Simultaneous determination of epinephrine and ascorbic acid at the electrochemical sensor of triazole SAM modified gold electrode

The electrochemical sensor of triazole (TA) self-assembled monolayer (SAM) modified gold electrode (TA SAM/Au) was fabricated. The electrochemical behaviors of epinephrine (EP) at TA SAM/Au have been studied. The TA SAM/Au shows an excellent electrocatalytic activity for the oxidation of EP and accelerates electron transfer rate. The diffusion coefficient is 1.135 × 10⁻⁶ cm² s⁻¹. Under the optimum experiment conditions (i.e. 0.1 mol L⁻¹, pH 4.4, sodium borate buffer, accumulation time: 180 s, accumulation potential: 0.6 V, scan rate: 0.1 Vs⁻¹), the cathodic peak current of EP versus its concentration has a good linear relation in the ranges of 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol L⁻¹ and 1.0 × 10⁻⁵ to 6.0 × 10⁻⁴ mol L⁻¹ by square wave adsorptive stripping voltammetry (SWASV), with the correlation coefficient of 0.9985 and 0.9996, respectively. Detection limit is down to 1.0 × 10⁻⁸ mol L⁻¹. The TA SAM/Au can be used for the determination of EP in practical injection. Meantime, the oxidative peak potentials of EP and ascorbic acid (AA) are well separated about 200 ± 10 mV at TA SAM/Au, the oxidation peak current increases approximately linearly with increasing concentration of both EP and AA in the concentration range of 2.0 × 10⁻⁵ to 1.6 × 10⁻⁴ mol L⁻¹. It can be used for simultaneous determination of EP and AA.     

Perchlorate-selective polymeric membrane electrode based on a cobaloxime as a suitable carrier

A cobaloxime ([chlorobis(dimethylglyoximeato)(triphenylphosphine)] cobalt (III), [Co(dmgH)₂pph₃Cl]) incorporated in a plasticized poly(vinyl chloride) membrane was used to develop a perchlorate-selective electrode. The influence of membrane composition on the electrode response was studied. The electrode exhibits a Nernstian response over the perchlorate concentration range 1.0 × 10⁻⁶ to 1 × 10⁻¹ mol l⁻¹ with a slope of −56.8 ± 0.7 mV per decade of concentration, a detection limit of 8.3 × 10⁻⁷, a wide working pH range (3–10) and a fast response time (<15 s). The electrode shows excellent selectivity towards perchlorate with respect to many common anions. The electrode was used to determine perchlorate in water and human urine.     

Tuning the push–pull configuration for efficient second-order nonlinear optical properties in some chalcone derivatives

Using the density functional theory methods, we effectively tune the second-order nonlinear optical (NLO) properties in some chalcone derivatives. Various unique push–pull configurations are used to efficiently enhance the intramolecular charge transfer process over the designed derivatives, which result in significantly larger amplitudes of the first hyperpolarizability as compared to their parent molecule. The ground state molecular geometries have been optimized using B3LYP/6-311G** level of theory. A variety of methods including B3LYP, CAM-B3LYP, PBE0, M06, BHandHLYP and MP2 are tested with 6-311G** basis set to calculate the first hyperpolarizability of parent system 1. The results of M06 are found closer to highly correlated MP2 method, which has been selected to calculate static and frequency dependent first hyperpolarizability amplitudes of all selected systems. At M06/6-311G** level of theory, the permanent electronic dipole moment (μ_tot), polarizability (α₀) and static first hyperpolarizability (β_tot) amplitudes for parent system 1 are found to be 5.139 Debye, 274 a. u. and 24.22 × 10⁻³⁰ esu, respectively. These amplitudes have been significantly enhanced in designed derivatives 2 and 3. More importantly, the (β_tot) amplitudes of systems 2 and 3 mount to 75.78 × 10⁻³⁰ and 128.51 × 10⁻³⁰ esu, respectively, which are about 3 times and 5 times larger than that of their parent system 1. Additionally, we have extended the structure-NLO property relationship to several newly synthesized chalcone derivatives. Interestingly, the amplitudes of dynamic frequency dependent hyperpolarizability μβ_ω (SHG) are also significantly larger having values of 366.72 × 10⁻⁴⁸, 856.32 × 10⁻⁴⁸ and 1913.46 × 10⁻⁴⁸ esu for systems 1–3, respectively, at 1400 nm of incident laser wavelength. The dispersion behavior over a wide range of change in wavelength has also been studied adopting a range of wavelength from 1907 to 544 nm. Thus, the present work realizes the potential of designed derivatives as efficient NLO-phores for modern NLO applications.     

