A hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin in Hb–Ag sol films

Hemoglobin (Hb) was used as a template to fabricate hemoglobin–silver (Hb–Ag) sol in which the hemoglobin showed direct electrochemistry on a glass carbon (GC) electrode. Ultraviolet–visible (UV–vis) spectra and reflectance absorption infrared (RAIR) spectra suggested that hemoglobin in Hb–Ag sol retained its native secondary structure. Scanning electron microscopy (SEM) demonstrated that the morphology of the Hb film was much different from the Hb–Ag sol film. The Hb–Ag film proved to exhibit a good electrocatalytic activity for the reduction of hydrogen peroxide. Based on this, a novel amperometric hydrogen peroxide biosensor was developed, which showed a sensitive response to the reduction of H₂O₂ without any electron mediator. Under optimum conditions, the biosensor responded linearly to H₂O₂ in the concentration range of 1 × 10⁻⁶ to 2.5 × 10⁻² M with detection limit of 1 × 10⁻⁷ M at 3σ. Moreover, the studied biosensor exhibited high sensibility, good reproducibility, and long-term stability.     

A wireless, remote-query sensor for real-time detection of Escherichia coli O157:H7 concentrations

This paper describes the real-time detection of Escherichia coli O157:H7 concentrations using a remote-query (wireless, passive) magnetoelastic sensor. The resonance frequency of a liquid immersed magnetoelastic sensor, measured through magnetic field telemetry, changes mainly in response to bacteria adhesion to the sensor and the liquid properties (viscosity, density, elasticity, etc.) of the culture medium. In the described application, during its growth and reproduction we find E. coli consumes nutrients from a liquid culture medium that decreases the solution viscosity, and in turn changes the resonance frequency of the medium-immersed magnetoelastic sensor. Using the described technique we are able to directly quantify E. coli O157:H7 concentrations of 2 × 10² to 3 × 10⁶ cells ml⁻¹, and quantify the effect of gentamycin sulfate injection (GSI) on proliferation of the bacteria. The lack of any physical connections between the sensor and the monitoring electronics facilitates aseptic operation, and makes the sensor platform ideally suited for monitoring bacteria from within, for example, sealed food containers.     

DNA hybridization measurement by self-sensing piezoresistive microcantilevers in CMOS biosensor

Understanding the mechanism of how biological reactions produce mechanical loadings is fundamental to biomedical developments. A CMOS biosensor chip is developed to measure in situ the induced surface stress change by DNA hybridization. For 20-mer thiol-modified single stranded DNA (ssDNA), the mechanism of ssDNA attached to gold surface via a sulfur–gold linkage can be investigated by using the Langmuir adsorption model. Experimental results indicate that the immobilization response is less than 1 s, the total number of ssDNA molecules on the cantilever is about 3 × 10¹¹, and the induced surface stress is 0.15 N/m. The surface stress sensitivity of the sensor is about 3.5 × 10⁻⁵ m/N. The estimated adsorption rate of the ssDNA is 0.005 s⁻¹. The biosensor is capable of discriminating complimentary molecular targets and thus may provide a powerful platform for high throughput real-time analysis of DNA.     

Correctness of concurrent processes

A new notion of correctness for concurrent processes is introduced and investigated. It is a relationship P sat S between process terms P built up from operators of CCS [24], CSP [18] and COSY [20] and logical formulas S specifying sets of finite communication sequences as in [38]. The definition of P sat S is based on a Petri net semantics for process terms [27]. The main point is that P sat S requires a simple liveness property of the net denoted by P. This implies that P is divergence free and externally deterministic. Process correctness P sat S determines a new semantic model for process terms and logical formulas. It is a modification ^* of the readiness semantics [28] which is fully abstract with respect to the relation P sat S. The model ^* abstracts from the concurrent behaviour of process terms and certain aspects of their internal activity. In ^* process correctness P sat S boils down to semantic equality: ^*P = ^*S. The modified readiness equivalence is closely related to failure equivalence [7] and strong testing equivalence [9].     

