High-performance flexible resistive random-access memory based on SnS2 quantum dots with a charge trapping/de-trapping effect.

The application of resistive random-access memory (RRAM) in storage and neuromorphic computing has attracted widespread attention. Benefitting from the quantum effect, transition metal dichalcogenides (TMD) quantum dots (QDs) exhibit distinctive optical and electronic properties, which make them promising candidates for emerging RRAM. Here, we show a high-performance forming-free flexible RRAM based on high-quality tin disulfide (SnS2) QDs prepared by a facile liquid phase method. The RRAM device demonstrates high flexibility with a large on/off ratio of ∼106 and a long retention time of over 3 × 104 s. The excellent switching behavior of the memristor is elucidated by a charge trapping/de-trapping mechanism where the SnS2 QDs act as charge trapping centers. This study is of significance for the understanding and development of TMD QD-based flexible memristors.

Improving Microbial Cell Factory Performance by Engineering SAM Availability.

Methylated natural products are widely spread in nature. S-Adenosyl-l-methionine (SAM) is the secondary abundant cofactor and the primary methyl donor, which confer natural products with structural and functional diversification. The increasing demand for SAM-dependent natural products (SdNPs) has motivated the development of microbial cell factories (MCFs) for sustainable and efficient SdNP production. Insufficient and unsustainable SAM availability hinders the improvement of SdNP MCF performance. From the perspective of developing MCF, this review summarized recent understanding of de novo SAM biosynthesis and its regulatory mechanism. SAM is just the methyl mediator but not the original methyl source. Effective and sustainable methyl source supply is critical for efficient SdNP production. We compared and discussed the innate and relatively less explored alternative methyl sources and identified the one involving cheap one-carbon compound as more promising. The SAM biosynthesis is synergistically regulated on multilevels and is tightly connected with ATP and NAD(P)H pools. We also covered the recent advancement of metabolic engineering in improving intracellular SAM availability and SdNP production. Dynamic regulation is a promising strategy to achieve accurate and dynamic fine-tuning of intracellular SAM pool size. Finally, we discussed the design and engineering constraints underlying construction of SAM-responsive genetic circuits and envisioned their future applications in developing SdNP MCFs.

Efficient De Novo Biosynthesis of Curcumin in Escherichia coli by Optimizing Pathway Modules and Increasing the Malonyl-CoA Supply.

Curcumin is a natural phenylpropanoid compound with various biological activities and is widely used in food and pharmaceuticals. A de novo curcumin biosynthetic pathway was constructed in Escherichia coli BL21(DE3). Optimization of the curcumin biosynthesis module achieved a curcumin titer of 26.8 ± 0.6 mg/L. Regulating the metabolic fluxes of the ß-oxidation pathway and fatty acid elongation cycle and blocking the endogenous malonyl-CoA consumption pathway increased the titer to 113.6 ± 7.1 mg/L. Knockout of endogenous curcumin reductase (curA) and intermediate product detoxification by heterologous expression of the solvent-resistant pump (srpB) increased the titer to 137.5 ± 3.0 mg/L. A 5 L pilot-scale fermentation, using a three-stage pH alternation strategy, increased the titer to 696.2 ± 20.9 mg/L, 178.5-fold higher than the highest curcumin titer from de novo biosynthesis previously reported, thereby laying the foundation for efficient biosynthesis of curcumin and its derivatives.

Sensitive Determination of Arsenic by Photochemical Vapor Generation with Inductively Coupled Plasma Mass Spectrometry: Synergistic Effect from Antimony and Cadmium.

