Reduced-Dimensionality Al Nanocrystals: Nanowires, Nanobars, and Nanomoustaches.

Aluminum nanocrystals created by catalyst-driven colloidal synthesis support excellent plasmonic properties, due to their high level of elemental purity, monocrystallinity, and controlled size and shape. Reduction in the rate of nanocrystal growth enables the synthesis of highly anisotropic Al nanowires, nanobars, and singly twinned "nanomoustaches". Electron energy loss spectroscopy was used to study the plasmonic properties of these nanocrystals, spanning the broad energy range needed to map their plasmonic modes. The coupling between these nanocrystals and other plasmonic metal nanostructures, specifically Ag nanocubes and Au films of controlled nanoscale thickness, was investigated. Al nanocrystals show excellent long-term stability under atmospheric conditions, providing a practical alternative to coinage metal-based nanowires in assembled nanoscale devices.

Tailoring the aluminum nanocrystal surface oxide for all-aluminum-based antenna-reactor plasmonic photocatalysts.

Aluminum nanocrystals (AlNCs) are of increasing interest as sustainable, earth-abundant nanoparticles for visible wavelength plasmonics and as versatile nanoantennas for energy-efficient plasmonic photocatalysis. Here, we show that annealing AlNCs under various gases and thermal conditions induces substantial, systematic changes in their surface oxide, modifying crystalline phase, surface morphology, density, and defect type and concentration. Tailoring the surface oxide properties enables AlNCs to function as all-aluminum-based antenna-reactor plasmonic photocatalysts, with the modified surface oxides providing varying reactivities and selectivities for several chemical reactions.

Facet Tunability of Aluminum Nanocrystals.

Aluminum nanocrystals (Al NCs) with a well-defined size and shape combine unique plasmonic properties with high earth abundance, potentially ideal for applications where sustainability and cost are important factors. It has recently been shown that single-crystal Al {100} nanocubes can be synthesized by the decomposition of AlH3 with Tebbe's reagent, a titanium(IV) catalyst with two cyclopentadienyl ligands. By systematically modifying the catalyst molecular structure, control of the NC growth morphology is observed spectroscopically, as the catalyst stabilizes the {100} NC facets. By varying the catalyst concentration, Al NC faceted growth is tunable from {100} faceted nanocubes to {111} faceted octahedra. This study provides direct insight into the role of catalyst molecular structure in controlling Al NC morphology.

A Dual Catalyst Strategy for Controlling Aluminum Nanocrystal Growth.

The synthesis of Al nanocrystals (Al NCs) is a rapidly expanding field, but there are few strategies for size and morphology control. Here we introduce a dual catalyst approach for the synthesis of Al NCs to control both NC size and shape. By using one catalyst that nucleates growth more rapidly than a second catalyst whose ligands affect NC morphology during growth, one can obtain both size and shape control of the resulting Al NCs. The combination of the two catalysts (1) titanium isopropoxide (TIP), for rapid nucleation, and (2) Tebbe's reagent, for specific facet-promoting growth, yields {100}-faceted Al NCs with tunable diameters between 35 and 65 nm. This dual-catalyst strategy could dramatically expand the possible outcomes for Al NC growth, opening the door to new controlled morphologies and a deeper understanding of earth-abundant plasmonic nanocrystal synthesis.

Al@TiO2 Core-Shell Nanoparticles for Plasmonic Photocatalysis.

Plasmon-induced photocatalysis is a topic of rapidly increasing interest, due to its potential for substantially lowering reaction barriers and temperatures and for increasing the selectivity of chemical reactions. Of particular interest for plasmonic photocatalysis are antenna-reactor nanoparticles and nanostructures, which combine the strong light-coupling of plasmonic nanostructures with reactors that enhance chemical specificity. Here, we introduce Al@TiO2 core-shell nanoparticles, combining earth-abundant Al nanocrystalline cores with TiO2 layers of tunable thickness. We show that these nanoparticles are active photocatalysts for the hot electron-mediated H2 dissociation reaction as well as for hot hole-mediated methanol dehydration. The wavelength dependence of the reaction rates suggests that the photocatalytic mechanism is plasmonic hot carrier generation with subsequent transfer of the hot carriers into the TiO2 layer. The Al@TiO2 antenna-reactor provides an earth-abundant solution for the future design of visible-light-driven plasmonic photocatalysts.

