly Uniform and Efficient SERS Enhancement

A seed-mediated electroless deposition (SMED) approach for fabrication of large-area and uniform gold nanoparticle films as efficient and reproducible as surface-enhanced Raman scattering (SERS) substrates was presented. This approach involved a seeding pretreatment procedure and a subsequent growth step. The former referred to activation of polylysine-coated glass slides in gold seed solution, and the latter required a careful control of the reactant concentration and reaction time. With the aid of gold seeds and appropriate reaction conditions, a large-area and uniform nanofilm with evenly distributed gold nanoparticles (Au NPs) was formed on the surface of the substrates after adding a mixed solution containing ascorbic acid and trisodium citrate. The morphology of the Au nanofilm was examined by scanning electron microscopy. The size evolution of Au NPs on the surface of the substrates was analyzed in detail. The nanofilm substrate was prepared by reaction conditions of the seeded activation process: 10 mL ascorbic acid and trisodium citrate mixture and 30 min of soaking time, which exhibited an excellent uniformity and reproducibility of SERS enhancement with relative standard deviation (RSD) values of less than 8% (particularly, a RSD value of 3% can be reached for the optimized measurement). Compared to the common electroless deposition, the seed-mediated electroless deposition possessed inherent advantages in controllability, reproducibility, and economic benefit.

Thiol-free oligonucleotide surface modification of gold nanoparticles for nanostructure assembly

Gold nanoparticles (AuNPs) decorated with thiol-modified DNA (HS-DNA) strands are an extensively studied, easily adjustable, and highly controllable material for constructing 3D nanostructures with various shapes and functions. However, few reproducible and robust methods involving DNA templates as a key reagent are available for obtaining 3D nanoparticle assemblies. It is still challenging to strictly control the number and location of DNA strands on the AuNP surface. Here, we introduce an efficient approach for the surface modification of AuNPs using unmodified DNA oligonucleotides by building DNA cages that trap the nanoparticles. This enables us to vary the process of nanostructure assembly and create anisotropic nanoparticles that are necessary for directed structure construction. This developed method simplifies the production process in comparison with conventional HS-DNA modification protocols and helps to precisely control the density and position of functional DNA strands designed for further hybridization with other AuNP conjugates.

Self-assembly of nickel: from nanoparticles to foils with tunable magnetic properties

Self-assembly of nickel from nanoparticles to nanowires and foils can be achieved by controlling the concentrations of sodium citrate during the electroless deposition process.