Polymerization-Like Co-Assembly of Silver Nanoplates and Patchy Spheres

Hierarchically Responsive Alternating Nano-Copolymers with Tailored Interparticle Bonds

Self-assembly of inorganic nanoparticles (NPs) is an essential tool for constructing structured materials with a wide range of applications. However, achieving ordered assembly structures with externally programmable properties in binary NP systems remains challenging. In this work, we assemble binary inorganic NPs into hierarchically pH-responsive alternating copolymer-like nanostructures in an aqueous medium by engineering the interparticle electrostatic interactions. The polymer-grafted NPs bearing opposite charges are viewed as nanoscale monomers ("nanomers"), and copolymerized into alternating nano-copolymers (ANCPs) driven by the formation of interparticle "bonds" between nanomers. The resulting ANCPs exhibit reversibly responsive "bond" length (i.e., the distance between nanomers) in response to the variation of pH in a range of ~7-10, allowing precise control over the surface plasmon resonance of ANCPs. Moreover, specific interparticle "bonds" can break up at pH≥11, leading to the dis-assembly of ANCPs into molecule-like dimers and trimers. These dimeric and trimeric structures can reassemble to form ANCPs owing to the resuming of interparticle "bonds", when the pH value of the solution changes from 11 to 7. The hierarchically responsive nanostructures may find applications in such as biosensing, optical waveguide, and electronic devices.

Supramolecular Polymerization of Polymeric Nanorods Mediated by Block Copolymers

Introducing a second component is an effective way to manipulate polymerization behavior. However, this phenomenon has rarely been observed in colloidal systems, such as polymeric nanoparticles. Here, we report the supramolecular polymerization of polymeric nanorods mediated by block copolymers. Experimental observations and simulation results illustrate that block copolymers surround the polymeric nanorods and mainly concentrate around the two ends, leaving the hydrophobic side regions exposed. These polymeric nanorods connect in a side-by-side manner through hydrophobic interactions to form bundles. As polymerization progresses, the block copolymers gradually deposit onto the bundles and finally assemble into helical nanopatterns on the outermost surface, which terminates the polymerization. It is anticipated that this work could offer inspiration for a general strategy of controllable supramolecular polymerization.

Solvent-induced assembly of mono- and divalent silica nanoparticles

Particles with attractive patches are appealing candidates to be used as building units to fabricate novel colloidal architectures by self-assembly. Here, we report the synthesis of one-patch silica nanoparticles, which consist of silica half-spheres whose concave face carries in its center a polymeric patch made of grafted polystyrene chains. The multistage synthesis allows for a fine control of the patch-to-particle size ratio from 0.23 to 0.57. The assembly of the patchy nanoparticles can be triggered by reducing the solvent quality for the polystyrene chains. Dimers or trimers can be obtained by tuning the patch-to-particle size ratio. When mixed with two-patch nanoparticles, one-patch nanoparticles control the length of the resulting chains by behaving as colloidal chain stoppers. The present strategy allows for future elaboration of novel colloidal structures by controlled assembly of nanoparticles.

Symmetry-breaking in patch formation on triangular gold nanoparticles by asymmetric polymer grafting

Synthesizing patchy particles with predictive control over patch size, shape, placement and number has been highly sought-after for nanoparticle assembly research, but is fraught with challenges. Here we show that polymers can be designed to selectively adsorb onto nanoparticle surfaces already partially coated by other chains to drive the formation of patchy nanoparticles with broken symmetry. In our model system of triangular gold nanoparticles and polystyrene-b-polyacrylic acid patch, single- and double-patch nanoparticles are produced at high yield. These asymmetric single-patch nanoparticles are shown to assemble into self-limited patch‒patch connected bowties exhibiting intriguing plasmonic properties. To unveil the mechanism of symmetry-breaking patch formation, we develop a theory that accurately predicts our experimental observations at all scales—from patch patterning on nanoparticles, to the size/shape of the patches, to the particle assemblies driven by patch‒patch interactions. Both the experimental strategy and theoretical prediction extend to nanoparticles of other shapes such as octahedra and bipyramids. Our work provides an approach to leverage polymer interactions with nanoscale curved surfaces for asymmetric grafting in nanomaterials engineering.

