Plasmon-Generated Solvated Electrons for Chemical Transformations.

Methods for generating solvated electrons─free electrons in solution─have focused primarily on alkali metal ionization or high-energy electrons or photons. Here we report the generation of solvated electrons by exciting the plasmon resonance of Al nanocrystals suspended in solution with visible light. Two chemical reactions were performed: a radical-addition reaction with the spin-trap 2-methyl-2-nitrosopropane, and a model cyclization reaction with the radical clock 6-bromohex-1-ene. A quantum efficiency of at least ∼1.1% for plasmon absorbed photon to solvated electron generation can be inferred from the measured radical clock reaction concentration. This study demonstrates a simple way to generate solvated electrons for driving reductive organic chemical reactions in a quantifiable and controlled manner.

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.

Aluminum Nanocrystals Grow into Distinct Branched Aluminum Nanowire Morphologies.

Plasmonic nanowires (NWs) have generated great interest in their applications in nanophotonics and nanotechnology. Here we report the synthesis of Al nanocrystals (NCs) with controlled morphologies that range from nanospheres to branched NW and NW bundles. This is accomplished by catalyzing the pyrolysis of triisobutyl aluminum (TIBA) with Tebbe's reagent, a titanium(III) catalyst with two cyclopentadienyl ligands. The ratio of TIBA to Tebbe's reagent is critical in determining the morphology of the resulting Al NC. The branched Al NWs grow in their ⟨100⟩ directions and are formed by oriented attachment of isotropic Al NCs on their {100} facets. Branched NWs are strongly absorptive from the UV to the mid-IR, with longitudinal dipolar, higher-order, and transverse plasmons, all contributing to their broadband response. This rapid Al NW synthesis enables the expanded use of Al for plasmonic and nanophotonic applications in the ultraviolet, visible, and infrared regions of the spectrum.

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.

Acoustic Vibrations of Al Nanocrystals: Size, Shape, and Crystallinity Revealed by Single-Particle Transient Extinction Spectroscopy.

Acoustic vibrations in plasmonic nanoparticles, monitored by an all-optical means, have attracted significant increasing interest because they provide unique insight into the mechanical properties of these metallic nanostructures. Al nanostructures are a recently emerging alternative to noble metal nanoparticles, because their broad wavelength tunability and high natural abundance make them ideal for many potential applications. Here, we investigate the acoustic vibrations of individual Al nanocrystals using a combination of electron microscopy and single-particle transient extinction spectroscopy, made possible with a low-pulse energy, high sensitivity, and probe-wavelength-tunable, single-particle transient extinction microscope. For chemically synthesized, faceted Al nanocrystals, the observed vibration frequency scales with the inverse particle diameter. In contrast, triangularly shaped Al nanocrystals support two distinct frequencies, corresponding to their in- and out-of-plane breathing modes. Unlike ensemble measurements, which measure average properties, measuring the damping time of the acoustic vibrations for individual particles enables us to investigate variations of the quality factor on the particle-to-particle level. Surprisingly, we find a large variation in quality factors even for nanocrystals of similar size and shape. This observed heterogeneity appears to result from substantially varying degrees of nanoparticle crystallinity even for chemically synthesized nanocrystals.

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.

Polydopamine-Stabilized Aluminum Nanocrystals: Aqueous Stability and Benzo[a]pyrene Detection.

Aluminum nanocrystals have emerged as an earth-abundant material for plasmonics applications. Al nanocrystals readily oxidize in aqueous-based solutions, however, transforming into highly stratified γ-AlOOH nanoparticles with a 700% increase in surface area in a matter of minutes. Here we show that by functionalizing Al nanocrystals with the bioinspired polymer polydopamine, their stability in aqueous media is dramatically increased, maintaining their integrity in aqueous solution for over 2 weeks with no discernible structural changes. Polydopamine functionalization also provides a molecular capture layer that enables the capture of polycyclic aromatic hydrocarbon pollutants in H2O samples and their detection by surface-enhanced Raman spectroscopy, when polydopamine-stabilized Al nanocrystal aggregates are used as substrates. This approach was used to detect a prime carcinogenic H2O pollutant, benzo[a]pyrene with a sensitivity in the sub part-per-billion range.

Ligand-Dependent Colloidal Stability Controls the Growth of Aluminum Nanocrystals.

