Hierarchical self-assembly of a coiled-coil peptide into fractal structure

Here we report the hierarchical self-assembly of a cross-linkable coiled-coil peptide containing an internal cysteine. Atomic force microscopy (AFM) experiments revealed the fractal structure of the assemblies, and molecular simulations showed that the peptides cross-linked to form clusters of coiled-coils, which further assembled to form globules of tens of nanometers in diameter. Such hierarchical organization was modulated by pH or thiol-reducing agent. Exploitation of the fractal structures through chemical methods may be valuable for the fabrication of materials spanning multiple length scales.     

Simultaneous self-assembly, orientation, and patterning of peptide-amphiphile nanofibers by soft lithography

Self-assembled nanofibers of peptide-amphiphile molecules have been of great interest because of their bioactivity both in vitro and in vivo. In this work, we demonstrate the simultaneous self-assembly, alignment, and patterning of these nanofibers over large areas by a novel technique termed sonication-assisted solution embossing. In this soft lithographic technique, the nanostructures self-assemble by solvent evaporation while under the influence of ultrasonic agitation and confinement within the topographical features of an elastomeric stamp. The nanofibers orient parallel to the channels as they assemble out of solution, yielding bundles of aligned nanofibers on the substrate after the stamp is removed. Alignment is likely a result of steric confinement and possibly a transition to a lyotropic liquid crystalline phase as solvent evaporates. This technique is not limited to uniaxial alignment and is shown to be able to guide nanofibers around turns. Alignment of nanostructures by this method introduces the possibility of controlling macroscale cellular behavior or material properties by tuning the directionality of interactions at the nanoscale.     

Polymer nanocomposites processed via self-assembly through introduction of nanoparticles,nanosheets, and nanofibers

Nanocomposites offer the theoretical potential to achieve mechanical properties surpassing those of conventional (micro-scale) composites. The underlying reasons for the high potential of nanocomposites include the uniquely high mechanical attributes of nano-scale reinforcement, effective control of defect size and growth by nano-spaced interfaces, and interactions between the polymer matrix and the large surface areas of nanomaterials. Attempts to produce nanocomposites via conventional processing techniques have encountered challenges associated with thorough dispersion and effective interfacial interactions of nano-scale reinforcement with the polymer matrix. In order to address these challenges, materials were processed into polymer nanocomposites via electrostatically driven layer-by-layer self-assembly. Electrostatically dispersed nanomaterials and oppositely charged polyelectrolytes were sequentially built upon a substrate (cellular scaffold). The self-assembled nanocomposites, after complementary cross-linking, provided a unique balance of strength and ductility, which surpassed those of conventional (micro-scale) composites. Self-assembly was found to be an effective approach to producing nanocomposites embodying uniformly dispersed nanomaterials with controlled interfacial interactions. This approach is highly versatile and enables introduction of diverse nanomaterials into polymer nanocomposites. The work reported herein evaluated introduction of diverse categories of nanomaterials incorporating nanoparticles, nanosheets, nanotubes, and nanofibers. This investigation also evaluated the potential for a biomimetic approach to processing of light-weight structural systems by self-assembly of polymer nanocomposites onto cellular scaffolds.     

Water-inducing molecular self-assembly of amphiphilic molecules into nanofibers

We present investigations on the microcosmic self-assembly process of new synthesized amphiphilic TPDP molecules. It can be seen that pure TPDP nanofibers with smooth surfaces can be obtained by reprecipitation method using ethanol as good solvent and water as poor solvent. In the self-assembly process, during the water adding to the amphiphilic molecules’ saturated solution, the amphiphilic molecules firstly assembled into needle-like small rods. With an increase in the self-assembled time, a large number of the nanofibers are produced. The assembly behavior was revealed in the course of direct in situ monitoring of its growth with optical microscopy. Field emission scanning electron microscopy was adopted to characterize the morphologies of the products.     

Microwave synthesis of chain-like zircona nanofibers through carbon-induced self-assembly growth

Chain-like zircona (ZrO₂) nanofibers were prepared by microwave sintering without any surfactants or solid templates. Microwave sintering was conducted in a multimode microwave cavity with TE666 resonant mode at 2.45 GHz. Carbon particles were used to activate unique thermal processes when mixed with ZrO₂ precursor. The sintering condition was at 1300°C for 10 min. Samples were characterized by XRD, SEM, TEM techniques. It was found that both monolithic and tetragonal ZrO₂ co-existed in samples prepared fromthe mixture of ZrO₂ precursors and carbon by either microwave or conventional sintering. Only m-ZrO₂ exists in samples prepared by ZrO₂ precursors without carbon. ZrO₂ appeared as chain-like nanofibers, which might be attributed to a so-called carbon-induced self-assembly growth mechanism.     

