Helical Nanowires Research Articles

Au-polythionine nanocomposites: a novel mediator for bisphenol A dual-signal assay based on imprinted electrochemical sensor

In this work, a novel electrochemical sensor was developed by the modification of poly(p-aminobenzene sulfonic acid) (pABSA), Au-polythionine (Au-pTH) nanowires, and molecularly imprinted polymer (MIP) on glassy carbon electrode surface for bisphenol A (BPA) detection. The results of characterizations including scanning electron microscope, transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction showed the successful synthesis of helical structural Au-pTH nanowires, which acted as an electro-active probe for BPA detection. Cyclic voltammetry results illustrated that the modified pABSA, Au-pTH, and MIP endowed the sensor with good electrocatalytic activity, the second current signal, and recognition ability, respectively. Since the imprinted cavities provided electron transfer channels for thionine (TH) redox, the peak current of TH can be found in a blank electrolyte. The added BPA molecules can be rebound in imprinted cavities, which are oxidized and then display its current. The rebound BPA molecules in turn blocked the electron transfer channels for TH redox, resulting in the decrease of TH current. A double signal defined, as the sum of the changes of TH current (∆iTH|) and BPA current (|∆iBPA|) (|∆iTH|+|∆iBPA|), was employed as the detected signal for BPA sensitive detection, which was linearly proportional to the logarithm of concentration of BPA ranging from 8.0 × 10-8 to 1.0 × 10-4mol/L with a limit of detection of 3.8 × 10-8mol/L (S/N = 3) in a weakly acidic solution. Moreover, the natural recognition ability of MIP enabled the sensor to selectively detect BPA from its analogues. The proposed dual-signal strategy-based sensor provided a feasible tool for rapid, sensitive, and selective determination of BPA. Graphical abstract.

Morphologies Transformation of BODIPY-Based Main Chain Supramolecular Polymers Amphiphiles: From Helical Nanowires to Nanosheets.

The aggregate morphologies of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) main chain supramolecular polymer amphiphiles (SPA) are tunable by a fine balance of different non-covalent interactions. When the BODIPY segments and sodium cholate are mixed in aqueous solution, they form SPA by electrostatic attraction and hydrogen-bonds. This SPA displays helical nanowires' morphology. After the third component dimeric β-cyclodextrin (β-CD-C) is added, the hydrogen bonds between the cholate are substituted by the host-guest interaction between cholate and β-CD-C. Therefore, these SPA transform their aggregate morphologies into nanosheets' architecture. Therefore, a simple and effective way to regulate self-assembly by non-covalent forces is developed. This supramolecular method may provide an effective way to prepare various nanostructures in aqueous solution and show promising application in the future.

Solution synthesis of helical gold nanowire bundles

Helical nanostructures are important nanoscale building blocks. While only a few methods are available for synthesizing helical metal nanostructures, those involving collective twisting behaviour are even fewer. Here, we report a solution synthesis of Au nanowire bundles with hierarchical helical constructions. Ultrathin nanowires with diameters of only about 10 nm formed huge ribbon bundles that have a width of 0.5-1 μm and thickness of a few hundreds of nanometres. These bundles extended to hundreds of micrometres and curled into helices. Mechanism studies revealed that the white floccules formed by Au(i) and a thiol ligand are of critical importance for both the nanowire growth and helical bundle formation. The nanowire growth took place in the floccules following the previously reported active surface growth mode, and the bundle formation was due to the splitting of the active surface. Most importantly, the floccules assisted the strain-induced curling process that yielded helices. As the length of the bundles keeps increasing and they break out from the surrounding floccules, they would have to pass through the pores of the floccules. The imbalanced squeezing at the pore caused the bundles to curl into helices.

Unusually Long-Lived Photocharges in Helical Organic Semiconductor Nanostructures.

