Assembly Of Nanorods Research Articles

Weak Electrostatic Interaction Enabled Highly Oriented Assembly of Gold Nanorods onto Ultrathin Flagella Bionanofibers

Biological substrates are generally considered unfavored for electrostatic uptake of nanoparticles due to their low surface charges. Herein, the electrostatic interaction between weakly charged ultrathin flagella bionanofibers and gold nanorods (AuNRs) is investigated. It is discovered that compared with the reported AuNRs assembly onto one‐dimensional (1D) templates of strong charges, the weak electrostatic interaction here can generate more ordered 1D AuNRs array. Under strong attraction force, AuNRs can bind firmly on templates by either narrow heads or long sidewalls, resulting in less ordered 1D structure. While under weak attraction force, AuNRs can be captured only if interacting with flagella using their long sidewalls to obtain accumulative strong enough force. Another discovery is that under weak AuNRs–flagella electrostatic attraction force, the relatively stronger AuNRs–AuNRs repulsion force plays a significant role in determining the interparticle gap and the single‐ or double‐string pattern of AuNRs on ultrathin flagella. Advantage is also taken of the bio‐origin of flagella by assembling AuNRs onto flagella that are still attached to living bacterium. Such a capability makes our approach highly feasible for potential device fabrication, as individual nanoarray is hard to manipulate, but would be greatly facilitated if it is associated with a micron‐sized base, like bacteria.

Nanoscale Chemical Imaging of Nanoparticles under Real‐World Wastewater Treatment Conditions

AbstractUnderstanding nanomaterial transformations within wastewater treatment plants is an important step to better predict their potential impact on the environment. Here, spatially resolved, in situ nano‐X‐ray fluorescence microscopy is applied to directly observe nanometer‐scale dissolution, morphological, and chemical evolution of individual and aggregated ZnO nanorods in complex “real‐world” conditions: influent water and primary sludge collected from a municipal wastewater system. A complete transformation of isolated ZnO nanorods into ZnS occurs after only 1 hour in influent water, but larger aggregates of the ZnO nanorods transform only partially, with small contributions of ZnS and Zn‐phosphate (Zn3(PO4)2) species, after 3 hours. Transformation of aggregates of the ZnO nanorods toward mixed ZnS, Zn adsorbed to Fe‐oxyhydroxides, and a large contribution of Zn3(PO4)2 phases are observed during their incubation in primary sludge for 3 hours. Discrete, isolated ZnO regions are imaged with unprecedented spatial resolution, revealing their incipient transformation toward Zn3(PO4)2. Passivation by transformation(s) into mixtures of less soluble phases may influence the subsequent bioreactivity of these nanomaterials. This work emphasizes the importance of imaging the nanoscale chemistry of mixtures of nanoparticles in highly complex, heterogeneous semi‐solid matrices for improved prediction of their impacts on treatment processes, and potential environmental toxicity following release.

Growth transitions and critical behavior in the non-equilibrium aggregation of short, patchy nanorods.

We have carried out Monte Carlo simulations to study the non-equilibrium aggregation of short patchy nanorods in two dimensions. Below a critical value of patch size ([Formula: see text]), the aggregates have finite sizes with small radii of gyration, [Formula: see text]. At [Formula: see text], the average radius of gyration shows a power law increase with time such that [Formula: see text], where [Formula: see text]. Above, [Formula: see text], the aggregates are fractal in nature and their fractal dimension depends on the value of patch size. These morphological differences are due to the fact that below the critical value of patch size ([Formula: see text]), the growth of the clusters is suppressed and the system reaches an 'absorbed state.' Above [Formula: see text], the system reaches an 'active state,' in which the cluster size keeps growing with a fixed rate at long times. Thus, the system encounters a non-equilibrium phase transition. Close to the transition, the growth rate scales as [Formula: see text], where [Formula: see text]. The long-time growth rate varies as [Formula: see text] where [Formula: see text]. These scaling exponents indicate that the transition belongs to the directed percolation universality class. The patchy nanorods also display a threshold patch size ([Formula: see text]), beyond which the long-time growth rate remains constant. We present geometric arguments for the existence of [Formula: see text]. The fractal dimension of the aggregates increases from 1.75, at [Formula: see text], to 1.81, at [Formula: see text]. It remains constant beyond [Formula: see text].

