Metallic nanohelices are extremely rare and, to date, have never been synthesized by a direct solution method. In this work, we report ultralong Au nanohelices grown in solution under ambient conditions. They are ultralong with several tens of micrometers in length, with extraordinary aspect ratio (length/diameter greater than 22 300) and the number of pitches (more than 22 000 pitches). The pitch and width are uniform within each helix but vary widely among the helices. Crystal analyses showed that the facets, twin boundaries, grain sizes, and orientations are aperiodic along the helices. The apparent smooth curving is only possible with a large number of surface steps, suggesting that these structural features are the mere consequence of the helix formation rather than the cause. We propose that the nanowires are formed by the active surface growth mechanism and that the helicity originates from the random and asymmetrical blocking of nuclei embedded within the floccules of ligand complexes, in the form of either asymmetric binding of ligands or asymmetric diffusion of growth materials through the floccules. The separate growth environment of these nuclei causes constant helicity within each helix but differing helicity among the individuals. The embedding also provides a robust environment for the sustained growth of the nanohelices, leading to their record length and consistency.Keywords: ambient condition; asymmetric; gold; nanohelices; solution growth; ultralong;

World’s smallest screws with helical threads are synthesized via mild etching of Ag nanowires. With detailed characterization, we show that this nanostructure arises not from the transformation of the initial lattice, but the result of a unique etching mode. Three-dimensional printed models are used to illustrate the evolution of etch pits, from which a possible mechanism is postulated.

Depending on the synthetic methods, bimetallic nanoparticles can have either core–shell, phase segregated, alloy, or partially coalesced structures, presenting different degrees of atomic mixing on their surface. Along with the variations of size and morphology, the structural differences make it difficult to compare the catalytic activity of bimetallic nanoparticles. In this article, we developed a facile screening method that can focus on the synergistic effects rather than structural differences. Prefabricated nanoparticles are mixed together to form linear aggregates and coalesced to form bimetallic junctions. Their hollow silica shells allow materials transport but prevent further aggregation. With a level playing field, this screening platform can identify the best bimetallic combination for a catalytic reaction, before optimizing the synthesis. This approach is more advantageous than the conventional approaches where structural difference may have dominant effects on the catalytic performance.

We show that partial inhibition of the emerging Ag domain can be achieved by controlling the growth dynamics. With the symmetry broken by the “fresh” surface, sequentially growth gives (Au sphere)–(Ag wire)–(Ag plate) triblock nanostructures. This new understanding opens doors to sophisticated synthetic designs, broadening the horizon of our search for functional architectures.

We expand the scope of the previously developed Active Surface Growth mode for growing substrate-bound ultrathin Pd (d = 4 nm) and Ag nanowires (d = 30 nm) in aqueous solution under ambient conditions. Using Au nanorods as the seeds, selective growth at the contact line between the rod and the substrate eventually leads to an attached Pd nanoplate. The unique growth mode also allows sequential growth of different materials via a single seed, giving substrate-bound Au–Pd diblock nanowires. The new abilities to use seed shape to pre-define the active sites and to apply sequential growth open windows for new pathways to hybrid nanostructures.

We report a facile method to encapsulate Au nanoparticles (NPs) in an amphiphilic ABA triblock copolymer, poly(4-vinylpyridine)-block-polystyrene-block-poly(4-vinylpyridine) (P4VP-b-PS-b-P4VP), forming Au@P4VP-b-PS-b-P4VP core–shell nanostructures. On the basis of the hydrophobically funcationalized Au surface, we propose that the P4VP-b-PS-b-P4VP is folded into a U shape, so that the hydrophobic PS block attach to the Au surface and the hydrophilic P4VP blocks are dissolved in the solution facing outwards. As the polymer micelles transform from spheres to cylinders and vesicles, the embedded Au NPs are brought along in the process and end up in the complex polymer nanostructures. Driven by the tendency of the polymer to form cylindrical micelles, the positively charged core–shell NPs can assemble into chains, where the method was only demonstrated previously exploiting the negatively charged amphiphilic polystyrene-block-poly(acrylic acid) shells.