Sensitive PAT gene sequence detection by nano-SiO2/p-aminothiophenol self-assembled films DNA electrochemical biosensor based on impedance measurement

Nano-SiO₂/p-aminothiophenol (PATP) film was fabricated by self-assembly and electrodeposition methods. The immobilization and hybridization of DNA on the nano-SiO₂/PATP film were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). EIS was applied to label-free detection of the target DNA according to the increase of the electron transfer resistance (R_et) of the electrode surface after the hybridization of the probe DNA with the target DNA. This DNA electrochemical biosensor showed its own performance of simplicity, good stability, fine selectivity and high sensitivity, and was successfully applied to the detection of the PAT gene sequences by a label-free EIS method. The dynamic detection range was from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁶ mol/L 20-base sequence of the PAT gene, with the detection limit of 1.5 × 10⁻¹² mol/L. This DNA sensor has a good ability of recognizing single- or double-base mismatched DNA sequence with the complementary DNA sequence.     

Direct electrochemistry and electrocatalysis of myoglobin immobilized in zirconium phosphate nanosheets film

Myoglobin (Mb) is incorporated on a novel matrix—zirconium phosphate nanosheets (ZrPNS) and immobilized at a glassy carbon electrode surface. UV–vis spectra and electrochemical measurements show that the matrix is well biocompatible and can retain the bioactivity of immobilized Mb. The direct electron transfer between Mb and electrode exhibits a couple of well-defined redox peaks. The cathodic and anodic peaks are located at −0.340 and −0.280 V vs. Ag/AgCl, respectively. The ZrPNS can improve the electron transfer between Mb and electrode with an electron transfer constant of 5.6 s⁻¹. Meanwhile, the catalytic ability of the protein toward the reduction of H₂O₂, O₂, NaNO₂, trichloroacetic acid (TCA) is also studied and a third-generation biosensor is subsequently fabricated. The linear range of biosensor to H₂O₂ is from 8 × 10⁻⁷ to 1.28 × 10⁻⁵ M with the limit detection of 1.4 × 10⁻⁷ M. The small apparent Michaelis–Menten constant (34 μM) suggests that Mb/ZrPNS film performs good affinity with H₂O₂. The biosensor also exhibits acceptable stability and reproducibility. This work paves a way to develop other biologic active materials in this kind of nanosheets for constructing novel biosensors.     

Adsorptive voltammetry of Hg(II) ions at a glassy carbon electrode coated with electropolymerized methyl-red film

The glassy carbon electrode coated with electropolymerized methyl-red film, 1.2 × 10⁻⁶ m in thickness, (PMRE) showed high sensitivity towards Hg(II) ions. PMREs were adopted to accumulate and detect Hg(II) ions in a pH 2.56 Britton–Robinson buffer solution. Cyclic voltammogram of the accumulated Hg species on PMREs exhibited an anodic wave at 0.64 V and a cathodic wave at 0.13 V, due to the oxidation of accumulated Hg species on PMREs and the reduction of Hg(II) ions in the solution, respectively. For this heterogeneous adsorption of Hg(II) ions onto PMREs, the maximum surface concentration, adsorption equilibrium, and Gibbs energy change were evaluated to be 5.12 × 10⁻⁶ mol m⁻², 3.7 × 10⁵ l mol⁻¹, and −30.1 kJ mol⁻¹, respectively. The anodic peak current at 0.64 V was linear with the concentration of Hg(II) ions in the range of 1.1 × 10⁻¹⁰ to 1.1 × 10⁻⁷ M with a detection limit of 4.4 × 10⁻¹¹ M. The proposed method was utilized successfully for the detection of Hg(II) ions in the lake water.     

