The plasmid-encoded transcription factor ArdK contributes to the repression of the IMP-6 metallo-β-lactamase gene blaIMP-6, leading to a carbapenem-susceptible phenotype in the blaIMP-6-positive Escherichia coli strain A56-1S.

Carbapenemase-producing Enterobacteriaceae (CPE) are a global concern because these bacteria are resistant to almost all β-lactams. Horizontal interspecies gene transfer via plasmid conjugation has increased the global dissemination of CPE. Recently, an Enterobacteriaceae strain positive for carbapenemase gene but showing a carbapenem-susceptible phenotype was identified, suggesting that these susceptible strains may be challenging to detect solely via antimicrobial susceptibility tests without molecular analysis. Here, we isolated a blaIMP-6 carbapenemase-gene positive but imipenem- and meropenem-susceptible Escherichia coli (ISMS-E) strain A56-1S (imipenem and meropenem minimum inhibitory concentration, ≤ 0.125 mg/L), from a human urine specimen in Japan. A56-1S was carbapenemase negative by the Carba NP test, suggesting that IMP-6 production was low or undetectable. Thus, to characterize the mechanism of this phenotype, a meropenem-resistant E. coli A56-1R strain was obtained using meropenem-selection. A56-1R was positive for carbapenemase production by the Carba NP test, and blaIMP-6 transcription in A56-1R was 53-fold higher than in A56-1S, indicating that blaIMP-6 in A56-1S is negatively regulated at the transcriptional level. Comparative genomic analysis between the two strains revealed that the alleviation of restriction of DNA (ardK) gene encoding a putative transcription factor is disrupted by the IS26 insertion in A56-1R. A cotransformation assay of ardK and the regulatory element upstream of blaIMP-6 showed repression of blaIMP-6 transcription, indicating that ArdK negatively modulates blaIMP-6 transcription. ArdK binding and affinity assays demonstrated that ArdK directly binds to the regulatory element upstream of blaIMP-6 with dissociation constant values comparable to those of general transcription factors. The IMP-6 carbapenemase showed low hydrolytic activity against imipenem, resulting in an imipenem-susceptible and meropenem-resistant (ISMR) phenotype (previously reported as a stealth phenotype). However, the low expression of IMP-6 in the A56-1S strain could be a typical characteristic of ISMS-E due to gene repression, indicating that conventional antimicrobial susceptibility tests might be unable to detect such strains even when using both imipenem and meropenem. Bacteria that exhibit the ISMS phenotype could play a potential role as undetectable reservoirs and might facilitate gene transfer to other organisms while avoiding detection

Solution-Processed Short-Wave Infrared PbS Colloidal Quantum Dot/ZnO Nanowire Solar Cells Giving High Open-Circuit Voltage

A systematic investigation into the performance of PbS quantum dot (QD)/ZnO nanowire (NW) solar cells in the near-infrared (NIR) and short-wave infrared (SWIR) regions was carried out. The solar cells were confirmed to convert a wide range of solar energy (3.54–0.62 eV, corresponding to 0.35–2.0 μm). We found that the solar cells working in the SWIR region had a high open-circuit voltage (<i>V</i>_oc). A relatively high <i>V</i>_oc of 0.25 V was achieved even in solar cells whose photocurrent onsets were at approximately 0.64 eV (1.9 μm); this <i>V</i>_oc is as high as that of Ge solar cells, which have been used for III–V compound semiconductor triple-junction solar cells. Although short-circuit current density and fill factor have to be further increased, these results indicate that solution-processed colloidal QD solar cells with ZnO NWs are promising candidates for the middle and/or bottom subcells of multijunction solar cells

PbS-Quantum-Dot-Based Heterojunction Solar Cells Utilizing ZnO Nanowires for High External Quantum Efficiency in the Near-Infrared Region

