Neutral Phosphate Buffer Research Articles

Conducting-Polymer-Supported Bacterial Biofilms As Active Matrices for Noble Metal and Molecular Catalytic Centers: Enhancement of Electroreduction of Oxygen and Carbon Dioxide

Hybrid matrices composed of porous conducting polymer - polyaniline (PANI) or poly(3,4- ethylenedioxythiophene) (PEDOT) - underlayer, robust bacterial biofilm and the multi-walled carbon nanotubes have been demonstarted to function as highly active supports for dispersed catalztic centers (both noble metal nanoparticles and molecular ligand complexes). We explore unique properties of biofilms, i.e. polymeric aggregates of microorganisms, in which cells adhere to each other on the electrode surfaces. Such systems are characterized by extracellular electron transfers involving c-type cytochromes (heme-containing proteins). Biofilms grown on inert carbon electrode substrates tend to exhibit electrocatalytic properties towards oxygen and hydrogen peroxide reductions in neutral media. The processes have been found to be further enhanced by introduction of multi-walled carbon nanotubes (MCNTs) that are modified with ultra-thin layers of organic (e.g. 4-(pyrrole-l-yl) benzoic acid. We expect here attractive electrostatic interactions between carboxyl-group containing anionic adsorbates and positively charged domains of the biofilm with c-type cytochrome enzymatic sites. Coexistence of the above components leads to synergistic effect that is evident from positive shift of the oxygen reduction voltammetric potentials and significant increase of voltammetric currents. Most likely, the reduction of oxygen has been initiated at the molecular (e.g. intentionally added cobalt porphyrin redox centers), whereas the undesirable hydrogen peroxide intermediate are further decomposed at the cytochrome sites. Among other important observations is the significant enhancement of activity of Pt nanoparticles toward electroreduction of carbon dioxide in the presence of such a robust bacterial biofilm as Y. enterocolitica. Although interactions between platinum and such a complex ecosystem as biofilm are difficult to describe precisely, it is reasonable to postulate some inhibition of the hydrogen evolution (competitive reaction) at platinum nanoparticles in presence of bacterial microcolonies in favor of enhancement of the CO2-reduction. It is also noteworthy that biofilms are highly hydrated, and existence of open water channels between the bacterial microcolonies facilitates flow of supporting electrolyte. Combination of the hydrophobic polymer (PANI) structures with hydrophilic bacterial aggregates seems to produce attractive hybrid supports for electrocatalysts operating in aqueous media. Based on numerous repetitive diagnostic experiments in both argon and carbon dioxide saturated electrolytes, it can be stated that, by growing and supporting the biofilm onto the PANI polymer underlayer, the overall stability of the biofilm-based system has been improved. Indeed, we have not effectively observed any degradation of the hybrid catalytic films (both in terms of electrocatalytic activity and physicochemical stability) during our prolonged diagnostic experiments. Because measurements have been performed in neutral (phosphate buffer at pH=6.1) rather than acid medium, the PANI films (regardless of the presence of some HSO4 - anions) are not expected to be very well conducting. Consequently, we have also introduced MWCNTs to the electrocatalytic interface to facilitate charge distribution there.

Gelation of collagen under shearing to create a thick gel composed of uniaxially aligned fibrils

Gelation of collagen under shearing to create a thick gel composed of uniaxially aligned fibrils

Electrocatalytic water oxidation by a macrocyclic Cu(ii) complex in neutral phosphate buffer.

A single-site copper complex, [Cu(TMC)(H2O)](NO3)2 (1, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was found to be the most active copper-based catalyst towards electrocatalytic water oxidation in neutral aqueous solution. Complex 1 leads to a cathodic shift of approximately 200 mV in potential to reach a current density of 1 mA cm(-2) in comparison with that of the previously reported dinuclear copper complex under the same conditions. Upon immobilization of complex 1 on carbon cloth, it shows greatly improved activity than other copper-based WOCs including CuOx and Cu(2+).