Shining Light on Aluminum Nanoparticle Synthesis.

ConspectusAluminum in its nanostructured form is generating increasing interest because of its light-harvesting properties, achieved by excitation of its localized surface plasmon resonance. Compared to traditional plasmonic materials, the coinage metals Au and Ag, Al is far more earth-abundant and, therefore, more suitable for large-area applications or where cost may be an important factor. Its optical properties are far more flexible than either Au or Ag, supporting plasmon resonances that range from UV wavelengths, through the visible regime, and into the infrared region of the spectrum. However, the chemical synthesis of Al nanocrystals (NCs) of controlled size and shape has historically lagged far behind that of Au and Ag. This is partially due to the high reactivity of Al precursors, which react readily with O2, H2O, and many reagents used in traditional NC syntheses. The first chemical synthesis of Al NCs was demonstrated by Haber and Buhro in 1998, decomposing AlH3 using titanium isopropoxide (TIP), with a number of subsequent reports refining this protocol. The role of a catalyst in Al NC synthesis is, we believe, unique to this synthetic approach. In 2015, the first synthesis of size controlled Al NCs was published by our group. Since then, we have significantly advanced Al NC synthesis, postsynthetic modifications, and applications of Al nanoparticles (NPs)-NCs with additional surface modifications-in chemical sensing and photocatalysis. Colloidal Al synthesis has its unique challenges, differing markedly from the far more familiar Au and Ag syntheses, which currently appears to present a de facto barrier to broader research activity in this field.The goal of this Account is to highlight developments in controlled synthesis of Al NCs and applications of Al NPs over the last five years. We outline techniques for successful Al NC synthesis and address some of the problems that may be encountered in this synthesis. A mechanistic understanding of AlH3 decomposition using TIP has been developed, while new directions have been discovered for synthetic control. Facet-binding ligands, alternate Al precursors, new titanium-based reduction catalysts, even solvent composition have all been shown to control reaction products while also opening doors to future developments. A variety of postsynthetic modifications to the Al NC native oxide surface, including polymer, MOF, and transition metal island coatings have been demonstrated for applications in molecular sensing and photocatalysis. In this Account, we hope to convey that Al synthesis is more accessible than generally perceived and to encourage new synthetic development based on underlying mechanisms controlling size and shape. High selectivity in particle faceting and twinning, implementation of seeded growth principles for monodisperse samples, and the demonstration of new, practical applications of Al nanoparticles remain primary challenges in the field. As Al nanoparticle synthesis is refined and new applications emerge, colloidal Al will become an accessible and low-cost plasmonic nanomaterial complementary to Au and Ag.

Morphology-Dependent Reactivity of a Plasmonic Photocatalyst.

The shape of a plasmonic nanoparticle strongly controls its light-matter interaction, which in turn affects how specific morphologies may be used in applications such as sensing, photodetection, and active pixel displays. Here, we show that particle shape also controls plasmonic photocatalytic activity. Three different Al nanocrystal morphologies, octopods, nanocubes, and nanocrystals, all with very similar plasmon resonance frequencies, were used as photocatalysts for the H2 dissociation reaction. We observe widely varying reaction rates for the three different morphologies. Octopods show a 10 times higher reaction rate than nanocrystals and a 5 times higher rate than nanocubes, with lower apparent activation energies than either nanocubes or nanocrystals by 45% and 49%, respectively. A theoretical model of hot electron direct transfer from photoexcited Al nanoparticles to H2 molecules is consistent with this observed morphological dependence. This research strongly suggests that nanoparticle geometry, in addition to plasmon resonance energy, is a critical factor in plasmonic photocatalyst design.

Site-Selective Nanoreactor Deposition on Photocatalytic Al Nanocubes.

Photoactivation of catalytic materials through plasmon-coupled energy transfer has created new possibilities for expanding the scope of light-driven heterogeneous catalysis. Here we present a nanoengineered plasmonic photocatalyst consisting of catalytic Pd islands preferentially grown on vertices of Al nanocubes. The regioselective Pd deposition on Al nanocubes does not rely on complex surface ligands, in contrast to site-specific transition-metal deposition on gold nanoparticles. We show that the strong local field enhancement on the sharp nanocube vertices provides a mechanism for efficient coupling of the plasmonic Al antenna to adjacent Pd nanoparticles. A substantial increase in photocatalytic H2 dissociation on Pd-bound Al nanocubes relative to pristine Al nanocubes can be observed, incentivizing further engineering of heterometallic antenna-reactor photocatalysts. Controlled growth of catalytic materials on plasmonic hot spots can result in more efficient use of the localized surface plasmon energy for photocatalysis, while minimizing the amount and cost of precious transition-metal catalysts.