The improvement of solar cell performance in the near-infrared (near-IR) region is an important challenge to increase power conversion efficiency under one-sun illumination. PbS quantum-dot (QD)-based heterojunction solar cells with high efficiency in the near-IR region were constructed by combining ZnO nanowire arrays with PbS QDs, which give a first exciton absorption band centering at wavelengths longer than 1 μm. The morphology of ZnO nanowire arrays was systematically investigated to achieve high light-harvesting efficiency as well as efficient carrier collection. The solar cells with the PbS QD/ZnO nanowire structures made up of densely grown thin ZnO nanowires about 1.2 μm long yielded a maximum incident-photon-to-current conversion efficiency (IPCE) of 58% in the near-IR region (@1020 nm) and over 80% in the visible region (shorter than 670 nm). The power conversion efficiency obtained on the solar cell reached about 6.0% under simulated one-sun illumination

Temperature Effects on the Photovoltaic Performance of Planar Structure Perovskite Solar Cells

[EN] Temperature effects of CH3NH3PbI3 perovskite solar cells having simple planar architecture were investigated on the crystal structure and photovoltaic performance. The obvious changes in the CH3NH3PbI3 crystal structure were found by varying the temperature as a consequence to the augmentation in lattice parameters and expansion of the unit cell. The expansion of the crystal gave a serious influence on the performance of the solar cells, where the differences in the coefficients of the thermal expansion (CTEs) together with the lattice mismatch between TiO2 and perovskite materials might cause interfacial defects responsible for the deterioration in the photovoltaic performance. Interestingly, the hysteresis in the cubic phase is very small because of the less distorted angles of the CH3NH3PbI3 structure against the temperature fluctuation.The present work has been supported by New Energy and Industrial Technology Development Organization (NEDO, Japan) and Japan Society for the Promotion of Science (JSPS) for Overseas Researchers. The authors acknowledge Ajay Kumar Jena for his help.Cojocaru, L.; Uchida, S.; Sanehira, Y.; González-Pedro, V.; Bisquert, J.; Nakazald, J.; Kubo, T.... (2015). Temperature Effects on the Photovoltaic Performance of Planar Structure Perovskite Solar Cells. Chemistry Letters. 44(11):1557-1559. https://doi.org/10.1246/cl.150781S15571559441

Ultra‐Thin SnOx Buffer Layer Enables High‐Efficiency Quantum Junction Photovoltaics

Abstract Solution‐processed solar cells are promising for the cost‐effective, high‐throughput production of photovoltaic devices. Colloidal quantum dots (CQDs) are attractive candidate materials for efficient, solution‐processed solar cells, potentially realizing the broad‐spectrum light utilization and multi‐exciton generation effect for the future efficiency breakthrough of solar cells. The emerging quantum junction solar cells (QJSCs), constructed by n‐ and p‐type CQDs only, open novel avenue for all‐quantum‐dot photovoltaics with a simplified device configuration and convenient processing technology. However, the development of high‐efficiency QJSCs still faces the challenge of back carrier diffusion induced by the huge carrier density drop at the interface of CQDs and conductive glass substrate. Herein, an ultra‐thin atomic layer deposited tin oxide (SnOx) layer is employed to buffer this carrier density drop, significantly reducing the interfacial recombination and capacitance caused by the back carrier diffusion. The SnOx‐modified QJSC achieves a record‐high efficiency of 11.55% and a suppressed hysteresis factor of 0.04 in contrast with reference QJSC with an efficiency of 10.4% and hysteresis factor of 0.48. This work clarifies the critical effect of interfacial issues on the carrier recombination and hysteresis of QJSCs, and provides an effective pathway to design high‐performance all‐quantum‐dot devices

Enhancement of Near-IR Photoelectric Conversion in Dye-Sensitized Solar Cells Using an Osmium Sensitizer with Strong Spin-Forbidden Transition

A new osmium (Os) complex of the [Os­(tcterpy)-(4,4′-bis­(<i>p</i>-butoxystyryl)-2,2′-bipyridine)­Cl]­PF₆ (Os-stbpy) has been synthesized and characterized for dye-sensitized solar cells (DSSCs). The Os-stbpy dye shows enhanced spin-forbidden absorptions around 900 nm. The DSSCs with Os-stbpy show a wide-band spectral response up to 1100 nm with high overall conversion efficiency of 6.1% under standard solar illumination