Kinetically Programming Copolymerization-like Coassembly of Multicomponent Nanoparticles with DNA

Programmable coassembly of multicomponent nanoparticles (NPs) into heterostructures has the capability to build upon nanostructured metamaterials with enhanced complexity and diversity. However, a general understanding of how to manipulate the sequence-defined heterostructures using straightforward concepts and quantitatively predict the coassembly process remains unreached. Drawing inspiration from the synthetic concepts of molecular block copolymers is extremely beneficial to achieve controllable coassembly of NPs and access mesoscale structuring mechanisms. We herein report a general paradigm of kinetic pathway guidance for the controllable coassembly of bivalent DNA-functionalized NPs into regular block-copolymer-like heterostructures via the stepwise polymerization strategy. By quantifying the coassembly kinetics and structural statistics, it is demonstrated that the coassembly of multicomponent NPs, through directing the specific pathways of prepolymer intermediates, follows the step-growth copolymerization mechanism. Meanwhile, a quantitative model is developed to predict the growth kinetics and outcomes of heterostructures, all controlled by the designed elements of the coassembly system. Furthermore, the stepwise polymerization strategy can be generalized to build upon a great variety of regular nanopolymers with complex architectures, such as multiblock terpolymers and ladder copolymers. Our theoretical and simulation results provide fundamental insights on quantitative predictions of the coassembly kinetics and coassembled outcomes, which can aid in realizing a diverse set of supramolecular DNA materials by the rational design of kinetic pathways.

Two-dimensional assembled PVP-modified silver nanoprisms guided by butanol for surface-enhanced Raman scattering-based invisible printing platforms

This study proposes a methodology for the fabrication of two-dimensional assembled colloidal nanocrystals based on the classical theory for the surface excess of a short-chain alcohol (butanol) in an aqueous mixture and Rayleigh-Bénard-Marangoni convection caused by temperature and/or surface tension gradients due to the volatilization of butanol at the air-water interface. When polyvinylpyrrolidone (PVP)-modified anisotropic silver nanoprisms dispersed in butanol were added into the water phase, the nanoprisms were guided to the air-water interface via adsorbed butanol together with free butanol and formed dense two-dimensional assemblies through the lateral attraction between nanoprisms as the adsorbed butanol was volatilized. The obtained dense film composed of silver nanoprisms exhibited surface-enhanced Raman scattering (SERS) activity, and in particular, the activity was largely enhanced by low-pressure plasma treatment. A SERS-based invisible printing platform that could only be recognized by x-y SERS mapping was demonstrated with the patterned nanoprism films.

Real-Space Image of Charged Patches in Tunable-Size Nanocrystals

The remarkable dual nature of faceted-charge patchy metal fluoride nanocrystals arises from the spontaneous selective coordination of anionic and cationic ligands on the different facets of the nanocrystals. In previous studies, the identification and origin of the charge at the patches were obtained by combining computer simulations with indirect experimental evidence. Taking a step further, we report herein the first direct real-space identification by Kelvin probe force microscopy of the predicted faceted-charge patchy behavior, allowing the image of the dual faceted-charge surfaces. High-resolution transmission electron microscopy reveals the detailed nanocrystal faceting and allows unambiguously inferring the hydrophilic or hydrophobic role of each facet from the identification of the surface atoms exposed at the respective crystallographic planes. The success of the study lies in a foresighted synthesis methodology designed to tune the nanocrystal size to be suitable for microscopy studies and demanding applications.