Photocharge generation and formation of long-lived charge carriers are relevant in photosynthesis, photocatalysis, photovoltaics, and organic electronics. A better understanding of the factors that determine these processes in synthetic polymer semiconductors is crucial, but difficult due to their morphological inhomogeneity. Here, we report the formation of exceptionally long-lived photocharges in one-dimensional organic semiconductor nanostructures. These nanostructures consist of chiral oligopeptide-substituted thienothiophene-based chromophores and exhibit a well-defined helical arrangement of these chromophores at their core. The chromophores give rise to spectroscopic H-aggregates and show strong intermolecular excitonic coupling. We demonstrate that all of these parameters are the prerequisites required for the nanostructures to show the efficient formation of polaron-like photocharges upon irradiation with a low-power white light source. The observed charge carriers in the helical nanowires show an unusually long lifetime on the order of several hours and are formed at high concentrations of up to 3 mol % in the absence of any dedicated electron acceptor. They are observed in solution as well as in film and furthermore give rise to a light-induced increase of the macroscopic charge transport. By contrast, no such photocharge generation is observed either in non-aggregating reference systems of the same chromophores or in aggregated but non-helical systems that do not form one-dimensional nanostructures. Our results thus demonstrate a clear correlation between nanoscopic confinement and the generation of long-lived photocharges.

Twisting Ultrathin Au Nanowires into Double Helices

Previously, double helix nanowire was reported by coating Pd/Pt/Au onto Au-Ag alloy nanowire. Here, straight oleylamine-stabilized ultrathin Au nanowires with single crystalline fcc lattice are surprisingly converted into double helix helices upon reacting with Ag in tetrahydrofuran (THF). The obtained Au-Ag helical nanowires contain lattice distinctively different from the fcc lattice and are different in many aspects with the previous system. The discovery may expand the scope of nanoscale double helix formation and the understanding of lattice transformation among ultrafine nanostructures.

Circular Bragg supermirror

The helical nanowires of a chiral sculptured thin film (CSTF) were taken to be made from a weakly dissipative material while the void regions between nanowires were filled with an active material, and the planewave reflection/transmission characteristics were investigated numerically. The CSTF was found to simultaneously amplify left-circularly polarized incident light and attenuate right-circularly polarized incident light, or vice versa, depending upon its structural handedness. This polarization-state-dependent attenuation and amplification phenomenon is sensitive to the direction of incidence and the thickness of the CSTF. Furthermore, the presence of both dissipative and active materials allows the high reflectance to exceed unity across a substantial proportion of the circular Bragg spectral regime for incident light of one circular polarization state but not of the other circular polarization states. That is, the CSTF functions as a circular Bragg supermirror for one, and only one, circular polarization state.

Aggregation-induced CPL response from chiral binaphthyl-based AIE-active polymers via supramolecular self-assembled helical nanowires

In this paper chiral polymer R-P could be synthesized by click polymerization reaction of (R)-3,3′-diethynyl-2,2′-bis(octyloxy)-1,1′-binaphthalene (R-M-1) and 1,2-bis(4-azidophenyl)-1,2-diphenylethene (M-2), and S-P was obtained by click polymerization reaction of (S)-3,3′-diethynyl-2,2′-bis(octyloxy)-1,1′-binaphthalene (S-M-1) and M-2, respectively. R-/S-P enantiomers can show strong aggregation-induced circularly polarized luminescence (AICPL) emission signals in the aggregate and cast-spin film, and the dissymmetry factors (glum) can be up to 6.97 × 10−3 and 1.45 × 10−2, respectively. The SEM images further demonstrate that AICPL response behavior of R-/S-P can be attributed to the formation of the supramolecular self-assembled helical nanowires in the aggregation state at 90% of the fraction of water (fw).