A Boerdijk–Coxeter–Bernal (BCB) helix is made of linearly stacked regular tetrahedra (tetrahelix). As such, it is chiral without nontrivial translational or rotational symmetries. We demonstrate here an example of the chiral BCB structure made of totally symmetrical gold atoms, created in nanowires by direct chemical synthesis. Detailed study by high-resolution electron microscopy illustrates their elegant chiral structure and the unique one-dimensional “pseudo-periodicity”. The BCB-type atomic packing mode is proposed to be a result of the competition and compromise between the lattice and surface energy.

Amphiphilic block copolymers such as polystyrene-block-poly(acrylic acid) (PSPAA) give micelles that are known to undergo sphere-to-cylinder shape transformation. Exploiting this polymer property, core–shell nanoparticles coated in PSPAA can be “polymerized” into long chains following the chain-growth polymerization mode. This method is now extended to include a variety of different nanoparticles. A case study on the assembly process was carried out to understand the influence of the PAA block length, the surface ligand, and the size and morphology of the monomer nanoparticles. Shortening the PAA block promotes the reorganization of the amphiphilic copolymer in the micelles, which is essential for assembling large Au nanoparticles. Small Au nanoparticles can be directly “copolymerized” with empty PSPAA micelles into chains. The reaction time, acid quantity, and the [Au nanoparticles]/[PSPAA micelles] concentration ratio played important roles in controlling the sphere–cylinder–vesicle conversion of the PSPAA micelles, giving rise to different kinds of random “copolymers”. With this knowledge, a general method is then developed to synthesize homo, random, and block “copolymers”, where the basic units include small Au nanoparticles (d = 16 nm), large Au nanoparticles (d = 32 nm), Au nanorods, Te nanowires, and carbon nanotubes. Given the lack of means for assembling nanoparticles, advancing synthetic capabilities is of crucial importance. Our work provides convenient routes for combining nanoparticles into long-chain structures, facilitating rational design of complex nanostructures in the future.Keywords: assembly; chain growth polymerization; polymerization of nanoparticles; PSPAA micelle; vesicle

Chirality in nanoscience may offer new opportunities for applications beyond the traditional fields of chirality, such as the asymmetric catalysts in the molecular world and the chiral propellers in the macroscopic world. In the last two decades, there has been an amazing array of chiral nanostructures reported in the literature. This review aims to explore and categorize the common mechanisms underlying these systems. We start by analyzing the origin of chirality in simple systems such as the helical spring and hair vortex. Then, the chiral nanostructures in the literature were categorized according to their material composition and underlying mechanism. Special attention is paid to highlight systems with original discoveries, exceptional structural characteristics, or unique mechanisms.

The core–shell nanoparticle structure, which consists of an inner layer “guest” nanoparticle encapsulated inside another of a different material, is the simplest motif in two-component systems. In comparison to the conventional single-component systems, complex systems pose both challenges and opportunities. In this Account, we describe our recent progresses in using core–shell motif for exploring new and sophisticated nanostructures. Our discussion is focused on the mechanistic details, in order to facilitate rational design in future studies. We believe that systematic development of synthetic capability, particularly in complex and multifunctional systems, is of great importance for future applications.A key issue in obtaining core–shell nanostructures is minimizing the core-shell interfacial tension. Typically, one can coat the core with a ligand for better interaction with the shell. By selecting suitable ligands, we have developed general encapsulation methods in three systems. A variety of nanoparticles and nanowires were encapsulated using either amphiphilic block copolymer (polystyrene-block-poly(acrylic acid)), conductive polymer (polyaniline, polypyrrole, or polythiophene), or silica as the shell material.Obvious uses of shells are to stabilize colloidal objects, retain their surface ligands, prevent particle aggregation, or preserve the assembled superstructures. These simple capabilities are essential in our synthesis of surface-enhanced Raman scattering nanoprobes, in assigning the solution state of nanostructures before drying, and in developing purification methods for nano-objects. When it is applied in situ during nanocrystal growth or nanoparticle assembly, the intermediates trapped by shell encapsulation can offer great insights into the mechanistic details.On the other hand, having a shell as a second component provides a window for exploring the core–shell synergistic effects. Hybrid core–shell nanocrystals have interesting effects, for example, in causing the untwisting of nanowires to give double helices. In addition, partial polymer shells can bias nanocrystal growth towards one direction or promote the random growth of Au dendritic structures; contracting polymer shells can compress the embedded nanofilaments (Au nanowires or carbon nanotubes), forcing them to coil into rings. Also, by exploiting the sphere-to-cylinder conversion of block copolymer micelles, the Au nanoparticles pre-embedded in the polymer micelles can be assembled into long chains.Lastly, shells are also very useful for mechanistic studies. We have demonstrated such applications in studying the controlled aggregation of nanoparticles, in probing the diffusion kinetics of model drug molecules from nanocarriers to nanoacceptors, and in measuring the ionic diffusion through polyaniline shells.