Perchlorate selective membrane electrodes based on synthesized platinum(II) complexes for low-level concentration measurements

Three synthesized platinum(II) complexes, [PtR₂(NN)] (R = Me, p-MeC₆H₄ and p-MeOC₆H₄; NN = 2,2′-bipyridyl), were studied to characterize their ability as an anion carrier in a PVC membrane electrode. The polymeric membrane electrodes (PME) and also coated glassy carbon electrodes (CGCE) prepared with [Pt(p-MeOC₆H₄)₂(NN)] showed excellent response characteristics to perchlorate ions. The electrodes exhibited Nernstian responses to ClO₄⁻ ions over a wide concentration range from 5 × 10⁻⁷ to 4.0 × 10⁻¹ M for PME and 1.5 × 10⁻⁷ to 2.7 × 10⁻¹ M for CGCE with low detection limits (4.0 × 10⁻⁷ M for PME and 1.0 × 10⁻⁷ M for CGCE). The electrodes possess fast response time, satisfactory reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO₄⁻ relative to a variety of other common anions. The potentiometric response of the electrodes is independent of the pH of the test solution in the pH range 2.5–9.5. The proposed sensors were used in potentiometric determination of perchlorate ions in mineral water, urine samples and also samples containing interfering anions. The interaction of the ionophore with perchlorate ions was shown by UV–vis spectroscopy.     

Evaluation of the selective detection of 4,6-dinitro-o-cresol by a molecularly imprinted polymer based microsensor electrosynthesized in a semiorganic media

A carbon fiber microelectrode (CFME) was coated with a polymeric film, in order to synthesize an MIP based voltammetric microsensor for the selective determination of DNOC. The polymeric synthesis was carried out by electrocopolymerization of aniline and o-phenylenediamine (o-PD) in a water:methanol (1:1) media. The response of the MIP-sensor synthesized to the target analyte, was linear in a range from 8 × 10⁻⁷ to 10⁻⁴ M with a sensitivity of 1.6 × 10³ nA M⁻¹ and good stability and repeatability (<14%). Different rebinding experiments were carried out in order to evaluate the binding properties of the MIP-sensor. The experimental adsorption isotherms were fitted to Langmuir, Bi-Langmuir and Freundlich–Langmuir isotherms and the Langmuir model was chosen as the best fitting model. Under the optimized experimental conditions, the voltammetric microsensor was able to differentiate between DNOC and other closely related compounds such as other dinitrophenolic pesticides like binapacryl or dinobuton.     

A selective modified bentonite–porphyrin carbon paste electrode for determination of Mn(II) by using anodic stripping voltammetry

A novel voltammetric sensor based on chemically modified bentonite–porphyrin carbon paste electrode (MBPCE) has been introduced for the determination of trace amount of Mn(II) in wheat flour, wheat rice and vegetables. In this method Mn(II) gives well-defined voltammetric peak at the pH range of 3.5–7.5. For the preliminary screening purpose, the catalyst was prepared by modification of bentonite with porphyrin and characterized by thermogravimetric method (TG) and UV–vis spectroscopy. The detection limit (three times signal-to-noise) with 4 min accumulation is 1.07 × 10⁻⁷ mol L⁻¹ Mn(II). The peak currents increases linearly with Mn(II) concentration over the range of 6.0 × 10⁻⁷ to 5.0 × 10⁻⁴ mol L⁻¹ (r² = 0.9959). Statistical treatment of the results gave a relative standard deviation lower than 2.30%. The chemical and instrumental parameters have been optimized and the results showed that 1000-fold excess of the additive ions had not interferences on the determination of Mn(II).     

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.     

Characterizations of VO2-based uncooled microbolometer linear array

Vanadium dioxide (VO₂) thin films are materials for uncooled microbolometer due to their high temperature coefficient of resistance (TCR) at room temperature. This paper describes the design and fabrication of eight-element uncooled microbolometer linear array using the films and micromachining technology. The characteristics of the array is investigated in the spectral region of 8–12 μm. The fabricated detectors exhibit responsivity of over 10 kV/W, detectivity of approximate 1.94×10⁸ cm Hz^1/2/W, and thermal time constant of 11 ms, at 300 K and at a frequency of 30 Hz. Furthermore, the uncorrected response uniformity of the linear array bolometers is less than 20%.     

