A novel amperometric glucose biosensor based on poly(glycidyl methacrylate-co-(3-thienylmethylmethacrylate))

Two novel glucose oxidase (GOx) enzyme electrodes based on the copolymer of glycidyl methacrylate with 3-thienylmethyl methacrylate (poly(GMA-co-MTM)) with and without polypyrrole (PPyr) coating were prepared and employed in the amperometric determination of glucose levels. The effect of PPyr coating on the electrode properties was investigated in detail. Cyclic voltammetry studies showed that electrical conductivity of electrode B with PPyr coating (poly(GMA-co-MTM)/GOx/PPyr) was substantially higher than that of electrode A (poly(GMA-co-MTM)/GOx). On the other hand, electrode A showed better results in terms of sensitivity (10 nA/mM), limit of detection (50.2 μM), and response time (5 s). Electrodes A and B gave linear responses to the glucose concentrations in the range of 2–20 and 2–14 mM, respectively. The ranges of linearity for both enzyme electrodes are sufficient for the determination of physiological glucose concentrations in human blood. Moreover, PPyr coating of electrode B did not result in further stabilization of the enzyme electrode.     

Sensitization of uranium fluorescence using 2,6-pyridinedicarboxylic acid: Application for the determination of uranium in the presence of lanthanides

The 2,6-pyridinedicarboxylic acid (PDA) has been shown to efficiently sensitize and enhance the fluorescence of uranium in aqueous medium. Interestingly, this ligand stabilizes the UO₂²⁺ species, which without the ligand is known to be in a negligible concentration, in aqueous medium at pH 6. The ligand sensitized enhancement of UO₂²⁺ fluorescence by PDA, provides an analytical tool for the determination of uranium at trace levels, in aqueous medium. Furthermore, PDA is also known to enhance the fluorescence of lanthanides; consequently, the simultaneous determination of uranium and lanthanides, using PDA as a fluorescence sensitizing agent, becomes a possibility, which has been demonstrated in this work. We have shown that the use of PDA yields detection limits of 2.2×10⁻⁷ M for UO₂²⁺, 1×10⁻⁸ M for Tb³⁺ and 5×10⁻⁹ M for Eu³⁺ in the simultaneous determination of these analytes.     

1.54 μm room temperature emission from Er-doped Si nanocrystals deposited by ECR-PECVD

In this work, silicon nanocrystals (Si-nc) embedded in a silicon-rich silicon oxide (SRSO) matrix doped with Er³⁺ ions for different erbium and silicon concentrations have been deposited by electron-cyclotron resonance plasma-enhanced chemical-vapor-deposition (ECR-PECVD) technique. Their optical properties have been investigated by photoluminescence (PL) and reflectance spectroscopy.Room temperature emission bands centered at ∼1.54 and at 0.75 μm have been obtained for all samples. The most intense emission band at ∼1.54 μm was obtained for samples with concentrations of 0.45% and 39% for erbium and silicon, respectively. Moreover, it has been found that the broad emission band centered at ∼0.75 μm for all samples shows a very strong interference pattern related to the a specific sample structure and a high sample quality.     

Determination of Enantiomeric Compositions of Analytes Using Novel Fluorescent Chiral Molecular Micelles and Steady State Fluorescence Measurements