Assembling nanoparticles into well-defined structures is an important way to create and tailor the optical properties of materials. Most advances in metamaterials research to date have been based on structures fabricated in two-dimensional planar geometries. Here, we show an efficient method for assembling noble metal nanoparticles into stable, three-dimensional (3-D) clusters, whose optical properties can be highly sensitive or remarkably independent of cluster orientation, depending on particle number and cluster geometry. Some of the clusters, such as tetrahedra and icosahedra, could serve as the optical kernels for metafluids, imparting metamaterial optical properties into disordered media such as liquids, glasses, or plastics, free from the requirement of nanostructure orientation.

Growing oxide shells on seed nanoparticles requires the control of several processes: (a) the nucleation and growth of the shell material; (b) the “wetting” of the shell material on the seeds; and (c) the aggregation of the nanoparticles. These processes are influenced by a number of factors, many of which are related. Without understanding the interdependence of these contributing factors, it is difficult to circumvent problems and achieve rational synthesis. We first did a case study on encapsulating Au nanoparticles with ZnO to understand the multiple roles of polyvinylpyrrolidone (PVP) and their dependence on other factors. We developed a general method for coating ZnO on a variety of seeds, including metals, oxides, polymer nanoparticles, graphene oxide, and carbon nanotube. This method can be further extended to include Fe3O4, MnO, Co2O3, TiO2, Eu2O3, Tb2O3, Gd2O3, β-Ni(OH)2, ZnS, and CdS as the shell materials. The understanding obtained in this systematic study will aid rational design and synthesis of other core–shell nanostructures.

We report a nanowire growth that is highly unconventional: (1) nanowires can grow from substrate-bound seeds but cannot from colloidal seeds under otherwise the same conditions; (2) the nanowires grow from only one side of the seeds, with their diameter independent of the size of the seeds; and (3) vertically aligned ultrathin nanowires are obtained on substrates, using aqueous solution and ambient conditions. With carefully designed experiments, we propose and test a new mechanism that can explain these unusual phenonmena. It turns out that the strong binding of ligands in this system forces selective deposition of Au at the ligand-deficient interface between Au seeds and oxide substrates. This means of promoting anisotropic growth of nanocrystals into nanowires is previously unknown in the literature. We are able to pinpoint the site of active growth and explain the control of nanowire width. The sustained growth at the active site and the inhibited growth at its parameter push the nanocrystals upward into wires; their diameter is dependent on the dynamic competition of the two processes. The site-specific growth from substrate-anchored seeds provides a rare means to create substrate-nanowire hierarchical structures in aqueous solution under ambient conditions. Rendering a surface conductive, particularly one with complex surface morphology, is now made easy.Keywords: active site; anisotropic growth; hierarchical structure; ligand control; nanowire; substrate-bound seeds

Hydrophobic carbon nanotubes (CNTs) and hydrophilic nanofilaments such as oxidized CNTs, Pd nanowires (NWs), and MnO2 NWs are transformed from wires to rings by a general methodology. We show that both oil-in-water and water-in-oil emulsions, so long as their droplet size is sufficiently small, can exert significant force to the entrapped nanostructures, causing their deformation. This effect can be easily achieved by simply mixing a few solutions in correct ratios. Even preformed oil droplets can take in CNTs from the aqueous solution converting them into rings, indicating the important role of thermodynamics: The question here is not if the droplets can exert sufficient force to bend the nanofilaments, because their random vibration may be already doing it. As long as the difference in solvation energy is large enough for a nanofilament, it would “want” to move away from the bulk solution and fit inside tiny droplets, even at the cost of induced strain energy. That said, the specific interactions between a droplet and a filament are also of importance. For example, when an oil droplet rapidly shrinks in size, it can compress the entrapped CNTs in multiple stages into structures with higher curvatures (thus higher strain) than that of a circular ring, which has minimal induced strain inside a spherical droplet.

