Synthesis of High Aspect Ratio BaTiO3 Nanowires for High Energy Density Nanocomposite Capacitors

High energy density capacitors are critically important in advanced electronic devices and power systems since they can reduce the weight, size and cost required to meet a desired application. Nanocomposites hold strong potential for increasing the performance of high power energy sources; however, the energy density of most nanocomposites is still low compared to commercial capacitors and neat polymers. Here, we develop a new synthesis method for the growth of high aspect ratio barium titanate nanowires (BaTiO₃) nanowires (NWs) with high yield. High energy density nanocomposite capacitors are fabricated using surface‐functionalized high aspect ratio BaTiO₃ NWs in a poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) (P(VDF‐TrFE‐CFE)) matrix. At a 17.5% volume fraction, the nanocomposites show more than 45.3% increase in energy density above that of the pure P(VDF‐TrFE‐CFE) polymer (10.48 J/cc compared to 7.21 J/cc) at electric field 300 MV/m. This value is significant and exceeds those reported for the conventional polymer‐ceramic nanocomposites; it is also more than seven times larger than high performance commercial polypropylene capacitor (1.2 J/cc at 640 MV/m). In addition, our nanocomposite capacitor has a maximum power density as high as 1.2 MW/cc occurring only 1.52 μs after the start of discharge. The findings of this research could lead to enhanced interest in nanowires based nanocomposites due to their potential for achieving next generation energy storage devices.     

Assembly of multimeric phage nanostructures through leucine zipper interactions

One barrier to the construction of nanoscale devices is the ability to place materials into 2D- and 3D-ordered arrays by controlling the assembly and ordering of connections between nanomaterials. Ordered assembly of nanoscale materials may potentially be achieved using biological tools that direct specific connections between individual components. Recently, viruses were successfully employed as scaffolds for the nucleation of nanoparticles and nanowires (Mao et al., 2004); however, there is a paucity of methods for the higher order assembly of phage-templated materials. Here we describe a general strategy for the assembly of filamentous bacteriophages into long, wire-like or into tripod-like structures. To prepare the linear phage assemblies, dimeric leucine zipper protein domains, fused to the p3 and p9 proteins of M13 bacteriophage, were employed to direct the specific end-to-end self-association of the bacteriophage particles. Electron microscopy revealed that up to 90% of the phage displaying complementary leucine zipper domains formed linear multi-phage assemblies, composed of up to 30 phage in length. To prepare tripod-like assemblies, phage were engineered to express trimeric leucine zippers as p3 fusion proteins. This resulted in 3D assembly with three individual phages attached at a single point. These ordered phage structures should provide a foundation for self-assembly of virally templated nanomaterials into useful devices.     

Encoded metal nanoparticle-based molecular beacons for multiplexed detection of DNA

In this paper we describe a molecular beacon format assay in which encoded nanowire particles are used to achieve multiplexing. We demonstrate this principle with the detection of five viral pathogens; Hepatitis A virus, Hepatitis C virus, West Nile Virus, Human Immune Deficiency virus and Severe Acute Respiratory Syndrome virus. Oligonucleotides are designed complementary to a target sequence of interest containing a 3′ universal fluorescence dye. A 5′ thiol causes the oligonucleotides to self-assemble onto the metal nanowire. The single-stranded oligonucleotide contains a self-complementary hairpin stem sequence of 10 bases that forces the 3′ fluorophore to come into contact with the metallic nanowire surface, thereby quenching the fluorescence. Upon addition of target DNA, there is hybridization with the complementary oligonucleotides. The resulting DNA hybrid is rigid, unfolds the hairpin structure, and causes the fluorophore to be moved away from the surface such that it is no longer quenched. By using differently encoded nanowires, each conjugated with a different oligonucleotide sequence, multiplexed DNA assays are possible using a single fluorophore, from a multiplexed RT-PCR reaction.     

Unusual Formation of CoO@C “Dandelions” Derived from 2D Kagóme MOLs for Efficient Lithium Storage

Despite great breakthroughs, the search for anode materials with high performance for lithium‐ion batteries (LIBs) remains challenging. Hence, engineering advantageous structures via effective routes can bring new possibilities to the development of the LIB field. Herein, the precise synthesis of three‐dimensional (3D) hybrids of ultrathin carbon‐wrapped CoO (CoO@C) dandelions is reported by the pyrolysis of two‐dimensional (2D) Kagóme metal–organic layers (MOLs) at 400 °C under an Ar atmosphere. Due to the special coordination structure of the paternal MOLs, the resulting CoO nanowires show a small diameter of 5–10 nm and are uniformly confined within the ultrathin carbon layer. Based on the time‐dependent pyrolysis experiments, a crystal transformation mechanism of in situ self‐templated‐recrystallization‐self‐assembly accompanied by phase and morphology changes is first presented to reveal the formation of the 3D dandelion‐like spheres with assembly of nanowire arrays from a 2D Kagóme MOL. By virtue of structural and compositional features, including a 3D array structure, the small size of the primary ultrathin nanowires, and a uniform ultrathin graphitic carbon layer, these unique CoO@C dandelions display high specific capacity, good rate capability, and excellent cycling stability. Importantly, this approach can be extended to accurately synthesize other desired composite structures.     