A novel method for the determination of trace arsenic (As) by photochemical vapor generation (PVG) with inductively coupled plasma mass spectrometry measurement was developed in this study. The synergistic effect from antimony (Sb) and cadmium (Cd) was found for the photochemical reduction of As for the first time. Effective photochemical reduction of As was obtained in the system containing 10% (v/v) acetic acid, 5.0 mg L-1 Sb(III), and 20.0 mg L-1 Cd(II) with 100 s UV irradiation. Analytical sensitivity of As(III) was comparable with that of As(V) under the tested conditions, making direct determination of total As feasible. Compared to the pneumatic nebulization method, analytical sensitivity of the developed method was enhanced about 50 folds. The PVG efficiency was estimated up to be 99 ± 3%. The limit of detection (LOD) (3σ) was found to be 2.1 ng L-1 for As, which was improved about 30-fold compared to that using direct sample introduction solution nebulization. Considering the sample dilution prior to analysis (usually one-fold), the LOD was actually enhanced about 15 folds. The relative standard deviations of seven replicate measurements of 1.0 µg L-1 As(III) and As (V) standard solutions were 2.3 and 2.9% for As(III) and As(V), respectively. The proposed method was successfully applied for the detection of As in certified reference materials of sediments (GBW07303a and GBW07305a), as well as three water samples. The mechanism of the PVG system was investigated by using gas chromatography mass spectrometry, electron paramagnetic resonance, and X-ray photoelectron spectroscopy. (CH3)3As along with (CH3)3Sb were synthesized under UV irradiation. Besides, volatile species of Cd were also found. The result obtained in this study is useful for developing efficient "sensitizers" in PVG and understanding the transformation of As in the presence of hydride/cold vapor forming elements in the photochemical process.

A mutant fitness compendium in Bifidobacteria reveals molecular determinants of colonization and host-microbe interactions.

Bifidobacteria commonly represent a dominant constituent of human gut microbiomes during infancy, influencing nutrition, immune development, and resistance to infection. Despite interest as a probiotic therapy, predicting the nutritional requirements and health-promoting effects of Bifidobacteria is challenging due to major knowledge gaps. To overcome these deficiencies, we used large-scale genetics to create a compendium of mutant fitness in Bifidobacterium breve (Bb). We generated a high density, randomly barcoded transposon insertion pool in Bb, and used this pool to determine Bb fitness requirements during colonization of germ-free mice and chickens with multiple diets and in response to hundreds of in vitro perturbations. To enable mechanistic investigation, we constructed an ordered collection of insertion strains covering 1462 genes. We leveraged these tools to improve models of metabolic pathways, reveal unexpected host- and diet-specific requirements for colonization, and connect the production of immunomodulatory molecules to growth benefits. These resources will greatly reduce the barrier to future investigations of this important beneficial microbe.

Regulation of Ethanol Assimilation for Efficient Accumulation of Squalene in Saccharomyces cerevisiae.

Squalene is a triterpene that can be obtained from fish and plant oils. It is important in cosmetics and vaccines and is a precursor for many high-value terpenes and steroids. In order to increase squalene accumulation, the mevalonate pathway was systematically enhanced. Accumulation of squalene tended to increase when ethanol was added as a carbon source during fermentation, but a high concentration of ethanol affected both the strain growth and accumulation of products. By overexpressing the key trehalose synthesis gene TPS1 and the heat shock protein gene HSP104, the content of trehalose by Saccharomyces cerevisiae (S. cerevisiae) was enhanced, and stress caused by ethanol was relieved. The OD600 value of the modified S. cerevisiae strain was increased by 80.2%, its ethanol tolerance was increased to 30 g/L, and it retained excellent activity with 50 g/L ethanol. After optimizing the fermentation conditions, the squalene titer in a 5 L bioreactor reached 27.3 g/L and the squalene content was 650 mg/g dry cell weight, the highest squalene production parameters reported to date for a microorganism.

Engineering an efficient whole-cell catalyst for d-allulose production from glycerol.

d-Allulose has many health-benefiting properties and therefore sustainably applied in food, pharmaceutical, and nutrition industries. The aldol reaction-based route is a very promising alternative to Izumoring strategy in d-allulose production. Remarkable studies reported in the past cannot get rid of by-product formation and costly purified enzyme usage. In the present study, we explored the glycerol assimilation by modularly assembling the d-allulose synthetic cascade in Escherichia coli envelop. We achieved an efficient whole-cell catalyst that produces only d-allulose from cheap glycerol feedstock, eliminating the involvement of purified enzymes. Detailed process optimization improved the d-allulose titer by 1500.00%. Finally, the production was validated in 3-L scale using a 5-L fermenter, and 5.67 g L-1 d-allulose was produced with a molar yield of 31.43%.