Linear Assembly of Two-Patch Silica Nanoparticles and Control of Chain Length by Coassembly with Colloidal Chain Stoppers

The self-assembly of patchy nanosized building blocks is an efficient strategy for producing highly organized materials. Herein we report the chaining of divalent silica nanoparticles with polystyrene patches dispersed in tetrahydrofuran triggered by lowering the solvent quality. We study the influence of the patch-to-particle size ratio and show that the nature of the added nonsolvent, for example, ethanol, water, or salty water, and its volume fraction should be carefully adjusted. We demonstrate that colloidal assembly initially obeys the kinetic model of step-growth polymerization and that beyond a certain length, the chains have the possibility to cyclize. We also show that the length of the chains can be controlled by the addition of one-patch silica nanoparticles, which act as colloidal analogues of chain stoppers.

From colloidal particles to photonic crystals: advances in self-assembly and their emerging applications

Over the last three decades, photonic crystals (PhCs) have attracted intense interests thanks to their broad potential applications in optics and photonics. Generally, these structures can be fabricated via either "top-down" lithographic or "bottom-up" self-assembly approaches. The self-assembly approaches have attracted particular attention due to their low cost, simple fabrication processes, relative convenience of scaling up, and the ease of creating complex structures with nanometer precision. The self-assembled colloidal crystals (CCs), which are good candidates for PhCs, have offered unprecedented opportunities for photonics, optics, optoelectronics, sensing, energy harvesting, environmental remediation, pigments, and many other applications. The creation of high-quality CCs and their mass fabrication over large areas are the critical limiting factors for real-world applications. This paper reviews the state-of-the-art techniques in the self-assembly of colloidal particles for the fabrication of large-area high-quality CCs and CCs with unique symmetries. The first part of this review summarizes the types of defects commonly encountered in the fabrication process and their effects on the optical properties of the resultant CCs. Next, the mechanisms of the formation of cracks/defects are discussed, and a range of versatile fabrication methods to create large-area crack/defect-free two-dimensional and three-dimensional CCs are described. Meanwhile, we also shed light on both the advantages and limitations of these advanced approaches developed to fabricate high-quality CCs. The self-assembly routes and achievements in the fabrication of CCs with the ability to open a complete photonic bandgap, such as cubic diamond and pyrochlore structure CCs, are discussed as well. Then emerging applications of large-area high-quality CCs and unique photonic structures enabled by the advanced self-assembly methods are illustrated. At the end of this review, we outlook the future approaches in the fabrication of perfect CCs and highlight their novel real-world applications.

Directional and Reconfigurable Assembly of Metallodielectric Patchy Particles

Colloidal particles with surface patches can self-assemble with high directionality, but the resulting assemblies cannot reconfigure unless the patch arrangement (number, symmetry, etc.) is altered. While external fields with tunable inputs can guide the assembly of dynamic structures, they encourage particle alignment relative to its shape rather than the surface patterns. Here, we report on the synthesis of metallodielectric patchy particles and their assembly under the AC electric field, which gives rise to a series of structures including two-layer alternating chains, open-brick walls, staggering stacks, and vertical chains that are directed by the patches yet reconfigurable by the field. The configurations of the assemblies (e.g., the chains) can be further switched between a rigid and a flexible state emulating the conformations of polymers. Our work suggests that, for directed colloidal assembly, the particle complexities (patches and shapes) can be coupled with the external manipulations in a cooperative manner for creating materials with precise yet reconfigurable structures.

Designing Surface Charge Patterns for Shape Control of Deformable Nanoparticles

Designing reconfigurable materials based on deformable nanoparticles (NPs) hinges on an understanding of the energetically favored shapes these NPs can adopt. Using simulations, we show that hollow, deformable, patchy NPs tailored with surface charge patterns such as Janus patches, stripes, and polyhedrally distributed patches differently adapt their shape in response to changes in patterns and ionic strength, transforming into capsules, hemispheres, variably dimpled bowls, and polyhedra. The links between anisotropy in NP surface charge, shape, and the elastic energy density are discussed.

