Layered double hydroxides: an attractive material for electrochemical biosensor design

Electrochemical biosensors for phenol determination were developed based on the immobilization of polyphenol oxidase (PPO) within two different clay matrixes, one anionic (layered double hydroxide, LDH) and the other cationic (Laponite). The biosensor based on the enzyme immobilized in [Zn-Al-Cl] LDH shows greater sensitivity (7807 mA M(-1) cm(-2)) and maximum current (492 microA cm(-2)). Biosensor characteristics, such as Michaelis-Menten constant, recycling constant, activation energy, and permeability highlight the advantages of LDH matrixes to immobilize PPO. It appears that LDH provides a favorable environment to PPO activity. The best PPO/[Zn-Al-Cl] configuration was used to determine five different phenol derivatives reaching extremely sensitive detection limits (< or = 1 nM).     

Versatile new ion source for the analysis of materials in open air under ambient conditions

A new ion source has been developed for rapid, noncontact analysis of materials at ambient pressure and at ground potential. The new source, termed DART (for "Direct Analysis in Real Time"), is based on the reactions of electronic or vibronic excited-state species with reagent molecules and polar or nonpolar analytes. DART has been installed on a high-resolution time-of-flight mass spectrometer (TOFMS) that provides improved selectivity and accurate elemental composition assignment through exact mass measurements. Although DART has been applied to the analysis of gases, liquids, and solids, a unique application is the direct detection of chemicals on surfaces without requiring sample preparation, such as wiping or solvent extraction. DART has demonstrated success in sampling hundreds of chemicals, including chemical agents and their signatures, pharmaceutics, metabolites, peptides and oligosaccharides, synthetic organics, organometallics, drugs of abuse, explosives, and toxic industrial chemicals. These species were detected on various surfaces, such as concrete, asphalt, human skin, currency, airline boarding passes, business cards, fruits, vegetables, spices, beverages, body fluids, horticultural leaves, cocktail glasses, and clothing. DART employs no radioactive components and is more versatile than devices using radioisotope-based ionization. Because its response is instantaneous, DART provides real-time information, a critical requirement for screening or high throughput.     

Dithiobissuccinimidyl propionate as an anchor for assembling peroxidases at electrodes surfaces and its application in a H2O2 biosensor

Exposure of gold surfaces to solutions of dithiobis N-succinimidyl propionate (DTSP) gives rise to the modification of the surface with N-succinimidyl-3-thiopropionate (NSTP) which can, in turn, react with amino groups allowing for the covalent immobilization of enzymes such as horseradish peroxidase (HRP). The coverage of NSTP has been estimated to be of the order of 1.3 x 10(-10) from the charge consumed during its reductive desorption. The binding reaction of HRP with NSTP modified gold surfaces has been studied with the quartz crystal microbalance, and the results suggest that the immobilization process involves two steps in which the first (faster) appears to correspond to the rapid incorporation of the enzyme whereas the second is likely due to the slow incorporation of additional enzyme and/or reorganization of the immobilized layer. Spectrophotometric and electrochemical assays indicate that the immobilized HRP retains its enzymatic activity after immobilization onto the DTSP modified gold surface. The amount of immobilized (and active) HRP was estimated from QCM and spectrophotometric measurements to be of the order of 1.5 x 10(-11) mol/cm2. A peroxide biosensor was developed making use of a gold surface modified with DTSP and HRP employing Os and Ru complexes of 1,10-phenanthroline 5,6-dione (phen-dione) of the type [M(phendione)x(L)3-x]+2 (where L = 1,10-phenanthroline or 2,2'-bipyridine, x = 1-3) as mediators with the quinone moieties being the active component. The efficiency of the mediators increased with increasing number of phendione ligands.     

Pseudo-binary system Bi2O3-TeO2 in air

The phase equilibria in the pseudo-binary system Bi₂O₃-TeO₂ at 600° 950° C in air were examined by solid-state reaction techniques and X-ray powder diffraction method. Four pseudo-binary compounds appeared, i.e., -Bi₂O₃ type solid solution having a compositional range of (1-x)Bi₂O₃·xTeO₂ wherex=0 0.4 a new compound Bi₆Te₂O₁₅ which has an orthorhombic cell of a=2.27(4) nm, b=1.06(1) nm and c = 0.539(8) nm, 2Bi₂O₃ · 3TeO₂, and an unidentified phase Bi₂O₃·2TeO₂. The formation of the phase Bi₆Te₂O₁₅, in which all the Te ions are hexavalent, was confirmed by the thermogravimetry and by the Mössbauer spectra. The liquidus curves for whole system were determined by DTA method.     