Gaseous phase above Ru–O system: A thermodynamic data assessment

The present study is a critical assessment of thermochemical data for gaseous ruthenium oxides based on available experimental data. A full critical analysis and a reinterpretation of data are presented with a proposition for new accurate standard formation enthalpies values: Δ_f H°₂₉₈(RuO₄, g) = −197.6 ± 5.5 kJ mol⁻¹, Δ_f H°₂₉₈(RuO₃, g) = −53.0 ± 10 kJ mol⁻¹, Δ_f H°₂₉₈(RuO₂, g) = 158 ± 20 kJ mol⁻¹ and Δ_f H°₂₉₈(RuO, g) = 301 ± 28 kJ mol⁻¹.     

Theoretical studies on kinetics,mechanism and thermochemistry of gas-phase reactions of HFE-449mec-f with OH radicals and Cl atom

A theoretical study on the mechanism and kinetics of the gas phase reactions of CF₃CHFCF₂OCH₂CF₃ (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid modern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF₃CHFCF₂OCH₂CF₃ and the most stable one is considered for detailed study. Reaction profiles for OH-initiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH₂ group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for CH bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–450 K. The calculated rate constant values are found to be 9.10 × 10⁻¹⁵ and 4.77 × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹ for reactions with OH radicals and Cl atom, respectively. At 298 K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years.     

Electrochemical determination of ascorbic acid in fruits on a vanadium oxide polypropylene carbonate modified electrode

A novel vanadium oxide polypropylene carbonate modified glassy carbon electrode was developed and used for the measurement of ascorbic acid (AA). The electrode was prepared by casting a mixture of vanadium tri(isopropoxide) oxide (VO(OC₃H₇)₃) and poly(propylene carbonate) (PPC) onto the surface of a glassy carbon electrode. The electrochemical behavior of the VO(OC₃H₇)₃–PPC film modified glassy carbon electrode was investigated by cyclic voltammetry and amperometry. This modified electrode exhibited electrocatalytic response to the oxidation of ascorbic acid. Compared with a bare glassy carbon electrode, the modified electrode exhibits a 220 mV shift of the oxidation potential of ascorbic acid in the cathodic direction and a marked enhancement of the current response. The response current revealed a good linear relationship with the concentration of ascorbic acid in the range of 4 × 10⁻⁸ and 1 × 10⁻⁴ mol L⁻¹ and the detection limit of 1.5 × 10⁻⁸ mol L⁻¹ (S/N = 3) in the pH 8.06 Britton–Robinson solution. Quantitative recovery of the ascorbic acid in synthetic samples has been obtained and the interferences from different species have been studied. The method has been successfully applied to the determination of ascorbic acid in fruits. The concentrations of ascorbic acid measured by this method are in good agreement with the literature value. It is much promising for the modified films to be used as an electrochemical sensor for the detection of ascorbic acid.     

Performance enhancement of solution-processed amorphous WZTO TFT with HAO gate dielectric via power ultrasound technology

In this paper, power ultrasound technology (PUT) is employed to prepare the high-k hafnium-aluminum oxide (HAO) dielectric and thin film transistor (TFT). The continuous propagation of high-intensity ultrasonic waves in the metal oxide precursor solution can improve the dissolution efficiency of the solute and speed up the formation of the HAO precursor solution. The prepared HAO films have a smooth surface roughness of 0.36 nm and high optical transmittance of 85 %. Moreover, HAO films obtain excellent electrical properties with a relative permittivity of 15.9 and a leakage current density of 9.1 × 10⁻⁸ A/cm² at 2 MV/cm as well. Finally, we successfully fabricate TFT with HAO dielectric using PUT, these TFTs exhibit switch characteristics with field effect mobility of 18.7 cm²v⁻¹s⁻¹, threshold voltage (V_th) of −0.47 V, and Vth shift of 0.35 V under positive gate bias stress. The results show that the PUT is a promising method that can remarkably decrease the preparation time of the precursor solution and improve the TFT performance.     