Preparation of BST ferroelectric thin film by metal organic decomposition for infrared sensor

Barium strontium titanate (Ba_1−xSr_xTiO₃) ferroelectric thin films have been prepared by metal organic decomposition (MOD) on Pt/Ti/SiO₂/Si and on micromachined wafer with an aim to fabricate dielectric bolometer type infrared (IR) sensor. The XRD pattern and D–V hysteresis curve of the film have been measured in order to investigate the effects of the final annealing temperature and annealing time on the property of the film. The results show that the films annealed at 700 °C or 800 °C all have good perovskite structure, while the film annealed at 800 °C has better ferroelectric loops. Films annealed at 800 °C with different annealing time from 5 to 60 min show a similar perovskite structure, among which films annealed at 30 and 60 min condition have the better ferroelectric loops. Temperature coefficient of dielectric constant (TCD) of the MOD made BST thin film on micromachined substrate is about 1%/K. The uniformity of the BST film on micromachined Si wafer also has been confirmed to be good enough for operation of sensor array. Chopperless operation has been attained and infrared response evaluation of the fabricated sensor also has been carried out with R_v of 0.4 kV/W and D^* of 1.0×10⁸ cm Hz^1/2/W, respectively.     

Periodic solutions of a class of nonlinear difference equations via critical point method

In this paper, we obtain some new sufficient conditions for the existence of nontrivial m-periodic solutions of the following nonlinear difference equation

by using the critical point method, where f: Z × R → R is continuous in the second variable, m ≥ 2 is a given positive integer, p_n+m = p_n for any n  Z and f(t + m, z) = f(t, z) for any (t, z)  Z × R, (−1)^δ = −1 and δ > 0.     

The economic and health effects on introducing a safe manual handling code of practice

To reduce the incidence of injuries caused by manual handling it was proposed, by a Government Authority, to introduce a Code of Practice. Many industries objected to the introduction of a Code as such codes may have adverse effects on the economics of the industries involved. This paper presents and discusses the methodology used to investigate such effects in those industries in which 80% of reported back injuries occur. Methods were developed to estimate the net costs to industry to comply with the code and the potential effectiveness of the code in preventing injuries.

A survey method was developed which sampled 56% of the Australian work force (about 3.85 × 10⁶ people). Due to the difficulty of specifying, in quantitative terms, the causation of back injury due to manual handling, the scope of the survey method was limited to identifying those work stations where lifting more than 16 kg occurred. There was no modification of potential hazards by specifying other components of back injury causation.

The results indicated that, in Australia, the cost to implement the code would have been $831 × 10⁶ (Australian dollars, 1987) with a recurrent annual cost of $245 × 10⁶. Seventy-five percent of the capital cost and 58% of the recurrent annual cost (excluding the hospital sector) would be required to comply with the Code for lifting weights above 34 kg.

It is estimated that the code would be 27% effective in back injury prevention. The cost to industry for back injuries was $576 × 10⁶ per annum (1984/5 injuries in $A1987) and the projected savings $156 × 10⁶ per annum so the net annual recurrent cost would be reduced from $245 × 10⁶ to $89 × 10⁶.     

Flow over a bluff body from moderate to high Reynolds numbers using large eddy simulation

Large eddy simulation (LES) is performed to study the uniform approach flow over a square-section cylinder with different Reynolds numbers, ranging from 10³ to 5 × 10⁶. Two different sub-grid scale models, the Smagorinsky and a dynamic one-equation model, are employed. An incompressible finite-volume code, based on a non-staggered grid arrangement and an implicit fractional step method with second-order accuracy in space and time, is used.