Hierarchical architectures by synergy between dynamical template self-assembly and biomineralization

Diatoms, shells, bones and teeth are exquisite examples of well-defined structures, arranged from nanometre to macroscopic length scale, produced by natural biomineralization using organic templates to control the growth of the inorganic phase. Although strategies mimicking Nature have partially succeeded in synthesizing human-designed bio-inorganic composite materials, our limited understanding of fundamental mechanisms has so far kept the level of hierarchical complexity found in biological organisms out of the chemists' reach. In this letter, we report on the synthesis of unprecedented double-walled silica nanotubes with monodisperse diameters that self-organize into highly ordered centimetre-sized fibres. A unique synergistic growth mechanism is elucidated by the combination of light and electron microscopy, synchrotron X-ray diffuse scattering and Raman spectroscopy. Following this growth mechanism, macroscopic bundles of nanotubules result from the kinetic cross-coupling of two molecular processes: a dynamical supramolecular self-assembly and a stabilizing silica mineralization. The feedback actions between the template growth and the inorganic deposition are driven by a mutual electrostatic neutralization. This 'dynamical template' concept can be further generalized as a rational preparation scheme for materials with well-defined multiscale architectures and also as a fundamental mechanism for growth processes in biological systems.     

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.     

Hierarchical self-assembly of suspended branched colloidal nanocrystals into superlattice structures

Self-assembly of molecular units into complex and functional superstructures is ubiquitous in biology. The number of superstructures realized by self-assembly of man-made nanoscale units is also growing. However, assemblies of colloidal inorganic nanocrystals are still at an elementary level, not only because of the simplicity of the shape of the nanocrystal building blocks and their interactions, but also because of the poor control over these parameters in the fabrication of more elaborate nanocrystals. Here, we show how monodisperse colloidal octapod-shaped nanocrystals self-assemble, in a suitable solution environment, on two sequential levels. First, linear chains of interlocked octapods are formed, and subsequently the chains spontaneously self-assemble into three-dimensional superstructures. Remarkably, all the instructions for the hierarchical self-assembly are encoded in the octapod shape. The mechanical strength of these superstructures is improved by welding the constituent nanocrystals together.     

PH-dependent self-assembly of the short Surfactant-like peptide KA6

Self-assembly of amphiphilic peptides designed during the last ten years by different research groups lead to a large variety of 3D-structures that already found applications in e.g., for stabilization of large protein complexes, cell culturing systems etc. We present synthesis and characterization of a novel amphiphilic peptide KA6 that exhibits clear charge separation controllable by the pH of the environment. The self-assembly in this system is largely governed by electrostatic interaction, thus a change in pH will not only lead to a change in critical micellar concentration (CMC) of the peptide but also to the changes in micellar structure as revealed by atomic force microscopy (AFM) and circular dichroism (CD) study. At basic pH the micellar structure inverts exposing the opposite end of the peptide chain to the solution. This interesting phenomenon could provide basis for novel pH sensitive materials including drug delivery and controlled release systems.     

Hierarchical nanostructures by sequential self-assembly of styrene-dimethylsiloxane block copolymers of different periods

Poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) block copolymers with a period as low as 13 nm have been self-assembled on a template formed from PS-b-PDMS of a 34–40 nm period, which is itself templated by micron-scale substrate features prepared using conventional lithography. This hierarchical process provides a simple method for directing the self-assembly of sub-10 nm features and registering them on the substrate.     

Presentation and recognition of biotin on nanofibers formed by branched peptide amphiphiles

A branched peptide amphiphile system was designed for enhanced recognition of biotin on nanofibers formed by self-assembly of these molecules. Branching at a lysine residue was used to design peptide amphiphiles that are capable of presenting more than one epitope per molecule. We found that biotinylated branched structures form nanofibers that enhance recognition by the avidin protein receptor relative to similar nanostructures formed by linear peptide analogues. Biotin-avidin binding to the supramolecular nanofibers was characterized by measurement of fluorescence from nanofibers incubated with chromophore-conjugated avidin.     

