11 research outputs found

    Photocurrent Enhancement for Ti-Doped Fe<sub>2</sub>O<sub>3</sub> Thin Film Photoanodes by an In Situ Solid-State Reaction Method

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    In this work, a higher concentration of Ti ions are incorporated into hydrothermally grown Ti-doped (2.2% by atomic ratio) micro-nanostructured hematite films by an in situ solid-state reaction method. The doping concentration is improved from 2.2% to 19.7% after the in situ solid-state reaction. X-ray absorption analysis indicates the substitution of Fe ions by Ti ions, without the generation of Fe<sup>2+</sup> defects. Photoelectrochemical impedance spectroscopy reveals the dramatic improvement of the electrical conductivity of the hematite film after the in situ solid-state reaction. As a consequence, the photocurrent density increases 8-fold (from 0.15 mA/cm<sup>2</sup> to 1.2 mA/cm<sup>2</sup>), and it further increases up to ∼1.5 mA/cm<sup>2</sup> with the adsorption of Co ions. Our findings demonstrate that the in situ solid-state reaction is an effective method to increase the doping level of Ti ions in hematite films with the retention of the micro-nanostructure of the films and enhance the photocurrent

    Micro-Nano-Structured Fe<sub>2</sub>O<sub>3</sub>:Ti/ZnFe<sub>2</sub>O<sub>4</sub> Heterojunction Films for Water Oxidation

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    Iron­(III) oxide photoelectrodes show promise in water oxidation applications. In this study, micro-nano-structured hematite films are synthesized, and Ti ions are doped to improve photoelectric conversion efficiency. The photocurrent increases for enhanced electrical conductivity. Further enhanced photocurrent is achieved for Fe<sub>2</sub>O<sub>3</sub>:Ti/ZnFe<sub>2</sub>O<sub>4</sub> heterojunction electrodes. Cyclic voltammograms combined with optical absorbance examinations demonstrate that the conduction and valence band edges of ZnFe<sub>2</sub>O<sub>4</sub> shift from those of Ti doped Fe<sub>2</sub>O<sub>3</sub> to the negative direction, which facilitates the efficient separation of electron–hole pairs at the Fe<sub>2</sub>O<sub>3</sub>:Ti/ZnFe<sub>2</sub>O<sub>4</sub> interface. These findings demonstrate that, by doping hematite and by engineering the interface between the hematite and the electrolyte, charge separation can be effectively promoted and photocurrent density can be dramatically increased

    Extents of fusion increased by overexpressing the receptor for EBOV GP.

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    <p><b>(A)</b> Overexpression of NPC1 (second set of two bars) led to greater fusion with effector cells than did mock-transfected target cells (first set of bars). For these experiments, the effector cells were not thermolysin-treated (i.e., these experiments relied on endogenous levels of GP cleavage). For each set of experiments, a 10-min pH 5.7 pulse (labeled “pulse pH +”) led to more fusion than when pH was never lowered (-). For each condition, n = 4. <b>(B)</b> The addition of sNPC1 to the external solution leads to a greater extent of fusion. <i>Inset</i>: Coomassie staining verification of sNPC1. BSA serves as a loading control. <b>(C)</b> Reducing and increasing the expression levels of NPC1 results in changes in the amount of NPC1 on the plasma membrane. <b>(D)</b> Fluorescence profiles of NPC1 from flow cytometry.</p

    Images of fused effector and target cells.

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    <p>Effector (COS7) cells were loaded with calcein-AM (column 1, green), target cells were loaded with CMAC (column 2, blue) and both dyes are shown in column 3 (merged). The viral proteins expressed by transfecting effector cells are shown to the right of the images. Cells expressing EBOV GP were treated with 200 μg/ml thermolysin for 20 min; fusion was augmented with a 10-min pH 5.7 pulse. For cells expressing JSRV Env, a 10-min pH 5.0 pulse was used to trigger fusion. Effector cells expressing influenza virus (IAV) HA were treated with trypsin and neuraminidase as described [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005373#ppat.1005373.ref028" target="_blank">28</a>], bound to HEK 293T cells, and fusion was triggered with a 10-min pH 4.8 pulse. For mock-transfected effector cells, a 10-min pH 5.7 pulse was employed. Fused cells are marked by arrowheads. For this set of experiments, the extent of fusion 1 hr after reneutralization was about 80% for EBOV GP, 50% for JSRV Env, and 70% for IAV HA.</p

    The small molecule inhibitor 3.47 and the neutralizing antibody KZ52 against EBOV GP blocked GP mediated fusion.