A nano-Ni based ultrasensitive nonenzymatic electrochemical sensor for glucose: Enhancing sensitivity through a nanowire array strategy

Highly ordered Ni nanowire arrays (NiNWAs) were synthesized for the first time using a template-directed electropolymerization strategy with a nanopore polycarbonate (PC) membrane template, and their morphological characterization were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). A NiNWAs based electrode shows very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which has been utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 5.0 × 10⁻⁷ to 7.0 × 10⁻³ M, a high sensitivity of 1043 μA mM⁻¹ cm⁻², and a low detection limit of 1 × 10⁻⁷ M. The experiment results also showed that the sensor exhibits good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.     

Mesoporous TiO2‐Sn/C Core‐Shell Nanowire Arrays as High‐Performance 3D Anodes for Li‐Ion Batteries

Three‐dimensional mesoporous TiO₂‐Sn/C core‐shell nanowire arrays are prepared on Ti foil as anodes for lithium‐ion batteries. Sn formed by a reduction of SnO₂ is encapsulated into TiO₂ nanowires and the carbon layer is coated onto it. For additive‐free, self‐supported anodes in Li‐ion batteries, this unique core‐shell composite structure can effectively buffer the volume change, suppress cracking, and improve the conductivity of the electrode during the discharge‐charge process, thus resulting in superior rate capability and excellent long‐term cycling stability. Specifically, the TiO₂‐Sn/C nanowire arrays display rechargeable discharge capacities of 769, 663, 365, 193, and 90 mA h g^?1 at 0.1C, 0.5C, 2C 10C, and 30C, respectively (1C = 335 mA g^?1). Furthermore, the TiO₂‐Sn/C nanowire arrays exhibit a capacity retention rate of 84.8% with a discharge capacity of over 160 mA h g^?1, even after 100 cycles at a high current rate of 10C.     

Donor‐Acceptor Interfacial Interactions Dominate Device Performance in Hybrid P3HT‐ZnO Nanowire‐Array Solar Cells

The adsorption of self‐assembled monolayers (SAMs) on metal oxide surfaces is a promising route to control electronic characteristics and surface wettability. Here, arylphosphonic acid derivatives are used to modulate the surface properties of vertically oriented ZnO nanowire arrays. Arylphosphonate‐functionalized ZnO nanowires are incorporated into hybrid organic‐inorganic solar cells in which infiltrated poly(3‐hexylthiophene) (P3HT) serves as the polymer donor. Strong correlations between device short‐circuit current density (J _sc) and power conversion efficiencies (PCEs) with ZnO surface functionalization species are observed and a weak correlation in the open‐circuit voltage (V _oc) is observed. Inverted solar cells fabricated with these treated interfaces exhibit PCEs as high as 2.1%, primarily due to improvements in J _sc. Analogous devices using untreated ZnO arrays having efficiencies of 1.6%. The enhancement in J _sc is attributed to surface passivation of ZnO by SAMs and enhanced wettability from P3HT, which improve charge transfer and reduce carrier recombination at the organic‐inorganic interface in the solar cells.     

K+ and Na+-Induced Self-Assembly of Telomeric Oligonucleotide d(TTAGGG)n

Abstracts

The telomeric DNA oligomers, d(TTAGGG)_n where n=1, 2, 4, could self-associate into the multi-stranded structures in appropriate condition and exhibited a different CD spectra. The present of Na⁺ was more advantage to facilitate the formation of anti-parallel conformation, but the present of K⁺ enhanced their thermal stability. Spectroscopic analysis of 3, 3′- diethyloxadicarbocyanine (DODC) showed the formation of hairpin quadruplex structures for d(TTAGGG)₂ and d(TTAGGG)₄, but d(TTAGGG) could not. The four-stranded tetraplexes and branched nanowire formed in the present of K⁺ or Na⁺ alone were observed by atomic force microscopy (AFM). The ability to self-assemble of d(TTAGGG)_n into four-stranded tetraplexes and nanowires depends strongly on the number of repeating units and ionic environment. A model to explain how these structures formed is proposed.