Produce D-allulose from non-food biomass by integrating corn stalk hydrolysis with whole-cell catalysis.

D-allulose is a high-value rare sugar with many health benefits. D-allulose market demand increased dramatically after approved as generally recognized as safe (GRAS). The current studies are predominantly focusing on producing D-allulose from either D-glucose or D-fructose, which may compete foods against human. The corn stalk (CS) is one of the main agricultural waste biomass in the worldwide. Bioconversion is one of the promising approach to CS valorization, which is of significance for both food safety and reducing carbon emission. In this study, we tried to explore a non-food based route by integrating CS hydrolysis with D-allulose production. Firstly we developed an efficient Escherichia coli whole-cell catalyst to produce D-allulose from D-glucose. Next we hydrolyzed CS and achieved D-allulose production from the CS hydrolysate. Finally we immobilized the whole-cell catalyst by designing a microfluidic device. Process optimization improved D-allulose titer by 8.61 times, reaching 8.78 g/L from CS hydrolysate. With this method, 1 kg CS was finally converted to 48.87 g D-allulose. This study validated the feasibility of valorizing corn stalk by converting it to D-allulose.

Detection of trace antimony by vanadium (IV) ion assisted photochemical vapor generation with inductively coupled plasma mass spectrometry measurement.

In this work, a method for sensitive detection of trace antimony (Sb) was developed by inductively coupled plasma mass spectrometry (ICP MS) coupled with photochemical vapor generation (PVG). V(IV) ions were used as new "sensitizers" for improving the PVG efficiency of Sb. Factors influenced the PVG and the detection of Sb by ICP MS were investigated, including the type and concentration of low molecular weight organic acids, the UV irradiation time, the concentration of V(IV) ions, the air-liquid interface, the flow rate of Ar carrier gas, and interferences from co-existing ions. It was found that efficient reduction of Sb was obtained in the medium of 10% (v/v) formic acid (FA), 10% (v/v) acetic acid (AA), and 80 mg L-1 of V(IV) with 100 s UV irradiation. Under the selected conditions, there was no significant difference in analytical sensitivity between Sb(III) and Sb(V). The limit of detection (LOD, 3σ) was 4.7 ng L-1 for Sb with ICP MS measurement. Compared to traditional direct solution nebulization, the analytical sensitivity obtained in this work was enhanced about 19-fold. Relative standard deviations (RSDs, n = 7) were 1.9% and 2.3% for replicate measurement of 0.5 µg L-1 Sb(III) and Sb(V) standard solutions, respectively. The proposed method was applied for the determination of trace Sb in water samples and two certified reference materials (CRMs) of sediments with satisfactory results. Moreover, the generated volatile species of Sb in this work was found to be (CH3)3Sb.

Engineering heterologous enzyme secretion in Yarrowia lipolytica.

BACKGROUND: Eukaryotic cells are often preferred for the production of complex enzymes and biopharmaceuticals due to their ability to form post-translational modifications and inherent quality control system within the endoplasmic reticulum (ER). A non-conventional yeast species, Yarrowia lipolytica, has attracted attention due to its high protein secretion capacity and advanced secretory pathway. Common means of improving protein secretion in Y. lipolytica include codon optimization, increased gene copy number, inducible expression, and secretory tag engineering. In this study, we develop effective strategies to enhance protein secretion using the model heterologous enzyme T4 lysozyme. RESULTS: By engineering the commonly used native lip2prepro secretion signal, we have successfully improved secreted T4 lysozyme titer by 17-fold. Similar improvements were measured for other heterologous proteins, including hrGFP and [Formula: see text]-amylase. In addition to secretion tag engineering, we engineered the secretory pathway by expanding the ER and co-expressing heterologous enzymes in the secretion tag processing pathway, resulting in combined 50-fold improvement in T4 lysozyme secretion. CONCLUSIONS: Overall, our combined strategies not only proved effective in improving the protein production in Yarrowia lipolytica, but also hint the possible existence of a different mechanism of secretion regulation in ER and Golgi body in this non-conventional yeast.

