Remarkable Operational Stability Research Articles

Integration of Functionalized Polyelectrolytes onto Carbon Dots for Synergistically Improving the Tribological Properties of Polyethylene Glycol.

In this work, we carefully designed and synthesized a series of novel polyelectrolyte-functionalized carbon dots (CDs-PEI-X) by a facile and reversible phase transfer method based on the protonation reaction and anion exchange process executed on the surface of polyethylenimine-grafted CDs (CDs-PEI), where X denotes the anionic moieties of polyelectrolyte shells including hexafluorophosphate (PF6-), bis(trifluoromethane)sulfonimide (NTf2-), oleate (OL-), and bis(salicylato)borate (BScB-), respectively. Attributed to the favorable compatibility of these anions and polyethylene glycol (PEG) molecules, the hydrophobic CDs-PEI-X displayed excellent dispersibility and long-term stability in PEG200 base oil. Subsequently, the tribological behaviors of CDs-PEI-X as the lubricant additives of PEG200 were systematically investigated. It was proved that the anionic moieties of the polyelectrolyte shells of CDs-PEI-X played a crucial role in regulating their tribological behaviors. Particularly, CDs-PEI-OL was confirmed as an optimal additive, exhibiting the best lubricity, outstanding load-bearing capacity, long service life, and remarkable operational stability under boundary lubrication regime. Based on the tribological evaluations and worn surface analyses, the lubrication mechanism of CDs-PEI-OL was mainly attributed to the formation of the organic-inorganic hybrid adsorption film, the protective tribofilm, and its nanolubrication functions as scrollable "ball-bearing", i.e., the synergistic lubrication effects of surface polyelectrolyte shells and carbon cores. This study provides a feasible and versatile strategy to rapidly and effectively tailor the surface chemistry of CDs and discloses the essential contribution of carbon cores and surface groups on the lubrication process, which facilitates the development of advanced CDs-based nanolubricant additives.

Tuning the electronic structures of self-supported vertically aligned CoFe LDH arrays integrated with Ni foam toward highly efficient electrocatalytic water oxidation

The developed Ni/CoFe LDH as an anode can provide a current density of 10 mA cm−2 at 1.532 V vs. RHE, as well as remarkable operational stability, representing the best yet reported noble-metal-free water oxidation electrode.

Double-Halide Composition-Engineered SnO2-Triple Cation Perovskite Solar Cells Demonstrating Outstanding Performance and Stability

State-of-the-art perovskite solar cells (PSCs) have exhibited a record-breaking power conversion efficiency (PCE) of 25.2% with remarkable operational stability, surpassing the PCE of silicon-based...

A Haloalkane Dehalogenase from Saccharomonospora viridis Strain DSM 43017, a Compost Bacterium with Unusual Catalytic Residues, Unique (S)-Enantiopreference, and High Thermostability.

Haloalkane dehalogenases can cleave a carbon-halogen bond in a broad range of halogenated aliphatic compounds. However, a highly conserved catalytic pentad composed of a nucleophile, a catalytic base, a catalytic acid, and two halide-stabilizing residues is required for their catalytic activity. Only a few family members, e.g., DsaA, DmxA, or DmrB, remain catalytically active while employing a single halide-stabilizing residue. Here, we describe a novel haloalkane dehalogenase, DsvA, from a mildly thermophilic bacterium, Saccharomonospora viridis strain DSM 43017, possessing one canonical halide-stabilizing tryptophan (W125). At the position of the second halide-stabilizing residue, DsvA contains the phenylalanine F165, which cannot stabilize the halogen anion released during the enzymatic reaction by a hydrogen bond. Based on the sequence and structural alignments, we identified a putative second halide-stabilizing tryptophan (W162) located on the same α-helix as F165, but on the opposite side of the active site. The potential involvement of this residue in DsvA catalysis was investigated by the construction and biochemical characterization of the three variants, DsvA01 (F165W), DsvA02 (W162F), and DsvA03 (W162F and F165W). Interestingly, DsvA exhibits a preference for the (S)- over the (R)-enantiomers of β-bromoalkanes, which has not been reported before for any characterized haloalkane dehalogenase. Moreover, DsvA shows remarkable operational stability at elevated temperatures. The present study illustrates that protein sequences possessing an unconventional composition of catalytic residues represent a valuable source of novel biocatalysts.IMPORTANCE The present study describes a novel haloalkane dehalogenase, DsvA, originating from a mildly thermophilic bacterium, Saccharomonospora viridis strain DSM 43017. We report its high thermostability, remarkable operational stability at high temperatures, and an (S)-enantiopreference, which makes this enzyme an attractive biocatalyst for practical applications. Sequence analysis revealed that DsvA possesses an unusual composition of halide-stabilizing tryptophan residues in its active site. We constructed and biochemically characterized two single point mutants and one double point mutant and identified the noncanonical halide-stabilizing residue. Our study underlines the importance of searching for noncanonical catalytic residues in protein sequences.