Halogenated earth abundant metalloporphyrins as photostable sensitizers for visible-light-driven water oxidation in a neutral phosphate buffer solution.

Very photostable tetrachloro-metalloporphyrins were developed as sensitizers for visible-light-driven water oxidation coupled to cobalt based water-oxidation catalysts in concentrated (0.1 M) phosphate buffer solution. Potassium persulfate (K2S2O8) acts as a sacrificial electron acceptor to oxidize the metalloporphyrin photosensitizers in their excited states. The radical cations thus produced drive the cobalt based water-oxidation catalysts: Co4O4-cubane and Co(NO3)2 as pre-catalyst for cobalt-oxide (CoOx) nanoparticles. Two different metalloporphyrins (Cu(ii) and Ni(ii)) both showed very high photostability in the photocatalytic reaction, as compared to non-halogenated analogues. This indicates that photostability primarily depends on the substitution of the porphyrin macrocycle, not on the central metal. Furthermore, our molecular design strategy not only positively increases the electrochemical potential by 120-140 mV but also extends the absorption spectrum up to ∼600 nm. As a result, the solar photon capturing abilities of halogenated metalloporphyrins (Cu(ii) and Ni(ii)) are comparable to that of the natural photosynthetic pigment, chlorophyll a. We successfully demonstrate long-term (>3 h) visible-light-driven water oxidation using our molecular system based on earth-abundant (first-row transition) metals in concentrated phosphate buffer solution.

Non-Equilibrium Capillary Electrophoresis of Equilibrium Mixtures-Based Affinity Separation and Selective Enrichment of a Long-Length DNA Aptamer

Non-equilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) is a kinetic capillary electrophoresis method used for the affinity analysis of DNA binding to proteins or ligands as well as a rapid selection of DNA aptamers. However, long DNA strands (100-mer or more) are generally difficult to analyse by this method owing to their poor peak separation. Herein, we report optimized conditions (use of a neutral phosphate buffer with an ionic strength of 0.074 as a binding buffer and use of an 80-cm fused silica capillary with a 75-μm internal diameter) for the peak separation of a 100-mer thrombin-binding DNA aptamer-target complex and its consequent enrichment using the NECEEM-based capillary electrophoresis–systematic evolution of ligands by exponential enrichment (CE-SELEX) method.

Water oxidation electrocatalysis with iron oxide nanoparticles prepared via laser ablation

Iron oxide nanoparticles (FeOx NPs, 5–30 nm size) prepared via laser ablation in liquid were supported onto Indium Tin Oxide conductive glass slides by magnetophoretic deposition (MD) technique. The resulting FeOx@ITO electrodes are characterized by a low amount of iron coverage of 16–50 nmol/cm2, and show electrocatalytic activity towards water oxidation in neutral phosphate buffer pH 7 with 0.58 V overpotential and quantitative Faradaic efficiency towards oxygen production. XPS analysis on the oxygen region of the FeOx films reveals a substantial hydration of the surface after catalysis, recognized as a crucial step to access reactivity.

Overall Photoelectrochemical Water Splitting using Tandem Cell under Simulated Sunlight.

A stand-alone photoelectrochemical (PEC) water-splitting system driven only by sunlight was demonstrated with a tandem-scheme of Pt/CdS/CuGa3 Se5 /(Ag,Cu)GaSe2 photocathode and NiOOH/FeOOH/Mo:BiVO4 photoanode in a neutral phosphate buffer solution as an electrolyte. The as-prepared semi-transparent Mo:BiVO4 layer allows sunlight to pass through the top photoanode and reach the bottom photocathode. Consequently, the tandem cell showed stoichiometric hydrogen and oxygen evolution with a solar-to-hydrogen (STH) conversion efficiency of 0.67 % over 2 h without degradation. The stability and STH efficiency are the highest among similar configuration of PEC tandem cells.