The precise size- and shape-controlled synthesis of monodisperse Al nanocrystals remains an open challenge, limiting their utility for numerous applications that would take advantage of their size and shape-dependent optical properties. Here we pursue a molecular-level understanding of the formation of Al nanocrystals by titanium(IV) isopropoxide-catalyzed decomposition of AlH3 in Lewis base solvents. As determined by electron paramagnetic resonance spectroscopy of intermediates, the reaction begins with the formation of Ti3+-AlH3 complexes. Proton nuclear magnetic resonance spectroscopy indicates isopropoxy ligands are removed from Ti by Al, producing aluminum(III) isopropoxide and low-valent Ti3+ catalysts. These Ti3+ species catalyze elimination of H2 from AlH3 inducing the polymerization of AlH3 into colloidally unstable low-valent aluminum hydride clusters. These clusters coalesce and grow while expelling H2 to form colloidally stable Al nanocrystals. The colloidal stability of the Al nanocrystals and their size is determined by the molecular structure and density of coordinating atoms in the reaction, which is controlled by choice of solvent composition.

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.

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.

Au nanoparticle clusters from deposition of a coalescing emulsion.

HYPOTHESIS: Nanoparticle adsorption at the oil-water interface in an unstable, coalescing emulsion leads to cluster formation. EXPERIMENTS: Stable suspensions of clusters are prepared using a facile, two-step procedure involving few reagents and neither thiolated compounds nor chlorinated solvents. First, colloidal gold nanoparticles are assembled at the aqueous-hexanol interface in an emulsion that rapidly coalesces and spontaneously deposits a film on the interior surface of the glass container. The film is dissolved in ethanol with sonication to disperse the clusters. The film and clusters are characterized by transmission electron and atomic force microscopies as well as ultraviolet-visible spectrometry. FINDINGS: Clusters are observed to contain as few as 8 to as many as 24 Au nanoparticles. The clusters are anisotropic and can also be formed from larger nanoparticles. Hydrophobic and hydrophilic interactions are implicated in the formation of these clusters within the interfacial tension gradients of a coalescing emulsion. The clusters can be re-suspended in ethanol and water, maximizing the utility of these clusters with an extinction band in the near-Infrared region of the electromagnetic spectrum.

Social stressors and cardiovascular response: influence of ambivalent relationships and behavioral ambivalence.

OBJECTIVE: The protective influence of social relationships on health is well documented; however, not all relationships are positive and negative aspects of relationships may be detrimental. Relatively less is known about the relationships characterized by both positivity and negativity (i.e., ambivalence). The goal of this study was to examine the relative influence of ambivalence in relationship quality and social behavior on cardiovascular response. METHODS: 104 healthy young adults were randomly assigned to bring in either a supportive or ambivalent same-sex friend to the experiment. Participants were also randomly assigned to receive positive, negative, ambivalent or ambiguous feedback from their friend after giving a series of speeches. Cardiovascular response was obtained before, during, and after the social stressor (speech task). RESULTS: Results indicate a significant effect of relationship type before, during, and after the stressor task. Adjusting for baseline, heart rate reactivity and anxiety was significantly higher among those assigned to ambivalent friends relative to those assigned to supportive friends during the stressor task (ps<.05). There was also a significant effect of behavioral feedback during the speech task, such that those receiving ambivalent messages had the greatest systolic blood pressure (SBP) and diastolic blood pressure (DBP) reactivity (p<.05); however, there was no interaction between relationship and feedback conditions. Those in the ambivalent friend condition also exhibited significantly higher SBP, DBP, and anxiety during the baseline and recovery periods (ps<.05). CONCLUSIONS: These findings suggest that both relationship quality and the actions of relationships may have a significant influence on health-relevant physiology.

The promise of record linkage for assessing the uptake of health services in resource constrained settings: a pilot study from South Africa.

BACKGROUND: Health and Demographic Surveillance Systems (HDSS) have been instrumental in advancing population and health research in low- and middle- income countries where vital registration systems are often weak. However, the utility of HDSS would be enhanced if their databases could be linked with those of local health facilities. We assess the feasibility of record linkage in rural South Africa using data from the Agincourt HDSS and a local health facility. METHODS: Using a gold standard dataset of 623 record pairs matched by means of fingerprints, we evaluate twenty record linkage scenarios (involving different identifiers, string comparison techniques and with and without clerical review) based on the Fellegi-Sunter probabilistic record linkage model. Matching rates and quality are measured by their sensitivity and positive predictive value (PPV). Background characteristics of matched and unmatched cases are compared to assess systematic bias in the resulting record-linked dataset. RESULTS: A hybrid approach of deterministic followed by probabilistic record linkage, and scenarios that use an extended set of identifiers including another household member's first name yield the best results. The best fully automated record linkage scenario has a sensitivity of 83.6% and PPV of 95.1%. The sensitivity and PPV increase to 84.3% and 96.9%, respectively, when clerical review is undertaken on 10% of the record pairs. The likelihood of being linked is significantly lower for females, non-South Africans and the elderly. CONCLUSION: Using records matched by means of fingerprints as the gold standard, we have demonstrated the feasibility of fully automated probabilistic record linkage using identifiers that are routinely collected in health facilities in South Africa. Our study also shows that matching statistics can be improved if other identifiers (e.g., another household member's first name) are added to the set of matching variables, and, to a lesser extent, with clerical review. Matching success is, however, correlated with background characteristics that are indicative of the instability of personal attributes over time (e.g., surname in the case of women) or with misreporting (e.g., age).