CeO2-Cu2O composite nanofibers: Synthesis,characterization photocatalytic and electrochemical application

The present study describes fabrication and electrochemical classification of one-dimensional CeO₂-Cu₂O nanofibers for photocatalysis and supercapacitor application. The utilized CeO₂-Cu₂O composite was prepared by sol–gel electrospinning method using Polyvinylpyrrolidone (PVP), Ce(NO₃)₃?6H₂O and Cu(CH₃COO)₂ as precursors. The physicochemical properties of the synthesized samples were characterized using special characterization approaches such as X-ray diffractometer (XRD), energy dispersive X-ray analysis (EDX), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). As compared to pristine CeO₂, the UV–vis spectrum of CeO₂-Cu₂O composite exhibited the absorption peak which shifted to higher wavelength. The photocatalytic activity results indicated the substantial degradation of MB dye by ～92% over the surface of CeO₂-Cu₂O nanocomposite catalyst under visible light illumination. The CeO₂-Cu₂O composite possessed higher photocatalytic activity and electrochemical capacitance than the pristine samples as supercapacitor electrode materials. The CeO₂-Cu₂O composite exhibits a specific capacitance of 329.64 F g^?1 at 5 mV s^?1, which is higher than that of the pristine CeO₂ (192.5 F g^?1) nanofibers. These results suggest the applicability of fabricated composite nanofibers as visible light active photocatalyst and as electrode material for supercapacitors.     

Fabrication and electrochemical characterization of HRP-lipid Langmuir-Blodgett film and its application as an H2O2 biosensor

The formation of horseradish peroxidase-lipid Langmuir-Blodgett film and its applicability as a biosensor have been studied. HRP was spread directly onto the subphase covered with a layer of lipid in LB trough. Our experimental results showed that surface pressure of this film from liquid to solid state ranged between 15 to 25 mN/m. At surface pressure of 25 mN/m, the monolayer was successfully transferred onto the gold surface. In addition, electrochemical properties of this film showed that protein molecules still kept their natural structure and can give a well electrocatalytic activity to H₂O₂. As an H₂O₂ biosensor, this LB film was able to detect concentration of H₂O₂ which were 3 × 10^− 7 M.     

Genetically engineered pfabA pfabR bacteria: an electrochemical whole cell biosensor for detection of water toxicity

We describe here a bacterial sensor for electrochemical detection of toxic chemicals. The sensor constitutes recombinant bacteria harboring plasmids encoding the fabA and fabR genes and has high-resolution amperometric response to membrane-damaging chemicals. For example, it can detect phenol at concentrations ranging between 1.6 and 16 ppm within 20 min. The high sensitivity is achieved by using the fabA promoter fused to a reporter gene-encoded beta-galactosidase on a low copy number plasmid, under the control of the FabR repressor. The use of electrochemical whole cell sensors enables sensitive, fast, easy to operate, and cost-effective detection of water toxicity threats.     

N2O removal in N2 or air by ArF excimer laser photolysis at atmospheric pressure

A photochemical process is proposed as a new efficient N(2)O removal technique in N(2) or air at atmospheric pressure and room temperature without using any catalysts. N(2)O diluted in N(2) or air was decomposed into N(2), O(2), and NO by using a 193 nm ArF excimer laser. The maximum conversion of N(2)O in N(2)O/N(2) or N(2)O/N(2)/O(2) mixtures was 93% at a laser power of 136 mJ, a repetition frequency of 5 Hz, and an irradiation time of 30 min. The formation ratios of N(2):O(2):NO in N(2)O/N(2) and N(2)O/N(2)/O(2) mixtures were 64:31:5.1% and 60:27:13%, respectively. The decomposition mechanism of N(2)O under 193 nm photolysis was discussed by comparing experimental data with calculated model using known photochemical and gas kinetic data.     

Investigations on the MnO2-Fe2O3 system roasted in air atmosphere

Solid-state reaction method is a common and effective technique to synthesize ferrites. This work investigated the phase transformation of MnO₂ and Fe₂O₃ system roasted at 500–1400 °C in air atmosphere to understand the formation process of manganese ferrite. The results showed that the formation of manganese ferrite (Mn_xFe_3?xO₄) was derived from the reaction between Fe₂O₃ and Mn₃O₄ (the decomposition product of MnO₂). Below 900 °C, MnO₂ firstly decomposed to Mn₂O₃ and then to Mn₃O₄, and Fe₂O₃ was seldom reacted with Mn₂O₃ and Mn₃O₄. When the temperature went up to 1000 °C, Fe₂O₃ easily reacted with Mn₃O₄ to generate manganese ferrite. The reaction degree was enhanced dramatically with the rising of temperature. Moreover, the x value in the Mn_xFe_3?xO₄ increased from 0 to 1 from 900 °C to 1400 °C. In other words, the higher the temperature was, the closer the Mn_xFe_3?xO₄ was to MnFe₂O₄. Thermodynamic analysis of MnO₂-Fe₂O₃ system under different O₂ partial pressures was carried out to further explain the formation mechanism.     