Aluminum Nanocubes Have Sharp Corners.

Of the many plasmonic nanoparticle geometries that have been synthesized, nanocubes have been of particular interest for creating nanocavities, facilitating plasmon coupling, and enhancing phenomena dependent upon local electromagnetic fields. Here we report the straightforward colloidal synthesis of single-crystalline {100} terminated Al nanocubes by decomposing AlH3 with Tebbe's reagent in tetrahydrofuran. The size and shape of the Al nanocubes is controlled by the reaction time and the ratio of AlH3 to Tebbe's reagent, which, together with reaction temperature, establish kinetic control over Al nanocube growth. Al nanocubes possess strong localized field enhancements at their sharp corners and resonances highly amenable to coupling with metallic substrates. Their native oxide surface renders them extremely air stable. Chemically synthesized Al nanocubes provide an earth-abundant alternative to noble metal nanocubes for plasmonics and nanophotonics applications.

Photocatalytic Hydrogenation of Graphene Using Pd Nanocones.

Plasmonic photocatalytic processes typically use the interaction of light with metallic nanoparticles to drive chemical reactions on their surfaces. Here we show that a plasmonic photocatalyst can also induce a reaction on an adjacent material. A combination of spontaneous H2 dissociation and plasmon-induced H desorption from tilted palladium (Pd) nanocones yields reactive H atoms which, in the direct vicinity of a graphene monolayer, results in its local hydrogenation. The conversion of pristine to hydrogenated graphene, a semiconductor, is detectable by visible local fluorescence of the hydrogenated regions of the graphene sheet, as well as by Raman spectroscopic analysis. These results may lead to new approaches for local, light-driven functionalization of graphene and other 2D materials and for precision patterning of functional devices.

Metal-organic frameworks tailor the properties of aluminum nanocrystals.

Metal-organic frameworks (MOFs) and metal nanoparticles are two classes of materials that have received considerable recent attention, each for controlling chemical reactivities, albeit in very different ways. Here, we report the growth of MOF shell layers surrounding aluminum nanocrystals (Al NCs), an Earth-abundant metal with energetic, plasmonic, and photocatalytic properties. The MOF shell growth proceeds by means of dissolution-and-growth chemistry that uses the intrinsic surface oxide of the NC to obtain the Al3+ ions accommodated into the MOF nodes. Changes in the Al NC plasmon resonance provide an intrinsic optical probe of its dissolution and growth kinetics. This same chemistry enables a highly controlled oxidation of the Al NCs, providing a precise method for reducing NC size in a shape-preserving manner. The MOF shell encapsulation of the Al NCs results in increased efficiencies for plasmon-enhanced photocatalysis, which is observed for the hydrogen-deuterium exchange and reverse water-gas shift reactions.

Polymer-Directed Growth of Plasmonic Aluminum Nanocrystals.

The challenge of controllable chemical synthesis of aluminum nanocrystals (Al NCs) has been met with only limited success. A major barrier is the absence of effective ligands to control the nucleation and growth of Al NCs. Here we demonstrate the size- and shape-controlled synthesis of monodisperse Al NCs using a polymer ligand, cumyl dithiobenzoate-terminated polystyrene (CDTB-PS). Density functional theory (DFT) calculations indicate that CDTB-PS shows selective absorption on Al{100} facets, inducing the formation of nanocubes and trigonal bipyramids. An excess of CDTB-PS, however, decreases the supersaturation of Al atoms, leading to the formation of {111} facet-terminated octahedral and triangular plates. The concentration of the catalyst, titanium (IV) isopropoxide, determines the size of Al NCs by controlling the number of seeds. Depending on nanoparticle size, the solutions of Al NCs possess distinct colors, a characteristic feature of plasmonic nanomaterials. This robust and controlled chemical synthesis of Al NCs lays a foundation for Al as a sustainable plasmonic material for current and future applications.

Monolithic Polymer Nanoridges with Programmable Wetting Transitions.