Machine Learning to Reveal Nanoparticle Dynamics from Liquid-Phase TEM Videos

Liquid-phase transmission electron microscopy (TEM) has been recently applied to materials chemistry to gain fundamental understanding of various reaction and phase transition dynamics at nanometer resolution. However, quantitative extraction of physical and chemical parameters from the liquid-phase TEM videos remains bottlenecked by the lack of automated analysis methods compatible with the videos' high noisiness and spatial heterogeneity. Here, we integrate, for the first time, liquid-phase TEM imaging with our customized analysis framework based on a machine learning model called U-Net neural network. This combination is made possible by our workflow to generate simulated TEM images as the training data with well-defined ground truth. We apply this framework to three typical systems of colloidal nanoparticles, concerning their diffusion and interaction, reaction kinetics, and assembly dynamics, all resolved in real-time and real-space by liquid-phase TEM. A diversity of properties for differently shaped anisotropic nanoparticles are mapped, including the anisotropic interaction landscape of nanoprisms, curvature-dependent and staged etching profiles of nanorods, and an unexpected kinetic law of first-order chaining assembly of concave nanocubes. These systems representing properties at the nanoscale are otherwise experimentally inaccessible. Compared to the prevalent image segmentation methods, U-Net shows a superior capability to predict the position and shape boundary of nanoparticles from highly noisy and fluctuating background-a challenge common and sometimes inevitable in liquid-phase TEM videos. We expect our framework to push the potency of liquid-phase TEM to its full quantitative level and to shed insights, in high-throughput and statistically significant fashion, on the nanoscale dynamics of synthetic and biological nanomaterials.

Critical differences in 3D atomic structure of individual ligand-protected nanocrystals in solution

Precise three-dimensional (3D) atomic structure determination of individual nanocrystals is a prerequisite for understanding and predicting their physical properties. Nanocrystals from the same synthesis batch display what are often presumed to be small but possibly important differences in size, lattice distortions, and defects, which can only be understood by structural characterization with high spatial 3D resolution. We solved the structures of individual colloidal platinum nanocrystals by developing atomic-resolution 3D liquid-cell electron microscopy to reveal critical intrinsic heterogeneity of ligand-protected platinum nanocrystals in solution, including structural degeneracies, lattice parameter deviations, internal defects, and strain. These differences in structure lead to substantial contributions to free energies, consequential enough that they must be considered in any discussion of fundamental nanocrystal properties or applications.

Patterning of polyoxometalate rings on gold nanorods

We report a facile method for the self-assembly of various polyoxometalates (POMs) on cetyltriethylammonium bromide-covered gold nanorods (GNRs) into an ordered array of POM rings along their long axis. The periodic distance of POM rings can be tuned by the POM charge and the transverse curvature of GNRs.

A Polyaddition Model for the Prebiotic Polymerization of RNA and RNA-Like Polymers

Implicit in the RNA world hypothesis is that prebiotic RNA synthesis, despite occurring in an environment without biochemical catalysts, produced the long RNA polymers which are essential to the formation of life. In order to investigate the prebiotic formation of long RNA polymers, we consider a general solution of functionally identical monomer units that are capable of bonding to form linear polymers by a step-growth process. Under the assumptions that (1) the solution is well-mixed and (2) bonding/unbonding rates are independent of polymerization state, the concentration of each length of polymer follows the geometric Flory-Schulz distribution. We consider the rate dynamics that produce this equilibrium; connect the rate dynamics, Gibbs free energy of bond formation, and the bonding probability; solve the dynamics in closed form for the representative special case of a Flory-Schulz initial condition; and demonstrate the effects of imposing a maximum polymer length. Afterwards, we derive a lower bound on the error introduced by truncation and compare this lower bound to the actual error found in our simulation. Finally, we suggest methods to connect these theoretical predictions to experimental results.

Polymer-guided assembly of inorganic nanoparticles

The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.