Reprogramming Virus Coat Protein Carboxylate Interactions for the Patterned Assembly of Hierarchical Nanorods

The self-assembly system of the rod-shaped tobacco mosaic virus (TMV) has been studied extensively for nanoscale applications. TMV coat protein assembly is modulated by intersubunit carboxylate groups whose electrostatic repulsion limits the assembly of virus rods without incorporating genomic RNA. To engineer assembly control into this system, we reprogrammed intersubunit carboxylate interactions to produce self-assembling coat proteins in the absence of RNA and in response to unique pH and ionic environmental conditions. Specifically, engineering a charge attraction at the intersubunit E50-D77 carboxylate group through a D77K substitution stabilized the coat proteins assembly into virus-like rods. In contrast, the reciprocal E50K modification alone did not confer virus-like rod assembly. However, a combination of R46G/E50K/E97G substitutions enabled virus-like rod assembly. Interestingly, the D77K substitution displays a unique pH-dependent assembly-disassembly profile, while the R46G/E50K/E97G substitutions confer a novel salt concentration dependency for assembly control. In addition, these unique environmentally controlled coat proteins allow for the directed assembly and disassembly of chimeric virus-like rods both in solution and on substrate-attached seed rods. Combined, these findings provide a controllable means to assemble functionally discrete virus-like rods for use in nanotechnology applications.

Insulating and Robust Ceramic Nanorod Aerogels with High-Temperature Resistance over 1400 °C.

Ceramic aerogels, which present a unique combination of low thermal conductivity and excellent high-temperature stability, are attractive for thermal insulation under extreme conditions. However, most ceramic aerogels are constructed by oxide ceramic nanoparticles and thus are usually plagued by their brittleness and structural collapse at elevated temperatures (less than 1000 °C). Despite great progress achieved in this regard recently, it still remains a big challenge to design and fabricate intriguing ceramic aerogels with enhanced mechanical strength and remarkable thermal stability at ultrahigh temperature up to 1400 °C. To this end, we herein report a facile and scalable strategy to manufacture ceramic nanorod aerogels (CNRAs) with hierarchically macroporous and mesoporous structures by the controllable assembly of Al2O3 nanorods and SiO2 nanoparticles. Subsequently, the high-temperature annealing treatment of CNRAs significantly maximizes mechanical strength and promotes thermal tolerance. The obtained CNRAs demonstrate the integrated properties of super-strong heat resistance (up to 1400 °C), low thermal conductivity (0.026 W/m·K at 25 °C and 0.089 W/m·K at 1200 °C), high mechanical robustness (compressive strength 1.5 MPa), and low density (0.146 g/cm3). We envision that this novel nanorod-assembled ceramic aerogels offer considerable advantages than most of the state-of-the-art ceramic aerogels for thermal superinsulation upon exposure to extremely harsh environments.

Near-Infrared-Triggered Photothermal Aggregation of Polymer-Grafted Gold Nanorods in a Simulated Blood Fluid.

Gold nanorods were decorated with thermoresponsive copolymers of tailored architecture and constructed from N-isopropyl acrylamide and acrylamide. The copolymers were prepared via reversible addition-fragmentation chain transfer polymerization (RAFT) and immobilized on the gold nanorod surface taking advantage of the aurophilicity of its inherently formed trithiocarbonate groups. The topology as well as the average molecular weight of the copolymers was altered using either a monofunctional or 3-arm star RAFT agent. Two-dimensional arrays of the self-assembled core-shell nanostructures were fabricated by drop-casting showing tunable interparticle spacings. In a simulated blood fluid, the lower critical solution temperature of the nanohybrids could be modified over a significant temperature range around body temperature by adjusting the copolymer composition, the architecture, and/or the size of the polymer. The intrinsic photothermal properties of the gold nanorods were utilized to trigger particle aggregation by irradiation at 808 nm in the optical window of human tissues. In effect, a new nanohybrid system with remotely controllable aggregation via an external NIR-light stimulus for nanomedical applications was developed.

Molecular Modeling and Simulation of Polymer Nanocomposites with Nanorod Fillers.