Embedded PdFe@N-carbon nanoframes for oxygen reduction in acidic fuel cells

Carbon-supported metal nanoparticles are widely used as electrocatalysts in polymer electrolyte membrane fuel cells (PEMFCs), but still suffer from deactivation because of metal leaching and sintering at high temperature. Herein, we propose a novel and scalable metal coordination-polymer strategy for the facile synthesis of bimetallic PdFe nanoparticles embedded nitrogen-doped carbon (PdFe@N-C) nanoframes as a Mott-Schottky electrocatalyst to efficiently catalyze the oxygen reduction reaction (ORR) in PEMFCs. The metal coordination-polymer is formed through metal ions (Pd and Fe) mediated self-polymerization of 1-naphthylamine (NA), which allows alloy nanoparticles to bind tightly with N-carbon nanoframes after pyrolysis. It is found that PdFe nanoparticles with very small particle-size are uniformly embedded in the porous N-carbon nanoframes and physically separated from each other by the carbon matrix. Profited from the unique structure and composition merits, the half-wave potential of the developed PdFe@N-C nanoframes towards ORR is positively shifted by 30 and 50 mV compared to those of Pd@N-C and Pd/C, respectively. Importantly, the PdFe@N-C nanoframes derived acidic PEMFC delivers a high-power density of 0.91 W cm−2 together with remarkable operational stability after 10 h discharging. Such good performances make the metal-NA coordination-polymer an attractive precursor to design and synthesize high-performance electrocatalysts for fuel cells.

Ultrafast formation of an FeOOH electrocatalyst on Ni for efficient alkaline water and urea oxidation.

We report FeOOH supported on Ni foam which enables highly efficient UOR electrocatalysis and can be readily produced through a hydrolysis reaction. Our developed UOR catalyst as the anode can provide a current density of 200 mA cm-2 at 1.427 V vs. RHE, as well as remarkable operational stability, representing the best yet reported noble metal-free urea electrolyser.

Sonochemical synthesis of iron-graphene oxide/honeycomb-like ZnO ternary nanohybrids for sensitive electrochemical detection of antipsychotic drug chlorpromazine.

We report a novel electrochemical sensor for the sensitive and selective determination of the antipsychotic drug chlorpromazine (CPZ) based on the iron (Fe) nanoparticles-loaded graphene oxide (GO-Fe)/three dimensional (3D) honeycomb-like zinc oxide (ZnO) nanohybrid modified screen printed carbon electrode (SPCE). The 3D hierarchical honeycomb-like ZnO was synthesized using a novel aqueous hydrothermal method and the GO-Fe/ZnO nanohybrid was prepared based on an inexpensive and fast sonochemical method using a high-intensity ultrasonic bath (Delta DC200H, 200 W, 40 KHz). Characterizations including scanning electron microscopy, elemental mapping, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy were carried out as part of this work. The electrocatalytic oxidation behavior of CPZ at various electrodes was investigated using the cyclic voltammetry technique, through which the GO-Fe/ZnO modified SPCE was identified as the best performing electrode. The quantitative determination of CPZ was then performed using the differential pulse voltammetry technique. The as-prepared GO-Fe/ZnO/SPCE sensor exhibited a quick and sensitive response towards the oxidation of CPZ with linear concentration ranges from 0.02 to 172.74 μM and 222.48 to 1047.74 μM. The modified SPCE sensor displayed a low detection limit (LOD) of 0.02 µM and a high sensitivity of 7.56 µA µM-1 cm-2. The proposed sensor also showed remarkable operational and storage stability, reproducibility, and repeatability. Furthermore, the practicability of the GO-Fe/ZnO/SPCE sensor has been verified with real sample analysis using commercial antipsychotic CPZ tablets and human urine samples, and adequate recovery has been achieved.

Trace Ammonia Sensors Based on Fluorescent Near-Infrared-Emitting aza-BODIPY Dyes.