Novel fluorescent chiral molecular micelles (FCMMs) were synthesized, characterized, and employed as chiral selectors for enantiomeric recognition of non-fluorescent chiral molecules using steady state fluorescence spectroscopy. The sensitivity of the fluorescence technique allowed for investigation of low concentrations of chiral selector (3.0 × 10⁻⁵ M) and analyte (5.0 × 10⁻⁶ M) to be used in these studies. The chiral interactions of glucose, tartaric acid, and serine in the presence of FCMMs poly(sodium N-undecanoyl-l-tryptophanate) [poly-l-SUW], poly(sodium N-undecanoyl-l-tyrosinate) [poly-l-SUY], and poly(sodium N-undecanoyl-l-phenylalininate) [poly-SUF] were based on diastereomeric complex formation. Poly-l-SUW had a significant fluorescence emission spectral difference as compared to poly-l-SUY and poly-l-SUF for the enantiomeric recognition of glucose, tartaric acid, and serine. Studies with the hydrophobic molecule α-pinene suggested that poly-l-SUY and poly-l-SUF had better chiral discrimination ability for hydrophobic analytes as compared to hydrophilic analytes. Partial-least-squares regression modeling (PLS-1) was used to correlate changes in the fluorescence emission spectra of poly-l-SUW due to varying enantiomeric compositions of glucose, tartaric acid, and serine for a set of calibration samples. Validation of the calibration regression models was determined by use of a set of independently prepared samples of the same concentration of chiral selector and analyte with varying enantiomeric composition. Prediction ability was evaluated by use of the root-mean-square percent relative error (RMS%RE) and was found to range from 2.04 to 4.06%. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Determination of carboxylic acids in non-alcoholic beer samples by an ultrasonic-assisted dispersive micro-solid phase extraction based on Ni/Cu-Al layered double hydroxide nanocomposites followed by gas chromatography

Magnetically separable layered double hydroxide Ni/CuAl-LDH nanocomposites were synthesized and employed as ultrasonic-assisted dispersive micro-solid phase extraction (UA-D-μSPE) sorbent to extract several carboxylic acids (namely propionic, butyric, pentanoic, hexanoic, heptanoic, octanoic, and decanoic) from non-alcoholic beer samples. Ni/CuAl-LDH sorbent was characterized by Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). Effective variables such as amount of sorbent (mg), pH and ionic strength of sample solution, volume of eluent solvent (μL), vortex, and ultrasonic times (min) were investigated via fractional factorial design (FFD). The significant variables were optimized by a Box–Behnken design and combined by a desirability function (DF). Under optimized conditions, the calibration graphs of analytes were linear in a concentration range of 0.05–100 μg/mL and had correlation coefficients more than 0.997. The limits of detection and quantification were in the ranges of 16–40 μg/L and 53–133 μg/L, respectively. This procedure was successfully employed in the determination of target analytes in spiked beer samples, and the relative mean recoveries ranged from 87 to 110%.     

A novel amperometric glucose biosensor based on reconstitution of glucose oxidase on thiophene-3-boronic acid polymer layer

The biosensor was constructed for determination of glucose by using glucose oxidase enzyme immobilized on poly(thiophene-3-boronic acid) (PTBA). Boronic acid functionalized polythiophene layer was obtained by electrochemical polymerization of Thiophene (Th) and thiophene-3-boronic acid (TBA) with different monomer rations. The reconstitution of the apo-glucose oxidase (apo-GOx) on a complexed flavin adenine dinucleotide (FAD) linked to polythiophene boronic acid (PTBA) monolayer yields an electrically contacted enzyme monolayer. The GOx-reconstituted enzyme electrode exhibited excellent electrocatalytic activities toward the reduction and oxidation of hydrogen peroxide as well. The PTBA/FAD/GOx biosensor shows an excellent performance for glucose at +0.4 V with a high sensitivity (2.14 μA/mM) and lower response time (～5 s) in a wide concentration range of 0.5–18 mM (correlation coefficient of 0.9952). Furthermore, the effects of applied potential, pH, temperature, electroactive interference, stability and reusability of the biosensors were discussed.     

Simultaneous Determination of Mefenamic and Tolfenamic Acids in Real Samples by Terbium-Sensitized Luminescence