We present a coarse-grained (CG) molecular dynamics (MD) simulation study of polymer nanocomposites (PNCs) containing nanorods with homogeneous and patchy surface chemistry/functionalization, modeled with isotropic and directional nanorod-nanorod attraction, respectively. We show how the PNC morphology is impacted by the nanorod design (i.e., aspect ratio, homogeneous or patchy surface chemistry/functionalization) for nanorods with a diameter equal to the Kuhn length of the polymer in the matrix. For PNCs with 10 vol % nanorods that have an aspect ratio ≤5, we observe percolated morphology with directional nanorod-nanorod attraction and phase-separated (i.e., nanorod aggregation) morphology with isotropic nanorod-nanorod attraction. In contrast, for nanorods with higher aspect ratios, both types of attractions result in aggregated nanorods morphology due to the dominance of entropic driving forces that cause long nanorods to form orientationally ordered aggregates. For most PNCs with isotropic or directional nanorod-nanorod attractions, the average matrix polymer conformation is not perturbed by the inclusion of up to 20 vol % nanorods. The polymer chains in contact with nanorods (i.e., interfacial chains) are on average extended and statistically different from the conformations the matrix chains adopt in the pure melt state (with no nanorods); in contrast, the polymer chains far from nanorods (i.e., bulk chains) adopt the same conformations as the matrix chains adopt in the pure melt state. We also study the effect of other parameters, such as attraction strength, nanorod volume fraction, and matrix chain length, for PNCs with isotropic or directional nanorod-nanorod attractions. Collectively, our results provide valuable design rules to achieve specific PNC morphologies (i.e., dispersed, aggregated, percolated, and orientationally aligned nanorods) for various potential applications.

Branched In2O3 Mesocrystal of Ordered Architecture Derived from the Oriented Alignment of a Metal–Organic Framework for Accelerated Hydrogen Evolution over In2O3–ZnIn2S4

It is fascinating yet challenging to assemble anisotropic nanowires into ordered architectures of high complexity and intriguing functions. We exploited a facile strategy involving oriented etching of a metal-organic fragment (MOF) to advance the rational design of highly ordered nanostructures. As a proof of concept, a microscale MIL-68(In) single crystal was etched with a K3[Co(CN)6] solution to give a microtube composed of aligned MIL-68(In) nanorods. Annealing such a MIL-68(In) microtube readily created an unprecedented branched In2O3 mesocrystal by assembly of In2O3 nanorods aligned in order. The derived ordered-In2O3-ZnIn2S4 is more efficient in catalyzing visible-light-driven H2 evolution (8753 μmol h-1 g-1) outperforming the disordered-In2O3-ZnIn2S4 counterpart (2700 μmol h-1 g-1) as well as many other state-of-the-art ZnIn2S4-based photocatalysts. The ordered architecture significantly boosts the short-range electron transfer in an In2O3-ZnIn2S4 heterojunction but has a negligible impact on the long-range electron transfer among In2O3 mesocrystals. The density functional theory (DFT) calculation reveals that the oriented etching is achieved by the selective binding of the [Co(CN)6]3- etchant on the (110) plane of MIL-68(In), which can drag the In atoms out of the framework in order. Our findings could broaden the technical sense toward advanced photocatalyst design and impose scientific impacts on unveiling how ordered photosystems operate.

Near-Infrared Chiral Plasmonic Microwires through Precision Assembly of Gold Nanorods on Soft Biotemplates