Highly sensitive ammonia sensors for environmental monitoring are presented. The sensing materials are based on fluorescent BF2-chelated tetraarylazadipyrromethene dyes (aza-BODIPYs) dyes physically entrapped in polyurethane hydrogels and dispersed in silicone rubber. This layer is covered by a hydrophobic porous Teflon membrane used as an additional proton barrier and light scattering layer. The dual-lifetime referenced (DLR) sensors make use of near-infrared (NIR)-emitting Egyptian blue as a reference material and in combination with optical fibers are read-out via a compact phase-fluorometer. The detectable concentration range can be tuned by the choice of aza-BODIPY dye or/and the hydrogel matrix. The most sensitive sensor has a limit of detection (LOD) of 0.11 μg/L and the upper detectable concentration of 300 μg/L. No cross-sensitivity toward pH is observed. The sensors show remarkable operational stability with no noticeable drift over a period of 2 weeks.

Layer-by-layer assembled (high-energy carbon nanotube/conductive carbon nanotube)n nanocomposites for high volumetric capacitance supercapacitor electrodes

We report supercapacitor electrodes with high volumetric capacitance and remarkable operational stability using a ligand exchange layer-by-layer (LbL) assembly of high-energy multiwall carbon nanotube (MWCNT) hybrids and conductive MWCNTs.

Silk fibroin hydroxyapatite composite thermal stabilisation of carbonic anhydrase

Event Abstract Back to Event Silk fibroin hydroxyapatite composite thermal stabilisation of carbonic anhydrase Zishuai Zhang1, Joao J. Lopes1, Benedetto Marelli2, Forenzo F. Omenetto2, David D. Kaplan2, Jake E. Barralet1 and Geraldine Merle1 1 McGill University, Dentistry, Canada 2 Tufts University, Engineering, United States Enzyme immobilization has been widely developed as a method to maximise operational and thermal stability and minimise the cost by reuse[1]. Several approaches have been employed for enzyme immobilization, like adsorption, covalent binding, affinity immobilization and entrapment et al. However, the immobilized enzyme always has less catalytic activity due to the loss of active sites[2], which hampered its practical application. Carbonic anhydrase (CA), a zinc metalloenzyme which captures and transforms CO2 to protons and bicarbonate ions, was used as model enzyme[3]. Here we developed a novel technique to immobilise enzyme without altering its active conformation, preventing desorption and allowing its reuse1. Enzyme was adsorbed and entrapped during the self-assembly of hydroxyapatite via ultrasonic bonding and silk fibroin was deposited to prevent enzyme from desorption. This macromolecule was further assembled into organized crystalline domains of beta sheets and less organized more flexible domains[4] to create mechanically strong barrier very resistant to changes in temperature and moisture[5]. Briefly, HA nanoparticles were prepared by precipitation of a mixture of calcium nitrate tetrahydrate with ammonium phosphate dibasic. After HA nanoparticles were mixed with Na3PO4 solution and CA and subjected to an ultrasonic treatment[6]. In parallel, B.mori silkworm cocoons were boiled in Na2CO3 solution to remove sericin, then fibers were extracted and dried[7]. The fibers were dissolved into LiBr solution, and after 2 days at room temperature, fibroin solution was centrifuged. Silk fibroin layers were deposed on the surface of the enzymatic microparticles by alternating incubations cycles in 5wt% silk solution and ethanol solutions. Beside the determination of the physico-chemical properties of the microparticle such as specific surface area and morphology, enzymatic activity and stability measurements were performed. By applying ultrasound the initial HA nanoparticles formed mechanically robust HA microparticles (Figure 1A) that were separated from the unbounded nanoparticles by washing and sieving. As observed by SEM, the HA microparticles had a linear dimension of ~75-125μm (Figure 1A) and a nanoporosity of less than 100nm (Figure 1B). After consecutive heat treatments of one hour at temperatures increasing from 50°C to 140°C (Figure 2), the free enzyme degraded at 50°C with no catalytic activity measureable whereas the enzyme simply adsorbed on HA exhibited a gradual loss of activity with 30% of remaining activity at 90°C. However the thermal stability was much greater when the silk was incorporated with 80% of its initial activity retained up to 110°C. To better characterize this thermal stability, we also recorded the enzymatic activity in an amine solvent, MDEA at 80˚C. The enzymatic activity remained unchanged up to 3 days, decreased to 45% and then remained stable for 3 weeks. In summary, silk fibroin hydroxyapatite nano-composite showed a remarkable operational, storage and thermal stability, with enzymatic activity almost unchanged after a one hour’s treatment at 110°C and the assembly retained 45% of its initial activity after 3 weeks of continuous heating at 80°C in an amine solution. This thermal stability was excellent compared with described CA immobilization systems and indicates that silk fibroin may limit thermally induced enzyme conformation changes and prevent desorption.