This paper describes polymeric nanostructures with dynamically tunable wetting properties. Centimeter-scale areas of monolithic nanoridges can be generated by strain relief of thermoplastic polyolefin films with fluoropolymer skin layers. Changing the amount of strain results in polyolefin ridges with aspect ratios greater than four with controlled feature densities. Surface chemistry and topography are demonstrated to be able to be tailored by SF6 -plasma etching to access multiple wetting states: Wenzel, Cassie-Baxter, and Cassie-impregnating states. Reversible transitions among the wetting states can be realized in a programmable manner by cyclic stretching and reshrinking the patterned substrates without delamination and cracking.

Aluminum Nanorods.

Al nanocrystals can be synthesized by high-temperature decomposition of triisobutyl aluminum, creating a mixture of nanoparticle geometries with a significant fraction (∼15%) being single-crystalline Al nanorods. The Al nanorods are elongated along their ⟨110⟩ direction, and generally exhibit hexagonal cross sections consisting of two adjacent {111} facets separated by {100} facets on opposite sides. Dark-field scattering spectroscopy of individual Al nanorods reveals that rods of varying aspect ratios all possess transverse quadrupolar and octupolar modes in the visible (2-3 eV) and ultraviolet (3-5 eV) regimes. Theoretical modeling indicates that the longitudinal resonances of these nanorods span the near- and mid-infrared regions of the spectrum. This work introduces a new class of anisotropic metal nanocrystals composed of single-crystalline Al, opening the door to highly modifiable plasmonic nanorods from Earth-abundant metals.

Neuregulin upregulates microglial α7 nicotinic acetylcholine receptor expression in immortalized cell lines: implications for regulating neuroinflammation.

Neuregulin, previously known as ARIA, is a signaling protein involved in cell survival, synaptic plasticity, cell communication and differentiation. Neuregulin has also been described as a potent inducer of acetylcholine receptor transcription in muscle and although both neuregulin and acetylcholine have been individually described to have neuroprotective roles, their relationship in the cholinergic anti-inflammatory pathway of the brain has not been examined. Using three cell lines, BV-2, EOC-20 and RAW 264.7, we investigated the role that neuregulin signaling through the Erb family of tyrosine kinases may play in the anti-inflammatory process mediated by the α7 nicotinic acetylcholine receptors. Here we show that ErbB4 is expressed in all of our cell lines and is phosphorylated upon treatment with neuregulin. Neuregulin treatment further increases the expression of α7 nicotinic acetylcholine receptors in the microglial lines tested. Given the central role of α7 nicotinic acetylcholine receptors in regulating system inflammation we analyzed the expression of several pro-inflammatory cytokines in our system. Using ELISAs for TNF-α and IL-6 we show that treatment with NRG can produce a nearly a 33% decrease in the levels of tumor necrosis factor-α secreted by activated microglia and a nearly 88% decrease in IL-6. Given these results we propose a neuroprotective role for neuregulin wherein it modulates the expression of TNF-α and thus inflammation in the CNS via the upregulation of α7 nicotinic acetylcholine receptor expression in microglia in vitro. We suggest that the disregulation of neuregulin expression may be pivotal in neurological disorders characterized by inflammation.

Anatomy education in Namibia: balancing facility design and curriculum development.

The anatomy curriculum at Namibia's first, and currently only, medical school is clinically oriented, outcome-based, and includes all of the components of modern anatomical sciences i.e., histology, embryology, neuroanatomy, gross, and clinical anatomy. The design of the facilities and the equipment incorporated into these facilities were directed toward simplification of work flow and ease of use by faculty, staff, and students. From the onset, the integration of state of the art technology was pursued to facilitate teaching and promote a student-centered pedagogical approach to dissections. The program, as realized, is comprised of three 16-week semesters with seven hours of contact time per week, namely three hours of lectures and four hours of dissection laboratory and microscopy time. Set outcomes were established, each revolving around clinical cases with integrated medical imaging. The design of the facility itself was not constrained by a legacy structure, allowing the School of Medicine, in collaboration with architects and contractors, to design the building from scratch. A design was implemented that allows for the sequential processing of cadaveric material in a unidirectional flow from reception, to preparation, embalming, storage, dissection, and maceration. Importantly, the odor of formaldehyde typically associated with anatomy facilities was eliminated outside of the dissection areas and minimized within via a high-performance ventilation system. By holistically incorporating an integrated curriculum, facility design, and teaching at an early stage, the authors believe they have created a system that might serve as a model for new anatomy programs.