A simple luminescent methodology for the simultaneous determination of mefenamic and tolfenamic acids in pharmaceutical preparations and human urine is proposed. Since the native fluorescence of both analytes is not intense, the method takes advantage of the lanthanide-sensitized luminescence, which provides a higher sensitivity. Due to the strong overlapping between the luminescence spectra of both terbium complexes, the use of luminescence decay curves to resolve mixtures of the analytes is proposed, since these curves are more selective. A factorial design with three levels per factor coupled to a central composite design was selected to obtain a calibration matrix of thirteen standards plus eight blank samples that was processed using a partial least-squares (PLS) analysis. In order to assess the goodness of the proposed method, a prediction set of synthetic samples was analyzed, obtaining recovery percentages between 90 and 104?%. Limits of detection, calculated by means of a new criterion, were 14.85?μg L^?1 and 15.89?μg L^?1 for tolfenamic and mefenamic acids, respectively. The method was tested in a pharmaceutical preparation containing mefenamic acid, obtaining recovery percentages close to 100?%. Finally, the simultaneous determination of both fenamates in human urine samples was successfully carried out by means of a correction of the above-explained model. No extraction method neither prior separation of the analytes were needed.     

Existence of Different Structural Intermediates and Aggregates on the Folding Pathway of Ovalbumin

Structural modifications of ovalbumin in presence of different concentration of guanidine hydrochloride (Gdn HCl) and glucose were investigated by using intrinsic fluorescence, Fourier transform infra-red spectroscopy, circular dichroism and 8-anilino-1-naphthalene-sulphonic acid, to confirm that partially folded intermediates of ovalbumin lead to aggregation. The two partially folded intermediates of ovalbumin were observed one at 1 M Gdn HCl and another in the presence of 20 mM glucose at 3 M Gdn HCl. Both intermediates exist as compact states with altered intrinsic fluorescence, prominent β-sheet secondary structure and enhanced ANS binding. Ovalbumin in the presence of glucose required more concentration of Gdn HCl (3 M) to exist as an intermediate state than control (1 M). Such alpha-helix/beta-sheet transition of proteins is a crucial step in amyloidogenic diseases and represents an internal rearrangement of local contacts in an already folded protein. Further, incubation for 24 h resulted in the formation of aggregates as detected by thioflavin T-assay. On further increasing the concentration of glucose to 50 mM and incubation time for various days resulted in the formation of molten globule state of ovalbumin at 6th day. Later on, at 10th day advanced glycated end products were observed.     

First Derivative Synchronous Fluorescence Spectroscopy for the Simultaneous Determination of Sulpiride and Mebeverine Hydrochloride in Their Combined Tablets and Application to Real Human Plasma

A rapid, simple and highly sensitive first derivative synchronous fluorometric method has been developed for the simultaneous analysis of binary mixture of sulpiride (SUL) and mebeverine hydrochloride (MEB). The method is based upon measurement of the synchronous fluorescence intensity of these drugs at ∆λ = 100 nm in water. The different experimental parameters affecting the fluorescence of the two drugs were carefully studied and optimized. The fluorescence-concentration plots were rectilinear over the range of 0.05–1 μg/mL and 0.2–3.2 μg/mL for SUL and MEB respectively with lower detection limits (LOD) of 0.006 and 0.01 μg/mL and quantification limits (LOQ) of 0.0.02 and 0.05 μg/mL for SUL and MEB, respectively. The proposed method was successfully applied for the determination of the two compounds in synthetic mixtures and in commercial tablets. The high sensitivity attained by the proposed method allowed the determination of both of SUL and MEB metabolite (veratic acid) in real human plasma samples applying second derivative synchronous fluorometric technique. The mean% recoveries (n = 3) for both MEB metabolite (veratic acid) and SUL were 99.82 ± 2.53 and 98.84 ± 6.20 for spiked human plasma respectively, while for real human plasma, the mean% recoveries (n = 3) were 91.49 ± 4.25 and 91.36 ± 8.46 respectively.     

Research on a New Micro-Volume Fluorescence Capillary Biosensor Assay for Sequentially Quantifying Pyruvate and Lactate

It was studied that making conditions of a micro-volume fluorescence capillary biosensor for determining pyruvate (PA) and lactate (LA). The biosensor made under the optimized conditions could be used for sequential quantifications of LA in the range 0.10–1.2 mM and PA in 4–120 μM, and its recovery for PA and LA was in a satisfactory range 97–106% for human serum samples, with detection limits of 0.023 mM for LA (RSD < 1.89%, n = 11) and 0.87 μM for PA (RSD < 1.70%, n = 11). The new assay possessed these advantages that the LDH immobilizing on capillary realized the reuse of expensive enzyme in fluorospectrophotometry, and the consumption of serum samples or chemical reagents decreased to 9 μL in per assay, and the analytes no needed to preseparation, and it also are accurate and reliable. Consequently, the fluorescence capillary biosensor should have a good prospect in assaying PA and LA or LA/PA ratios for clinical medicines or biology field. The optimization conditions and parameters obtained in this study have also a certain guiding significance for the development of biochip based on glass substrate.     

