Redox coenzyme functionalization of electrochemically grown Prussian blue films

Thin solid films of the molecular semiconductor rubidium Prussian blue, RbFe₂(CN)₆, are electrochemically deposited on quartz-crystal microbalance electrodes. The films are found to surface-coordinate tightly both the oxidized and reduced forms of the redox coenzyme nicotinamide adanine dinucleotide (NAD⁺), presumably via the diphosphate linkage. Gravimetric and electrode potential measurements provide evidence that the surface-bound NAD⁺ can act as an electron-transfer mediator from solution to the Prussian blue. The electron transfer appears to result from an inner-sphere mechanism between NADH and Fe₂(CN)₆⁻; unbound NADH in solution does not reduce the Prussian blue films. Conversion of surface-bound NAD⁺ to NADH can be enacted enzymatically, with subsequent electron transfer regenerating NAD⁺. The semiconductive properties of the film transport surface electrons to the bulk, enabling near-quantitative reduction, with the bound coenzyme acting catalytically as an electron-transfer mediator. The potential application of these coenzyme-functionalized molecular semiconductor films to the area of biosensing is explored.     

Electrocatalytic oxidation of methanol and other short chain aliphatic alcohols on glassy carbon electrodes modified with conductive films derived from Ni-(N,N′-bis(2,5-dihydroxybenzylidene)-1,2-diaminobenzene)

Complexes of nickel(II) with the ligand N,N′-bis(2,5-dihydroxybenzylidene)-1,2-diaminobenzene (Ni^II-DHS) can be electropolymerized onto glassy carbon surfaces in alkaline solution to give electroactive films strongly adhered on the electrode surface. In alkaline solution, these poly-[Ni^II-DHS]/GC films present the typical voltammetric response of a surface-immobilized redox couple, as can be anticipated for the Ni²⁺/Ni³⁺ transitions into the film. In addition, the films exhibit a potent and persistent electrocatalytic activity towards the oxidation of methanol. The electrocatalytic currents are, at least, 80 times higher than those obtained for the oxidation of methanol at electrodes modified with nickel hydroxide films in alkaline solutions. In addition, the current is proportional to the concentration of methanol from 0.050 to 0.30 μM. The detection limit and the sensitivity were found to be 26 ± 2 nM and 7.4 × 10⁻² ± 6 × 10⁻³ A cm² mol⁻¹ M⁻¹, respectively. Electrodes modified with poly-[Ni^II-DHS]/GC films show a moderate electrocatalytic activity towards the oxidation of other aliphatic short chain alcohols, such as: ethanol, 1-propanol, 2-propanol and n-butanol. In all cases the catalytic currents present linear dependences with the concentration of alcohol in alkaline solution. The analytical properties of these potential alcohol sensors have also been studied.     

Humidity sensing properties of Nation and sol-gel derived SiO2/Nafion composite thin films

Nafion, sol-gel derived SiO₂ and SiO₂/Nafion composite films were prepared through casting and dip-coating methods. Impedance response of the films to relative humidity and the stability of the response against different aging environments were examined. The response to relative humidity of each film was analyzed with their complex impedance spectra at different humidities.     

Gasochromic effect of palladium doped peroxopolytungstic acid films prepared by the sol-gel route

Gasochromic palladium doped peroxopolytungstic acid (Pd:P-PTA) films have been prepared using dip-coating deposition from peroxopolytungstic acid (P-PTA) sols into which PdCl₂ was added in molar ratios Pd:W=1:125, 1:100, 1:53, and 1:40. These films exhibit reversible colouring/bleaching changes when exposed to hydrogen or hydrogen/argon mixture (4%) and air, alternatively. Gasochromically coloured and bleached films were characterised using in-situ Fourier transform infrared (FT-IR) spectroscopy. The vibrational modes of as-deposited, coloured and bleached films were assigned and the polaron absorption, which characterises the IR spectra of coloured films, was detected. Colouring/bleaching kinetics of films exposed to H₂ and H₂/Ar mixture as a function of the concentration of the catalyst and temperature of heat-treatment is reported. Proton (σ_pr) and electronic (σ_el) conductivities determined from impedance spectra revealed an increase in σ_el from 10⁻⁵ S cm⁻¹ in bleached state, to 10⁻³ S cm⁻¹ in coloured state, while σ_pr remained constant (10⁻² S cm⁻¹).     