α-Dystroglycan is essential for the induction of Egr3, a transcription factor important in muscle spindle formation.

Muscle spindle fibers are specialized stretch receptors that allow the perception and coordination of limb movement. The differentiation of these specialized structures is initiated by signals derived from the in growing Ia sensory neurons during development. While the direct molecular signaling mechanisms between sensory neurons and developing muscle at nascent spindle fibers have been well documented in past studies the roles of muscle basal lamina components on this process have not previously been described. As such, our initial experiments addressed potential roles for agrin (AGRN) and laminin (LN) in the expression of the transcription factor Egr3. Levels of Egr3 were monitored using immunoblot analysis and both basal lamina molecules proved effective in inducing Erg3 expression. Previous work had established neuregulin (NRG) as a critical signaling component in spindle fiber development so blocking experiments with NRG and ErbB inhibitors were then used to determine if LN-induced Egr3 expression was occurring as a result of NRG-ErbB signaling and not via other, novel pathway. Inhibiting signaling through this pathway did indeed reduce the expression of Egr3. Finally, we looked at alpha-dystrogylcan, a shared receptor for AGRN and LN at neuromuscular junctions. Using a alpha-dystroglycan (alpha-DG) silenced muscle cell line and an anti-alpha-DG antibody we attempted to block basal lamina/alpha-DG interactions. Again, and in both instances, Egr3 expression was significantly decreased. Taken together, analysis of the results from these experiments revealed that indeed AGRN, LN, and alpha-DG influence Egr3 levels and therefore may play an important role in spindle fiber differentiation.

Central nervous system regeneration inhibitors and their intracellular substrates.

Injury to the central nervous system (CNS) initiates a cascade of responses that is inhibitory to the regeneration of neurons and full recovery. At the site of injury, glial cells conspire with an inhibitory biochemical milieu to construct both physical and chemical barriers that prevent the outgrowth of axons to or beyond the lesion site. These inhibitors include factors derived from myelin, repulsive guidance cues, and chondroitin sulfate proteoglycans. Each bind receptors on the axon surface to initiating intracellular signaling cascades that ultimately result in cytoskeletal reorganization and growth cone collapse. Here, we present an overview of the molecules, receptors, and signaling pathways that inhibit CNS regeneration, with a particular focus on the intracellular signaling machinery that may function as convergent targets for multiple inhibitory ligands.

Hepatic transcriptome analysis of hepatitis C virus infection in chimpanzees defines unique gene expression patterns associated with viral clearance.

Hepatitis C virus infection leads to a high rate of chronicity. Mechanisms of viral clearance and persistence are still poorly understood. In this study, hepatic gene expression analysis was performed to identify any molecular signature associated with the outcome of hepatitis C virus (HCV) infection in chimpanzees. Acutely HCV-infected chimpanzees with self-limited infection or progression to chronicity were studied. Interferon stimulated genes were induced irrespective of the outcome of infection. Early induction of a set of genes associated with cell proliferation and immune activation was associated with subsequent viral clearance. Specifically, two of the genes: interleukin binding factor 3 (ILF3) and cytotoxic granule-associated RNA binding protein (TIA1), associated with robust T-cell response, were highly induced early in chimpanzees with self-limited infection. Up-regulation of genes associated with CD8+ T cell response was evident only during the clearance phase of the acute self-limited infection. The induction of these genes may represent an initial response of cellular injury and proliferation that successfully translates to a "danger signal" leading to induction of adaptive immunity to control viral infection. This primary difference in hepatic gene expression between self-limited and chronic infections supports the concept that successful activation of HCV-specific T-cell response is critical in clearance of acute HCV infection.

Agrin and neuregulin, expanding roles and implications for therapeutics.

Agrin and neuregulin are broadly expressed molecules that have significant developmental roles. Here we review the diverse temporal and spatial expression patterns and functions of these molecules and the impact that dysregulation may have on a number of disease states. Many know agrin as a modulator of synaptogenesis and the neuregulins for their prominent role in breast cancer; this review elaborates on many of the other proposed functions for these molecules both in the nervous system and elsewhere. In several instances we discuss the possible use of agrin, neuregulin and related molecules as therapeutic agents.