Structural and electrochemical investigation of novel hybridized MnO2/V2O5 nanocomposites prepared by one-step microwave-assisted method for electrochemical supercapacitor application

Journal of Materials Science: Materials in Electronics - Pure V2O5 and MnO2/V2O5 hybrid nanocomposites were synthesized by microwave-assisted method for electrochemical supercapacitor application....     

Facile synthesis of Au-nanoparticle/polyoxometalate/graphene tricomponent nanohybrids: an enzyme-free electrochemical biosensor for hydrogen peroxide

A green, facile, one-pot synthesis of well-defined Au NPs@POM-GNSs tricomponent nanohybrids is reported (POM stands for polyoxometalate and GNSs for graphene nanosheets). The synthesis is convenient, rapid and environmentally friendly. The POMs serve as both reducing, encapsulating molecules, and bridging molecules; this avoids the introduction of other organic toxic molecules. Characterization using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy analysis is performed, and the structure of the prepared nanohybrids of Au NPs@POM-GNSs is verified. Most importantly, the amperometric measurements show the Au NPs@POM-GNSs nanohybrids have high catalytic activity with good sensitivity, good long-term stability, wide linear range, low detection limit, and fast response towards H(2)O(2) detection for application as an enzyme-free biosensor. Transformation of the POMs during H(2)O(2) detection does not affect the catalytic activities of the nanohybrids. Thus, the synergistic effect of Au NPs and GNSs in the nanohybrids leads to the enhanced catalytic property.     

Hydrogen substitutes for the in situ generation of H2O2: an application in the Fenton reaction

This study investigates the ability of formic acid, hydrazine and hydroxylamine to act as H₂ substitutes in conducting phenol degradation by Fenton reaction using in situ generated hydrogen peroxide. The processes were performed with semi-heterogeneous (Pd/Al₂O₃ + soluble Fe²⁺) and fully heterogeneous (FePd/Al₂O₃) catalytic systems under ambient conditions. In contrast to bulk H₂O₂ production conditions, hydrazine is able to produce H₂O₂in situ followed by phenol degradation using Pd/Al₂O₃ + Fe²⁺ at pH 3 without the need for halide ions. However, a degree of mineralization exceeding 37% could not be achieved. The significant production of in situ H₂O₂ at the inherent acidic pH of hydroxylammonium sulfate in the presence of Pd/Al₂O₃ + Fe²⁺ was also found to differ from the bulk production of H₂O₂, in which no H₂O₂ was detected. A remarkable degree of mineralization (ca. 65%) as well as fast phenol degradation during the reaction started at pH 7 over FePd/Al₂O₃ may be an advantage of using hydroxylamine. On the other hand, using formic acid, H₂O₂ was produced at a moderate rate, thereby achieving higher efficiency in the mineralization of phenol. Most importantly, the catalysts were more stable in the presence of formic acid than hydrazine or hydroxylamine.     

Amplification of amperometric biosensor responses by electrochemical substrate recycling. 3. Theoretical and experimental study of the phenol-polyphenol oxidase system immobilized in Laponite hydrogels and layer-by-layer self-assembled structures

The amperometric response toward phenol of PPO-based rotating disk bioelectrodes is analyzed on the basis of a kinetic model taking into account internal and external mass transport effects and a CEC' electroenzymatic mechanism. Monophenolase activity of PPO catalyses the oxidation of phenol to o-quinone (step C). o-Quinone can then enter an amplification recycling process involving electrochemical reduction (step E) and enzymatic reoxidation (step C': catecholase activity). The rate-limiting steps such as monophenolase activity, catecholase recycling, permeability of the membrane, and activity and accessibility of the catalytic enzyme sites are theoretically considered and experimentally demonstrated for different electrode configurations including PPO immobilized in Laponite hydrogels and layer-by-layer self-assembled multilayers of PPO and poly(diallyldimethylammonium).     