Directing the assembly of plasmonic nanoparticles into chiral superstructures has diverse applications including, chiroptical sensing, nonlinear optics, and biomedicine. Though soft template-mediated assemblies of both spherical and nonspherical gold nanoparticles have made significant progress, most approaches require sophisticated chemical synthesis or advanced methodologies. Besides, reports of structurally precise chiral plasmonic assemblies beyond nanoscale are limited. Here, we propose an efficient yet simple strategy to grow such precision assemblies up to mesoscale, which is beneficial for a broader community. Briefly, cationic gold nanorods (AuNRs) are allowed to systematically assemble along atomically precise, chiral, rodlike tobacco mosaic virus (TMV) particles via electrostatic attraction under ambient condition. This leads to spontaneous formation of helical hybrid microwires with high structural precision, as evidenced by cryogenic transmission electron microscopy and tomography. Resulting composite superstructures show a strong circular dichroism response at the plasmon wavelength of the AuNRs, which is supported by simulations using discrete dipole approximation. Further, chirality of the system is investigated at a single-microwire level using polarized dark-field scattering microscopy. An alternative chiral template, negatively charged colloidal cellulose nanocrystals, also arrange AuNRs into similar chiral microstructures. Thus, our report proposes a generic methodology to obtain chiral plasmonic response at the NIR region using inexpensive templates that will encourage the exploration of a wider range of nanoscale templates for creating hybrid mesostructures with emerging optoelectronic properties.

Retraction: Bhosale, S.V., et al. pH Dependent Molecular Self-Assembly of Octaphosphonate Porphyrin of Nanoscale Dimensions: Nanosphere and Nanorod Aggregates. Int. J. Mol. Sci. 2011, 12, 1464-1473.

The journal retracts the article, "pH Dependent Molecular Self-Assembly of Octaphosphonate Porphyrin of Nanoscale Dimensions: Nanosphere and Nanorod Aggregates" [...].

High spatial and energy resolution electron energy loss spectroscopy of the magnetic and electric excitations in plasmonic nanorod oligomers.

We leverage the high spatial and energy resolution of monochromated aberration-corrected scanning transmission electron microscopy to study the hybridization of cyclic assemblies of plasmonic gold nanorods. Detailed experiments and simulations elucidate the hybridization of the coupled long-axis dipole modes into collective magnetic and electric dipole plasmon resonances. We resolve the magnetic dipole mode in these closed loop oligomers with electron energy loss spectroscopy and confirm the mode assignment with its characteristic spectrum image. The energy splitting of the magnetic mode and antibonding modes increases with the number of polygon edges (n). For the n=3-6 oligomers studied, optical simulations using normal incidence and s-polarized oblique incidence show the respective electric and magnetic modes' extinction efficiencies are maximized in the n=4 arrangement.

Alignment of Au nanorods along de novo designed protein nanofibers studied with automated image analysis.

In this study, we focus on exploring the directional assembly of anisotropic Au nanorods along de novo designed 1D protein nanofiber templates. Using machine learning and automated image processing, we analyze scanning electron microscopy (SEM) images to study how the attachment density and alignment fidelity are influenced by variables such as the aspect ratio of the Au nanorods, and the salt concentration of the solution. We find that the Au nanorods prefer to align parallel to the protein nanofibers. This preference decreases with increasing salt concentration, but is only weakly sensitive to the nanorod aspect ratio. While the overall specific Au nanorod attachment density to the protein fibers increases with increasing solution ionic strength, this increase is dominated primarily by non-specific binding to the substrate background, and we find that greater specific attachment (nanorods attached to the nanofiber template as compared to the substrates) occurs at the lower studied salt concentrations, with the maximum ratio of specific to non-specific binding occurring when the protein fiber solutions are prepared in 75 mM NaCl concentration.

Interfacial assembly of nanorods: smectic alignment and multilayer stacking.

Large-scale spatial arrangement and orientation ordering of nanorod assembly on substrates are critical for nanodevice fabrication. However, complicated processes and templates or surface modification of nanorods are often required. In this work, we demonstrate, by dissipative particle dynamics simulations, that various ordered structures of adsorbed nanorods on smooth substrates can be simply achieved by non-affinity adsorption. The structures of interfacial assembly, including monolayers with a nematic-like arrangement and multilayer stacking with a smectic-like arrangement, depend on the nanorod concentration and the solvent size. As the nanorod concentration increases, the adsorbed layer becomes densely packed and the arrangement of nanorods changes from nematic-like to smectic. The assembly process driven by entropy is a two-dimensional layer-by-layer growth. Multilayer stacking with a smectic-like arrangement takes place at dilute concentrations of nanorods for large solvents such as pentamers, but at concentrated concentrations, it takes place for small solvents such as monomers. Moreover, nanorod bundles appear in the bulk phase for large solvents at dilute concentrations. The proposed strategy for interfacial assembly is caused by the free volume released for solvents, which is independent of the chemical compositions of substrates and nanorods.