Tunable Supramolecular Helical Aggregate and Optoelectrical Properties of Perylene Diimides by Stereoisomerism of Sugar

In the present study, two sugar-based perylenediimide derivatives (PDIs) substituted at the imide positions with carbohydrate groups were synthesized to investigate the impact of the stereoisomerism of the sugar on the aggregation morphology and optoelectrical properties. The results showed that right-handed and left-handed helical nanowire fibers were obtained in tetrahydrofuran (THF)/H2O solution for α-d-glucopyranoside- and β-d-glucopyranoside-substituted PDIs, respectively. Determination of the electrical current in hydrazine vapor revealed that both sugar-based chiral PDIs exhibited enhanced current changes compared to their achiral counterpart because of the larger π–π orbital overlap between their adjacent perylene cores. A larger π–π orbital overlap and a smaller π–π interplanar spacing increased the electrical current of the α-d-glucopyranoside-substituted PDI more markedly than that of the β-d-glucopyranoside-substituted PDI. The results of this study suggest that the stereoisomerism of chiral s...

Design of Nano Screw Pump for Water Transport and its Mechanisms

Nanopumps conducting fluids through nanochannels have attracted considerable interest for their potential applications in nanofiltration, water desalination and drug delivery. Here, we demonstrate by molecular dynamics (MD) simulations that a nano screw pump is designed with helical nanowires embedded in a nanochannel, which can be used to drive unidirectional water flow. Such helical nanowires have been successfully synthesized in many experiments. By investigating the water transport mechanism through nano screw pumps with different configuration parameters, three transport modes were observed: cluster-by-cluster, pseudo-continuous, and linear-continuous, in which the water flux increases linearly with the rotating speed. The influences of the nanowires’ surface energy and the screw’s diameter on water transport were also investigated. Results showed that the water flux rate increases as the decreasing wettability of helical nanowires. The deviation in water flux in screw pumps with smaller radius is attributed to the weak hydrogen bonding due to space confinement and the hydrophobic blade. Moreover, we also proposed that such screw pumps with appropriate diameter and screw pitch can be used for water desalination. The study provides an insight into the design of multifunctional nanodevices for not only water transport but water desalination in practical applications.

Spirals and helices by asymmetric active surface growth.

We show that spiral and helical Au nanowires can be directly grown via the active surface growth mechanism. The formation of spiral nanowires as opposed to straight nanowires is not triggered by the presence of a particular reactant, but controlled by the ratio of reactant concentrations. We propose that the asymmetric blocking of the Au-substrate interface induces imbalanced growth of the nanowire, causing it to curve. Blocking a single corner of the active interface leads to spiral nanowires whereas blocking two corners leads to helical nanowires. Spiral and helical nanowires become more frequent when the diffusion of Au is the limiting factor, as the reactant ratio falls below a critical value. The transition from helices to spirals and finally to nearly straight nanowires indicates a gradual loss of the blocked sites, hence supporting the asymmetric blocking mechanism.

Reversal aggregation-induced circular dichroism from axial chirality transfer via self-assembled helical nanowires

Two chiral binaphthyl-based enantiomers, (R/S)-7, can produce gradual reversal AICD signals from solution to aggregation, which can be attributed to axial chirality transfer to self-assembled helical nanowires in aggregation state.

Tunable Nanosupramolecular Aggregates Mediated by Host–Guest Complexation

AbstractNanosupramolecular assemblies with controlled topological features have inventive applications in fundamental studies and material manufacturing. Herein, a variety of morphologically interesting aggregates have been constructed using the supramolecular modulation with bipyridinium‐modified diphenylalanine derivative (BP‐FF). Benefiting from the high binding affinity of bipyridinium group with four different macrocyclic receptors, namely cucurbit[7]uril, cucurbit[8]uril, pillar[5]arene, and tetrasulfonated crown ether, we have succeeded in tuning the topological aggregates of BP‐FF from fine nanofibers to nanorods, octahedron‐like nanostructure, helical nanowires, and rectangular nanosheets without any tedious chemical modification. This supramolecular approach may provide us a powerful method to construct well‐defined nanostructures with different morphologies that can be conveniently controlled by facile host–guest interactions.

Tunable Nanosupramolecular Aggregates Mediated by Host-Guest Complexation.