High-performance nonenzymatic electrochemical glucose biosensor based on AgNP-decorated MoS2 microflowers

A facile hydrothermal route was used to synthesize silver nanoparticle (AgNP)-decorated microflower molybdenum disulfide (MoS₂-MF) for bio-electrochemical platform fabrication to detect nonenzymatic glucose concentration. The morphologies of the materials were studied by scanning electron microscopy, and their structural characteristics were analyzed by X-ray diffractometry and energy-dispersive X-ray spectroscopy. The electrochemical characteristics of the AgNPs/MoS₂-MF/PtE biosensor were studied by cyclic voltammetry. The obtained data indicated that the developed nonenzymatic glucose sensor has a large linear response between 1.0 and 15.0 mM, a limit of detection of as low as 1.0 mM, and a sensitivity of 46.5 μA nM⁻¹ cm⁻². The biosensor also displayed outstanding selectivity, stability, reproducibility, and repeatability. Additionally, the AgNPs/MoS₂-MF/PtE biosensor was utilized to detect glucose concentration in real sample and showed practical application potential for glucose detection.     

Determination of lead at physiological level in human biological materials using the total reflection X‐ray fluorescence analysis

Total reflection X‐ray fluorescence (TXRF) analysis was applied in determination of low concentration of lead in samples of human biological materials. The determination of lead in human serum and hair samples is presented as an example. In serum samples, lead concentration was in the range from 0.013 to 0.051 μg/g (median 0.024 μg/g). The reference ranges of lead content in hair are from 1.41 to 4.08 μg/g for men and from 1.18 to 3.29 μg/g for women groups, respectively. Because of Pb concentration range close to the detection limit of the TXRF method, the measurement needed evaluation of the best analytical conditions. This paper presents the results of this evaluation, namely internal standard selection, measurement conditions, and quantitative calibration of the spectrometer. Finally, as a result of evaluation, the detection limit was found on the level 0.001 μg/g (water solution) and about 0.005 μg/g for human hair samples and 0.007 μg/g for serum samples. The obtained values reach nearly the physiological lead level. The presented results are of practical importance for lead concentration studies in human biological materials using the TXRF method. Copyright © 2016 John Wiley & Sons, Ltd.     

Mono(pyridine-N-oxide) analog of DOTA as a suitable organic reagent for a sensitive and selective fluorimetric determination of Ln(III) ions

The mono(pyridine-N-oxide) analog of the H₄dota macrocylic ligand, H₃do3a-py^NO, is capable of forming thermodynamically stable and kinetically inert Ln(III) complexes. Its Eu(III) and Tb(III) complexes display a strong long-lived fluorescence as a result of the antenna effect of the pyridine-N-oxide fluorophore in the reagent. It is shown that H₃do3a-py^NO can be used as a fluorogenic reagent for the determination of Eu(III) and Tb(III) at pH 6.5 and c_L=1 mM. At an excitation wavelength of 286 nm, the emission maxima are 615 nm (Eu(III)-complex), and 547 nm (Tb(III)complex). Detection limits are at concentrations around 1.0 μM and linearity of the method spans over 2 orders of magnitude. The method was applied to artificial and real samples (spiked mineral waters, extracts from cathode ray tube luminophore dust) and gave satisfactory results. The method is simple, rapid, and hardly interfered by other metal ions.     