We show that embedding of a surface ligand can dramatically affect the metal–metal interfacial energy, making it possible to create nanostructures in defiance of traditional wisdom. Despite matching Au–Ag lattices, Au–Ag hybrid NPs can be continuously tuned from concentric core–shell, eccentric core–shell, acorn, to dimer structures. This method can be extended to tune even Au–Au and Ag–Ag interfaces.

We demonstrate a unique capability in partially oxidizing the oligoaniline shell on gold nanoparticles to polyaniline. Because of the solubility difference, the unreacted inner shell section can be selectively dissolved by 2-propanol, giving yolk-shell nanostructures and, thus, making it possible for assessing the oxidized section. The ionic diffusion through the polymer shell is found to be the rate-determining step in the overall process. Conservative estimates show that the diffusion coefficient of AuCl4– is at least 700 times slower than that of the typical rate values in traditional studies. It is most likely caused by the lack of micropores in the polymer structures. Such mircopores are hard to avoid in preparing polymer membranes by casting or drying of polymers dissolved in organic solvents. We can rule out the presence of irregular pores on the basis of the uniformly oxidized shell section. With the nanoscale shells, the system is sensitive enough to detect minute changes in the shell or small differences among the individual nanoparticles. Even with a small increase in porosity, for example, when the polyaniline shell is swollen using small amounts of DMF (3%, 5%, or 10% in aqueous solutions), the diffusion coefficient of AuCl4– increases to 4, 11, and 17 times, respectively. Thus, our study demonstrates a new methodology for studying the diffusion of ions in hydrophobic polymers.

We show that seeded growth can be applied to creating two-dimensional (2D) dendritic Au nanostructures on sample grids, which can be directly characterized by transmission electron microscopy (TEM). The 2D synthesis of highly consistent structures offers a novel mechanistic perspective on the aggregation of colloidal Au nanocrystals on a surface.

Growth of polythiophene (PTh) on five-fold twinned Ag nanowires (NWs) is not symmetrical due to preferred etching of their intrinsic defects. This imbalance of polymer formation leads to consistent bending action along the etched NWs, coiling the resulting Ag-PTh nanocomposites into planar spirals. We studied the etching intermediates and also the effects of the surface ligands in order to understand the symmetry-breaking action. The defect-dependent etching chemistry offers a new means to induce motion and a novel perspective in the ordered occurrence of certain defects. We demonstrate that Ag can be deposited back onto the coiled Ag-PTh composite to form metallic spirals.Keywords: defects; induced coiling; polythiophene; selective etching; silver nanowires

We show that bundles of carbon nanotubes can be coiled into ring structures by controlling the contraction of their polymer shells. With the robust carbon nanotubes, we demonstrate their reversible transformation between circular and compressed rings in a colloid.

We demonstrate that the silica shell on nanoparticles formed by a typical Stöber method is inhomogeneous in nature. The outer layer of the shell is chemically more robust than the inner layer, which can be selectively etched by hot water. Methods are developed to “harden” the soft silica shells. These new understandings are exploited to develop versatile and template-free approaches for fabricating sophisticated yolk–shell nanostructures.

We report a new type of water-soluble ultrathin Au–Ag alloy nanowire (NW), which exhibits unprecedented behavior in a colloidal solution. Upon growth of a thin metal (Pd, Pt, or Au) layer, the NW winds around itself to give a metallic double helix. We propose that the winding originates from the chirality within the as-synthesized Au–Ag NWs, which were induced to untwist upon metal deposition.

Composite vesicles with embedded Au nanoparticles are directly prepared from thiophene and Au nanoparticles in aqueous solution in the presence of H2O2 and a catalytic amount of FeCl3. The number, shape, and structure of the vesicles thereof can be readily controlled. We provide evidence that these vesicles contain an aqueous phase in their cavities. The direct synthesis offers an economical route to nanoscale containers and also a rare example for the minimal conditions of vesicle formation.