Simultaneous determination of lead and cadmium at a glassy carbon electrode modified with Langmuir–Blodgett film of p-tert-butylthiacalix[4]arene

A glassy carbon electrode (GCE) modified with a Langmuir–Blodgett (LB) film of p-tert-butylthiacalix[4]arene (TCA) has been investigated as a disposable sensor for measuring the trace levels of lead and cadmium. The possibility of determining lead and cadmium at trace levels was examined with differential pulse stripping voltammetry in the measurement step. The electrochemical response was characterized with respect to supporting electrolyte, pH of solution, accumulation time, accumulation potential, layers of the LB films, and possible interferences. Calibration plots were found to be linear in the range 2 × 10⁻⁷ to 5 × 10⁻⁵ mol l⁻¹ (Cd²⁺) and 1 × 10⁻⁷ to 2.5 × 10⁻⁵ mol l⁻¹ (Pb²⁺); the detection limits were 2 × 10⁻⁸ mol l⁻¹ (Cd²⁺) and 8 × 10⁻⁹ mol l⁻¹ (Pb²⁺). Possible recognition mechanism was also discussed. From the analysis of real samples (river, lake and tap water) it can be concluded that the method is sensitive and reproducible in determining of these elements and can be used in the analysis of natural water samples.     

Electric and ferroelectric properties of PZT/SBT multilayer films prepared by photochemical metal-organic deposition

The electric and ferroelectric properties of lead zirconate titanate and strontium bismuth tantalate multilayer films prepared using photosensitive starting precursors were characterized. The electric and ferroelectric properties were investigated by characterization of the effect of stacking order of four ferroelectric layers of PZT or SBT in the multilayer films of 4-PZT, PZT/2-SBT/PZT, SBT/2-PZT/SBT, and 4-SBT. The P_r value of the 4-SBT multilayer film was relatively small (6 μC/cm²) and a two times higher value (12 μC/cm²) was obtained with the SBT/2-PZT/SBT multilayer film. The films with SBT layers at the top and bottom showed improved leakage current and fatigue resistance compared to the films with PZT layers at the top and bottom. It was revealed that the defect dipole was reduced at the SBT/Pt interface due to a self-regulation layer such as (Bi₂O₂)²⁺ in the SBT film. Also, the bottom layer on the Pt substrate showed a significant influence on the growth orientation of the entire ferroelectric films.     

Coupled phase diagram and thermodynamic analysis of the 18 binary systems formed among Li2Co3, K2Co3,Na2Co3, Lioh, Koh, Naoh, Li2So4, K2So4 and Na2So4

Available phase diagram and thermodynamic data on the eighteen binary systems containing Li⁺ , Na⁺, K⁺, S0₄⁼, CO₃⁼, and OH⁻ have been collected and critically assessed. A set of self-consistent thermodynamic parameters describing the free energies of the compounds, solid solutions, and liquid solutions in the binary systems has been formulated. The phase diagrams have been calculated, and estimated error limits of all diagrams are given.     

Analysis of Parallel Algorithms for Matrix Chain Product and Matrix Powers on Distributed Memory Systems