The development and validation of dried blood spots for external quality assurance of syphilis serology.

BACKGROUND: Syphilis causes up to 1,500,000 congenital syphilis cases annually. These could be prevented if all pregnant women were screened, and those with syphilis treated with a single dose of penicillin before 28 weeks gestation. In recent years, rapid point-of-care tests have allowed greater access to syphilis screening, especially in rural or remote areas, but the lack of quality assurance of rapid testing has been a concern. We determined the feasibility of using dried blood spots (DBS) as specimens for quality assurance of syphilis serological assays. METHODS: We developed DBS extraction protocols for use with Treponema pallidum particle agglutination assay (TPPA), Treponema pallidum haemagglutination assay (TPHA) and an enzyme immunoassay (EIA) and compared the results with those using matching plasma samples from the same patient. RESULTS: Since DBS samples showed poor performance with TPHA and EIA (TPHA sensitivity was 50.5% (95% confidence interval: 39.9-61.2%) and EIA specificity was 50.4% (95% CI: 43.7-57.1%), only the DBS TPPA was used in the final evaluation. DBS TPPA showed an sensitivity of 95.5% (95% CI: 91.3-98.0%) and a specificity of 99.0% (95% CI: 98.1-99.5%) compared to TPPA using plasma samples as a reference. CONCLUSION: DBS samples can be recommended for use with TPPA, and may be of value for external quality assurance of point-of-care syphilis testing.

The impact of antiretroviral therapy on adult mortality in rural Tanzania.

OBJECTIVE: To describe the impact of antiretroviral therapy (ART) on mortality rates among adults participating in an HIV community cohort study in north-west Tanzania. METHODS: Serological and demographic surveillance rounds have been undertaken in a population of approximately 30,000 people since 1994. Free HIV care including ART has been available since 2005. Event history analysis was used to compare mortality rates among HIV-negative and HIV-positive adults in the 5-year period before and after the introduction of ART. Crude and adjusted hazard ratios were calculated using exponential regression models. Interaction between time period and HIV status was assessed to investigate whether there was a non-linear relationship between these two variables. RESULTS: Male and female mortality patterns varied over the pre- and post-ART period. In women, the crude death rate fell for both HIV negatives and HIV positives hazard rate ratio (HRR = 0.71; 95%CI 0.51-0.99 and HRR = 0.68; 95%CI: 0.46-0.99, respectively). For men, the mortality among the HIV negatives increased (HRR = 1.47; 95%CI: 1.06-2.03) while the decline in mortality among the HIV positives (HRR = 0.77; 95%CI 0.52-1.13) was not statistically significant. The largest decrease in HIV-positive mortality over the two periods was among the 30- to 44-year-old age group for women and among the 45- to 59-year-old age group for men. CONCLUSION: There has been a modest effect on mortality in the study population following the introduction of free ART 5 years ago. Improving access to treatment and placing greater focus on retaining individuals on treatment are essential if the full potential of treatment for reducing HIV-related mortality is to be realised.

Profile: Agincourt health and socio-demographic surveillance system.

The Agincourt health and socio-demographic surveillance system (HDSS), located in rural northeast South Africa close to the Mozambique border, was established in 1992 to support district health systems development led by the post-apartheid ministry of health. The HDSS (90 000 people), based on an annual update of resident status and vital events, now supports multiple investigations into the causes and consequences of complex health, population and social transitions. Observational work includes cohorts focusing on different stages along the life course, evaluation of national policy at population, household and individual levels and examination of household responses to shocks and stresses and the resulting pathways influencing health and well-being. Trials target children and adolescents, including promoting psycho-social well-being, preventing HIV transmission and reducing metabolic disease risk. Efforts to enhance the research platform include using automated measurement techniques to estimate cause of death by verbal autopsy, full 'reconciliation' of in- and out-migrations, follow-up of migrants departing the study area, recording of extra-household social connections and linkage of individual HDSS records with those from sub-district clinics. Fostering effective collaborations (including INDEPTH multi-centre work in adult health and ageing and migration and urbanization), ensuring cross-site compatibility of common variables and optimizing public access to HDSS data are priorities.

Assessing health and well-being among older people in rural South Africa.