We show that the microstructures of polycrystalline ice can serve as a confining template for one-dimensional assembly of colloidal nanoparticles. Upon simply freezing an aqueous colloid, the nanoparticles are excluded from ice grains and form chains in the ice veins. The nanoparticle chains are transferable and can be strengthened by polymer encapsulation. After coating with polyaniline shells, simple sedimentation is used to remove large aggregates, enriching single-line chains of 40 nm gold nanoparticles with a total length of several micrometers. When gold nanorods were used, they formed one-dimensional aggregates with specific end-to-end conformation, indicating the confining effects of the nanoscale ice veins at the final stage of freezing. The unbranched and ultralong plasmonic chains are of importance for future study of plasmonic coupling and development of plasmonic waveguides.Keywords: nanoparticle assembly; one-dimensional; polycrystalline ice; superstructure; template

We report ensemble-averaged measurements of colloidal hotspots enabled by the synthesis of highly uniform dimers and trimers of Au@Ag nanoparticles and the quantification of the relative concentrations of the nanoclusters.

We demonstrate a facile colloidal method for synthesizing Janus nanoparticles, whose eccentric polymer shells are exploited to fabricate eccentric bimetallic cores.

We report the controllable coiling of colloidal gold nanowires induced by the contraction of their polymer shells. The mechanical energy stored in this process can be released upon removal or swelling of the polymer shells.

In this report, we focus on the synthetic challenges for nanoscale 3D fractal architectures, namely the multi-generation growth with control in both size uniformity and colloidal stability; by directing the simultaneous growth of Au and polyaniline on Au seeds, fractal nanoparticles can be achieved with a topology distinctively different from those of spheres, cubes or rods.

We report a new approach to study the kinetics of ligand exchange on colloidal gold nanoparticles, where the coordination and dissociation of surface ligands could be monitored in situ by surface-enhanced Raman scattering.

Understanding the mechanism of nanoparticle self-assembly is of critical significance for developing synthetic strategies for complex nanostructures. By encapsulating aggregates of Au nanospheres in shells of polystyrene-block-poly(acrylic acid), we prevent the dissociation and aggregation typically associated with the drying of solution samples on TEM/SEM substrates. In our study of the salt-induced aggregation of 2-naphthalenethiol-functionalized Au nanospheres in DMF, the trapping of the solution species under various experimental conditions permits new insights in the mechanism thereof. We provide evidence that the spontaneous linear aggregation in this system is a kinetically controlled process and hence the long-range charge repulsion at the “transition state” before the actual contact of the Au nanospheres is the key factor. Thus, the charge repulsion potential (i.e. the activation energy) a nanosphere must overcome before attaching to either end of a nanochain is smaller than attaching on its sides, which has been previously established. This factor alone could give rise to the selective end-on attachment and lead to the linear assembly of originally isotropic Au nanospheres.

The most studied effect of surface-enhanced Raman scattering (SERS) hotspots is the enormous Raman enhancement of the analytes therein. A less known effect, though, is that the formation of hotspots may cause the trapped analytes to change molecular orientation, which in turn leads to pronounced changes in SERS fingerprints. Here, we demonstrate this effect by creating and characterizing hotspots in colloidal solutions. Anisotropically functionalized Au nanorods were synthesized, whereby the sides were specifically encapsulated by polystyrene-block-poly(acrylic acid), leaving the ends unencapsulated and functionalized by a SERS analyte, 4-mercaptobenzoic acid. Upon salt treatment, these nanorods assemble into linear chains, forming hotspots that incorporate the SERS analyte. Enormous SERS enhancement was observed, particularly for some weak/inactive SERS modes that were not present in the original spectrum before the hotspots formation. Detailed spectral analysis showed that the variations of the SERS fingerprint were consistent with the reorientation of analyte molecules from nearly upright to parallel/tilted conformation on the Au surface. We propose that the aggregation of Au nanorods exerts physical stress on the analytes in the hotspots, causing the molecular reorientation. Such a hotspot-induced variation of SERS fingerprints was also observed in several other systems using different analytes.Keywords: Au nanorod; fingerprint; hotspot; linear aggregation; SERS

