A donor-supply electrode (DSE) for colloidal quantum dot photovoltaics

The highest-performing colloidal quantum dot (CQD) photovoltaics (PV) reported to date have relied on high-temperature (>500°C) annealing of electron-accepting TiO2. Room-temperature processing reduces energy payback time and manufacturing cost, enables flexible substrates, and permits tandem solar cells that integrate a small-bandgap back cell atop a low-thermal-budget larger-bandgap front cell. Here we report an electrode strategy that enables a depleted-heterojunction CQD PV device to be fabricated entirely at room temperature. We find that simply replacing the high-temperature-processed TiO2 with a sputtered version of the same material leads to poor performance due to the low mobility of the sputtered oxide. We develop instead a two-layer donor-supply electrode (DSE) in which a highly doped, shallow work function layer supplies a high density of free electrons to an ultrathin TiO2 layer via charge-transfer doping. Using the DSE we build all-room-temperature-processed small-bandgap (1 eV) colloidal quantum dot solar cells having 4% solar power conversion efficiency and high fill factor. These 1 eV bandgap cells are suitable for use as the back junction in tandem solar cells. The DSE concept, combined with control over TiO2 stoichiometry in sputtering, provides a much-needed tunable electrode to pair with quantum-size-effect CQD films.     

Sulfotyrosine recognition as marker for druggable sites in the extracellular space

Chemokine signaling is a well-known agent of autoimmune disease, HIV infection, and cancer. Drug discovery efforts for these signaling molecules have focused on developing inhibitors targeting their associated G protein-coupled receptors. Recently, we used a structure-based approach directed at the sulfotyrosine-binding pocket of the chemokine CXCL12, and thereby demonstrated that small molecule inhibitors acting upon the chemokine ligand form an alternative therapeutic avenue. Although the 50 members of the chemokine family share varying degrees of sequence homology (some as little as 20%), all members retain the canonical chemokine fold. Here we show that an equivalent sulfotyrosine-binding pocket appears to be conserved across the chemokine superfamily. We monitored sulfotyrosine binding to four representative chemokines by NMR. The results suggest that most chemokines harbor a sulfotyrosine recognition site analogous to the cleft on CXCL12 that binds sulfotyrosine 21 of the receptor CXCR4. Rational drug discovery efforts targeting these sites may be useful in the development of specific as well as broad-spectrum chemokine inhibitors.     

A novel organometallic ReI complex with favourable properties for bioimaging and applicability in solid-phase peptide synthesis

Organometallic complexes possess great potential for imaging applications in biology, due to their kinetic stability and often favourable intrinsic properties. In this work we present a new class of Re(I) -tricarbonyl complexes with a substituted bis(phenanthridinylmethyl)amine (bpm) ligand. The complex Re(CO)(3) (R-bpm) could be conveniently prepared by microwave synthesis from [Re(CO)(3)(H(2)O)(3) ]Br and a suitably substituted bis(phenanthridinylmethyl)amine (R-bpm). Complex 5, with R=CH(2)-CO(2)-CH(3) , was characterized by a single-crystal X-ray structure. Complex 6 (R=CH(2)-C(6)H(4)-CO(2)H) was used in solid-phase peptide synthesis (SPPS) to label the neurotensin(8-13) (NT) fragment N-terminally. The complexes show luminescence emission with large Stokes shifts (λ(ex) =350 nm, λ(em) =570 nm). Cellular uptake and intracellular localization studies in several cell lines demonstrate the utility of the new Re(CO)(3) (R-bpm) complexes for fluorescence imaging and reveal significant differences between the simple methyl ester 5 and the NT bioconjugate 7.     

Thermal neutron detection with Ce doped LiCaAlF6 single crystals

Cerium-doped LiCaAlF₆ (Ce:LiCAF) crystals have been studied as scintillators in application to thermal neutron detection. Three crystals: high-doping Ce:LiCAF, low-doping Ce:LiCAF with 50% enrichment of ⁶Li (both 10 mm×10 mm×2 mm, rectangular) and high-doping Ce:LiCAF with 95% enrichment of ⁶Li (Ø50.8 mm×2 mm, discus) coupled to Photonis XP5300B PMT, were tested. The response of these crystals to neutrons emitted from a paraffin moderated ²³⁸PuBe source has been investigated. Thermal neutron peaks have been found at a Gamma Equivalent Energy (GEE) of ∼2.5 MeV for high-doping Ce:LiCAF (50% ⁶Li), ∼2 MeV for low-doping Ce:LiCAF (50% ⁶Li) and ∼1.9 MeV for high-doping Ce:LiCAF (95% ⁶Li). The light output of Ce:LiCAF was also measured (175-250 phe/MeV from sample to sample). Lithium-6 glass GS20 from Saint Gobain was used as a reference scintillator (Ø50 mm×2 mm, circle). Relative neutron efficiency, normalized to that of GS20 lithium glass, as well as gamma-neutron intrinsic efficiency for all tested samples was calculated. Intrinsic efficiency on thermal neutron detection for small Ce:LiCAF samples was estimated at about 32-35% of that of GS20 and for large Ce:LiCAF sample as about 82% of that of GS20.     