Performance evaluation of aluminum/phosphate cell for powering small electronic devices

We report on an innovative membrane-free aluminum/phosphate cell based on the activation of aluminum (Al) as anodic material using ZnO nanocrystal in phosphate rich electrolyte that is capable of generating sufficient power to power a light-emitting diode (LED), selected as a model of a small electronic device. The energy from the cell is periodically supplied in high power bursts due to the charge and discharge cycle of the capacitor. The entire process is controlled by a switched capacitor regulator. The Al/phosphate cell was studied in neutral 100mM phosphate buffer solution (7.4) at a temperature of 25°C. We demonstrate that two Al/phosphate cells connected in series can generate an open circuit voltage (Voc) up to 1.66V to continuously power a LED via a switched capacitor regulator circuit. The switched capacitor regulator circuit enabled the 1μF capacitor to store the incoming power from the cell and discharge it in a large power burst to supply the necessary drive strength required by the LED. This new Al/phosphate cell configuration is a ‘green’ alternative to the use of glucose abiotic and biofuel cells for powering ultra-low power implantable electronic devices.

Porous Carbon Nanosheets Codoped with Nitrogen and Sulfur for Oxygen Reduction Reaction in Microbial Fuel Cells.

In this work, a simple synthesis strategy has been developed for the preparation of nitrogen- and sulfur-codoped porous carbon nanosheets (N/S-CNS) as a cathode catalyst for microbial fuel cells (MFCs). The as-prepared N/S-CNS showed favorable features for electrochemical energy conversion such as high surface area (1004 m(2) g(-1)), defect structure, and abundant exposure of active sites that arose primarily from porous nanosheet morphology. Benefiting from the unique nanostructure, the resulting nanosheets exhibited effective electrocatalytic activity toward oxygen reduction reaction (ORR). The onset potential of the N/S-CNS in linear-sweep voltammetry was approximately -0.05 V vs Ag/AgCl in neutral phosphate buffer saline. Electrochemical impedance spectroscopy showed that the ohmic and charge-transfer resistance of the codoped catalyst were 1.5 and 14.8 Ω, respectively, both of which were lower than that of platinum/carbon (Pt/C). Furthermore, the electron-transfer number of the N/S-CNS was calculated to be ∼3.5, suggesting that ORR on the catalyst proceeds predominantly through the favorable four-electron pathway. The MFC with N/S-CNS as a cathode catalyst generated current density (6.6 A m(-2)) comparable to that with Pt/C (7.3 A m(-2)). The high durability and low price indicate that N/S-CNS can be a competitive catalyst for applications of MFCs.

Energy conversion from aluminium and phosphate rich solution via ZnO activation of aluminium

Electrochemical power sources have motivated intense research efforts in the development of alternative ‘green’ power sources for ultra-low powered bioelectronic devices. Biofuel cells employ immobilized enzymes to convert the available chemical energy of organic fuels directly into electricity. However, biofuel cells are limited by short lifetime due to enzyme inactivation and frequent need to incorporate mediators to shuttle electrons to the final electron acceptor. In this context, other electrochemical power sources are necessary in energy conversion and storage device applications. Here we report on the fabrication and characterization of a membrane-free aluminium/phosphate cell based on the activation of aluminium (Al) using ZnO nanocrystal in an Al/phosphate cell as a ‘green’ alternative to the traditional enzymatic biofuel cells. The hybrid cell operates in neutral phosphate buffer solution and physiological saline buffer. The ZnO modifier in the phosphate rich electrolyte activated the pitting of Al resulting in the production of hydrogen, as the reducing agent for the reduction of H2PO4− ions to HPO32− ions at a formal potential of −0.250 V vs. Ag/AgCl. Specifically, the fabricated cell operating in phosphate buffer and physiological saline buffer exhibit an open-circuit voltage of 0.810 V and 0.751 V and delivered a maximum power density of 0.225 mW cm−2 and 1.77 mW cm−2, respectively. Our results demonstrate the feasibility of generating electricity by activating Al as anodic material in a hybrid cell supplied with phosphate rich electrolyte. Our approach simplifies the construction and operation of the electrochemical power source as a novel “green” alternative to the current anodic substrates used in enzymatic biofuel cells for low power bioelectronics applications.