Controls in coating gold nanoparticles with conductive polymers are reported, where uniform core/shell nanoparticles with tailored core aggregation and shell thickness are unambiguously demonstrated. In the presence of sodium dodecylsulfate (SDS), the adsorption and in situpolymerization of aniline or pyrrole on the surface of gold nanoparticles gives uniform polymer shells. A typical single encapsulation of 10 nm gold nanoparticles gave ∼99.1% monomers out of 1074 particles surveyed. The shell growth was found to be kinetically controlled; polyaniline was successively grown on 22 nm gold nanoparticles by multiple growth cycles, giving shell thicknesses of 14, 31, 61 and 92 nm, respectively. We show that the aggregation of gold nanoparticles can be controllably promoted in this system, by simply timing SDS addition, to give linearly aggregated cores of 2–20 particles. The in situ formation of conductive polymer shells has allowed the isolation and unambiguous characterization of these nanochains for the first time. The one-step, “mix-and-wait” synthesis solely utilizes inexpensive starting materials and is, therefore, well-suited for fabrication of large quantities of core/shell nanoparticles. The core/shell nanoparticles form stable colloidal suspensions and can be readily purified by centrifugation.

Triple-layer (Au@Ag)@polypyrrole core–shell nanoparticles are fabricated by a one-step synthesis involving simultaneous reduction of AgNO3 and polymerization of pyrrole in the presence of Au nanoparticles; the Ag layer in the resulting nanoparticles is etched to give a (Au@H2O)@polypyrrole yolk–shell structure.

A templated fabrication of open nanocavities is reported, where rational control of partial polymer attachment on sacrificial metal cores introduces openings in the polymer shells. This approach provides a facile means to modify the structural features of polymer nanocavities by manipulating the surface chemistry of colloidal nanoparticles. In particular, the anisotropic geometry of gold nanorods is exploited to promote the anisotropic polymer attachment, such that two diametric openings occurred in the polymer shell. After etching the gold nanorods, this approach yields open nanochannels that are tunable in both diameter and length. The synthetic scope of the anisotropic core/shell nanoparticles is expanded, supporting the previously proposed mechanism. We demonstrate that reducing the symmetry of nano-objects could open up new ways to create structural features using simple assembly and etching techniques. The thermostability of the open polymer nanostructures is also investigated.Keywords: anisotropic encapsulation; etching; linear aggregation; nanocavity; self-assembly

Rational assembly of nanoparticles is of vital importance for exploring fundamental electronic and optical properties and for constructing novel nanoscale devices. Through controlling aggregation kinetics, dimers and trimers of gold nanoparticles were generated and encapsulated with polymer by using a one-pot synthesis that involved simple heating and cooling. Dimers of gold nanoparticles were enriched from the resulting solution by centrifugation. The polymer shells maintain the stability of the nanoparticle organization, preventing aggregation and disintegration during subsequent purification, enrichment, and application. A typical enriched sample showed that the dimer population reached 61% among 989 nanoparticles surveyed. In a proof-of-concept application, the gold nanoparticle dimers were used as catalyst to guide the growth of dimeric zinc oxide nanowires. Nanowire dimers with unprecedented narrow spacing (20 to 60 nm) were achieved using a vapor transport growth method; dimeric nanowire population reached ∼25%.

Controlling shape and orientation is important for the synthesis of functional nanomaterials. In this work, nanoscale Cu3Si triangles, squares, and wires have been grown on Si(111), (100), and (110) substrates, respectively, through a template-free Au-nanoparticle-assisted vapor transport method. The sides of nanotriangles and nanosquares and the growth direction of the nanowires are all along Si ⟨110⟩, giving rise to long-range ordering of the nanostructures. Au nanoparticles absorb Cu vapor and facilitate the rate-limited diffusion of Si, which is critical for the shape-controlled growth of Cu3Si. This bottom-up approach to synthesize shape- and orientation-controlled Cu3Si nanostructures might be applicable to the tailored growth of other materials.

