Programmable Supra‐Assembly of a DNA Surface Adapter for Tunable Chiral Directional Self‐Assembly of Gold Nanorods

An important challenge in molecular assembly and hierarchical molecular engineering is to control and program the directional self‐assembly into chiral structures. Here, we present a versatile DNA surface adapter that can programmably self‐assemble into various chiral supramolecular architectures, thereby regulating the chiral directional “bonding” of gold nanorods decorated by the surface adapter. Distinct optical chirality relevant to the ensemble conformation is demonstrated from the assembled novel stair‐like and coil‐like gold nanorod chiral metastructures, which is strongly affected by the spatial arrangement of neighboring nanorod pair. Our strategy provides new avenues for fabrication of tunable optical metamaterials by manipulating the directional self‐assembly of nanoparticles using programmable surface adapters.     

Polystyrene‐Core–Silica‐Shell Hybrid Particles Containing Gold and Magnetic Nanoparticles

Polystyrene‐core–silica‐shell hybrid particles were synthesized by combining the self‐assembly of nanoparticles and the polymer with a silica coating strategy. The core–shell hybrid particles are composed of gold‐nanoparticle‐decorated polystyrene (PS‐AuNP) colloids as the core and silica particles as the shell. PS‐AuNP colloids were generated by the self‐assembly of the PS‐grafted AuNPs. The silica coating improved the thermal stability and dispersibility of the AuNPs. By removing the “free” PS of the core, hollow particles with a hydrophobic cage having a AuNP corona and an inert silica shell were obtained. Also, Fe₃O₄ nanoparticles were encapsulated in the core, which resulted in magnetic core–shell hybrid particles by the same strategy. These particles have potential applications in biomolecular separation and high‐temperature catalysis and as nanoreactors.     

Synthesis of stable “gold nanoparticle–polymeric micelle” conjugates: A new class of star “molecular chimera” that self‐assemble into linear arrays of spherical micelles

Stable and aggregation‐free “gold nanoparticle–polymeric micelle” conjugates were prepared using a new and simple protocol enabled by the hydrogen bonding between surface‐capping ligands and polymeric micelles. Individual gold nanoparticles were initially capped using a phosphatidylthio–ethanol lipid and further conjugated with a star poly(styrene‐block‐glutamic acid) copolymer micelle using a one‐pot preparation method. The morphology and stability of these gold–polymer conjugates were characterized using transmission electron microscopy (TEM) and UV–vis spectroscopy. The self‐assembly of this class of polymer‐b‐polypeptide in aqueous an medium to form spherical micelles and further their intermicelle reorganization to form necklace‐like chains was also investigated. TEM and laser light scattering techniques were employed to study the morphology and size of these micelles. Polymeric micelles were formed with diameters in the range of 65–75 nm, and supermicellular patterns were observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3570–3579, 2007     

Polyoxometalate-Engineered Building Blocks with Gold Cores for the Self-Assembly of Responsive Water-Soluble Nanostructures

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle-like organizations. Using cryo-TEM imaging and ¹H DOSY NMR spectroscopy, we then provide an unprecedented “solution-state” picture of how the micelle-like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water-soluble assemblies.     

Programming the Nucleation of DNA Brick Self‐Assembly with a Seeding Strand

Recently, the DNA brick strategy has provided a highly modular and scalable approach for the construction of complex structures, which can be used as nanoscale pegboards for the precise organization of molecules and nanoparticles for many applications. Despite the dramatic increase of structural complexity provided by the DNA brick method, the assembly pathways are still poorly understood. Herein, we introduce a “seed” strand to control the crucial nucleation and assembly pathway in DNA brick assembly. Through experimental studies and computer simulations, we successfully demonstrate that the regulation of the assembly pathways through seeded growth can accelerate the assembly kinetics and increase the optimal temperature by circa 4–7 °C for isothermal assembly. By improving our understanding of the assembly pathways, we provide new guidelines for the design of programmable pathways to improve the self‐assembly of DNA nanostructures.     

Programming the Nucleation of DNA Brick Self-Assembly with a Seeding Strand

Recently, the DNA brick strategy has provided a highly modular and scalable approach for the construction of complex structures, which can be used as nanoscale pegboards for the precise organization of molecules and nanoparticles for many applications. Despite the dramatic increase of structural complexity provided by the DNA brick method, the assembly pathways are still poorly understood. Herein, we introduce a “seed” strand to control the crucial nucleation and assembly pathway in DNA brick assembly. Through experimental studies and computer simulations, we successfully demonstrate that the regulation of the assembly pathways through seeded growth can accelerate the assembly kinetics and increase the optimal temperature by circa 4–7 °C for isothermal assembly. By improving our understanding of the assembly pathways, we provide new guidelines for the design of programmable pathways to improve the self-assembly of DNA nanostructures.     