High Catalytic Activity of Amorphous Ir-Pi for Oxygen Evolution Reaction.

Large-scale production of hydrogen gas by water electrolysis is hindered by the sluggish kinetics of oxygen evolution reaction (OER) at the anode. The development of a highly active and stable catalyst for OER is a challenging task. Electrochemically prepared amorphous metal-based catalysts have gained wide attention after the recent discovery of a cobalt-phosphate (Co-Pi) catalyst. Herein, an amorphous iridium-phosphate (Ir-Pi) is investigated as an oxygen evolution catalyst. The catalyst is prepared by the anodic polarization of carbon paper electrodes in neutral phosphate buffer solutions containing IrCl3. The Ir-Pi film deposited on the substrate has significant amounts of phosphate and Ir centers in an oxidation state higher than +4. Phosphate plays a significant role in the deposition of the catalyst and also in its activity toward OER. The onset potential of OER on the Ir-Pi is about 150 mV lower in comparison with the Co-Pi under identical experimental conditions. Thus, Ir-Pi is a promising catalyst for electrochemical oxidation of water.

Development of lattice-inserted 5-Fluorouracil-hydroxyapatite nanoparticles as a chemotherapeutic delivery system.

Developing an effective vehicle for cancer treatment, hydroxyapatite nanoparticles were fabricated for drug delivery. When 5-Fluorouracil, a major chemoagent, is combined with hydroxyapatite nanocarriers by interclay insertion, the modified hydroxyapatite nanoparticles have superior lysosomal degradation profiles, which could be leveraged as controlled drug release. The decomposition of the hydroxyapatite nanocarriers facilitates the release of 5-Fluorouracil into the cytoplasm causing cell death. Hydroxyapatite nanoparticles with/without 5-Fluorouracil were synthesized and analyzed in this study. Their crystallization properties and chemical composition were examined by X-ray diffraction and Fourier transforms infrared spectroscopy. The 5-Fluorouracil release rate was determined by UV spectroscopy. The biocompatibility of hydroxyapatite-5-Fluorouracil extraction solution was assessed using 3T3 cells via a WST-8 assay. The effect of hydroxyapatite-5-Fluorouracil particles which directly work on the human lung adenocarcinoma (A549) cells was evaluated by a lactate dehydrogenase assay via contact cultivation. A 5-Fluorouracil-absorbed hydroxyapatite particles were also tested. Overall, hydroxyapatite-5-Fluorouracils were prepared using a co-precipitation method wherein 5-Fluorouracil was intercalated in the hydroxyapatite lattice as determined by X-ray diffraction. Energy dispersive scanning examination showed the 5-Fluorouracil content was higher in hydroxyapatite-5-Fluorouracil than in a prepared absorption formulation. With 5-Fluorouracil insertion in the lattice, the widths of the a and c axial constants of the hydroxyapatite crystal increased. The extraction solution of hydroxyapatite-5-Fluorouracil was nontoxic to 3T3 cells, in which 5-Fluorouracil was not released in a neutral phosphate buffer solution. In contrast, at a lower pH value (2.5), 5-Fluorouracil was released by the acidic decomposition of hydroxyapatite. Finally, the results of the lactate dehydrogenase assay revealed that 5-Fluorouracil-hydroxyapatite was highly toxic to A549 cells through direct culture, this phenomenon may result from lysosomal decomposition of particles causing 5-Fluorouracil releasing. The pH-responsive hydroxyapatite-5-Fluorouracil nanoparticles have the potential to be part of a selective drug-delivery system in chemotherapy for cancer treatment.