BACKGROUND: The population in developing countries is ageing, which is likely to increase the burden of non-communicable diseases and disability. OBJECTIVE: To describe factors associated with self-reported health, disability and quality of life (QoL) of older people in the rural northeast of South Africa. DESIGN: Cross-sectional survey of 6,206 individuals aged 50 and over. We used multivariate analysis to examine relationships between demographic variables and measures of self-reported health (Health Status), functional ability (WHODASi) and quality of life (WHOQoL). RESULTS: About 4,085 of 6,206 people eligible (65.8%) completed the interview. Women (Odds Ratio (OR) = 1.30, 95% CI 1.09, 1.55), older age (OR = 2.59, 95% CI 1.97, 3.40), lower education (OR = 1.62, 95% CI 1.31, 2.00), single status (OR = 1.18, 95% CI 1.01, 1.37) and not working at present (OR = 1.29, 95% CI 1.06, 1.59) were associated with a low health status. Women were also more likely to report a higher level of disability (OR = 1.38, 95% CI 1.14, 1.66), as were older people (OR = 2.92, 95% CI 2.25, 3.78), those with no education (OR = 1.57, 95% CI 1.26, 1.97), with single status (OR = 1.25, 95% CI 1.06, 1.46) and not working at present (OR = 1.33, 95% CI 1.06, 1.66). Older age (OR = 1.35, 95% CI 1.06, 1.74), no education (OR = 1.39, 95% CI 1.11, 1.73), single status (OR = 1.28, 95% CI 1.10, 1.49), a low household asset score (OR = 1.52, 95% CI 1.19, 1.94) and not working at present (OR = 1.32; 95% CI 1.07, 1.64) were all associated with lower quality of life. CONCLUSIONS: This study presents the first population-based data from South Africa on health status, functional ability and quality of life among older people. Health and social services will need to be restructured to provide effective care for older people living in rural South Africa with impaired functionality and other health problems.

Improving public health training and research capacity in Africa: a replicable model for linking training to health and socio-demographic surveillance data.

BACKGROUND: Research training for public health professionals is key to the future of public health and policy in Africa. A growing number of schools of public health are connected to health and socio-demographic surveillance system field sites in developing countries, in Africa and Asia in particular. Linking training programs with these sites provides important opportunities to improve training, build local research capacity, foreground local health priorities, and increase the relevance of research to local health policy. OBJECTIVE: To increase research training capacity in public health programs by providing targeted training to students and increasing the accessibility of existing data. DESIGN: This report is a case study of an approach to linking public health research and training at the University of the Witwatersrand. We discuss the development of a sample training database from the Agincourt Health and Socio-demographic Surveillance System in South Africa and outline a concordant transnational intensive short course on longitudinal data analysis offered by the University of the Witwatersrand and the University of Colorado-Boulder. This case study highlights ways common barriers to linking research and training can be overcome. RESULTS AND CONCLUSIONS: This collaborative effort demonstrates that linking training to ongoing data collection can improve student research, accelerate student training, and connect students to an international network of scholars. Importantly, the approach can be adapted to other partnerships between schools of public health and longitudinal research sites.

Adenosine-evoked hyperpolarization of retinal ganglion cells is mediated by G-protein-coupled inwardly rectifying K+ and small conductance Ca2+-activated K+ channel activation.

Adenosine is a neuromodulator that activates presynaptic receptors to regulate synaptic transmission and postsynaptic receptors to hyperpolarize neurons. Here, we report that adenosine-induced hyperpolarization of retinal ganglion cells is produced by the activation of A(1) receptors, which initiates a signaling cascade that activates G-protein-coupled inwardly rectifying K(+) (GIRK) channels and small conductance Ca(2+)-activated K(+) (SK) channels. Rat retinal ganglion cells were stimulated by focal ejection of the adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) while cell activity was monitored with whole-cell patch recordings and Ca(2+) imaging. Focal ejections of NECA evoked outward currents in all cells tested and reduced light- and depolarization-induced spiking. The NECA-evoked current was abolished by the A(1) antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) but was unaffected by A(2a), A(2b), and A(3) antagonists, indicating that the response was mediated entirely by A(1) receptors. The GIRK channel blocker rTertiapin-Q diminished the NECA-evoked inhibitory current by 56 +/- 12%, whereas the SK channel blocker apamin decreased the NECA-induced current by 42 +/- 7%. The SK component of the NECA-evoked current coincided with an increase in intracellular Ca(2+) and was blocked by IP(3) receptor antagonists and depletion of internal Ca(2+) stores, suggesting that A(1) receptor activation leads to an increase in IP(3), which then elevates intracellular Ca(2+) and activates SK channels. This A(1)-mediated, prolonged SK channel activation has not been described previously. The coactivation of GIRK and SK channels represents a novel mechanism of adenosine-mediated neuromodulation that could contribute to the regulation of retinal ganglion cell activity.