Using hierarchical self-assembly to form three-dimensional lattices of spheres

Friction-directed self-assembly of Janus lithographic microgels into anisotropic 2D structures

We present a method for creating ordered 2D structures with material anisotropy from self-assembling micro-sized hydrogel particles (microgels). Microgel platelets of polygonal shapes (hexagon, square, and rhombus), obtained by a continuous scalable lithographic process, are suspended in an aqueous environment and sediment on an inclined plane. As a consequence of gravitational pull, they slide over the plane. Each half of the microgel is composed of a different type of hydrogel [poly(N-isopropylacrylamide) (PNIPAM), and poly(ethylene glycol) diacrylate (PEGDA), respectively] which exhibit different frictional coefficients when sheared over a substrate. Hence the microgels self-orientate as they slide, and the side with the lower frictional coefficient positions in the direction of sliding. The self-oriented microgels concentrate at the bottom of the tilted plane. Here they form densely packed structures with translational as well as orientational order.

Robust Carbonated Structural Color Barcodes with Ultralow Ontology Fluorescence as Biomimic Culture Platform

Photonic crystal (PC) barcodes are a new type of spectrum-encoding microcarriers used in multiplex high-throughput bioassays, such as broad analysis of biomarkers for clinical diagnosis, gene expression, and cell culture. Unfortunately, most of these existing PC barcodes suffered from undesired features, including difficult spectrum-signal acquisition, weak mechanical strength, and high ontology fluorescence, which limited their development to real applications. To address these limitations, we report a new type of structural color-encoded PC barcodes. The barcodes are fabricated by the assembly of monodisperse polydopamine- (PDA-) coated silica (PDA@SiO₂) nanoparticles using a droplet-based microfluidic technique and followed by pyrolysis of PDA@SiO₂ (C@SiO₂) barcodes. Because of the templated carbonization of adhesive PDA, the prepared C@SiO₂ PC beads were endowed with simultaneous easy-to-identify structural color, high mechanical strength, and ultralow ontology fluorescence. We demonstrated that the structural colored C@SiO₂ barcodes not only maintained a high structural stability and good biocompatibility during the coculturing with fibroblasts and tumor cells capture but also achieved an enhanced fluorescent-reading signal-to-noise ratio in the fluorescence-reading detection. These features make the C@SiO₂ PC barcodes versatile for expansive application in fluorescence-reading-based multibioassays.

Layered assemblers for scalable parallel integration

Many complex natural and artificial systems are composed of large numbers of elementary building blocks, such as organisms made of many biological cells or processors made of many electronic transistors. This modular substrate is essential to the evolution of biological and technological complexity, but has been difficult to replicate for mechanical systems. This study seeks to answer if layered assembly can engender exponential gains in the speed and efficacy of block or cell-based manufacturing processes. A key challenge is how to deterministically assemble large numbers of small building blocks in a scalable manner. Here, we describe two new layered assembly principles that allow assembly faster than linear time, integrating n modules in O(n^2/3) and O(n^1/3) time: one process uses a novel opto-capillary effect to selectively deposit entire layers of building blocks at a time, and a second process jets building block rows in rapid succession. We demonstrate the fabrication of multi-component structures out of up to 20 000 millimetre scale spherical building blocks in 3 h. While these building blocks and structures are still simple, we suggest that scalable layered assembly approaches, combined with a growing repertoire of standardized passive and active building blocks could help bridge the meso-scale assembly gap, and open the door to the fabrication of increasingly complex, adaptive and recyclable systems.

Real-Time Monitoring of Hierarchical Self-Assembly and Induction of Circularly Polarized Luminescence from Achiral Luminogens

Constructing artificial helical structures through hierarchical self-assembly and exploring the underlying mechanism are important, and they help gain insight from the structures, processes, and functions from the biological helices and facilitate the development of material science and nanotechnology. Herein, the two enantiomers of chiral Au(I) complexes ( S)-1 and ( R)-1 were synthesized, and they exhibited impressive spontaneous hierarchical self-assembly transitions from vesicles to helical fibers. An impressive chirality inversion and amplification was accompanied by the assembly transition, as elucidated by the results of in situ and time-dependent circular dichroism spectroscopy and scanning electron microscope imaging. The two enantiomers could serve as ideal chiral templates to co-assemble with other achiral luminogens to efficiently induce the resulting co-assembly systems to show circularly polarized luminescence (CPL). Our work has provided a simple but efficient way to explore the sophisticated self-assembly process and presented a facile and effective strategy to fabricate architectures with CPL properties.