Nanosupramolecular assemblies with controlled topological features have inventive applications in fundamental studies and material manufacturing. Herein, a variety of morphologically interesting aggregates have been constructed using the supramolecular modulation with bipyridinium-modified diphenylalanine derivative (BP-FF). Benefiting from the high binding affinity of bipyridinium group with four different macrocyclic receptors, namely cucurbit[7]uril, cucurbit[8]uril, pillar[5]arene, and tetrasulfonated crown ether, we have succeeded in tuning the topological aggregates of BP-FF from fine nanofibers to nanorods, octahedron-like nanostructure, helical nanowires, and rectangular nanosheets without any tedious chemical modification. This supramolecular approach may provide us a powerful method to construct well-defined nanostructures with different morphologies that can be conveniently controlled by facile host-guest interactions.

Manipulation of wavefront using helical metamaterials.

Helical metamaterials, a kind of 3-dimensional structure, has relatively strong coupling effect among the helical nano-wires. Therefore, it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. In this paper, using the finite-difference time-domain (FDTD) method, we studied the phase shift properties in the helical metamaterials. It is found that the phase shift occurs for both transmitted and reflected light waves. And the maximum of reflection coefficients can reach over 60%. In addition, the phase shift (φ) is dispersionless in the range of 600 nm to 860 nm, that is, it is only dominated by the initial angle (θ) of the helix. The relationship between them is φ = ± 2θ. Using Jones calculus we give a further explanation for these properties. Finally, by arranging the helixes in an array with a constant phase gradient, the phenomenon of anomalous refraction was also observed in a broad wavelength range.

Poly(ethylene oxide) Functionalized Graphene Nanoribbons with Excellent Solution Processability.

Structurally well-defined graphene nanoribbons (GNRs) have attracted great interest as next-generation semiconductor materials. The functionalization of GNRs with polymeric side chains, which can widely broaden GNR-related studies on physiochemical properties and potential applications, has remained unexplored. Here, we demonstrate the bottom-up solution synthesis of defect-free GNRs grafted with flexible poly(ethylene oxide) (PEO) chains. The GNR backbones possess an armchair edge structure with a width of 1.0-1.7 nm and mean lengths of 15-60 nm, enabling near-infrared absorption and a low bandgap of 1.3 eV. Remarkably, the PEO grafting renders the GNRs superb dispersibility in common organic solvents, with a record concentration of ∼1 mg mL(-1) (for GNR backbone) that is much higher than that (<0.01 mg mL(-1)) of reported GNRs. Moreover, the PEO-functionalized GNRs can be readily dispersed in water, accompanying with supramolecular helical nanowire formation. Scanning probe microscopy reveals raft-like self-assembled monolayers of uniform GNRs on graphite substrates. Thin-film-based field-effect transistors (FETs) of the GNRs exhibit a high carrier mobility of ∼0.3 cm(2) V(-1) s(-1), manifesting promising application of the polymer-functionalized GNRs in electronic devices.

Helical Growth of Ultrathin Gold–Copper Nanowires

In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold-copper nanowires have never been reported previously.

High-efficiency wavefront control with based on helical metamaterials

Metamaterials or metasurfaces have been widely studied to manipulate the propagation of light by controlling the wavefront. In previous work, more and more structures were designed to study the reflected or the transmitted light. However, as far as we know, it is rarely reported how to efficiency tailor the wavefront, especially for transmitted light. Helical metamaterial, which has a relatively strong coupling effect among the helical nanowires, may provide an alternative to the wavefront control. In this study, a kind of complementary helical metamaterial with a left-handedness and a right-handedness helixes coupled to each other is proposed. The complementary helical metamaterial has a strong circular conversion dichroism, and it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. Using the finite-difference time-domain method, we find that this kind of helix has a high circular polarization conversion in a broadband, which often implies a high efficiency of the transmitted light. Moreover, it is also found that the structure will introduce a controllable phase shift（) between the incident and the transmitted light whose polarizations are orthogonal to each other. By calculating the surface current density of the helix, the performance of high circular polarization conversion is explained. Meanwhile, we also find that the phase shift has a linear relationship with the initial angle of the helix（), which is =2. This relationship can be explained exactly by Jones calculus. According to the generalized Snell's law, the refracted beam can have an arbitrary direction by designing a suitable constant gradient of phase discontinuity. And then, by arranging 12 helixes in an array with a constant phase gradient along the X-axis, the phenomenon of anomalous refraction with a high efficiency（64%) is observed in the near infrared range（1.0-1.4 m). The angle of the anomalous refraction is in good agreement with the theoretical value. Compared with the metasurface, the helical metamaterial has a relatively complex structure. But with the development of the nanotechnology, there are several methods that can complete the propagations of nano helical structures, such as the direct laser writing, the glancing angle deposition, and the molecular self-assembly techniques. And by carefully designing the structure parameters of the helix, this kind of complementary helical metamaterial is expected to be an ideal candidate not only for traditional optics but also for biological detection and medical science.