Polyoxometalate‐Engineered Building Blocks with Gold Cores for the Self‐Assembly of Responsive Water‐Soluble Nanostructures

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle‐like organizations. Using cryo‐TEM imaging and ¹H DOSY NMR spectroscopy, we then provide an unprecedented “solution‐state” picture of how the micelle‐like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water‐soluble assemblies.     

Blend Composites Based on Polystyrene–CdSe Quantum Dots and Polystyrene–Gold Nanoparticles Hybrid Systems

Polystyrenes of different molecular masses are synthesized by controlled radical polymerization via the reversible addition fragmentation chain transfer mechanism. The resulting polymers are used for designing nanocomposites based on cadmium selenide quantum dots and gold nanoparticles. It is demonstrated that the photoluminescence of quantum dots in the sol grows appreciably during continuous irradiation for 5–6 h but is reduced during the “light switching off–switching on” process. It is shown that, upon the addition of gold nanoparticles, the photoluminescence of quantum dots in the sols changes insignificantly.     

Sol–gel synthesis of porous inorganic materials using “core–shell” latex particles as templates

Here we report on the sol–gel synthesis of porous inorganic materials based on manganese, molybdenum, and tungsten compounds using the “core–shell” siloxane-acrylate latex as a template. The chemical composition and structural characteristics of the materials obtained have been investigated. It was shown that temperature conditions and gaseous media composition during the template destruction controlled the composition and structure of porous materials. To obtain porous inorganic materials for catalytic applications, the “core–shell” latex template was preliminarily functionalized by gold and palladium nanoparticles obtained by thermal reduction of noble metal ions-precursors in a polycarboxylic “shell”. Upon the template removal, noble metals nanoparticles of a size of dozens of nanometers were homogeneously distributed in the material porous structure. The evaluation of the catalytic activity of macroporous manganese, tungsten, and molybdenum oxides under the conditions of liquid phase catalytic oxidation of organic dyes has been performed. The prospects of employing macroporous oxide systems with immobilized nanoparticles of noble metals in the processes of hydrothermal oxidation of radionuclide organic complexes in radioactive waste decontamination have been demonstrated.     

Electrochemical deposition of gold at liquid–liquid interfaces studied by thin organic film-modified electrodes

The unique physico-chemical properties of gold nanoparticles portrayed in their chemical stability, the size-dependent electrochemistry, and the unusual optical properties make them suitable modifiers of various surfaces used in the fields of optical devices, electronics, and biosensors. In this work we present two different methods to obtain metallic gold nanoparticles at a liquid–liquid interface, and to control their growth by adjusting the experimental conditions. Decamethylferrocene (DMFC), used as an oxidizable compound dissolved in an organic solvent that is spread as a thin film on the surface of graphite electrode, serves as a redox partner to exchange electrons across the liquid–liquid interface with the other redox counter-partner [AuCl₄]^? present in the conjoined water phase. The interfacial electron transfer between the DMFC and the [AuCl₄]^? ions leads to deposition of metallic gold nanoparticles at the liquid–liquid interface. The structure and features of the deposited Au nanoparticles were studied by means of microscopic and voltammetric techniques. The morphology of the Au deposit depends on the concentration ratio of redox partners and both electrode and liquid–liquid interfacial potential differences. Depending on whether the Au deposit was obtained by ex situ (at open circuit potential) or by “in situ” (by cycling of the electrode potential) approach, we observed quite different effects to the ion transfer reactions probed by the thin-film electrode set-up. The possible reasons for the different behavior of the Au nanoparticles are discussed in terms of the structure and the properties of the obtained Au deposit. In separate experiments, we have demonstrated catalytic effects of the Au nanoparticles towards enhancing the electron transfer between DMFC and two aqueous redox substrates, hexacyanoferrate and hydrogen peroxide.     

Self‐Organized Nanocomposite of Gold Nanoparticles and π‐Electron Organic Molecules

Aggregates of gold nanoparticles were formed by simple addition of a dithiafulvene derivative (DF) to an acetonitrile solution containing gold ions. The discrete gold nanoparticles in the aggregates were separated by monolayers of oxidized DF. No aggregation was observed with the addition of poly(vinylpyrrolidone) (PVP), which acted as a strong stabilizer and inhibited self‐assembly of the gold nanoparticles. DF acted as a reducing agent for gold ions, a stabilizer, and a tether for the resulting gold nanoparticles. Intermolecular S···S interaction and Au–S bonds might be the driving force for the self‐assembly of the gold nanoparticles.     