Given N matrices A₁, A_2,...,A_N of size NtimesN, the matrix chain product problem is to compute A₁timesA₂times...timesA_N. Given an NtimesN matrix A, the matrix powers problem is to calculate the first N powers of A, that is, A, A², A³,..., A^N. We solve the two problems on distributed memory systems (DMSs) with p processors that can support one-to-one communications in T(p) time. Assume that the fastest sequential matrix multiplication algorithm has time complexity O(N^alpha), where the currently best value of a is less than 2.3755. Let p be arbitrarily chosen in the range 1lesplesN^alpha+1/(log N)². We show that the two problems can be solved by a DMS with p processors in T_chain(N,p)=O((N^alpha+1/p)+T(p))((N^2(2+1/alpha/p^2/alpha)(log+p/N)^1-2/alpha+log+((p log N)/N^alpha)) and T_power (N,p)=O(N^alpha+1/p+T(p)((N^2(1+1/alpha)/p^2/alpha)(log+p/2 log N)^1-2/alpha+(log N)²))) times, respectively, where the function log+ is defined as follows: log+ x=log x if xges1 and log+ x=1 if 0相似文献   

Chemical deposition of nanocrystalline nickel oxide from urea containing bath and its use in liquefied petroleum gas sensor

Nanocrystalline nickel oxide (NiO) was deposited onto glass substrates using a chemical deposition method from a bath containing nickel (Ni²⁺) ions and urea at 363 K. The deposition process was based on the reaction between Ni²⁺ and hydroxide ions released from the protolysis of ammonia formed in the decomposition of urea heated at 363 K, which caused to form nickel hydroxide. The structural properties of nickel oxide films were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analyses showed that nanocrystalline nature remained after heating at 523 K for 2 h. Surface morphology of the nickel oxide film showed worm-like mesoporous structure with pore size in a nanometer range. The chemically deposited nickel oxide films were effectively used as a liquefied petroleum gas (LPG) sensor and the maximum response of 36.5% was recorded on exposure to 0.3 vol% of LPG at 698 K.     

Quartic discriminants and tensor invariants

Discusses the calculation of discriminants of polynomials. The discriminant is a function of the coefficients that indicates if the polynomial has any double roots. The discriminant Δ₄ of a homogeneous quartic f(x,w) = Ax⁴+4Bx³w+6Cx² w²+4Dxw³+Ew⁴ = 0 is Δ₄ = 27(I₃)²-(I₂)³, where I₂ = AE-4BD+3C² and I₃ = ACE-AD ²-B²E+2BCD-C³ (this is the Hilbert representation). The author shows how to write the discriminant as a tensor diagram. The discriminant of a polynomial is an example of an invariant quantity. Tensor diagrams are particularly useful to express invariant quantities. Adding a dimension moves us from the world of (1D) homogeneous polynomials to 2D homogeneous (2DH) geometry (curves in the projective plane). It is shown that a relationship exists between the possible root structures of a 4th-order polynomial and the possible degeneracies of a 3rd-order curve     

Gas sensing properties of the composite Langmuir–Blodgett films: effects of the film thickness and the Cd addition into the subphase

It was discovered in the previous studies that the kinetic response of NO sensors based on copper tetra-tert-butyl phthalocyanine (CuTTBPc) Langmuir–Blodgett films (LB films) could be greatly improved if CuTTBPc mixed with arachidic acid (AA) in optimized molar ratios was used instead of the phthalocyanine derivative alone. In this paper we investigate the effects of the film thickness and the ionic content of the subphase on gas-sensitive properties of CuTTBPc:AA (1:1 molar ratio) LB films with respect to NO. It was shown that both the sensitivity and the kinetic response of the LB films were influenced by the Cd²⁺ addition into the subphase. These distinctions, being rather small for the thinnest films, became much more pronounced for thicker ones. If “pure” water was used as a subphase, experimental data could be explained mainly by the gas diffusion into the film bulk whereas the surface adsorption was a predominant process in the case of the Cd²⁺-containing subphase. Obtained results are discussed as regards the sensor performance optimization.     

Study of the potentiometric response towards sodium ions of Na0.44−xMnO2 for the development of selective sodium ion sensors

Single phase Na_0.44MnO₂ powder was synthetized by a classical solid-state reaction. Using a plastic technology, we studied the potentiometric response versus Na⁺ ions in aqueous medium. A Nernstian-like response (55 mV/dec) was obtained for concentrations ranging from 1 M to 2 × 10⁻⁴ M with a quite good selectivity towards Li⁺, K⁺, Mg²⁺ and Ca²⁺. Through an ageing study of this material in aqueous solution, we clearly identified the sensing material as being the Na_0.33MnO₂ phase. Furthermore, we proved that the sensing activity of this compound is routed in its ability to reversibly insert/de-insert Na⁺ ions.     