We show that seeded growth can be applied to creating two-dimensional (2D) dendritic Au nanostructures on sample grids, which can be directly characterized by transmission electron microscopy (TEM). The 2D synthesis of highly consistent structures offers a novel mechanistic perspective on the aggregation of colloidal Au nanocrystals on a surface.

Composite vesicles with embedded Au nanoparticles are directly prepared from thiophene and Au nanoparticles in aqueous solution in the presence of H2O2 and a catalytic amount of FeCl3. The number, shape, and structure of the vesicles thereof can be readily controlled. We provide evidence that these vesicles contain an aqueous phase in their cavities. The direct synthesis offers an economical route to nanoscale containers and also a rare example for the minimal conditions of vesicle formation.

In this report, we focus on the synthetic challenges for nanoscale 3D fractal architectures, namely the multi-generation growth with control in both size uniformity and colloidal stability; by directing the simultaneous growth of Au and polyaniline on Au seeds, fractal nanoparticles can be achieved with a topology distinctively different from those of spheres, cubes or rods.

Triple-layer (Au@Ag)@polypyrrole core–shell nanoparticles are fabricated by a one-step synthesis involving simultaneous reduction of AgNO3 and polymerization of pyrrole in the presence of Au nanoparticles; the Ag layer in the resulting nanoparticles is etched to give a (Au@H2O)@polypyrrole yolk–shell structure.

Chirality in nanoscience may offer new opportunities for applications beyond the traditional fields of chirality, such as the asymmetric catalysts in the molecular world and the chiral propellers in the macroscopic world. In the last two decades, there has been an amazing array of chiral nanostructures reported in the literature. This review aims to explore and categorize the common mechanisms underlying these systems. We start by analyzing the origin of chirality in simple systems such as the helical spring and hair vortex. Then, the chiral nanostructures in the literature were categorized according to their material composition and underlying mechanism. Special attention is paid to highlight systems with original discoveries, exceptional structural characteristics, or unique mechanisms.

We report a new approach to study the kinetics of ligand exchange on colloidal gold nanoparticles, where the coordination and dissociation of surface ligands could be monitored in situ by surface-enhanced Raman scattering.

Controls in coating gold nanoparticles with conductive polymers are reported, where uniform core/shell nanoparticles with tailored core aggregation and shell thickness are unambiguously demonstrated. In the presence of sodium dodecylsulfate (SDS), the adsorption and in situpolymerization of aniline or pyrrole on the surface of gold nanoparticles gives uniform polymer shells. A typical single encapsulation of 10 nm gold nanoparticles gave ∼99.1% monomers out of 1074 particles surveyed. The shell growth was found to be kinetically controlled; polyaniline was successively grown on 22 nm gold nanoparticles by multiple growth cycles, giving shell thicknesses of 14, 31, 61 and 92 nm, respectively. We show that the aggregation of gold nanoparticles can be controllably promoted in this system, by simply timing SDS addition, to give linearly aggregated cores of 2–20 particles. The in situ formation of conductive polymer shells has allowed the isolation and unambiguous characterization of these nanochains for the first time. The one-step, “mix-and-wait” synthesis solely utilizes inexpensive starting materials and is, therefore, well-suited for fabrication of large quantities of core/shell nanoparticles. The core/shell nanoparticles form stable colloidal suspensions and can be readily purified by centrifugation.

Understanding the mechanism of nanoparticle self-assembly is of critical significance for developing synthetic strategies for complex nanostructures. By encapsulating aggregates of Au nanospheres in shells of polystyrene-block-poly(acrylic acid), we prevent the dissociation and aggregation typically associated with the drying of solution samples on TEM/SEM substrates. In our study of the salt-induced aggregation of 2-naphthalenethiol-functionalized Au nanospheres in DMF, the trapping of the solution species under various experimental conditions permits new insights in the mechanism thereof. We provide evidence that the spontaneous linear aggregation in this system is a kinetically controlled process and hence the long-range charge repulsion at the “transition state” before the actual contact of the Au nanospheres is the key factor. Thus, the charge repulsion potential (i.e. the activation energy) a nanosphere must overcome before attaching to either end of a nanochain is smaller than attaching on its sides, which has been previously established. This factor alone could give rise to the selective end-on attachment and lead to the linear assembly of originally isotropic Au nanospheres.