Detection of ultra-high energy cosmic ray showers with a single-pixel fluorescence telescope

We present a concept for large-area, low-cost detection of ultra-high energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report first results of a FAST prototype installed at the Telescope Array site, consisting of a single 200 mm photomultiplier tube at the focal plane of a 1 m2 Fresnel lens system taken from the prototype of the JEM-EUSO experiment. The FAST prototype took data for 19 nights, demonstrating remarkable operational stability. We detected laser shots at distances of several kilometers as well as 16 highly significant UHECR shower candidates.

Formation of a p–n heterojunction on GaP photocathodes for H2production providing an open-circuit voltage of 710 mV

Photocatalytic water splitting for the sustainable production of hydrogen using a two-photon tandem device requires careful optimization of the semiconductors used as photon absorbers. In this work we show how the open-circuit voltage of photocathodes for the hydrogen evolution reaction based on p-GaP was increased considerably by sputtering of different n-type metal oxides on the surface and thereby forming an effective p–n heterojunction. Both n-TiO2 and n-Nb2O5 increased the VOC of the photocathodes, with the latter giving an ultimate VOC of 710 mV using Pt as the cocatalyst. This value is unprecedented for a p-GaP-based HER photocathode operating in an acidic electrolyte under simulated 1 Sun illumination. An additional, but highly significant benefit of a TiO2 layer is that it provides a remarkable operational stability of more than 24 h under constant operation. It was found that TiO2 and Nb2O5 overlayers, which were characterized by high donor density, caused a large built-in potential drop that is located almost exclusively in the p-type substrate. The large built-in potential drop in the GaP effectively separates charge carriers driving photogenerated electrons toward the surface of the electrode to perform the HER. According to this result, a further careful choice of materials having specific properties, such as optimal carrier concentration and band positions, could potentially increase VOC even more, paving the way for the realization of a non-assisted two-photon solar water splitting device.

Cauliflower polyaniline/multiwalled carbon nanotube electrode and its applications to hydrogen peroxide and glucose detection*

Vertically aligned polyaniline (PANI) structures were prepared by controlling the deposition current density during a stepwise template-free electrochemical deposition process of aniline on a glassy carbon electrode (GCE). Scanning electron micrographs (SEMs) showed the formation of cauliflower PANI structures, each with a diameter of approximately 2–3 and 10 μm in length. The cauliflower-like PANI electrode was modified with multiwalled carbon nanotubes (cauliflower PANI/MWCNTs) and used as the working electrode for electrochemical detections where H2O2 and glucose were used as the models for the chemical sensor and biosensor, respectively. The sensor provided linearity in the range of 1.0 to 150 μM of H2O2 with the limit of detection (LOD) of 50 nM. This is 100-fold better than the LOD of the bare GCE. Moreover, this sensor exhibited remarkable operational stability, i.e., 50 μM H2O2 could be analyzed up to 140 times with a 2.7 % relative standard deviation (RSD). A glucose biosensor was prepared using the modified cauliflower PANI/MWCNT electrode. This had a 3.4 times higher sensitivity than an electrode modified with PANI film/MWCNTs. The regular size and high surface-to-volume ratio of the cauliflower PANI electrode will provide good opportunities for further biosensor applications.

Amperometric Biosensor for Direct Blood Lactate Detection

An amperometric sensor for lactate quantification is presented. The developed biosensor requires only 0.2 U of lactate oxidase, which is immobilized in a mucin/albumin hydrogel matrix. By protecting the platinum surface with a Nafion membrane, typical interference related to negatively charged species such as ascorbic acid has been minimized to practically undetectable levels. Electrochemical properties associated with the Nafion membrane are assessed as a function of Nafion concentration. In a phosphate buffer solution of pH 7.0, linear dependence of the catalytic current upon lactate bulk concentration was obtained between 2 and approximately 1000 microM. A detection limit of 0.8 microM can be calculated considering 3 times the standard deviation of the blank signal divided by the sensitivity of the sensor. The lactate biosensor presents remarkable operational stability and sensitivity (0.537 +/- 0.007) mA.M(-1), where the error is the standard deviation of the slope calculated from the linear regression of the calibration curve of a fresh biosensor. In this regard, the sensor keeps practically the same sensitivity for 5 months, while the linear range decreases until an upper value of 0.8 mM is reached. Assays performed with whole blood samples spiked with 100 microM lactate gave (89 +/- 6)% of recovery.