Effect of the support material type on the electrocatalytic activity of Pd–Au electrodeposits in neutral electrolyte

Pd–Au co-deposits were produced by electrochemical deposition on nickel foam, carbon felt and porous graphite. The morphology of the obtained electrodeposits was analyzed by scanning electron microscopy. The electrocatalytic activity of Pd–Au co-deposits towards hydrogen evolution reaction in neutral phosphate buffer solution was examined by means of linear voltammetry. The quantities of the produced hydrogen gas with different electrocatalysts were calculated from data obtained by chronoamperometry. The highest hydrogen production rate of 26 mL mg−1 cm−2 h−1 was achieved using Pd–Au co-deposits on Ni-foam. The contribution of the explored support materials to the total electrode activity was evaluated by comparison of the results obtained with the supported catalysts and corresponding bare supports.

Visible light-driven water oxidation promoted by host-guest interaction between photosensitizer and catalyst with a high quantum efficiency.

A highly active supramolecular system for visible light-driven water oxidation was developed with cyclodextrin-modified ruthenium complex as the photosensitizer, phenyl-modified ruthenium complexes as the catalysts, and sodium persulfate as the sacrificial electron acceptor. The catalysts were found to form 1:1 host-guest adducts with the photosensitizer. Stopped-flow measurement revealed the host-guest interaction is essential to facilitate the electron transfer from catalyst to sensitizer. As a result, a remarkable quantum efficiency of 84% was determined under visible light irradiation in neutral aqueous phosphate buffer. This value is nearly 1 order of magnitude higher than that of noninteraction system, indicating that the noncovalent incorporation of sensitizer and catalyst is an appealing approach for efficient conversion of solar energy into fuels.

A novel fabrication method to create a thick collagen bundle composed of uniaxially aligned fibrils: an essential technology for the development of artificial tendon/ligament matrices.

In this study, we developed a fabrication method for thick collagen gel bundles comprising uniaxially aligned fibrils of sufficient size for filling defects in ligament tissues. The fabrication involved rotary shearing to dense collagen sols using a rheometer and then warming them from 23°C to 37°C to trigger gelation upon rotation. Gelation due to collagen fibril formation was accelerated by increased concentrations of neutral phosphate buffer, and fibril alignment occurred within 20 s during the early stage of rapid gelation. Fabrication of gels was completed with slippage between gels and the movable upper plate, and well-aligned fibrils along the rotation direction were observed in the marginal regions of disc-shaped gels. Gel thickness could be increased from 1 to 3 mm with homogeneous alignment of fibrils in the entire sample. The alignment of fibrils improved mechanical properties against tensile loads that were placed parallel to the alignment axis. Elongation of cultured fibroblast along the alignment was observed on the gels. The present method will enable the bottom-up fabrication of an artificial tendon for ligament reconstruction and repair.

New Nanobiocomposite Materials for Bioelectronic Devices

We have developed and synthesized nanobiocomposite materials based on graphene, poly(3,4-ethylenedioxythiophene), and glucose oxidase immobilized on the surface of various nanomaterials (gold nanoparticles and multi-walled carbon nanotubes) of different sizes (carbon nanotubes of different diameters). Comparative studies of the possible influence of the nanomaterial's nature on the bioelectrocatalytic characteristics of glucose- oxidizing bioanodes in a neutral phosphate buffer solution demonstrated that the bioelectrocatalytic current densities of nanocomposite-based bioanodes are only weakly dependent on the size of the nanomaterial and are primarily defined by its nature. The developed nanobiocomposites are promising materials for new bioelectronic devices due to the ease in adjusting their capacitive and bioelectrocatalytic characteristics, which allows one to use them for the production of dual-function electrodes: i.e., electrodes which are capable of generating and storing electric power simultaneously.