ZnO/CoO and ZnCo2O4 Hierarchical Bipyramid Nanoframes: Morphology Control, Formation Mechanism, and Their Lithium Storage Properties

Mastery over the structure of nanoscale materials can effectively tailor and regulate their electrochemical properties, enabling improvement in both rate capability and cycling stability. We report the shape-controlled synthesis of novel mesoporous bicomponent-active ZnO/CoO hierarchical multilayered bipyramid nanoframes (HMBNFs). The as-synthesized micro/nanocrystals look like multilayered bipyramids and consist of a series of structural units with similar frames and uniform sheet branches. The use of an appropriate straight-chain monoalcohol was observed to be critical for the formation of HMBNFs. In addition, the structure of HMBNFs could be preserved only in a limited range of the precursor ratio. An extremely fast crystal growth process and an unusual transverse crystallization of the ZnCo-carbonate HMBNFs were newly discovered and proposed. By calcination of ZnCo-carbonate HMBNFs at the atmosphere of nitrogen and air, ZnO/CoO and ZnCo2O4 HMBNFs were obtained, respectively. Compared to the ZnCo2O4 HMBNFs, the ZnO/CoO HMBNFs with a uniform distribution of nanocrystal ZnO and CoO subunits exhibited enhanced electrochemical activity, including greater rate capability and longer cycling performance, when evaluated as an anode material for Li-ion batteries. The superior electrochemical performance of the ZnO/CoO HMBNFs is attributed to the unique nanostructure, bicomponent active synergy, and uniform distribution of ZnO and CoO phases at the nanoscale.

Multilevel and Multicomponent Layer-by-Layer Assembly for the Fabrication of Nanofibrillar Films

In this study, we demonstrate multilevel and multicomponent layer-by-layer (LbL) assembly as a convenient and generally applicable method for the fabrication of nanofibrillar films by exploiting the dynamic nature of polymeric complexes. The alternate deposition of poly(allylamine hydrochloride)-methyl red (PAH-MR) complexes with poly(acrylic acid) (PAA) produces nanofibrillar PAH-MR/PAA films, which involves the disassembly of PAH-MR complexes, the subsequent assembly of PAH with PAA, and the PAA-induced assembly of MR molecules into MR nanofibrils via a π-π stacking interaction. The aqueous solution of weak polyelectrolyte PAA with a low solution pH plays an important role in fabricating nanofibrillar PAH-MR/PAA films because proton transfer from acidic PAA to MR molecules induces the formation of MR nanofibrils. The generality of the multilevel and multicomponent LbL assembly is verified by alternate assembly of complexes of 1-pyrenylbutyric acid (PYA) and PAH with PAA to fabricate PAH-PYA/PAA films with organized nanofibrillar structures. Unlike the traditional static LbL assembly, the multilevel and multicomponent LbL assembly is dynamic and more flexible and powerful in controlling the interfacial assembly process and in fabricating composite films with sophisticated structures. These characteristics of multilevel and multicomponent LbL assembly will enrich the functionalities of the LbL-assembled films.

Staging the self-assembly process: inspiration from biological development

One of the practical challenges facing the creation of self-assembling systems is being able to exploit a limited set of fixed components and their bonding mechanisms. The method of staging divides the self-assembly process into time intervals, during which components can be added to, or removed from, an environment at each interval. Staging addresses the challenge of using components that lack plasticity by encoding the construction of a target structure in the staging algorithm itself and not exclusively in the design of the components. Previous staging strategies do not consider the interplay between component physical features (morphological information). In this work we use morphological information to stage the self-assembly process, during which components can only be added to their environment at each time interval, to demonstrate our concept. Four experiments are presented, which use heterogeneous, passive, mechanical components that are fabricated using 3D printing. Two orbital shaking environments are used to provide energy to the components and to investigate the role of morphological information with component movement in either two or three spatial dimensions. The benefit of our staging strategy is shown by reducing assembly errors and exploiting bonding mechanisms with rotational properties. As well, a doglike target structure is used to demonstrate in theory how component information used at an earlier time interval can be reused at a later time interval, inspired by the use of a body plan in biological development. We propose that a staged body plan is one method toward scaling self-assembling systems with many interacting components. The experiments and body plan example demonstrate, as proof of concept, that staging enables the self-assembly of more complex morphologies not otherwise possible.

