Lawrence F. Drummy

Regenerated silk fiber wet spinning from an ionic liquid solution

Regenerated silk fibroin from Bombyx mori silkworms was extruded into fibers from a 1-ethyl-3-methylimidazolium chloride ionic liquid solvent system; the drawn fibers rinsed in methanol exhibit alignment of the β-sheet crystallites along the fiber axis.

Nanolaminates: increasing dielectric breakdown strength of composites.

Processable, low-cost, high-performance hybrid dielectrics are enablers for a vast array of green technologies, including high-temperature electrical insulation and pulsed power capacitors for all-electric transportation vehicles. Maximizing the dielectric breakdown field (E(BD)), in conjunction with minimization of leakage current, directly impacts system performance because of the fields quadratic relationship with electrostatic energy storage density. On the basis of the extreme internal interfacial area and ultrafine morphology, polymer-inorganic nanocomposites (PNCs) have demonstrated modest increases in E(BD) at very low inorganic loadings, but because of insufficient control of the hierarchal morphology of the blend, have yielded a precipitous decline in E(BD) at intermediate and high inorganic volume fractions. Here in, we demonstrate that E(BD) can be increased up to these intermediate inorganic volume fractions by creating uniform one-dimensional nanocomposites (nanolaminates) rather than blends of spherical inorganic nanoparticles and polymers. Free standing nanolaminates of highly aligned and dispersed montmorillonite in polyvinyl butyral exhibited enhancements in E(BD) up to 30 vol % inorganic (70 wt % organically modified montmorillonite). These relative enhancements extend up to five times the inorganic fraction observed for random nanoparticle dispersions, and are anywhere from two to four times greater than observed at comparable volume fraction of nanoparticles. The breakdown characteristics of this model system suggested a trade-off between increased path tortuosity and polymer-deficient structural defects. This implies that an idealized PNC morphology to retard the breakdown cascade perpendicular to the electrodes will occur at intermediate volume fractions and resemble a discotic nematic phase where highly aligned, high-aspect ratio nanometer thick plates are uniformly surrounded by nanoscopic regions of polymer.

Morphological control and assembly of zinc oxide using a biotemplate.

Zinc oxide is a wide band gap material that has significant applications in photovoltaics, piezoelectrics and optoelectronics. Traditionally, ZnO has been synthesized using high temperatures and harsh reaction conditions. Recently, benign reaction conditions have been used to synthesize ZnO using amine and citrate additives. In this study, peptide phage display was performed to identify a peptide, termed Z1, that binds to and directs the growth of ZnO hexagonal nanocrystals. By altering the concentration of Z1 peptide, the ZnO nanocrystal morphology can be tailored. Additionally, Z1 peptide was used to direct the growth of ZnO structures on free-standing silk films. The results presented here demonstrate the utility of peptides in controlling the structure and deposition of ZnO.

Correlation of the β-sheet crystal size in silk fibers with the protein amino acid sequence

Low voltage transmission electron microscopy (LVTEM) and wide angle X-ray scattering (WAXS) are used to independently determine the size of the β-sheet crystalline regions in Bombyx mori silk fibers. The peak in the size distributions of the major and minor axes of the anisotropic crystallites measured from the LVTEM images compare well with the average sizes as determined by Scherrer analysis of the X-ray fiber diagrams. These values are then discussed in the context of the B. mori fibroin heavy chain amino acid sequence, and the underlying mechanism for the organisms control on fiber crystallite size, and therefore mechanical properties, is proposed.

Large Scale Solution Assembly of Quantum Dot–Gold Nanorod Architectures with Plasmon Enhanced Fluorescence

Tailoring the efficiency of fluorescent emission via plasmon-exciton coupling requires structure control on a nanometer length scale using a high-yield fabrication route not achievable with current lithographic techniques. These systems can be fabricated using a bottom-up approach if problems of colloidal stability and low yield can be addressed. We report progress on this pathway with the assembly of quantum dots (emitter) on gold nanorods (plasmonic units) with precisely controlled spacing, quantum dot/nanorod ratio, and long-term colloidal stability, which enables the purification and encapsulation of the assembled architecture in a protective silica shell. Overall, such controllability with nanometer precision allows one to synthesize stable, complex architectures at large volume in a rational and controllable manner. The assembled architectures demonstrate photoluminescent enhancement (5×) useful for applications ranging from biological sensing to advanced optical communication.