Measuring the order parameter of vertically aligned nanorod assemblies.

Vertically aligned nanorod assemblies are of great interest both for fundamental studies of anisotropic physical properties arising from the structures and for the development of functional devices utilizing such anisotropic characteristics. Simultaneous measurement of the homeotropic order parameter (Shomeo) of assemblies in dynamic states can allow further optimization of the assembly process and the device performance. Although many techniques (e.g. birefringence measurement, SAXS analysis, and high-resolution microscopy) have been proposed to characterise Shomeo, these do not yet meet the essential criteria such as for rapid, in situ and non-destructive analyses. Here, we propose a novel approach employing a unique photoluminescence behaviour of lanthanide-doped crystalline nanorods, of which the emission spectrum contains the detailed information on the structure of the assembly. We demonstrate a rapid in situ determination of Shomeo of Eu3+-doped NaYF4 nanorods of which the orientation is controlled under an external electric field. The method does not require the consideration of polarization and can be performed using a conventional fluorescence microscopy setup. This new methodology would provide a more in-depth examination of various assembled nanostructures and the collective dynamics of their building blocks.

Controlled Synthesis of BaCO3 Microstructures Using Various Natural Gums - A Biomimetic Approach

In this study, Barium carbonate microstructures assembled from nanorods are successfully synthesized at room temperature and screw capped method at 100C. The experiments show that the protocol followed for the synthesis of BaCO3 as well as the concentration of various gums used, play an important role in the size and morphology of BaCO3. Here in, we obtained witherite type nanorods aggregates with unusual morphologies via transformation of metal carbonates at different conditions using natural gums as additives. A rational mechanism based on the oriented self-assembly of BaCO3 nuclei is proposed for the formed architectures. The crystals undergo an interesting morphology changes and have been well characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and Fourier Transform Infrared spectroscopy (FT-IR) techniques. This method is simple, low-cost and environmentally friendly route for the synthesis of BaCO3 microstructures with altogether different morphologies.

Self-ordered cellulose nanocrystals and microscopic investigations

Abstract Cellulose nanocrystals were extracted from cotton. The cellulose nanocrystals made a self-assembly structure when dried under slow conditions, as it was revealed by the characterization made to the material. The AFM images of the nanocrystals showed that they had a changing local orientation, pointing in a preferred direction that underwent a periodic change. This periodic change resembles the orientation of a chiral nematic phase. The TEM images showed that the nanocrystals had a rod-like appearance with average length size of 98.5 nm and a diameter of 4.7 nm. The TEM characterization showed the nanocrystals with more details than AFM. In this paper, the self-assembling of CNC was observed by AFM, and further investigations were done by TEM, deconvoluting the process of CNC nanorods aggregation.

Helically Grooved Gold Nanoarrows: Controlled Fabrication, Superhelix, and Transcribed Chiroptical Switching

Plasmonic chiroptical materials, coupled by chirality and surface plasmons, have been attracting great interest due to their potential applications, such as photonics, chiral recognition, asymmetri...

Plasmon-Enhanced Optical Chirality through Hotspot Formation in Surfactant-Directed Self-Assembly of Gold Nanorods.

Plasmonically enhanced optical dichroism has attracted substantial interest for its application in optical sensing, where the interplay between chirality emanating from both molecules and plasmon-supporting structures has been regarded as a critical ingredient. Here, we experimentally demonstrate that suitably self-assembled achiral plasmonic nanostructures produce a high degree of enhancement in the optical dichroism observed from chiral molecules placed in their vicinity. Specifically, we identify a near-field enhancement associated with plasmonic hotpots as the mechanism enabling our observation of visible-NIR circular dichroism emanating from small amounts of chiral molecules. Our structures consist of linear arrays of gold nanorods obtained by introducing chiral anionic surfactants, such as modified bile salts, which lead to selective destabilization of a cetyltrimethylammonium bromide coating layer on Au nanorods, thereby promoting a tip-to-tip oriented assembly. The proposed mechanism of plasmonically-enhanced circular dichroism is supported by deriving a simple, yet general theoretical formalism that confirms the observed results, revealing the role of optical hotspots at the gaps of linear tip-to-tip nanorod assemblies as the origin of enhancement in the dichroism from chiral molecules. Importantly, it is the refractive rather than the absorption-mediated chiral response of the molecules that produces dichroism in the visible-NIR plasmonic regime, far from their UV absorption resonances. The observed self-assembly mechanism suggests that chiral analytes not directly interacting with the nanorod surfaces, but just able to induce tip-to-tip aggregation, can be revealed by a CD signature in the plasmonic region, thereby supporting potential applications in ultrasensitive analysis.