Effect of in-situ formed MgO on the microstructure of thixomolded AZ91 magnesium alloy

ABSTRACT

In-situ magnesium matrix nano-composites were produced through a reaction of CO₂ with the AZ91 alloy at a semi-solid temperature range. The process was performed at 595°C, which corresponded to about 10% of solid fraction, under shear and mixing conditions generated by a screw-barrel system. As a result, nano-scale native MgO (30–50?nm) and a small amount of Al₄C₃ carbide within an eutectic consisting of α(Mg), β-Mg₁₇Al₁₂ were formed. Homogeneously distributed α(Mg) globular grains with volume 8–12% were visible. AZ91 composites revealed yield strength of 220?MPa at compression strength of 460?MPa and hardness 103?±?2?HV.     

Mechanism of cellular uptake of genotoxic silica nanoparticles

ABSTRACT: Mechanisms for cellular uptake of nanoparticles have important implications for nanoparticulate drug delivery and toxicity. We have explored the mechanism of uptake of amorphous silica nanoparticles of 14 nm diameter, which agglomerate in culture medium to hydrodynamic diameters around 500 nm. In HT29, HaCat and A549 cells, cytotoxicity was observed at nanoparticle concentrations 1 mug/ml, but DNA damage was evident at 0.1 mug/ml and above. Transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy confirmed entry of the silica particles into A549 cells exposed to 10 mug/ml of nanoparticles. The particles were observed in the cytoplasm but not within membrane bound vesicles or in the nucleus. TEM of cells exposed to nanoparticles at 4 C for 30 minutes showed particles enter cells when activity is low, suggesting a passive mode of entry. Plasma lipid membrane models identified physical interactions between the membrane and the silica NPs. Quartz crystal microbalance experiments on tethered bilayer lipid membrane systems show that the nanoparticles strongly bind to lipid membranes, forming an adherent monolayer on the membrane. Leakage assays on large unilamellar vesicles (400 nm diameter) indicate that binding of the silica NPs transiently disrupts the vesicles which rapidly self-seal. We suggest that an adhesive interaction between silica nanoparticles and lipid membranes could cause passive cellular uptake of the particles.     

Speciation analysis of arsenic in terrestrial plants from arsenic contaminated area

Arsenic speciation analysis was carried out in plants collected from arsenic contaminated area. Two plant species were chosen for the investigation: Reed Grass (Calamagrostis arundinacea) and Lady Fern (Athyrium filix-femina). To characterize arsenic species several different extraction procedures were applied including enzymatic extraction and extraction using surfactant solution (SDS). Two-step sequential extraction (water + SDS) that assures the highest extraction efficiency was applied to extract arsenic species from plant material. HPLC with anion-exchange column was used to separate extracted arsenic compounds and ICP-MS was applied for quantitative arsenic determination after species separation.     

Discovery of factors influencing patent value based on machine learning in patents in the field of nanotechnology

Patents represent the technological or inventive activity and output across different fields, regions, and time. The analysis of information from patents could be used to help focus efforts in research and the economy; however, the roles of the factors that can be extracted from patent records are still not entirely understood. To better understand the impact of these factors on patent value, machine learning techniques such as feature selection and classification are used to analyze patents in a sample industry, nanotechnology. Each nanotechnology patent was represented by a comprehensive set of numerical features that describe inventors, assignees, patent classification, and outgoing references. After careful design that included selection of the most relevant features, selection and optimization of the accuracy of classification models that aimed at finding most valuable (top-performing) patents, we used the generated models to analyze which factors allow to differentiate between the top-performing and the remaining nanotechnology patents. A few interesting findings surface as important such as the past performance of inventors and assignees, and the count of referenced patents.     

Analysis of non-quarter-wave grating by a modified Fourier-transform method

When unity reflectance is approached, the Fourier-transform method of calculating the reflectance spectrum of an optical grating modulated by a slowly varying envelope becomes unacceptably inaccurate. The modified Fourier transform method of Bovard [Appl. Opt. 29, 24 (1990)] can achieve complete accuracy for quarter-wave gratings. We report herein the extension of Bovard's method to non-quarter-wave gratings. We demonstrate the accurate deployment of our simplified modified Fourier-transform method to apodized linear gratings and optically apodized nonlinear gratings.