Four‐Dimensional Deoxyribonucleic Acid–Gold Nanoparticle Assemblies

Organization of gold nanoobjects by oligonucleotides has resulted in many three‐dimensional colloidal assemblies with diverse size, shape, and complexity; nonetheless, autonomous and temporal control during formation remains challenging. In contrast, living systems temporally and spatially self‐regulate formation of functional structures by internally orchestrating assembly and disassembly kinetics of dissipative biomacromolecular networks. We present a novel approach for fabricating four‐dimensional gold nanostructures by adding an additional dimension: time. The dissipative character of our system is achieved using exonuclease III digestion of deoxyribonucleic acid (DNA) fuel as an energy‐dissipating pathway. Temporal control over amorphous clusters composed of spherical gold nanoparticles (AuNPs) and well‐defined core–satellite structures from gold nanorods (AuNRs) and AuNPs is demonstrated. Furthermore, the high specificity of DNA hybridization allowed us to demonstrate selective activation of the evolution of multiple architectures of higher complexity in a single mixture containing small and larger spherical AuNPs and AuNRs.     

A new peptide-based method for the design and synthesis of nanoparticle superstructures: construction of highly ordered gold nanoparticle double helices

Left-handed gold nanoparticle double helices were prepared using a new method that allows simultaneous synthesis and assembly of discrete nanoparticles. This method involves coupling the processes of peptide self-assembly of and peptide-based biomineralization of nanoparticles. In this study, AYSSGAPPMPPF (PEPAu), an oligopeptide with an affinity for gold surfaces, was modified with an aliphatic tail to generate C12-PEPAu. In the presence of buffers and gold salts, amphiphilic C12-PEPAu was used to both control the formation of monodisperse gold nanoparticles and simultaneously direct their assembly into left-handed gold nanoparticle double helices. The gold nanoparticle double helices are highly regular, spatially complex, and they exemplify the utility of this methodology for rationally controlling the topology of nanoparticle superstructures and the stereochemical organization of discrete nanoparticles within these structures.     

Controllable Assembly and Separation of Colloidal Nanoparticles through a One‐Tube Synthesis Based on Density Gradient Centrifugation

Self‐assembly of gold nanoparticles into one‐dimensional (1D) nanostructures with finite primary units was achieved by introducing a thin salt (NaCl) solution layer into density gradient before centrifugation. The electrostatic interactions between Au nanoparticles would be affected and cause 1D assembly upon passing through the salt layer. A negatively charged polymer such as poly(acrylic acid) was used as an encapsulation/stabilization layer to help the formation of 1D Au assemblies, which were subsequently sorted according to unit numbers at succeeding separation zones. A centrifugal field was introduced as the external field to overcome the random Brownian motion of NPs and benefit the assembly effect. Such a facile “one‐tube synthesis” approach couples assembly and separation in one centrifuge tube by centrifuging once. The method can be tuned by changing the concentration of interference salt layer, encapsulation layer, and centrifugation rate. Furthermore, positively charged fluorescent polymers such as perylenediimide‐poly(N,N‐diethylaminoethyl methacrylate) could encapsulate the assemblies to give tunable fluorescence properties.     

Giant surfactants based on molecular nanoparticles: Precise synthesis and solution self‐assembly

Giant surfactants are polymer‐tethered molecular nanoparticles (MNPs) and can be considered as a subclass of giant molecules. The MNPs serve as functionalized heads with persistent shape and volume, which may vary in size, symmetry, and surface chemistry. The covalent conjugation of MNPs and polymer tails affords giant surfactants with diverse composition and architecture. Synthetic strategies such as “grafting‐from” and “grafting‐onto” have been successfully applied to the precise synthesis of giant surfactants, which is further facilitated by the emergence of “click” chemistry reactions. In many aspects, giant surfactants capture the essential features of small‐molecule surfactants, yet they have much larger sizes. They bridge the gap between small‐molecule surfactants and traditional amphiphilic macromolecules. Their self‐assembly behaviors in solution are summarized in this Review. Micelle formation is affected not only by their primary chemical structures, but also by the experimental conditions. This new class of materials is expected to deliver general implications on the design of novel functional materials based on MNP building blocks in the bottom‐up fabrication of well‐defined nanostructures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1309–1325     