Marked Efficiency Improvement of FAPb0.7Sn0.3Br3 Perovskite Light-Emitting Diodes by Optimization of the Light-Emitting Layer and Hole-Transport Layer.

Highly luminescent FAPb0.7Sn0.3Br3 nanocrystals with an average photoluminescence (PL) quantum yield of 92% were synthesized by the ligand-assisted reprecipitation method. The 41-nm-thick perovskite film with a smooth surface and strong PL intensity was proven to be a suitable luminescent layer for perovskite light-emitting diodes (PeLEDs). Electrical tests indicate that the double hole-transport layers (HTLs) played an important role in improving the electrical-to-optical conversion efficiency of PeLEDs due to their cascade-like level alignment. The PeLED based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,40-(N-(p-butylphenyl))-diphenylamine)] (TFB)/poly(9-vinylcarbazole) (PVK) double HTLs produced a high external quantum efficiency (EQE) of 9%, which was improved by approximately 10.9 and 5.14 times when compared with single HTL PVK or the TFB device, respectively. The enhancement of the hole transmission capacity by TFB/PVK double HTLs was confirmed by the hole-only device and was responsible for the dramatic EQE improvement.

Performance Enhancement of Perovskite Quantum Dot Light-Emitting Diodes via Management of Hole Injection.

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is widely used in optoelectronic devices due to its excellent hole current conductivity and suitable work function. However, imbalanced carrier injection in the PEDOT:PSS layer impedes obtaining high-performance perovskite light-emitting diodes (PeLEDs). In this work, a novel poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,40-(N-(p-butylphenyl))diphenylamine)] (TFB) is applied as the hole transport layers (HTLs) to facilitate the hole injection with cascade-like energy alignment between PEDOT:PSS and methylammonium lead tribromide (MAPbBr3) film. Our results indicate that the introduced TFB layer did not affect the surface morphology or lead to any additional surface defects of the perovskite film. Consequently, the optimal PeLEDs with TFB HTLs show a maximum current efficiency and external quantum efficiency (EQE) of 21.26 cd A-1 and 6.68%, respectively. Such EQE is 2.5 times higher than that of the control devices without TFB layers. This work provides a facile and robust route to optimize the device structure and improve the performance of PeLEDs.

Highly Luminescent CsPbBr3@Cs4PbBr6 Nanocrystals and Their Application in Electroluminescent Emitters.

Zero-dimensional perovskite nanocrystals (NCs) are becoming the most attractive material due to their excellent optical performance and better stability compared with high-dimensional perovskite. However, their application in electroluminescent (EL) emitters for high-quality displays is still limited. In this work, we successfully achieved CsPbBr3@Cs4PbBr6 NCs around 13.9 ± 0.2 nm by using the hot-injection method. Additional SnBr2 was mixed in the PbBr2 precursor to provide extra Br- ions and reduce the excessive amount of Pb2+ ions to promote the formation of CsPbBr3@Cs4PbBr6. Time resolution photoluminescence analysis indicated that the green emission of our CsPbBr3@Cs4PbBr6 NCs originated from the embedded CsPbBr3 NCs, which corresponds to our previous research. The Cs4PbBr6 crystals passivated the surface of CsPbBr3 NCs, resulting in the absence of trions for the high photoluminescence quantum yield. The as-synthesized CsPbBr3@Cs4PbBr6 NCs were used to fabricate quantum dot light-emitting diode (QLED) devices with the highest current efficiency of 4.89 cd/A. This is the best performance of the CsPbBr3@Cs4PbBr6-system QLED device, which reveals the great potential of CsPbBr3@Cs4PbBr6 NCs and will inspire further study of zero-dimensional perovskite composite NCs for EL emitters.

Long-term functional recovery after orthotopic spiral ileal bladder substitution.