Reversible Polymerization-like Kinetics for Programmable Self-Assembly of DNA-Encoded Nanoparticles with Limited Valence

A similarity between the polymerization reaction of molecules and the self-assembly of nanoparticles provides a unique way to reliably predict structural characteristics of nanoparticle ensembles. However, the quantitative elucidation of programmable self-assembly kinetics of DNA-encoded nanoparticles is still challenging due to the existence of hybridization and dehybridization of DNA strands. Herein, a joint theoretical-computational method is developed to explicate the mechanism and kinetics of programmable self-assembly of limited-valence nanoparticles with surface encoding of complementary DNA strands. It is revealed that the DNA-encoded nanoparticles are programmed to form a diverse range of self-assembled superstructures with complex architecture, such as linear chains, sols, and gels of nanoparticles. It is theoretically demonstrated that the programmable self-assembly of DNA-encoded nanoparticles with limited valence generally obeys the kinetics and statistics of reversible step-growth polymerization originally proposed in polymer science. Furthermore, the theoretical-computational method is applied to capture the programmable self-assembly behavior of bivalent DNA-protein conjugates. The obtained results not only provide fundamental insights into the programmable self-assembly of DNA-encoded nanoparticles but also offer design rules for the DNA-programmed superstructures with elaborate architecture.

Construction and Properties of Sierpiński Triangular Fractals on Surfaces

Fractal structures are of fundamental importance in science, engineering, mathematics, and aesthetics. Construction of molecular fractals on surfaces can help to understand the formation mechanism of fractals and a series of achievements have been acquired in the preparation of molecular fractals. This review focuses on Sierpiński triangles (STs), representatives of various prototypical fractals, on surfaces. They are investigated by Monte Carlo simulations and ultra-high vacuum scanning tunneling microscopy. STs are bonded through halogen bonds, hydrogen bonds, metal-organic coordination bonds and covalent bonds. The coexistence of and competition between fractals and crystals are realized for a hydrogen-bonded system. Electronic properties of two types of STs are summarized.

Investigation of Geometric Landscape and Structure-Property Relations for Colloidal Superstructures Using Genetic Algorithm

Over the past two decades, colloidal particles with a variety of shapes, sizes, and compositions have been synthesized and characterized successfully. One of the most important applications for colloidal building blocks is to engineer functional structures as mechanical, electrical, and optical metamaterials. However, complex interaction dynamics between the building blocks as well as sophisticated structure-property relationships make it challenging to design structures with predictable target properties. In this paper, we implement an inverse material design framework using Genetic Algorithm (GA)-based techniques to streamline the design of colloidal structures based on target properties. We investigate spherical particles as well as colloidal molecules of different sizes and shapes and evaluate a Geometric Landscape Accessibility parameter that identifies the size of feasible domains within the geometric phase space of each structure. Considering target photonic properties, our GA-assisted framework is further utilized to identify sets of building blocks and structures that lead to various target values for the size of the photonic band gaps. The proposed framework in this study will provide new insight for predictive computational material design approaches and help establish more efficient ways of understanding structure-property relations in sub-micrometer-scale materials.

Dimension-shifting multifunctional biocompatible nanocomposites

A facile method to prepare dimension-shifting biocompatible multifunctional nanocomposites is described. The design is based on magnetic - and electrostatic - induced transitions from the dispersed state to the assembled state of zero-dimensional nanoparticles, resulting in dimension conversion.

Hierarchical self-assembly of 3D lattices from polydisperse anisometric colloids

Colloids are mainly divided into two types defined by size. Micron-scale colloids are widely used as model systems to study phase transitions, while nanoparticles have physicochemical properties unique to their size. Here we study a promising yet underexplored third type: anisometric colloids, which integrate micrometer and nanometer dimensions into the same particle. We show that our prototypical system of anisometric silver plates with a high polydispersity assemble, unexpectedly, into an ordered, three-dimensional lattice. Real-time imaging and interaction modeling elucidate the crucial role of anisometry, which directs hierarchical assembly into secondary building blocks-columns-which are sufficiently monodisperse for further ordering. Ionic strength and plate tip morphology control the shape of the columns, and therefore the final lattice structures (hexagonal versus honeycomb). Our joint experiment-modeling study demonstrates potentials of encoding unconventional assembly in anisometric colloids, which can likely introduce properties and phase behaviors inaccessible to micron- or nanometer-scale colloids.