A new approach to in-situ "micromanufacturing": microfluidic fabrication of magnetic and fluorescent chains using chitosan microparticles as building blocks

An in situ microfluidic assembly approach is described that can both produce microsized building blocks and assemble them into complex multiparticle configurations in the same microfluidic device. The building blocks are microparticles of the biopolymer chitosan, which is intentionally selected because its chemistry allows for simultaneous intraparticle and interparticle linking. Monodisperse chitosan-bearing droplets are created by shearing off a chitosan solution at a microfluidic T-junction with a stream of hexadecane containing a nonionic detergent. These droplets are then interfacially crosslinked into stable microparticles by a downstream flow of glutaraldehyde (GA). The functional properties of these robust microparticles can be easily varied by introducing various payloads, such as magnetic nanoparticles and/or fluorescent dyes, into the chitosan solution. The on-chip connection of such individual particles into well-defined microchains is demonstrated using GA again as the chemical "glue" and microchannel confinement as the spatial template. Chain flexibility can be tuned by adjusting the crosslinking conditions: both rigid chains and semiflexible chains are created. Additionally, the arrangement of particles within a chain can also be controlled, for example, to generate chains with alternating fluorescent and nonfluorescent microparticles. Such microassembled chains could find applications as microfluidic mixers, delivery vehicles, microscale sensors, or miniature biomimetic robots.

Growth of dandelion-shaped CuInSe2 nanostructures by a two-step solvothermal process

CuInSe(2) (CIS) nanodandelion structures were synthesized by a two-step solvothermal approach. First, InSe nanodandelions were prepared by reacting In(acac)(3) with trioctylphosphine-selenide (TOP-Se) in 1-octadecene (ODE) at 170 °C in the presence of oleic acid. These InSe dandelions were composed of polycrystalline nanosheets with thickness < 10 nm. The size of the InSe dandelions could be tuned within the range of 300 nm-2 µm by adjusting the amount of oleic acid added during the synthesis. The InSe dandelion structures were then reacted with Cu(acac)(2) in the second-step solvothermal process in ODE to form CIS nanodandelions. The band gap of the CIS dandelions was determined from ultraviolet (UV) absorption measurements to be ∼ 1.36 eV, and this value did not show any obvious change upon varying the size of the CIS dandelions. Brunauer-Emmett-Teller (BET) measurements showed that the specific surface area of these CIS dandelion structures was 44.80 m(2) g(-1), which was more than five times higher than that of the CIS quantum dots (e.g. 8.22 m(2) g(-1)) prepared by using reported protocols. A fast photoresponsive behavior was demonstrated in a photoswitching device using the 200 nm CIS dandelions as the active materials, which suggested their possible application in optoelectronic devices.

Facile fabrication of pomponlike microarchitectures of lanthanum molybdate via an ultrasound route

Pomponlike La(2)(MoO(4))(3) microstructures assembled with single-crystalline nanoflakes have been facilely fabricated via a surfactant-assisted ultrasound route for the first time. Various synthesis conditions were examined, such as the surfactant concentration, the molecular structure of surfactants, and the pH value. The obtained pomponlike microstructures were characterized by X-ray diffraction (XRD), (field-emission) scanning electron microscopy [(FE)SEM], transmission electron microscopy (TEM), and nitrogen adsorption/desorption isotherms. It has been revealed that a minimum concentration of sodium dodecylsulfate (SDS) was required for the formation of pomponlike La(2)(MoO(4))(3) microstructures. When the SDS concentration is above 0.02 mol L(-1), the pomponlike microstructures become more perfect, and the size is also increased with the increasing SDS concentration. Under the same sonication, similar pomponlike microstructures were obtained when a cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used instead of the anionic surfactant SDS, indicating that the hydrophobic alkyl chains are an important factor for the formation of the pomponlike La(2)(MoO(4))(3) microstructures. It is also found that the pomponlike La(2)(MoO(4))(3) microstructures can only be obtained within an optimal pH range of 8.0-9.0 under sonication. Based on TEM, Fourier transform infrared spectroscopy (FT-IR) and solubilization experiment, a formation mechanism of pomponlike La(2)(MoO(4))(3) microstructures was proposed, in which the collaborative action of surfactants and sonication plays a key role. Furthermore, the porosity of the pomponlike La(2)(MoO(4))(3) microstructures were discussed.