Flow-injection determination of iron(III) in soil by biamperometry using two independent redox couples

A flow-injection biamperometric method for the determination of iron(III) has been described. The detector consists of two chambers separated by a salt bridge, and one platinum wire working electrode is embedded in each chamber, respectively. When iron(III) solution and hydrogen peroxide solution simultaneously flow through two chambers, the reduction of iron(III) at one platinum electrode is associated with the oxidation of hydrogen peroxide at the other platinum electrode, forming such a system as similar to a reversible couple one. The biamperometric system can perform the determination of iron(III) without any external potential difference. The linear relationship is obtained from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol l⁻¹ with a detection limit of 6.0 × 10⁻⁷ mol l⁻¹. The proposed method exhibits the satisfactory reproducibility with a relative standard derivation (R.S.D.) of 1.4% for 17 successive determinations of 2.0 × 10⁻⁵ mol l⁻¹ iron(III) and is applied to the determination of iron(III) in soil.     

Enhanced electrophoresis separation of non-electroactive amino acids on poly(dimethylsiloxane) microchip coupled with direct electrochemical detection on a copper electrode

Electrochemical determination of amino acids on a Cu electrode was established as an attractive scheme for non-electroactive amino acids after microchip electrophoresis separation. Five amino acids (arginine, proline, histidine, valine, and serine) achieved efficient separation within 60 s on a titanium dioxide nanoparticles (TiO₂ NPs) coated poly(dimethylsiloxane) (PDMS) microchip, and then successfully detected on a Cu electrode in end-channel detection mode. In the slightly basic borate medium, anodic currents occur for amino acids due to their ability to form Cu(II) complexes and thereby enhance the electrochemical dissolution of Cu electrode substrate. The increase of the anodic current measured is proportional to the amino acid concentration added to the solution, and therefore, enables direct detection of non-electroactive amino acids on the Cu electrode. The detection limits (S/N = 3) for arginine, proline, histidine, valine, and serine were measured to be 7, 6, 5, 6, and 5 μM, respectively, with the linear ranges all from 25 to 500 μM. In addition, compared with the native PDMS microchip, resolutions and separation efficiencies of amino acids on the modified microchip were considerably enhanced with the theoretical plate numbers of 8.9 × 10³, 6.6 × 10⁴, 4.8 × 10⁴, 5.6 × 10⁴, and 4.4 × 10⁴ plates m⁻¹, respectively. The proposed Cu electrode response demonstrated good reproducibility and stability, with no apparent loss of response for periods as long as 4 weeks.     

Evaluation of response characteristics of resistive oxygen sensors based on porous cerium oxide thick film using pressure modulation method

In order to reduce the response time of resistive oxygen sensors using porous cerium oxide thick film, it is important to ascertain the factors controlling response. Pressure modulation method (PMM) was used to find the rate-limiting step of sensor response. This useful method measures the amplitude of sensor output (H(f)) for the sine wave modulation of oxygen partial pressure at constant frequency (f). In PMM, “break” response time, which is minimum period in which the sensor responds precisely, can be measured. Three points were examined: (1) simulated calculations of PMM were carried out using a model of porous thick film in which spherical particles are connected in a three-dimensional network; (2) sensor response speed was experimentally measured using PMM; and (3) the diffusion coefficient and surface reaction coefficient were estimated by comparison between experiment and calculation. The plot of log f versus log H(f) in the high f region was found to have a slope of approximately −0.5 for both porous thick film and non-porous thin film, when the rate-limiting step was diffusion. Calculations showed the response time of porous thick film was 1/20 that of non-porous thin film when the grain diameter of the porous thick film was the same as the thickness of non-porous thin film. At 973 K, “break” response time (t_b) of the resistive oxygen sensor was found by experiment to be 109 ms. It was concluded that the response of the resistive oxygen sensor prepared in this study was strongly controlled by diffusion at 923–1023 K, since the experiment revealed that the slope of plot of log f versus log H(f) in the high f region was approximately −0.5. At 923–1023 K, the diffusion coefficient of oxygen vacancy in porous ceria (D_V) was expressed as follows: D_V (m²s⁻¹) = 5.78 × 10⁻⁴ exp(−1.94 eV/kT). At 1023 K, the surface reaction coefficient (K) was found to exceed 10⁻⁴ m/s.     