Optimization of ultrasound-assisted dispersive solid-phase microextraction based on nanoparticles followed by spectrophotometry for the simultaneous determination of dyes using experimental design

A simple, low cost and ultrasensitive method for the simultaneous preconcentration and determination of trace amount of auramine-O and malachite green in aqueous media following accumulation on novel and lower toxicity nanomaterials by ultrasound-assisted dispersive solid phase micro-extraction (UA-DSPME) procedure combined with spectrophotometric has been described. The Mn doped ZnS nanoparticles loaded on activated carbon were characterized by Field emission scanning electron microscopy (FE-SEM), particle size distribution, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) analyses and subsequently were used as green and efficient material for dyes accumulation. Contribution of experimental variables such as ultrasonic time, ultrasonic temperature, adsorbent mass, vortex time, ionic strength, pH and elution volume were optimized through experimental design, and while the preconcentrated analytes were efficiently eluted by acetone. Preliminary Plackett–Burman design was applied for selection of most significant factors and giving useful information about their main and interaction part of significant variables like ultrasonic time, adsorbent mass, elution volume and pH were obtained by central composite design combined with response surface analysis and optimum experimental conditions was set at pH of 8.0, 1.2 mg of adsorbent, 150 μL eluent and 3.7 min sonication. Under optimized conditions, the average recoveries (five replicates) for two dyes (spiked at 500.0 ng mL⁻¹) changes in the range of 92.80–97.70% with acceptable RSD% less than 4.0% over a linear range of 3.0–5000.0 ng mL⁻¹ for the AO and MG in water samples with regression coefficients (R²) of 0.9975 and 0.9977, respectively. Acceptable limits of detection of 0.91 and 0.61 ng mL⁻¹ for AO and MG, respectively and high accuracy and repeatability are unique advantages of present method to improve the figures of merit for their accurate determination at trace level in complicated materials.     

Selective and sensitive determination of dopamine via suppressing ascorbic acid using an N-(1-H-indole-3yl) methylene thiazole-2-amine thin film-modified glassy carbon electrode

The selective determination of dopamine (DA) was performed using a glassy carbon (GC) electrode modified with N-(1-H-indole-3yl) methylene thiazole-2-amine (IMT2A). IMT2A was deposited on the GC electrode by cyclic voltammetry. This modified electrode demonstrated an electrocatalytic effect on the oxidation of DA in the presence of uric acid (UA) and ascorbic acid (AA) using differential pulse voltammetry (DPV) method in 0.1 M phosphate buffer solution (PBS) of pH 7. Selective determination was realized in elimination of AA response on the IMT2A-modified electrode. The oxidation peak currents increased linearly with two concentration intervals of DA at pH 7 phosphate buffer. One of them is 0.25–9.15 μM, and the other is 9.15–95.1 μM. The limit of detection (LOD) was found as 0.086 μM. The proposed electrode was applied to the determination of DA in pharmaceutical preparations and human urine sample with satisfactory results.

     

Room temperature phosphorescence lifetime and quantum yield of erythrosine B and rose bengal in aerobic alkaline aqueous solution

The room-temperature phosphorescence behavior of erythrosine B (ER) and rose bengal (RB) in aerobic aqueous solution at pH 10 (10^?4 M NaOH) is investigated. The samples were excited with sliced second harmonic pulses of a Q-switched Nd:glass laser. A gated photomultiplier tube was used for instantaneous fluorescence signal discrimination and a digital oscilloscope was used for signal recording. For phosphorescence lifetime measurement the oscilloscope response time was adjusted to appropriate time resolution and sensitivity by the ohmic input resistance. In the case of phosphorescence quantum yield determination the gated photomultiplier – oscilloscope arrangement was operated in integration mode using 10 MΩ input resistance. Phosphorescence quantum yield calibration was achieved with erythrosine B and rose bengal doped starch films of known quantum yields. The determined phosphorescence lifetimes (quantum yields) of ER and RB in 0.1 mM NaOH are τ_P=1.92±0.1 μs (?_P=(1.5±0.3)×10^?5) and 2.40±0.1 μs ((5.7±0.9)×10^?5), respectively. The results are discussed in terms of triplet state deactivation by dissolved molecular oxygen.     