BACKGROUND: To explore the value of orthotopic spiral ileal bladder substitution (OSIBS) following radical cystectomy in treating bladder cancer patients by investigating the short- and long-term postoperative complications and assessing the quality of life in patients who had undergone OSIBS. METHODS: The post-operative complications were retrospectively analyzed among bladder cancer patients who had undergone radical cystectomy + OSIBS in our center from January 2001 to January 2017. The quality of life was assessed by using the Function Assessment of Cancer Therapy-Bladder Cancer Form (FACT-BL). Patients were followed up by mails, telephone, and outpatient visits. RESULTS: A total of 68 subjects were included in this study. All patients undergoing radical cystectomy + OSIBS were followed up for an extended period. The patients aged 39-68 years (mean: 60.34±9.43 years). The surgeries were completed, and all the patients were smoothly discharged after good postoperative recovery. Of the 68 patients who had completed the follow-up visits, 10 had early complications (14.71%), and 11 (17.64%) developed late complications. The blood urea nitrogen (BUN) (t=0.358, P=0.764) and serum creatinine (Cr) (t=1.305, P=0.196) levels showed no significant difference before and after surgery. The serum potassium (t=1.347, P=0.169), sodium (t=-1.748, P=0.144), and calcium (t=1.097, P=0.319) levels also showed no significant changes before and after surgery. However, the change in serum chlorine level was statistically significant (t=-4.701, P=0.000). To support urinary function, the patients were encouraged to take exercises During the 10-year follow-up period, the daytime urinary continence rate reached 94.1% (n=64) in the daytime, and the nighttime incontinence rate was 13.2% (n=9). Six months after the surgery, the neobladder capacity was (365.02±45.11) mL, the maximum flow rate was (14.36±1.41) mL/s, and the post-voiding residual (PVR) was (26.01±8.10) mL. The total FACT-BL score was (124.8±13.4) during the 10-year follow-up. CONCLUSIONS: After 10 years of follow-up, the early and late complications in patients who had undergone radical cystectomy + OSIBS were within acceptable range and the daily and nightly continence levels allowed normal daily life. OSIBS not only preserves the physical integrity of the body but also has normal physiological characteristics of the bladder. It remarkably improves the postoperative quality of life and can be easily accepted by patients. Therefore, it is an ideal surgical procedure.

Long-term outcome of spiral ileal neobladder with orthotopic ureteral reimplantation.

PURPOSE: The purpose of this study was to analyze long-term complications, urodynamics, and quality of life (QoL) of patients after orthotopic ileal neobladder with orthotopic ureteral reimplantation to enrich clinical data and provide a basis for clinical use of this surgery. METHODS: Between January 2007 and January 2013, 72 consecutive patients who underwent spiral ileal neobladder following radical cystectomy were enrolled. The neobladder was created using a modified Camey-II technique. Complications were reviewed and staged according to Clavien-Dindo classification and evaluated in long-term follow-up. Urodynamics were performed, and QoL was assessed by the Functional Assessment of Cancer Therapy for Bladder Cancer (FACT-BL) instrument. RESULTS: The total follow-up time was 60 months, and the total survival rates at 3 and 5 years after surgery were 76.4% (55/72) and 65.3% (47/72), respectively. There were 34 (47.2%) early complications in 23 (31.9%) patients and 42 (58.3%) late complications in 35 (48.6%) patients. The total satisfactory control rates were 69.1% and 66.0% at 3 and 5 years after the surgery, respectively. Urodynamic studies were performed in some patients, and the receiver operating characteristic curve analysis showed that pressure at maximum capacity, compliance, and post void residual urine had predictive value for mortality (P < 0.05). The total FACT-BL scores of patients at 1, 3, and 5 years postoperation were 125.0 ± 15.2, 127.0 ± 16.2, and 120.6 ± 13.5, respectively, and it decreased at 5 years postoperation (P < 0.05). CONCLUSION: Spiral ileal neobladder with orthotopic ureteral reimplantation offers satisfactory long-term results, and urodynamic monitoring might have prognostic value.

Electric Bias Induced Degradation in Organic-Inorganic Hybrid Perovskite Light-Emitting Diodes.