Hierarchical assembly of inorganic nanostructure building blocks to octahedral superstructures-a true template-free self-assembly

A room temperature, template-free, wet chemical synthesis of ceria nanoparticles and their long term ageing characteristics are reported. High resolution transmission electron microscopy and UV-visible spectroscopy techniques are used to observe the variation in size, structure and oxidation state, respectively as a function of time. The morphology variation and the hierarchical assembly (octahedral superstructure) of nanostructures are imputed to the inherent structural aspects of cerium oxide. It is hypothesized that the 3-5?nm individual building blocks will undergo an intra-agglomerate re-orientation to attain the low energy configuration. This communication also emphasizes the need for long term ageing studies of nanomaterials in various solvents for multiple functionalities.     

Nanorod formation of cyclodextrin-covered sudan dyes through supramolecular self-assembly

Cyclodextrin-covered sudan III (SDIII) and sudan IV (SDIV) dyes produced various nanostructures such as pseudorotaxanes through supramolecular self-assembly, studied by absorption, fluorescence, time-resolved fluorescence, SEM, TEM, FT-IR, DSC, PXRD and ¹H NMR. Solvent study shows that azo–hydrazo tautomer is present in sudan dyes. Absorption and fluorescence spectroscopy data gave evidence for the formation of 1:2 inclusion complexes. Big nanorod (～36 nm) surrounded by small nanorod (～3 nm) was identified in SDIV/α-CD complexes. This confirms that the rigid molecular nanorod aggregates of α-CD and β-CD complexes are formed through the initial formation of smaller nanorods. An unequal morphology noticed in SDIII/CD suggests that the 1:2 inclusion complexes were self-assembled into irregular arrangement. The thermodynamic parameters (ΔH, ΔG and ΔS) of inclusion processes were determined from semi-empirical PM3 calculations.     

Particulate pattern formation and its morphology control by convective self-assembly

Bottom-up self-organization approaches are promising for fabricating higher-order patterned surfaces composed of colloidal particles. The first example among the patterns that have been extensively studied would be stripes; however, the formation of stripe patterns has so far been confined to partially or fully hydrophobic surfaces. By contrast, we have succeeded in preparing well-defined stripe patterns even on strongly hydrophilic substrates via a convective self-assembly technique. By using this technique, a stripe pattern was produced simply by suspending a substrate in a dilute suspension, without any complicated procedure; the stripes spontaneously aligned parallel to the contact line. Driven by this finding, we further investigate this self-assembly process, and find out that the convective self-assembly is quite promising as a template-free pattern formation technique. In the present paper, we first overview the convective self-assembly technique which is originally developed for uniform film formation, and then present our recent results on the pattern formation of colloidal particles through the convective self-assembly. This technique can produce various patterns including stripes, cluster arrays, and grids in response to macroscopic experimental parameters such as particle concentration and temperature.     

Peptide self-assembly into lamellar phases and the formation of lipid-peptide nanostructures

Nano Research - Lipids exhibit an extraordinary polymorphism in self-assembled mesophases, with lamellar phases as the most relevant biological representative. To mimic lipid lamellar phases with...     

Hierarchical nanostructures of PbTiO3 through mesocrystal formation

Novel hierarchical self-assembled structures; bur-like PbTiO3 nanostructures were made by self-assembly of PbTiO3 nanocrystals under hydrothermal conditions using sodium dodecylbenzene sulfonate surfactant. The bur-like nanostructures exhibit a unique geometrical shape with cores of agglomerated nanocrystals and outershells of nanorods. The nanorods were between 30 nm and 100 nm in diameter and from several hundred nm up to 2 microm in length. We demonstrate that these nanostructures are formed in a two step process where agglomeration of PbTiO3 nanoparticles into microspheres occurs in a first step, followed by assembly of cube-shaped nanoparticle building blocks into PbTiO3 mesocrystals in a second step. The mesocrystals continuously grow into nanorods from the surface of the microspheres acting as a substrate.     

Boron carbonitride nanofibers: synthesis,characterization, and photoluminescence properties

Large-scale highly aligned boron carbonitride (BCN) nanofibers with controllable orientations and chemical compositions were synthesized directly on nickel substrates from a gas mixture of N2, H2, CH4, and B2H6 by plasma-enhanced hot filament chemical vapor deposition. The morphology of the BCN nanofibers was examined by scanning electron microscopy, the microstructures were studied by high-resolution transmission electron microscopy, and the bonding states as well as chemical compositions were determined by electron energy loss spectroscopy. To our knowledge, this is the first report on the photoluminescent properties of BCN nanofibers that shows that they are interesting blue- and violet-light-emitting materials with tunable wavelengths. Further studies on field electron emission suggest that BCN nanofibers are also promising candidates for field emission sources.