The Effect of Altered pH on Push-Out Bond Strength of Biodentin, Glass Ionomer Cement, Mineral Trioxide Aggregate and Theracal

Summary Introduction Throughout the history of dentistry, a wide variety of materials such as gold-foil, silver posts, amalgam, zinc oxide eugenol, glass ionomer cements, mineral trioxide aggregate have been used as retrograde fillings. Altered pH in periapical lesions can affect push-out bond strength of these materials. The aim of this study was to evaluate the effect of altered pH on push-out bond strength of Biodentin, Glass ionomer cement (GIC), Mineral trioxide aggregate (MTA) and Theracal. Material and Methods Forty-eight dentin slices of extracted single-rooted human teeth were sectioned and their canal portion instrumented to achieve a diameter of 1.4 mm. The specimens were then assigned into the four groups (one group for each material) with 12 samples in each group. All groups were further divided into 3 subgroups (with 4 specimens in each subgroup): acidic (butyric acid buffered at pH 6.4), neutral (phosphate buffer saline solution at pH 7.4) and alkaline (buffered potassium hydroxide at pH 8.4). Samples were incubated for 4 days at 37°C in acidic, neutral or alkaline medium. Push-out bond strength was measured using a Universal Testing Machine. The slices were examined under a stereomicroscope to determine the nature of bond failure. Results GIC showed the highest bond strength (33.33MPa) in neutral and acidic medium (26.75MPa) compared to other materials. Biodentin showed the best result in alkaline medium. Conclusion Altered pH level affected push-out bond strength of root end materials. GIC demonstrated good push-out bond strength that increased with decrease of pH whereas newer materials Biodentin and Theracal showed satisfying results in altered pH.

Binding affinities of folic acid and related pterins with biological macromolecules under physiological conditions

Abstract Folic acid and pterin derivatives are important heterocyclic compounds found in a variety of biological systems and have been shown to be photochemically active. Understanding the amount of binding that various pterins have with biological macromolecules under physiological conditions is important in predicting what specific biomolecules will bind with pterins and may, therefore, result in photochemical damage from charge-transfer reactions. The relative binding of folic acid, or pteroyl-L-glutamic acid (PteGlu), 6-methylpterin (Mep), 6-hydroxymethylpterin (Hmp), 6-formylpterin (Fop), and 6-carboxypterin (Cap) with bovine serum albumin (BSA), electrically neutral lipid (ENL), polyguanylic acid (Poly G), polycytidylic acid (Poly C), polyadenylic acid (Poly A), polythymidylic acid (Poly T), Micrococcus luteus DNA (72% GC), Escherichia coli DNA (50% GC), calf thymus DNA (42% GC), and Clostridium perfrigens DNA (27% GC) in neutral phosphate buffer were studied. Our results indicate that PteGlu demonstrated strong binding to neutral lipids, while the other pterins showed minimal binding, and BSA had a significant binding to PteGlu, Cap, and especially Fop. Our results also reveal a high affinity for DNA by PteGlu, which suggests that a relatively high percentage of folic acid is bound to DNA before photochemistry occurs.

Graphene-Co3O4 nanocomposite as electrocatalyst with high performance for oxygen evolution reaction

Graphene-Co3O4 composite with a unique sandwich-architecture was successfully synthesized and applied as an efficient electrocatalyst for oxygen evolution reaction. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses confirmed that Co3O4 nanocrystals were homogeneously distributed on both sides of graphene nanosheets. The obtained composite shows enhanced catalytic activities in both alkaline and neutral electrolytes. The onset potential towards the oxygen evolution reaction is 0.406 V (vs. Ag/AgCl) in 1 M KOH solution, and 0.858 V (vs. Ag/AgCl) in neutral phosphate buffer solution (PBS), respectively. The current density of 10 mA/cm2 has been achieved at the overpotential of 313 mV in 1 M KOH and 498 mV in PBS. The graphene-Co3O4 composite also exhibited an excellent stability in both alkaline and neutral electrolytes. In particular, no obvious current density decay was observed after 10 hours testing in alkaline solution and the morphology of the material was well maintained, which could be ascribed to the synergistic effect of combining Co3O4 and graphene.

Platinum(ii)–porphyrin as a sensitizer for visible-light driven water oxidation in neutral phosphate buffer

A water-soluble Pt(ii)–porphyrin with a high potential for one-electron oxidation (∼1.42 V vs. NHE) proves very suitable for visible-light driven water oxidation in neutral phosphate buffer solution in combination with a variety of WOCs.