Design and simulation of pyroelectric detectors with nanometer size spider-web for low thermal conductance

We report the design and simulation of uncooled pyroelectric detectors which utilizes a nanometer sized mesh or truss to support the suspended detector. Pyroelectric detector is a class of thermal detector in which the change in temperature causes the change in the spontaneous polarization in the sensing material. Ca modified lead titanate (PCT) was selected as the thermometer in the detector because of its high pyroelectric figure of merit. The design and simulation of pyroelectric detectors have been conducted by simulating the structure with Intellisuite™. Finite element method (FEM) was used to simulate the structural and thermal properties of the device. The simulated detectors had a spider web-like structure with each of the strut (ring) of spider web had a width of 100 nm. In the design, the pyroelectric detectors utilized Ni_0.8Cr_0.2 absorber, PCT sensing layer, Ti electrodes, Al₂O₃ structural layer to obtain low thermal conductance between the detector and Si substrate. Three different types of pyroelectric detectors were designed and analyzed. The first design had linear electrode and simple spider web support. The value of the thermal conductance of this detector was found to be 3.98 × 10⁻⁸ W/K. The second design had a longer thermal path than the first one and the thermal conductivity of this device was found to be 2.41 × 10⁻⁸ W/K. High detectivity was obtained by reducing the thermal conductance between the sensing layer and the substrate or the heat sink in the third design. The design was optimized for the best result by modifying the shape, dimension and thickness of various layers namely absorber, electrodes, sensing layer, and struts. The thermal conductance between the sensor and the substrate using the third design was found to be as low as 4.57 × 10⁻⁹ W/K which is significantly lower than previously reported values. The thicknesses of the web structure, web support, electrodes, sensing layer, and absorber of the final structure were 2, 1, 0.5, 2, and 0.2 µm respectively for this value of thermal conductance. The absorber diameter was 50 µm and the diameter of the spider web was 200 µm. A total of 80 struts with 100 nm width were used in the design.

     

A vertical structure photodetector based on all‐inorganic perovskite quantum dots

In this work, the vertical structure photodetector based on CsPbBr₃ quantum dots (QDs) with a structure of indium tin oxide (ITO)/zinc oxide (ZnO)/CsPbBr₃ QDs/Au is reported. In this device, CsPbBr₃ QDs film works as the light‐harvesting layer, and ZnO QDs film acts as the electron transport channel, which can extract the electron efficiently and improve the quality of CsPbBr₃ QDs film. As a result, the on/off ratio, detectivity and rise time (decay time) of CsPbBr₃/ZnO hybrid photodetector are measured to be 2.4 × 10⁶, 2.25 × 10¹¹, and 62 milliseconds (82 ms) under 0‐V bias. This work inspires the development of vertical structure photodetectors based on the all‐inorganic perovskite QDs.     

Chromium(III)-selective sensor based on tri-o-thymotide in PVC matrix

Tri-o-thymotide (I) has been used as an electroactive material in PVC (poly(vinyl chloride)) matrix for fabrication of chromium(III)-selective sensor. The membrane containing tri-o-thymotide, sodium tetraphenyl borate (NaTPB), dibutyl phthalate (DBP) and PVC in the optimum ratio 5:1:75:100 (w/w) exhibits a working concentration range of 4.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a Nernstian slope of 20.0 ± 0.1 mV/decade of activity in the pH range of 2.8–5.1. The detection limit of this sensor is 2.0 × 10⁻⁷ M. The electrode exhibits a fast response time of 15 s, shows good selectivity towards Cr³⁺ over a number of mono-, bi- and trivalent cations and can also be used in partially non-aqueous medium (up to 15%, v/v) also. The assembly has been successfully used as an indicator electrode in the potentiometric titration of chromium(III) against EDTA and also to determine Cr(III) quantitatively in electroplating industry waste samples.     