Understanding the carbon-monoxide oxidation mechanism on ultrathin palladium nanowires: a density functional theory study.

The CO oxidation mechanism catalyzed by ultrathin helical palladium nanowires (PdNW) was investigated by density functional theory (DFT) calculation. The helical PdNW structure was constructed on the basis of the simulated annealing basin-hopping (SABH) method with the tight-binding potential and the penalty method in our previous studies (J. Mater. Chem., 2012, 22, 20319). The low-lying adsorption configurations as well as the adsorption energies for O2 and CO molecules on different PdNW adsorption sites were obtained by DFT calculation. The most stable adsorption configurations for the Langmuir-Hinshelwood (LH) mechanism processes were considered for investigating the CO oxidation mechanism. The nudged elastic band (NEB) method was adopted to obtain the transition state configuration and the minimum energy pathways (MEPs).

The CO oxidation mechanism on the W(111) surface and the W helical nanowire investigated by the density functional theory calculation.

Two CO oxidation reactions (CO + O2 → CO2 + O and CO + O → CO2) were considered in the Eley-Rideal (ER) reaction mechanism. These oxidation processes on the W(111) surface and the W helical nanowire were investigated by the density functional theory (DFT) calculation. The stable adsorption sites of O2 and O as well as their adsorption energies were obtained first. In order to understand the catalytic properties of the W helical nanowire, the Fukui function and local density of state (LDOS) profiles were determined. The nudged elastic band (NEB) method was applied to locate transition states and minimum energy pathways (MEPs) of CO oxidation processes on the W helical nanowire and on the W(111) surface. In this study, we have demonstrated that the catalytic ability of the W helical nanowire is superior to that of the W(111) surface for CO oxidation.

Self-Assembly of a Functional Oligo(Aniline)-Based Amphiphile into Helical Conductive Nanowires.

A tetra(aniline)-based cationic amphiphile, TANI-NHC(O)C5H10N(CH3)3+Br– (TANI-PTAB) was synthesized, and its emeraldine base (EB) state was found to self-assemble into nanowires in aqueous solution. The observed self-assembly is described by an isodesmic model, as shown by temperature-dependent UV–vis investigations. Linear dichroism (LD) studies, combined with computational modeling using time-dependent density functional theory (TD-DFT), suggests that TANI-PTAB molecules are ordered in an antiparallel arrangement within nanowires, with the long axis of TANI-PTAB arranged perpendicular to the nanowire long axis. Addition of either S- or R- camphorsulfonic acid (CSA) to TANI-PTAB converted TANI to the emeraldine salt (ES), which retained the ability to form nanowires. Acid doping of TANI-PTAB had a profound effect on the nanowire morphology, as the CSA counterions’ chirality translated into helical twisting of the nanowires, as observed by circular dichroism (CD). Finally, the electrical conductivity of CSA-doped helical nanowire thin films processed from aqueous solution was 2.7 mS cm–1. The conductivity, control over self-assembled 1D structure and water-solubility demonstrate these materials’ promise as processable and addressable functional materials for molecular electronics, redox-controlled materials and sensing.