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    <p><b>(A)</b> The inhibitor 3.47 (1 μM) was specific for EBOV GP, not affecting fusion mediated by SFV E1/E2 or IAV HA. <b>(B)</b> The inhibition of fusion by KZ52 (5.0 μg/ml) was also specific to EBOV GP. In all experiments of <b>(A)</b> and <b>(B)</b> a 10-min low pH pulse (pH 5.7 for EBOV GP, pH 5.4 for SFV E1-E2, pH 4.8 for IAV HA cleaved by trypsin) was employed. Results are at least four independent experiments. A 10-min pH 5.7 pulse augmented fusion for each protein. A comparison was made between pH 5.7 and 7.2 in each column. <b>(C)</b> Fluorescence intensity of the FITC-conjugated antibody measured by FACS showed that the presence of BafA1 reduced cleavage of plasma membrane GP. <b>(D)</b> The addition of BafA1 appeared to result in an increase of total GP in the plasma membrane. <b>(E)</b> BafA1 reduced the normalized cleaved GP on cell surface. In all figures, error bars are SEM; * p < 0.05; ** p < 0.01; *** p < 0.001.</p

    Schematic diagram illustrating control of fusion by cleavage of EBOV GP and its transport to the cell surface.

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    <p>EBOV GP is synthesized in ER, transported to Golgi complexes where it is processed into GP1 and GP2 subunits, and ultimately targeted to the plasma membrane. EBOV GP can undergo endocytosis from the plasma membrane and eventually reach late endosomes and lysosomes. It is then further cleaved by cellular cathepsins, bound by NPC1, and recycled back to plasma membrane. Alternatively, EBOV GP is directly cleaved by cathepsins on the plasma membrane or by thermolysin treatment. EBOV GP proteins do not permanently remain on the surface, but rather undergo continual delivery and removal. Cleaved GP accumulates at potential fusion sites, leading to the observed increased fusion over time. Solid arrows denote pathways definitively established in the present study. Dashed arrows denote pathways that are likely to occur based on data of the present study. Light dashed arrows denote pathways suggested by data of the present study.</p

    Thermolysin treatment results in greater extents of fusion between cells.

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    <p><b>(A)</b> schematic of the experimental protocol is shown above the bar graph. E, effector cells; T, target cells, Th, thermolysin. Bar graph: Fusion of thermolysin-treated effector cells expressing EBOV GP (columns 1 and 2, dark red) was greater than for untreated cells (columns 3 and 4, dark yellow). For both thermolysin-treated and non-treated cells, a 10-min pH 5.7 pulse applied at room temperature augmented fusion, measured after an additional 2 h incubation at neutral pH. For each condition, at least 7 experiments were performed. Typical images used to obtain the data of the bar graph are shown on the right: in top images, cells were treated with 200 μg/ml thermolysin; in bottom images, cells were not treated. Cells that have fused are marked by arrows. <b>(B)</b> The kinetics of fusion for thermolysin-treated (dark red squares) and untreated (dark yellow circles) effector cells. Cleaving EBOV GP by thermolysin speeds fusion kinetics, but extents of fusion are the same for treated and untreated cells after a pH 5.7 pulse at 10°C is followed by a 4 h reneutralization. * p <0.05; *** p < 0.001.</p

    Reduced infection caused by mutations within EBOV GP correlates with reduced fusion.

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    <p><b>(A)</b> The reduction in retroviral MLV pseudotyped infection is shown for a series of EBOV GP mutants. <b>(B)</b> The mutations that resulted in reduced infection also led to reduced cell-cell fusion. <b>(C)</b> Each of the mutants was expressed well on the cell surface as determined by flow cytometry using an anti-FLAG antibody.</p

    Electrical measurements demonstrate the slow, limited growth of EBOV GP-mediated pores.

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    <p><b>(A)</b> Conductance traces of the three fusion pores, as detected by capacitance measurements are shown. None appreciably enlarged. <b>(B)</b> Representative pores induced by fusion proteins of different viruses are compared to the EBOV GP pore. HIV: Human Immunodefiency Virus 1; ASLV: Avian Sarcoma and Leukosis Virus. The illustrated representative EBOV GP pore is the same pore shown in the first trace of panel A.</p

    After EBOV GP is cleaved, GP-mediated fusion is independent of pH.

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    <p><b>(A)</b> Blocking delivery of EBOV GP to the cell surface yields pH-independent fusion: BFA was added to effector cells 45 min prior to mixing them with target cells, and then maintained to prevent EBOV GP trafficking to the plasma membrane. This eliminated the pH-dependence of fusion for thermolysin-treated effector cells. <b>(B)</b> Utilizing the standard fusion protocol, but with a cathepsin B inhibitor (100 μM) used to pretreat effector cells for 45 min and maintained at all times, fusion of thermolysin-treated effector cells with target cells was independent of pH. Fusion was much greater in the absence of the inhibitor. More importantly, inhibition of cathepsin activity eliminates the pH-dependence of fusion.</p
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