Building Block Design for Rapid Mass Transport in Quasi-Solid-State Solar Cells

Mesoscopic solar cells have rapidly emerged as a promising alternative to conventional silicon photovoltaics due to the combined benefits of low-cost, simple fabrication and competitive solar energy conversion efficiency. Recent success in low light absorption cobalt (II/III) polypyridyl complexes has led to encouraging solar energy conversion efficiencies in excess of 13%. Moreover, as one-electron redox mediators, cobalt (II/III) complexes based DSC systems also show a lower overpotential for dye regeneration and better compatibility with flexible metal substrates than iodide/tri-iodide. Such efforts open up great possibilities towards commercial applications.In contrast to the conventional organic liquid electrolytes that commonly have challenges durable encapsulation of the devices due to solvent evaporation, gel electrolytes have exhibited an impressive long-term stability, especially for outdoor applications where temperature of the DSC system can reach 80-85 oC under sunlight. Improvement on mass transport of the considerably large sized cobalt (II/III) complexes, particularly in high viscosity electrolyte, is crucial for solid-state dye-sensitized solar cells (SS-DSCs) to reach a reliable high efficiency toward practical applications.In this work, titania nanorod aggregates (TNA) with a great specific surface area and well-developed crystalline network were synthesized through a solvothermal approach and utilized as photoanode building blocks for application in cobalt (II/III) tris(2′2-bipyridine) complexes based solid-state electrolyte. An initial efficiency excess 7.1% and a long term stable efficiency of approximately 8.0% were achieved at full sun illumination by freshly assembled and aged TNA SS-DSCs, respectively. This represents dramatic enhancements of nearly 35% and 100% against the SS-DSCs prepared from two standard TiO2 nanoparticle samples – CCIC (approx. 5.9%) and Degussa P25 (approx. 4.0%), correspondingly. The TNA is characterised by a combination of mesopores within each aggregate and macro inter-aggregates voids, a high specific surface area and a great light scattering ability; such features make the aggregates superior photoanode building blocks for the application in bulky cobalt redox mediator based SS-DSCs system.

Depletion-Mediated Uniform Deposition of Nanorods with Patterned, Multiplexed Assembly.

Device-scale, uniform, and controllable deposition of nanoparticles on various substrates is fundamentally important not only for the fabrication of thin-film devices but also for the large sample statistics of single-particle performances. However, it is challenging to obtain such predefined depositions using a simple and efficient method. Here, we present a novel strategy for obtaining the uniform and particle density/spacing-tunable deposition of nanorods on a linker-free substrate. The deposition is driven by the tailored particle-substrate depletion attraction owing to the size-matched design of the substrate roughness and the nanorod diameter. Both gold nanorods and upconversion nanorods were applied to demonstrate the generality of the method. The high particle density of more than 21 per μm2 and correspondingly the small particle spacing of fewer than 0.3 μm were achieved on a scalable substrate template. On this basis, orientational ordering and pattern-selective deposition of nanorods were realized by controlling the liquid flow rate and employing the substrate with patterned roughness areas, respectively. With the roughness-directed density-tunable depositions of nanorods integrated onto a single platform, multiplexed gold nanorod assembly and programmable surface-enhanced Raman mapping were achieved, with a promising prospect in information encoding by using the Raman signals as the translation units. The thermal stability and related transition temperature of about 160 °C of gold nanorods were also revealed as an application of single-particle statistics. This practical method could be extended to wide ranges of potential applications in plasmonic coupling devices, cryptography, or single-particle performance statistics with the feature of the high-throughput, low-cost, and scalable fabrication.