Sequence-Regulated Supracolloidal Copolymers via Copolymerization-Like Coassembly of Binary Mixtures of Patchy Nanoparticles

Synthetic copolymers of molecular systems serve as an inspiration for creation of one-dimensional copolymer-like superstructures via coassembly of anisometric nanoparticles. In contrast to the covalent and molecular copolymers, the details of formation mechanisms of copolymer-like superstructures, as well as the factors determining their length and the sequences of arranged nanoparticles, are still poorly understood. Herein, we propose a joint theoretical-computational framework to probe into the coassembly mechanism and kinetics of binary mixtures of patchy nanoparticles. By applying the coarse-grained molecular dynamics simulations, it is demonstrated that the coassembly of patchy nanoparticles markedly resembles many aspects of molecular step-growth copolymerization, and the sequences of nanoparticles inside the copolymer-like superstructures can be finely regulated by the relative activity and the initial ingredient of patchy nanoparticles as well as the coassembly strategy. A quantitatively copolymerization-like model is developed to account for the coassembly kinetics of patchy nanoparticles and the sequence distribution of arranged nanoparticles, all governed by the elaborate design of lower-level building units. The jointly theoretical and simulated studies offer mechanistic insights into the copolymerization-like kinetics and the sequence prediction for the coassembly of binary mixtures of patchy nanoparticles, paving the way toward the rational design of copolymer-like superstructures with various sequences and functionalities.

Polymerization-like kinetics of the self-assembly of colloidal nanoparticles into supracolloidal polymers

The self-assembly of colloidal nanoparticles is conceptually analogous to the polymerization of reactive monomers in molecular systems. However, less is known about the polymerization of colloidal nanoparticles into supracolloidal polymers. Herein, using coarse-grained molecular dynamics and theoretical analysis, we reveal the self-assembly mechanism and kinetics of colloidal nanoparticles constructed from triblock terpolymers. The results show that the formation pathway of supracolloidal polymers involves monomer condensation and oligomer coalescence through the manner of end-to-end collisions. In contrast to the polymerization kinetics of molecular systems, the simulations and theoretical analysis definitely demonstrate that the growth of supracolloidal polymers obeys diffusion-controlled step-growth polymerization kinetics with a variable rate coefficient, where the growth rate is dependent upon the concentration of colloidal nanoparticles and the molecular information of triblock terpolymers. Our findings possess wide implications for understanding the growth of supracolloidal polymers, which is important for the rational and precise design of one-dimensional self-assembled superstructures with new horizons for biomedical applications.

Self-Assembly of Quantum Dot-Gold Heterodimer Nanocrystals with Orientational Order

The self-assembly of nanocrystals into ordered superlattices is a powerful strategy for the production of functional nanomaterials. The assembly of well-ordered target structures, however, requires control over the building blocks' size and shape as well as their interactions. While nanocrystals with homogeneous composition are now routinely synthesized with high precision and assembled into various ordered structures, high-quality multicomponent nanocrystals and their ordered assemblies are rarely reported. In this paper, we demonstrate the synthesis of quantum dot-gold (QD-Au) heterodimers. These heterodimers possess a uniform shape and narrow size distribution and are capped with oleylamine and dodecyltrimethylammonium bromide (DTAB). Assembly of the heterodimers results in a superlattice with long-range orientational alignment of dimers. Using synchrotron-based X-ray measurements, we characterize the complex superstructure formed from the dimers. Molecular dynamics simulations of a coarse-grained model suggest that anisotropic interactions between the quantum dot and gold components of the dimer drive superlattice formation. The high degree of orientational order demonstrated in this work is a potential route to nanomaterials with useful optoelectronic properties.