Microbeads on microposts: an inverted architecture for bead microarrays

The rapid development of genomics and proteomics requires accelerated improvement of the microarrays density, multiplexing, readout capabilities and cost-effectiveness. The bead arrays are increasingly attractive because of their self-assembly-based fabrication, which alleviates many problems of top-down microfabrication. Here we present a simple, reliable, robust and modular technique for the fabrication of bead microarrays, which combines the directed assembling of beads in microstructures and PDMS-based replica molding. The beads are first self-assembled in pyramidal microwells fabricated by anisotropic etching of silicon substrates, then transferred on the apex of PDMS pyramids that replicate the silicon microstructures. The arrays are chemically and biochemically robust; they are spatially addressable and have the potential for being informationally addressable; and they appear to offer better readout capabilities than the classical microarrays.

Fabrication of a modular tissue construct in a microfluidic chip

By combining microfluidics and soft-lithographic molding of gels containing mammalian cells, a device for three-dimensional (3D) culture of mammalian cells in microchannels was developed. Native components of the extracellular matrix, including collagen or Matrigel, made up the matrix of each molded piece (module) of cell-containing gel. Each module had at least one dimension below approximately 300 microm; in modules of these sizes, the flux of oxygen, nutrients, and metabolic products into and out of the modules was sufficient to allow cells in the modules to proliferate to densities comparable to those of native tissue (10(8)-10(9) cells cm(-3)). Packing modules loosely into microfluidic channels and chambers yielded structures permeated with a network of pores through which cell culture medium could flow to feed the encapsulated cells. The order in the packed assemblies increased as the width of the microchannels approached the width of the modules. Multiple cell types could be spatially organized in the small microfluidic channels. Recovery and analysis of modules after 24 h under constant flow of medium (200 microL h(-1)) showed that over 99% of encapsulated cells survived this interval in the microfluidic chamber.

Controlled construction of uniform pompon-shaped microarchitectures self-assembled from single-crystalline lanthanum molybdate nanoflakes

Uniform three-dimensional La2(MoO4)3 nanostructures with a pompon shape have been successfully constructed by a simple surfactant-free hydrothermal approach via self-assembly from single-crystalline nanoflakes. The formation of the uniform pompon-shaped La2(MoO4)3 microarchitectures is closely related to the presence of a proper amount of ammonium ions, and it is proposed that the pompon-shaped microarchitecture forms through an electrostatic attraction/repulsion effect between the oppositely charged flat surface and the edge of nanoflakes. Without the introduction of ammonium ions, no pompon-shaped microarchitectures can be formed, and while under the presence of excess ammonium ions, the nanoflakes on the micropompons become amorphous, twisted, and rugged. The novel microarchitectures of the product can be successfully modified from spherical to columelliform by using a mixed solvent of water/ethanol. This simple and efficient method may provide a practical reference to the controlled synthesis of other microarchitectures.

A hierarchical self-assembly route to three-dimensional polymer-quantum dot photonic arrays