A gramicidin analogue that exhibits redox potential-dependent cation influx

A synthetic analogue of gramicidin A, gram-2-(nicotinamidyl)ethyl carbamate (gAN) was found to regulate the influx of potassium ions depending on its redox state. At potentials less than −0.52 (±0.05) V, the nicotinamide group in gAN is reduced and allows charge- and size-selective influx of cations. In the oxidised state, charge repulsion between the positively charged nicotinamide group and the cations prevents any influx of cations. Chronoamperometric experiments were conducted to determine permeabilities of Eu³⁺, Tl⁺, K⁺ ions in a BLM porated with gAN. Scanning electrochemical microscopy (SECM) experiments were conducted with two ions: permeant K⁺ ions and the larger (CH₃)₄N⁺ ion which blocks the channel. The switching potential for gAN, at which the channel allows flux monovalent cations, is shown to be potential and pH-dependent and temperature-independent.     

A Method for the Representation, Evaluation and Display of CSG Models in PHIGS and PHIGS+

The Programmer's Hierarchical Interactive Graphics System (PHIGS) is about to become a standard graphics system ^† which caters for the definition, display and modification of two and three-dimensional graphical data.
PHIGS , however, is mainly a wireframe system, and the PHIGS⁺ , extensions to it have been put forward to allow the incorporation of shaded 3D graphics into PHIGS. ,
One area that is important to a large constituency and which has so far not been considered in PHIGS , and PHIGS⁺ , is that of solid modelling. This paper addresses one aspect of solid modelling by describing a simple method for the representation, evaluation and display of Constructive Solid Geometry (CSG) models in PHIGS , and PHIGS⁺. .     

Titania NOx sensors for exhaust monitoring

Oxide semiconductors have been examined to develop NO_x sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al³⁺, Sc³⁺, Ga³⁺ or In³⁺, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NO_x has been fabricated. Many kinds of interference gases, such as C₃H₆, CO and SO₂, have been found to have only a slight influence on the sensor response to NO. The influence of O₂ and H₂O is also negligible, except for the cases of 0% H₂O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases.     

The limitedness problem on distance automata: Hashiguchi''s method revisited

Hashiguchi has studied the limitedness problem of distance automata (DA) in a series of paper [(J. Comput System Sci. 24 (1982) 233; Theoret. Comput. Sci. 72 (1990) 27; Theoret. Comput. Sci. 233 (2000) 19)]. The distance of a DA can be limited or unbounded. Given that the distance of a DA is limited, Hashiguchi has proved in Hashiguchi (2000) that the distance of the automaton is bounded by 2^{4n3+nlg(n+2)+n}, where n is the number of states. In this paper, we study again Hashiguchi's solution to the limitedness problem. We have made a number of simplification and improvement on Hashiguchi's method. We are able to improve the upper bound to 2^{3n3+nlgn+n−1}.     

Inhibitive determination of metal ions by an amperometric glucose oxidase biosensor: Study of the effect of hydrogen peroxide decomposition

An amperometric glucose biosensor based on glucose oxidase immobilized in electrosynthesized poly-o-phenylenediamine was successfully applied to the determination of a wide group of heavy metals of environmental interest. The inhibition effects of Hg²⁺, Ag⁺, Cu²⁺, Cd²⁺, Pb²⁺, Cr³⁺, Fe³⁺, Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺ and also CrO₄²⁻ on glucose oxidase were studied. Collected data showed a reversible inhibition mechanism. Results about the quantitative analysis of metal ions in terms of detection limit, linear range, sensitivity and R.S.D. are discussed for each tested metal ion. The biosensor was able to discriminate two different oxidation states of chromium being able to reject Cr³⁺ and to detect the toxic species CrO₄²⁻. Also biosensor storage stability and response reproducibility were investigated.