For organic-inorganic perovskite to be considered as the most promising materials for light emitting diodes and solar cell applications, the active materials must be proven to be stable under various conditions, such as ambient environment, heat and electrical bias. Understanding the degradation process in organic-inorganic perovskite light emitting diodes (PeLEDs) is important to improve the stability and the performance of the device. We revealed that electrical bias can greatly influence the luminance and external quantum efficiency of PeLEDs. It was found that device performance could be improved under low voltage bias with short operation time, and decreased with continuous operation. The degradation of perovskite film under high electrical bias leads to the decrease of device performance. Variations in the absorption, morphology and element distribution of perovskite films under different electrical bias revealed that organic-inorganic perovskites are unstable at high electrical bias. We bring new insights in the PeLEDs which are crucial for improving the stability.

Less-Lead Control toward Highly Efficient Formamidinium-Based Perovskite Light-Emitting Diodes.

A formamidinium (FA)-based perovskite is an ideal option for the potential efficient light-emitting diode (LED) in view of its high tolerance factor closer to 1. In this work, FA cation-based perovskite nanocrystals FA0.8Cs0.2Pb xBr3 ( x = 1.0, 0.8, 0.7, and 0.6) are fabricated with stoichiometric modification. The adoption of less-lead precursor is confirmed to be a feasible and effective approach in inhibiting nonradiative recombination by diminishing the presence of uncoordinated metallic Pb atoms. Note that the subsequent devices require the optimized lead ratio for an optimum behavior, a clear influence of Pb ratio on a perovskite LED has been established. No surprisingly, the less-lead perovskites exert positive roles on the perovskite LED performance, not only in terms of efficiency but also in stability. With an optimized composition FA0.8Cs0.2Pb0.7Br3, the perovskite LED displays the prominent performance with a current efficiency of 28.61 cd A-1, about 11-fold improvement than the previous best record of pure FA-based perovskite. Additionally, the perovskite device degradation can be mitigated under operating conditions by properly altering precursor stoichiometry, which can be attributed to the hydrogen reaction under moisture-induced ambient. The stoichiometric optimization of the metal Pb in the perovskite is an important strategy on the road to the further development of perovskite LEDs.

High-Performance Quantum Dot Light-Emitting Diodes Based on Al-Doped ZnO Nanoparticles Electron Transport Layer.

ZnO nanoparticles (NPs) are widely used as the electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) owing to their suitable electrical properties. However, because of the well-aligned conduction band levels, electrons in QDs can be spontaneously transferred to adjacent ZnO NPs, leading to severe exciton dissociation, which reduces the proportion of radiative recombination and deteriorates the device efficiency. In this work, Al-doped ZnO NPs are thoroughly investigated as a replacement of ZnO for QLEDs. The energy band structures of Al-doped ZnO are modified by adjusting the concentration of Al dopants. With the increasing Al content, the work function and the conduction band edge of ZnO are gradually raised, and thus the charge transfer at the interface of QDs/ETL is effectively suppressed. Consequently, the green QLEDs with 10% Al-doped ZnO NPs exhibit maximum current efficiency and external quantum efficiency of 59.7 cd/A and 14.1%, which are about 1.8-fold higher than 33.3 cd/A and 7.9% of the devices with undoped ZnO NPs. Our work suggests that Al-doped ZnO NPs can serve as a good electron transport/injection material in QLEDs and other optoelectronic devices.

High-Performance CsPb1-x Snx Br3 Perovskite Quantum Dots for Light-Emitting Diodes.

All inorganic CsPbBr3 perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot-injection method to partially replace the toxic Pb2+ with highly stable Sn4+ . Meanwhile, the absolute photoluminescence quantum yield of CsPb1-x Snx Br3 increased from 45 % to 83 % with SnIV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr3 and CsPb0.67 Sn0.33 Br3 QDs at various excitation fluences were determined by femtosecond transient absorption, time-resolved photoluminescence, and single-dot spectroscopy, providing clear evidence for the suppression of trion generation by Sn doping. These highly luminescent CsPb0.67 Sn0.33 Br3 QDs emit at 517 nm. A device based on these QDs exhibited a luminance of 12 500 cd m-2 , a current efficiency of 11.63 cd A-1 , an external quantum efficiency of 4.13 %, a power efficiency of 6.76 lm w-1 , and a low turn-on voltage of 3.6 V, which are the best values among reported tin-based perovskite quantum-dot LEDs.