We demonstrate a new hierarchical self-assembly strategy for the formation of photonic arrays containing quantum dots (QDs), in which sequential self-assembly steps introduce organization on progressively longer length scales, ranging from the nanoscale to the microscale regimes. The first step in this approach is the self-assembly of diblock copolymers to form block ionomer reverse micelles (SA1); within each micelle core, a single CdS QD is synthesized to yield the hybrid building block BC-QD. Once SA1 is completed, the hydrophobic BD-QD building blocks are blended with amphiphilic block copolymer stabilizing chains in an organic solvent; water addition induces secondary self-assembly (SA2) to form quantum dot compound micelles (QDCMs). Finally, aqueous dispersions of QDCMs are slowly evaporated to induce the formation of three-dimensional (3D) close-packed arrays in a tertiary self-assembly step (SA3). The resulting hierarchical assemblies, consisting of a periodic array of hybrid spheres each containing multiple CdS QDs, exhibit the collective property of a photonic stop band, along with photoluminescence arising from the constituent QDs. A high degree of structural control is possible at each level of organization by judicious selection of experimental variables, allowing various parameters governing the collective optical properties, including QD size, nanoparticle spacing, and mesocale periodicity, to be independently tuned. The resulting control over optical properties via successive self-assembly steps should provide new opportunities for hierarchical materials for QD lasers and all-optical switching.

Optical intensity gradient by colloidal photonic crystals with a graded thickness distribution

Gradient colloidal crystals with a thickness gradient were prepared by the vertical deposition technique with vertically graded concentration suspensions. The thickness of the gradient colloidal crystal gradually changes at different positions along the specific gradient direction of the crystal. The thickness gradient was determined by the concentration gradient, depending on the initial colloidal concentration and the settling time. The optical transmission intensity at the dip wavelength can be tuned by changing the thickness of the colloidal crystals. The gradient colloidal crystals lead to a gradient of optical intensity at the dip in transmission light. The gradient of optical intensity at the dip increases as the thickness gradient of the colloidal crystal increases.

Immobilization of polysaccharides on a fluorinated silicon surface

A self-assembled monolayer (SAM) of fluoroalkyl silane (FAS) was deposited on a silicon surface by chemical vapor deposition (CVD) at room temperature under 1.01x10(5)Pa nitrogen. Using this new approach, the quality and reproducibility of the SAM are better than those prepared either in solution or by vapor phase deposition, and the deposition process is simpler. In this modified CVD process, the silane monomers, instead of the oligomeric species, are the primary reactants. Full coverage of the silicon surface by FAS molecules was achieved within 5 min. Heparin and hyaluronan, two naturally occurring biocompatible polysaccharides, were successfully covalently attached on the FAS SAM/Si surface by photo-immobilization. Atomic force microscopy (AFM) revealed the morphologic changes after the immobilization of heparin and hyaluronan, and X-ray photoelectron spectroscopy (XPS) confirmed the change in chemical compositions. Such combination of coatings is expected to enhance the stability and biocompatibility of the base material.

Planar tripods of platinum: formation and self-assembly

This communication describes a synthesis of planar tripods of platinum and their assembly into two-dimensional (2D) nano-structures using the Langmuir-Blodgett (LB) technique.

Mesoscale Organization of CuO Nanoribbons: Formation of “Dandelions”

A two-tiered organizing scheme with multiple-length scales for construction of dandelion-like hollow CuO microspheres has been elucidated: (1) mesoscale formation of rhombic building units from smaller nanoribbons via oriented aggregation and (2) macroscopic organization of these units into the CuO microspheres. This self-assembly concept may also be applicable to other metal oxides by creating geometric constraints for constructional units.

Nanotechnology and medicine

Nanotechnology, or systems/device manufacture at the molecular level, is a multidisciplinary scientific field undergoing explosive development. The genesis of nanotechnology can be traced to the promise of revolutionary advances across medicine, communications, genomics and robotics. On the surface, miniaturisation provides cost effective and more rapidly functioning mechanical, chemical and biological components. Less obvious though is the fact that nanometre sized objects also possess remarkable self-ordering and assembly behaviours under the control of forces quite different from macro objects. These unique behaviours are what make nanotechnology possible, and by increasing our understanding of these processes, new approaches to enhancing the quality of human life will surely be developed. A complete list of the potential applications of nanotechnology is too vast and diverse to discuss in detail, but without doubt one of the greatest values of nanotechnology will be in the development of new and effective medical treatments (i.e., nanomedicine). This review focuses on the potential of nanotechnology in medicine, including the development of nanoparticles for diagnostic and screening purposes, artificial receptors, DNA sequencing using nanopores, manufacture of unique drug delivery systems, gene therapy applications and the enablement of tissue engineering.