Moreover, this study represents the first attempt of evaluating the effect of the hydrogen peroxide decomposition by metal ions on the response of an enzymatic biosensor based on the amperometric detection of the hydrogen peroxide. Experiments were performed with the aim to quantitatively evaluate, for any single metal ion, if this process is competitive with the inhibition of enzymatic reaction in the adopted experimental conditions.     

Bulk-Micromachined Test Structure for Fast and Reliable Determination of the Lateral Thermal Conductivity of Thin Films

A novel bulk-micromachined test structure is presented for the fast and reliable determination of the lateral thermal conductivity of thin films. The device is composed of a heater resistor and thermocouples that are fabricated in polysilicon (poly-Si), and the associated processing and DC measurement procedures are straightforward. The validity of the method is supported by numerical simulations and verified by experimental determination of the lateral thermal conductivity of aluminum (Al), aluminum nitride (AlN), p-doped poly-Si, and silicon nitride (SiN) thin films. For Al, an average value of 217 W m^-1 K^-1 was found for 1-mum thick layers. For the other layers, a number of thicknesses were studied, and the increase of thermal conductivity with thickness was effectively detected: for AlN, values from 7 to 11.5 W m^-1 K^-1 were found, and for p-doped poly-Si, values went from 21 to 46 W m^-1 K^-1 for thicknesses from 0.15 to 1 mum. For SiN, a value of 1.8 was extracted for layers thicker than 0.5 mum.     

Trace detection of nitroaromatic compounds with layer-by-layer assembled {SBA/PSS}n/PDDA modified electrode

The {SBA/PSS}_n/PDDA films modified electrode was prepared by layer-by-layer (LBL) assembly with mesoporous SiO₂ (SBA), poly(sodium 4-styrene-sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) in this paper. SBA is a large pore-size mesoporous material with highly ordered hexagonally arranged mesochannels and high thermal stability etc. The electrochemical characteristics of the {SBA/PSS}_n/PDDA films have been studied by electrochemical impedance spectroscopy in 0.1 M KCl solution containing 5.0 mM Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ at the formal potential of 0.230 V. The ultratrace nitroaromatic compounds (NACs) such as TNT, TNB, DNT and DNB were determined by differential pulse voltammetry (DPV) measurement. The sensitivities for NACs determination with {SBA/PSS}_n/PDDA modified electrode were dependent on the number of layers, pH and ionic strength of electrolyte, based on which a set of optimized conditions for film fabrication was inferred. The current responses were linear with NACs ranging from 10⁻⁹ to 10⁻⁷ mol/l. The results showed that the {SBA/PSS}_n/PDDA modified electrode established a new way for fast, simple and sensitive analysis of NACs.     

Notch Root Oxide Formation During Fatigue of Polycrystalline Silicon Structural Films

This paper investigates the fatigue behavior of n⁺-type 2-mum- thick polycrystalline silicon films that exhibit an initially thin (~2-3 nm) native oxide layer. The testing of kilohertz-frequency resonators provided accurate stress-life fatigue data at 30 and 50% relative humidity (RH) in the low (< 10⁶)and high (up to 10¹¹) cycle regimes. Long fatigue life specimens were associated with larger decreases in the natural frequency of the resonator and very smooth failure origins (at the notch) that encompassed several grains. Additional testing at various humidity levels highlighted the critical influence of humidity on the fatigue damage accumulation rate, which was measured via changes in the natural frequency. Finally, Auger electron spectroscopy (AES) characterized the formation of a nanometer-scale oxygen-rich reaction layer during cyclic loading. Although AES revealed a thin 2-3-nm initial oxide layer on a control specimen, measurements on a long-life fatigued specimen revealed an increased oxygen concentration over the first 10 nm of the material at the notch root. These findings demonstrate that the reaction-layer fatigue mechanism for silicon structural films operates even when reaction layers are initially very thin.