A highly stable whole‐cell biocatalyst for the enantioselective synthesis of optically active alpha‐hydroxy acids

AbstractBACKGROUND: Biocatalysts have gained increasing attention because of their inherent advantages over chemical catalysts. However, the poor operational stability has always prevented their broad application. In this study, (R)‐mandelic acid was chosen as a model compound of alpha‐hydroxy acids. The objective was to obtain a new biocatalyst with desired operational stability for the preparation of (R)‐mandelic acid as well as other optically pure alpha‐hydroxy acids of pharmaceutical importance.RESULTS: Using a two‐step screening strategy, Saccharomyces ellipsoideus GIM2.105 was selected as an effective biocatalyst with high enantioselectivity and remarkable operational stability. After 20 cycles of reuse, whole cells of S. ellipsoideus GIM2.105 maintained its activity, and no obvious decrease in conversion or enantiomeric excess (ee) was observed. Furthermore, effects of various reaction parameters, including pH, temperature, co‐substrate (type, concentration), substrate concentration and reaction time, on the bioreduction were studied. Under optimal conditions, (R)‐mandelic acid and four substituted aromatic (R)‐alpha‐hydroxy acids were prepared in high ee (95–>99%) and good conversion (>90%).CONCLUSION: The high enantioselectivity, remarkable operational stability and mild reaction conditions showed S. ellipsoideus GIM2.105 to be an economical biocatalyst with great industrial application potential for the production of optically active alpha‐hydroxy acids. Copyright © 2009 Society of Chemical Industry

Laccase electrode for direct electrocatalytic reduction of O 2 to H 2O with high-operational stability and resistance to chloride inhibition

Laccase from Trametes hirsuta basidiomycete has been covalently bound to graphite electrodes electrochemically modified with phenyl derivatives as a way to attach the enzyme molecules with an adequate orientation for direct electron transfer (DET). Current densities up to 0.5 mA/cm 2 of electrocatalytic reduction of O 2 to H 2O were obtained in absence of redox mediators, suggesting preferential orientation of the T1 Cu centre of the laccase towards the electrode. The covalent attachment of the laccase molecules to the functionalized electrodes permitted remarkable operational stability. Moreover, O 2 bioelectroreduction based on DET between the laccase and the electrode was not inhibited by chloride ions, whereas mediated bioelectrocatalysis was. In contrast, fluoride ions inhibited both direct and mediated electron transfers-based bioelectrocatalytic reduction of O 2. Thus, two different modes of laccase inhibition by halides are discussed.

An HRP-based amperometric biosensor fabricated by thermal inkjet printing

Direct inkjet printing of a complete and working amperometric biosensor for the detection of hydrogen peroxide, based on horseradish peroxidase (HRP), has been demonstrated. The device has been realized with a commercial printer. A thin layer of PEDOT:PSS, which was in turn covered with HRP, was inkjet printed on top of an ITO-coated glass slide. The active components of the device retained their properties after the thermal inkjet printing. The whole device has been encapsulated by means of a selectively permeable cellulose acetate membrane. The successful electron transfer between the PEDOT:PSS covered electrode and the enzyme has been demonstrated, and the biosensor evidenced very good sensitivity, in line with the best devices realized with other techniques, and a remarkable operational stability. This result paves the way for an extensive application of “biopolytronics”, i.e. the utilization of conductive/semiconductive polymers and biologically active molecules to design bioelectronic devices using a common PC, and exploiting normal commercial printers to print them out.

Chemiluminescence assay for uric acid in human serum and urine using flow-injection with immobilized reagents technology.

A novel chemiluminescence (CL) flow sensor for the determination of uric acid in human urine and serum has been developed by using controlled-reagent-release technology. The reagents involved in the chemiluminescence (CL) reaction, luminol and periodate, are immobilized on anion-exchange resin packed in a column. After injection of water, chemiluminescence generated by released luminol and periodate in alkaline media is inhibited in presence of uric acid. By measuring the decreased chemiluminescence (CL) intensity the uric acid is sensed. The decreased response is linear in the 5.0-500.0 ng mL(-1) range, with a detection limit of 1.8 ng mL(-1). The flow sensor showed remarkable operational stability and could be easily reused for over 80 h with sampling frequency of 100 h(-1). The proposed sensor was applied to the determination of uric acid in human urine and serum, and monitoring metabolic uric acid in human urine with RSD less than 3.0%.

A process for bioconversion of cephalosporin C by Rhodotorula gracilis D-amino acid oxidase

A process for the production (in a stirred tank reactor) of glutaryl-7-ACA from cephalosporin C using immobilized D-amino acid oxidase is described. Results so obtained under optimal conditions (1.2 mg coupled enzyme/L, pH 8.5, 2 mM cephalosporin C) point to a system which shows high conversion efficiency and a remarkable operational stability. No exogenous H2O2 is requested to shift the reaction equilibrium toward glutaryl-7-ACA production, nor any side product is detected. The immobilized system productivity was 54 g/day/mg of enzyme. This process represents the first reported case of a reactor successfully developed with a DAAO for bioconversion of cephalosporin C.