Fabrication of Large-Area Arrays of Vertically Aligned Gold Nanorods

Anisotropic nanoparticles, such as nanorods and nanoprisms, enable packing of complex nanoparticle structures with different symmetry and assembly orientation, which result in unique functions. Despite previous extensive efforts, formation of large areas of oriented or aligned nanoparticle structures still remains a great challenge. Here, we report fabrication of large-area arrays of vertically aligned gold nanorods (GNR) through a controlled evaporation deposition process. We began with a homogeneous suspension of GNR and surfactants prepared in water. During drop casting on silicon substrates, evaporation of water progressively enriched the concentrations of the GNR suspension, which induces the balance between electrostatic interactions and entropically driven depletion attraction in the evaporating solution to produce large-area arrays of self-assembled GNR on the substrates. Electron microscopy characterizations revealed the formation of layers of vertically aligned GNR arrays that consisted of hexagonally close-packed GNR in each layer. Benefiting from the close-packed GNR arrays and their smooth topography, the GNR arrays exhibited a surface-enhanced Raman scattering (SERS) signal for molecular detection at a concentration as low as 10^-15 M. Because of the uniformity in large area, the GNR arrays exhibited exceptional detecting reproducibility and operability. This method is scalable and cost-effective and could lead to diverse packing structures and functions by variation of guest nanoparticles in the suspensions.

Seeded Growth Synthesis of Gold Nanotriangles: Size Control, SAXS Analysis, and SERS Performance

We studied the controlled growth of triangular prismatic Au nanoparticles with different beveled sides for surface-enhanced Raman spectroscopy (SERS) applications. First, in a seedless synthesis using 3-butenoic acid (3BA) and benzyldimethylammonium chloride (BDAC), gold nanotriangles (AuNTs) were synthesized in a mixture with gold nanooctahedra (AuNOCs) and separated by depletion-induced flocculation. Here, the influence of temperature, pH, and reducing agent on the reaction kinetics was initially investigated by UV-vis and correlated to the size and yield of AuNT seeds. In a second step, the AuNT size was increased by seed-mediated overgrowth with Au. We show for the first time that preformed 3BA-synthesized AuNT seeds can be overgrown up to a final edge length of 175 nm and a thickness of 80 nm while maintaining their triangular shape and tip sharpness. The NT morphology, including edge length, thickness, and tip rounding, was precisely characterized in dispersion by small-angle X-ray scattering and in dry state by transmission electron microscopy and field-emission scanning electron microscopy. For sensor purposes, we studied the size-dependent SERS performance of AuNTs yielding analytical enhancement factors between 0.9 × 10⁴ and 5.6 × 10⁴ and nanomolar limit of detection (10^-8-10^-9 M) for 4-mercaptobenzoic acid and BDAC. These results confirm that the 3BA approach allows the fabrication of AuNTs in a whole range of sizes maintaining the NT morphology. This enables tailoring of localized surface plasmon resonances between 590 and 740 nm, even in the near-infrared window of a biological tissue, for use as colloidal SERS sensing agents or for optoelectronic applications.

Cluster-mediated assembly enables step-growth copolymerization from binary nanoparticle mixtures with rationally designed architectures

Multicomponent nanoparticle chains structurally analogous to random, block, and alternating copolymers, respectively, have been fabricated by a cluster-mediated self-assembly process.

Directed co-assembly of binary nanoparticles (NPs) into one-dimensional copolymer-like chains is fascinating but challenging in the realm of material science. While many strategies have been developed to induce the polymerization of NPs, it remains a grand challenge to produce colloidal copolymers with widely tailored compositions and precisely controlled architectures. Herein we report a robust colloidal polymerization strategy, which enables the growth of sophisticated NP chains with elaborately designed structures. By quantifying NP assembly statistics and kinetics, we establish that the linear assembly of colloidal NPs, with the assistance of PbSO₄ clusters, follows a step-growth polymerization mechanism, and on the basis of this, we design and fabricate NP chains structurally analogous to random, block, and alternating copolymers, respectively. Our studies offer mechanistic insights into cluster-mediated colloidal polymerization, paving the way toward the rational synthesis of colloidal copolymers with quantitatively predicted architectures and functionalities.