Detection of approximately 10(3) copies of DNA by an electrochemical enzyme-amplified sandwich assay with ambient O(2) as the substrate

The electrochemical sandwich-type, enzyme-amplified assay of Zhang, Kim, and Heller (Anal. Chem. 2003, 75, 3267-3269) was simplified by replacing the amplifying horseradish peroxidase with bilirubin oxidase (BOD). BOD catalyzes the reduction of ambient O(2) to water and obviates the need for adding H(2)O(2). Femtomolar (10(-)(15) M) concentrations of DNA were detected at a 10-microm-diameter tip of a carbon fiber electrode. Correspondingly, a few thousand copies of DNA were detected in approximately 5-microL samples. The sandwich is formed in an electron-conducting redox hydrogel, to the polymer of which a DNA capture sequence is bound. Capture of the analyte DNA and its hybridization with a BOD-labeled complementary DNA sequence, electrically connects the BOD label to the electron-conducting redox polymer, which is in electrical contact with the electrode. Placing the BOD in contact with the redox polymer thus converts the noncatalytic base layer into a catalyst for the electroreduction of O(2) to water at +0.12 V (vs Ag/AgCl) (Figure 1). In an exemplary assay, approximately 3000 copies of the iron transporting sequence of the sit gene of Shigella flexneri were detected without PCR amplification.     

Synthesis of new compounds of the pseudo-ternary system SrO-Bi2O3-TeO2 in air

The phase equilibria of the pseudo-ternary system SrO-Bi₂O₃-TeO₂ at 600 to 850 C were examined in air by solid-state reaction techniques and X-ray powder diffraction. Three pseudo-ternary compounds were found: a hexagonal solid solution Bi₂O₃ · 2xSrO · 5xTeO₂ (x = 0.02 to 0.20,a = 0.394(1) to 0.399(5),c = 1.89(6) to 1.86(7) nm), a rhombohedral phase Bi₄Sr₃Te₅O₁₉ (a = 0.405(2),c = 2.71 (5) nm in hexagonal terms) and a cubic phase Bi₂SrTeO₇ (a = 1.086(9) nm). The Mössbauer spectra of¹²⁵Te in the compounds indicated that the tellurium atoms were mostly in the state of Te⁺⁴ in the former two compounds but were exclusively Te⁺⁶ in Bi₂SrTeO₇. The electrical conductivity of the first two were about 10^–2–1 cm^–1 at 600 C. However, Bi₂SrTeO₇ was an electrical insulator.     

A multi-criteria analysis for an internet of things application recommendation system

Various internet of things applications are available that cover every aspect of daily life and users can subscribe to numerous IoT applications. Selecting the most suitable IoT applications for individual users is a critical challenge. This study aims to solve this challenge by proposing recommendation system using a hybrid multicriteria decision-making approach based on the analytical hierarchy process and simple additive weight methods. Based on the opinions and preferences of experts, the model and the hierarchy were designed to assess and compare three crucial criteria, namely smart objects, applications, and providers. The results show that applications criterion is more important for users than the other two criteria. In specific, privacy, reliability, and availability are crucial criteria for IoT applications.     

以PR方程为基础的氧—氮—氩系统气液平衡计算及在空分操作中应用

综合分析了多组分相平衡理论特点,介绍利用Peng—Robinson(PR)立方型状态方程进行氧—氮—氩系统气液平衡计算的方法(泡点、露点和闪蒸计算),对该计算方法的准确性进行分析和验证,并举例分析了空分设备的运行工况。     

Different types of MnO2 recovered from spent LiMn2O4 batteries and their application in electrochemical capacitors

Three types (λ, γ, and β) of MnO₂ have been successfully prepared from spent LiMn₂O₄ electrode materials and utilized as electrode materials for electrochemical capacitors. Experiments show that the obtained λ-MnO₂ sample has particle sizes ranging from 0.2 to 3 μm and the as-prepared β-MnO₂ and γ-MnO₂ samples both exist in nanorods with diameters of about 100 nm. The length of β-MnO₂ nanorods varies from 0.2 to 3 μm, while γ-MnO₂ nanorods have lengths of 0.2–2 μm. The main results of electrochemical tests indicate that these MnO₂ electrodes exhibit good supercapacitive performances which are dependent on their morphology and microstructure. As electrode material, λ-MnO₂ sample presents a specific capacitance of 200.55 F g^?1, which is higher than those of other two types of MnO₂. However, β-MnO₂ electrode shows superior long-term cyclic stability and rate performance to other two MnO₂ samples. These results indicate that manganese dioxides recycled from spent LiMn₂O₄ batteries show great potential in application as the active materials for electrochemical capacitors. This study could provide a novel and useful approach to the recovery and reuse of spent LiMn₂O₄ batteries.