A Gas Diffusion Technique Coupled with Flow Injection Systems. Optimization of the Process in its Application to the Fluorimetric Determination of Ammonium in Water Samples

A novel flow injection-gas-diffusion (GD-FI) system has been developed for the on-line analysis of ammonium ion in waters with fluorimetric detection, using an acceptor solution containing the Eosin-Bluish (EB) acid-base indicator. This, together with optimization of the process of gas transfer through the membrane, increases the sensitivity of the method to a considerable extent. Under optimum conditions, it is possible to determine the analyte within the 0.02–1.5 mg l^-1 range, with a limit of detection of 5 μg l^-1 and relative standard deviations (n = 12, [NH₄⁺] = 50 μg l^-1 and 0.05 μg l^-1) of 3.4% and 3.0% respectively. The determination rate was 15 samples per hour.     

Optical Detection of Some Hydrazine Compounds Based on the Surface Plasmon Resonance Band of Silver Nanoparticles

An indirect colorimetric method is presented for spectrophotometric determination of hydrazine, phenylhydrazine, and isoniazid. Reduction of silver ions to silver nanoparticles (AgNPs) by these analytes as active reducing agents in the presence of polyvinylpyrrolidone (PVP) and also cetyltrimethylammonium chloride (CTAC) as a stabilizer is the basis of the proposed method. The changes in plasmon absorbance of the AgNPs at λ = 415 nm in the presence of PVP were proportional to concentration of hydrazine, phenylhydrazine, and isoniazid in the ranges of 4.0–150.0 µM, 1.0–55.0 µM, and 2.0–30.0 µM, respectively, and the detection limit obtained was 0.79 µM. In the presence of CTAC, the linear ranges were 0.5–10.0 and 10.0–300.0 µM for hydrazine, 1.0–40.0 µM for phenylhydrazine, and 0.2–10.0 and 10.0–90.0 µM for isoniazid, and the detection limit was 0.12 µM. The method has been applied for determination of these analytes in different real samples such as boiler feed water and tablet.     

Degradation behaviors and failure analysis of Ni–BaTiO3 base-metal electrode multilayer ceramic capacitors under highly accelerated life test

The degradation in insulation resistance under highly accelerated test conditions was investigated in terms of micro-structural and micro-chemical changes in dielectric layer of multilayer ceramic capacitor. The ceramic capacitors were prepared by using BaTiO₃ powder with different size of 0.52 μm, 0.55 μm, and 0.58 μm. As the particle size of BaTiO₃ powder was increased, the capacitance and the dissipation factor were decreased. According to the result of highly accelerated test conducted at 150 °C, 75 V, and 20 h, failure in insulation resistance was increased with the particle size and the calculated FITs (failure in term) were 1.10 at 0.52 μm, 2.11 at 0.55 μm, and 6.69 at 0.58 μm, respectively. The failure was examined by X-ray photoelectron spectroscopy and transmission electron microscopy, which was attributed to the oxidation of Ni inner electrode that could create oxygen vacancies and increase electric conduction of the ceramic capacitors.     

Dispersion of hydrophobic magnetic nanoparticles using ultarsonic-assisted in combination with coacervative microextraction for the simultaneous preconcentration and determination of tricyclic antidepressant drugs in biological fluids

A two-step sample preparation technique based on dispersive micro solid-phase extraction combined with coacervative microextraction is presented for preconcentration and determination of tricyclic antidepressant drugs in biological samples. An important feature of the method is the application of hydrophobic magnetic nanoparticles, which in combination with coacervative microextraction method enables development of rapid and efficient extraction procedure in order to achievement of a high extraction efficiency. Simultaneous optimization by experimental design lead to improvement of method with low cost which supply useful information about interaction among variables. Under the optimized conditions, a linear range of 5–1000 ng mL⁻¹ with detection limits from 0.51 to 1.4 ng mL⁻¹ were obtained for target analytes. The method was successfully used for the determination of analytes in biological fluids (plasma and urine) with relative recoveries in the range of 89–105% (RSDs < 3.5%).