First-order piezoresistance coefficients in heavily doped p-type silicon crystals

The first-order piezoresistance coefficients π₁₁, π₁₂, π₄₄ were calculated for heavily doped p-type silicon crystals. The analytical calculation was carried out within the framework of the three-band model taking into account effect of anisotropy and influence of the spin-orbit split-off band (here the SO band) on shape of heavy and light hole bands as well as direct contribution of the SO band into magnitude of the piezoresistance coefficients. The letter is negligible for shear piezoresistance coefficient π₄₄ but for values of piezoresistance coefficients π₁₁ and π₁₂ its contribution reaches 30%. In correspondence with experimental data the calculated values of piezoresistance coefficients π₁₁ and π₁₂ have opposite signs for scattering by acoustic phonons or by ionized impurities.There is a good agreement between our numerical results (for scattering by ionized impurities) and experimental data for shear piezoresistance coefficient π₄₄ at temperatures 190–375 K. It has been obtained in wide range of impurity concentrations (5 × 10¹⁹–2 × 10²¹ cm⁻³).     

Bulk-modified amperometric biosensors for hypoxanthine based on sol–gel technique

Graphite–ceramic amperometric biosensors for hypoxanthine (Hx) have been fabricated and applied to the measurement of fish meat quality. The fabrication process involves the immobilization of xanthine oxidase in the bulk of a silica-graphite matrix by sol–gel techniques and the assembly of the enzyme-modified matrix into a glass tube to form a disk electrode whose surface can be easily renewed by simple mechanical polishing. Michaelis–Menten constants (K_m^app) of 0.45, 0.64, 0.35 mM were determined from three different types of Hx sensors operating in the unmediated hydrogen peroxide oxidation mode, the unmediated and the benzyl viologen-mediated oxygen reduction modes, respectively. The sensors delivered good linear response over a wide range of concentrations of ca. 1×10⁻⁶–1×10⁻³ M, with respective detection limits of 1.3×10⁻⁶, 5.6×10⁻⁶and 3.8×10⁻⁷ M in 0.05 M phosphate buffer (pH 7.6). The use of bulk immobilization and the possibility of renewable surfaces have enabled the easy operation of these sensors with high stability. Satisfactory results were obtained from the determination of the freshness of carp tissues stored under different conditions.     

Persistence of turbulent flow in microchannels at very low Reynolds numbers

A fully resolved numerical simulation of a turbulent microchannel flow, with uniformly spaced two-dimensional obstruction elements mounted at the wall and normal to the flow direction, was carried out at a very low Reynolds number of Re ≃ 970 based on the centerline velocity and the microchannel height. Employing the lattice Boltzmann numerical technique, all energetic scales of turbulence were resolved with about 19 × 10⁶ grid points (1261 × 129 × 128 in the x ₁, x ₂, and x ₃ directions). The simulated results confirm the self-maintenance of turbulence at such a low Reynolds number. Turbulence persisted over more than 1,000 turnover times, which was sufficiently long to prove its self-maintenance. These findings support the conjecture that turbulence developing in microchannels having rough walls can not only be initiated but also maintained at very low Reynolds numbers.     

Fabrication of microfluidic devices for packaging CMOS MEMS impedance sensors

This work presents a polydimethylsiloxane (PDMS) microfluidic device for packaging CMOS MEMS impedance sensors. The wrinkle electrodes are fabricated on PDMS substrates to ensure a connection between the pads of the sensor and the impedance instrument. The PDMS device can tolerate an injection speed of 27.12 ml/h supplied by a pump. The corresponding pressure is 643.35 Pa. The bonding strength of the device is 32.44 g/mm². In order to demonstrate the feasibility of the device, the short circuit test and impedance measurements for air, de-ionized water, phosphate buffered saline (PBS) at four concentrations (1, 2 × 10⁻⁴, 1 × 10⁻⁴, and 6.7 × 10⁻⁵ M) were performed. The experimental results show that the developed device integrated with a sensor can differentiate various samples.     