A Model Based Iterative Reconstruction Algorithm For High Angle Annular Dark Field-Scanning Transmission Electron Microscope (HAADF-STEM) Tomography

High angle annular dark field (HAADF)-scanning transmission electron microscope (STEM) data is increasingly being used in the physical sciences to research materials in 3D because it reduces the effects of Bragg diffraction seen in bright field TEM data. Typically, tomographic reconstructions are performed by directly applying either filtered back projection (FBP) or the simultaneous iterative reconstruction technique (SIRT) to the data. Since HAADF-STEM tomography is a limited angle tomography modality with low signal to noise ratio, these methods can result in significant artifacts in the reconstructed volume. In this paper, we develop a model based iterative reconstruction algorithm for HAADF-STEM tomography. We combine a model for image formation in HAADF-STEM tomography along with a prior model to formulate the tomographic reconstruction as a maximum a posteriori probability (MAP) estimation problem. Our formulation also accounts for certain missing measurements by treating them as nuisance parameters in the MAP estimation framework. We adapt the iterative coordinate descent algorithm to develop an efficient method to minimize the corresponding MAP cost function. Reconstructions of simulated as well as experimental data sets show results that are superior to FBP and SIRT reconstructions, significantly suppressing artifacts and enhancing contrast.

pH-Triggered SERS via Modulated Plasmonic Coupling in Individual Bimetallic Nanocobs

Abstract : In this Communication, we demonstrate the pH-triggered SPR and SERS properties of silver nanowires functionalized with gold nanoparticles in both solution and dry states. In contrast with previous examples of such bimetallic nanocobs, we utilize here a responsive polyacrylic acid (PAA) nanocoating that acts as a linker between the nanoparticles and nanowire. The pH-responsive nature of the PAA nanocoating, which is sensitive to the environmental pH, is employed to vary the separation distance between the gold nanoparticles and the silver nanowire and thus control plasmon coupling. Moreover, placing nanoparticles inside a polymer-gel layer in close proximity to the nanowire surface effectively prevents any potential aggregation of nanoparticles under variable environmental conditions, in contrast with regular nanoparticle solutions, which easily precipitate with changing conditions.

Harvesting electrical energy from carbon nanotube yarn twist

Making the most of twists and turns The rise of small-scale, portable electronics and wearable devices has boosted the desire for ways to harvest energy from mechanical motion. Such approaches could be used to provide battery-free power with a small footprint. Kim et al. present an energy harvester made from carbon nanotube yarn that converts mechanical energy into electrical energy from both torsional and tensile motion. Their findings reveal how the extent of yarn twisting and the combination of homochiral and heterochiral coiled yarns can maximize energy generation. Science, this issue p. 773 Twisted and coiled carbon nanotubes can harvest electrical energy from mechanical motion. Mechanical energy harvesters are needed for diverse applications, including self-powered wireless sensors, structural and human health monitoring systems, and the extraction of energy from ocean waves. We report carbon nanotube yarn harvesters that electrochemically convert tensile or torsional mechanical energy into electrical energy without requiring an external bias voltage. Stretching coiled yarns generated 250 watts per kilogram of peak electrical power when cycled up to 30 hertz, as well as up to 41.2 joules per kilogram of electrical energy per mechanical cycle, when normalized to harvester yarn weight. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, and used to power a light-emitting diode and to charge a storage capacitor.

Ag shell morphology on Au nanorod core: role of Ag precursor complex

Multicomponent nanostructures have substantial potential in a wide range of applications due to their unique chemical, optical, and magnetic properties, which arise from their architecture, composition, and associated heterojunctions. Colloidal approaches provide synthetic routes to fabricate these multicomponent metal nanostructures; however the complexity of processing parameters many times limits reproducibility and minimization of undesired secondary structures. By comparing the architecture across a diverse set of processing parameters for Ag shell growth on Au nanorods (NRs), we demonstrate that the composition and size of the in situ formed Ag precursor complex are the most critical contribution to the growth mechanism. Systematic control of these characteristics by varying hexadecyltrimethylammonium bromide (CTAB) concentration and aging time of the precursor-template solution, as well as pH and temperature of the final reaction solution, enables reproducible and continuous variation of the Ag shell architecture from conformal to rectilinear, and provides a unifying view of prior literature reports.

Epidermal growth factor: layered silicate nanocomposites for tissue regeneration.

Wound healing is a complex, multistep process that can be summarized into three stages, namely, hemostasis and inflammation, proliferation, and finally, tissue remodeling. Battlefield wound healing demands rapid hemostasis using clotting or cauterizing agents to immediately limit blood loss, but this occurs at the expense of proper tissue repair beyond hemostasis. Layered silicate clays such as kaolin and montmorillonite (MMT) have been previously shown to induce blood clotting due to their ability to form charged interactions with clotting factors. The charge characteristics of sodium MMT (Na-MMT) also enable functionalization with active biomolecules. Herein we functionalized Na-MMT with epidermal growth factor (EGF) via ion exchange reaction to create a nanocomposite (MMT-EGF) with approximately 0.004 EGF molecules per Na(+) exchange site and conduct biochemical analyses of keratinocytes after treatment with MMT-EGF. Our results demonstrate that EGF immobilized on MMT retains the ability to activate the epidermal growth factor receptor (EGRF), causing phosphorylation of the AKT and MEK1 pathways, as well as upregulation of its downstream target gene expression involved in cell growth and migration. This study also shows that like EGF, MMT-EGF treatment can stimulate cell migration in vitro, which is dependent on ERK1/2 phosphorylation.