Plasmonic-based colorimetric and spectroscopic discrimination of acetic and butyric acids produced by different types of Escherichia coli through the different assembly structures formation of gold nanoparticles

We present a plasmonic-based strategy for the colourimetric and spectroscopic differentiation of various organic acids produced by bacteria. The strategy is based on our discovery that particular concentrations of dl-lactic, acetic, and butyric acids induce different assembly structures, colours, and optical spectra of gold nanoparticles. We selected wild-type (K-12 W3110) and genetically-engineered (JHL61) Escherichia coli (E. coli) that are known to primarily produce acetic and butyric acid, respectively. Different assembly structures and optical properties of gold nanoparticles were observed when different organic acids, obtained after the removal of acid-producing bacteria, were mixed with gold nanoparticles. Moreover, at moderate cell concentrations of K-12 W3110 E. coli, which produce sufficient amounts of acetic acid to induce the assembly of gold nanoparticles, a direct estimate of the number of bacteria was possible based on time-course colour change observations of gold nanoparticle aqueous suspensions. The plasmonic-based colourimetric and spectroscopic methods described here may enable onsite testing for the identification of organic acids produced by bacteria and the estimation of bacterial numbers, which have applications in health and environmental sciences.     

Gold nanoparticle patterning of silicon wafers using chemical e-beam lithography

This paper demonstrates a novel facile method for fabrication of patterned arrays of gold nanoparticles on Si/SiO2 by combining electron beam lithography and self-assembly techniques. Our strategy is to use direct-write electron beam patterning to convert nitro functionality in self-assembled monolayers of 3-(4-nitrophenoxy)-propyltrimethoxysilane to amino functionality, forming chemically well-defined surface architectures on the 100 nm scale. These nanopatterns are employed to guide the assembly of citrate-passivated gold nanoparticles according to their different affinities for amino and nitro groups. This kind of nanoparticle assembly offers an attractive new option for nanoparticle patterning a silicon surface, as relevant, for example, to biosensors, electronics, and optical devices.     

Metastable Self‐Assembly of Theta‐Shaped Colloids and Twinning of Their Crystal Phases

Anisotropic colloids self‐assemble into different crystal structures compared to spherical colloids. Exploring and understanding their self‐assembly behavior could lead to creation of new materials with hierarchical structures through a bottom‐up process. Herein, we report metastable self‐assembly of theta‐shaped SiO₂ colloids interacting with a depletion force in a quasi‐two‐dimensional space and we demonstrate that both a metastable “prone” crystal phase and a stable “standing” crystal phase can be formed, depending on the self‐assembly path. Path selection stems from an interplay between particle–particle interactions and particle–wall interactions. In particular, a twinning of the metastable crystals was observed and two twinning mirror axes were found. A variety of complex twinned crystals were formed by each individual mirror axis or their combinations.     

Self-Assembly in Natural and Unnatural Systems

Although there are no fundamental factors hindering the development of nanoscale structures, there is a growing realization that “engineering down” approaches, in other words a reduction in the size of structures generated by lithographic techniques below the present lower limit of roughly 1 μm, may become impractical. It has, therefore, become increasingly clear that only by the development of a fundamental understanding of the self-assembly of large-scale biological structures, which exist and function at and beyond the nanoscale, downwards, and the extension of our knowledge regarding the chemical syntheses of small-scale structures upwards, can the gap between the promise and the reality of nanosystems be closed. This kind of construction of nanoscale structures and nanosystems represents the so-called “bottom up” or “engineering up” approach to device fabrication. Significant progress can be made in the development of nanoscience by transferring concepts found in the biological world into the chemical arena. Central to this mission is the development of simple chemical systems capable of instructing their own organization into large aggregates of molecules through their mutual recognition properties. The precise programming of these recognition events, and hence the correct assembly of the growing superstructure, relies on a fundamental understanding and the practical exploitation of non-covalent bonding interactions between and within molecules. The science of supramolecular chemistry—chemistry beyond the molecule in its very broadest sense—has started to bridge the yawning gap between molecular and macro-molecular structures. By utilizing inter-actions as diverse as aromatic π–π stacking and metal–ligand coordination for the information source for assembly processes, chemists have, in the last decade, begun to use biological concepts such as self-assembly to construct nanoscale structures and superstructures with a variety of forms and functions. Here, we provide a flavor of how self-assembly operates in natural systems and can be harnessed in unnatural ones.