The structure of the flow is studied with the instantaneous and the mean quantities such as pressure, turbulent stresses, turbulent kinetic energy, vorticity, the second invariant of velocity gradient and streamlines. The Strouhal number, the mean and RMS values of the lift and drag are computed for various Reynolds numbers, which show a good agreement with the available experimental results. It is found that the effect of Reynolds number on the global quantities, the mean and the large scale instantaneous flow-structures is not much at the higher Reynolds numbers, i.e. Re > 2 × 10⁴. In this range of Reynolds numbers, the small scales of the instantaneous structures are more complex and chaotic as they compare with the larger ones.     

Phase change process with free convection in a circular enclosure: numerical simulations

A numerical study of unsteady natural convection flow during freezing of water in a circular enclosure is presented. Mathematical model for phase change is based on apparent capacity method formulation and the governing equations are discretized on a fixed grid by means of finite element method. Water’s temperature is initially higher than its freezing temperature. Then, the temperature of the enclosure’s boundary is dropped to a temperature lower than freezing temperature. Ice forms at the enclosure boundary while natural convection flow is induced in the liquid region. Calculations have been made for the rate of change of solid fraction and temperature distributions, for conduction and conduction plus convection modes of heat transfer, and density inversion near freezing temperature phenomenon of water is considered. High resolution capturing of solid/liquid moving boundary as well as the details of flow structure is presented. The results indicate that the effect of natural convection is dominant over conduction if the Rayleigh number is higher than 5 × 10⁶ and relatively insignificant if the Rayleigh number is less than 1 × 10⁶.     

An organically modified sol–gel membrane for detection of lead ion by using 2-hydroxy-1-naphthaldehydene-8-aminoquinoline as fluorescence probe

A fluorescent reagent, 2-hydroxy-1-naphthaldehydene-8-aminoquinoline (HNAAQ) was synthesized, and an organically modified sol–gel membrane for detection of lead ion by using HNAAQ as fluorescence probe was fabricated. Under the optimum conditions, by a coplanar effect and the degree of molecular conjugation due to the complexation of Pb²⁺ with HNAAQ the relative fluorescence intensity I₁₀₀/I₀ of the sensing membrane is linearly increased over the Pb²⁺ concentration range of 1.9 × 10⁻⁷ to 1.9 × 10⁻⁴ mol/L with the detection limit of 8.3 × 10⁻⁸ mol/L. The preparation of this organically modified sol–gel membrane and its characteristics were investigated in detail.     

A micromachined system for the separation of molecules using thermal field-flow fractionation method

All silicon-glass micromachined thermal field-flow fractionation (TFFF) microsystem has been developed and presented for the first time. The device consists of seven layers of double side, deep, selectively etched silicon and glass substrates, bonded anodically. The built-in fluidic heater and cooler allows producing the high thermal gradient. In the 30 μm deep, 2 mm wide and 50 mm long separation channel, the temperature gradient 1.5×10⁶ K/m has been obtained for relatively low heating agent temperature (343 K). The TFFF microsystem has been equipped with two integrated, three-electrodes conductivity detectors. Some basic separation properties have been evaluated for low concentrated KCl test samples in water. It has been found that retention time of 0.6 μl sample of 0.01 M KCl in water, for 293/321 K (cooling/heating agents) compared to 0.9×10⁶ K/m, is almost two times longer than it has been obtained in the device during the absence of the temperature gradient.     

Detection and discrimination of coliform bacteria with gas sensor arrays

Electronic noses, which are used for characterizing complex vapors and aromas, may be useful for detection of bacterial contamination or diagnosis of infections, if minimal standards of selectivity and sensitivity can be met. A culture of Enterobacter aerogenes is readily discriminated from an Escherichia coli strain using principal components analysis (PCA) of data generated by an array of eight quartz microbalance (QMB), eight metal oxide semiconductor (MOX), and four electrochemical gas sensors. Two strains of E. coli were not discriminated under identical conditions. Retaining headspace air in a sealed vial containing growing bacteria results in an enhancement of sensitivity, so that a concentration of bacteria of about 5×10⁸/ml may be both detected and distinguished from other species. Improvements in sensitivity to levels useful for practical applications will require enhancement of sensors, sampling system, and pattern classification.