Thermodynamic assessment of RuO4 oxide

RuO₄ oxide appears much less stable than RuO₂(s) in the Ru–O binary system with a melting point close to room temperature and a certain propensity to vaporize or decompose at low temperatures. Ab initio simulations in the framework of density functional theory (DFT) on RuO₄(s) are performed to analyze the cubic and monoclinic structures and to evaluate the heat capacities at low temperatures. Then, a critical evaluation of thermodynamic data from calorimetry and vapor pressure determinations - was carried out coupled with ab-initio calculations to propose new thermodynamic data: the entropy.S° (RuO_4, s, cubic, 298K) = 132.7 J·K⁻¹mol⁻¹ and formation enthalpy.Δ_fH° (RuO₄, s, cubic, 298K) = −252.4 ± 5.5 kJ mol⁻¹.     

Milk-sense: a volatile sensing system recognises spoilage bacteria and yeasts in milk

An electronic nose unit including 14 conducting polymer sensors, was used to detect the volatile profiles produced by uninoculated skimmed milk media or that inoculated with bacteria (Pseudomonas aureofaciens, P. fluorescens, Bacillus cereus) or yeasts (Candida pseudotropicalis, Kluyveromyces lactis) when grown for 5 h at 30°C. Using discriminant function analyses (DFA) it was possible to separate unspoiled milk and that containing spoilage bacteria or yeasts. The sensor array used was a useful discriminator of microbial volatile profiles. Quantitative differentiation between three different concentrations of P. aureofaciens (10⁶, 3.5×10⁸, 8×10⁸ CFUs ml⁻¹) was also investigated and showed that the system could effectively differentiate between treatments. Using an initial inoculum of about 10³–10⁴ CFUs ml⁻¹ it was possible to discriminate between unspoiled milk, yeasts and bacterial species (S. aureus, B. cereus and the Pseudomonas spp.) using principal component analyses (PCA), and also between the bacteria, the unspoiled milk, and the two yeasts C. pseudotropicalis and K. lactis with 85% of the data accounted for. The potential for differentiation between four of the five individual bacterial and yeast species was analysed after 5 h growth at 25°C by using a three-layer back propagation neural network (NN) of 46 input sensor parameters. This showed that it was possible to recognise, and differentiate, between species, the butanol and milk medium controls. Cross validation using labelled individual replicates of treatments as unknowns demonstrated that it was possible to differentiate between (a) butanol controls; (b) unspoiled milk medium; (c) S. aureus; (d) K. lactis; (e) C. psuedotropicalis; and (f) B. cereus. The potential for using an electronic nose system for early detection of microbial spoilage of milk-based products is discussed.     

Design,simulation and validation of a novel uncooled infrared focal plane array

This paper describes a novel single-layer bi-material cantilever microstructure without silicon (Si) substrate for focal plane array (FPA) application in uncooled optomechanical infrared imaging system (UOIIS). The UOIIS, responding to the radiate infrared (IR) source with spectral range from 8 to 14 μm, may receive an IR image through visible optical readout method. The temperature distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array, which is consisted of two materials with mismatching thermal expansion coefficients. In order to obtain a high detection to the IR object, gold (Au) film is coated alternately on silicon nitride (SiN_x) film in the flection beams of the cantilevers. And a thermal–mechanical model for such cantilever microstructure is proposed. The thermal and thermal–mechanical coupling field characteristics of the cantilever array structure are optimized through numerical analysis method and simulated by using the finite element simulation method. The thermal–mechanical rotation angle simulated and thermal–mechanical sensitivity tested in the experiment are 2.459 × 10⁻³ and 3.322 × 10⁻⁴ rad/K, respectively, generally in good agreement with what the thermal–mechanical model and numerical analysis forecast, which offers an effective reference for FPA structure parameters design in UOIIS.