Electrochemical Responses and Sensitivities of Films Based on Multi-Walled Carbon Nanotubes in Aqueous Solutions

Novel films consisting of multi-walled carbon nanotubes (MWCNTs) were fabricated by means of chemical vapor deposition with decomposition of either acetonitrile (ACN) or benzene (BZ) using ferrocene as catalyst. The electrochemical responses of MWCNT-based films towards the ferrocyanide/ferricyanide, [Fe(CN)₆]^3?/4? redox couple were probed by means of cyclic voltammetry and electrochemical impedance spectroscopy at 25.0?±?0.5?°C. Both MWCNT-based films exhibit Nernstian response towards [Fe(CN)₆]^3?/4? with some slight kinetic differences. Namely, heterogeneous electron transfer rate constants lying in ranges of 2.69?×?10^?2?C1.7?×?10^?3 and 9.0?×?10^?3?C2.6?×?10^?3?cm·s^?1 were obtained at v?=?0.05?V·s^?1 for MWCNT_ACN and MWCNT_BZ, respectively. The detection limit of MWCNT_ACN, estimated to be about 4.70?×?10^?7?mol·L^?1 at v?=?0.05?V·s^?1, tends to become slightly poorer with the increase of the scan rate, namely at v?=?0.10?V·s^?1 the detection limit of 1.70?×?10^?6?mol·L^?1 was determined. Slightly poorer response ability was exhibited by MWCNT_BZ; specifically the detection limits of 1.57?×?10^?6 and 4.35?×?10^?6?mol·L^?1 were determined at v?=?0.05 and v?=?0.10?V·s^?1, respectively. The sensitivities of MWCNT_ACN and MWCNT_BZ towards [Fe(CN)₆]^3?/4? were determined as 1.60?×?10^?7 and 1.51?×?10^?7?A·L·mol^?1·cm^?2, respectively. The excellent electrochemical performance of MWCNT_ACN is attributed to the presence of incorporated nitrogen in the nanotube??s structure.     

Assessment of effective radium content and radon exhalation rates in soil samples

Effective radium content and radon exhalation rates in soil samples have been measured by ??Sealed Can Technique?? using LR-115 type II plastic track detectors. The soil samples were collected from Farrukhabad city of Utter Pradesh, India. The values of effective radium content were found to vary from 5.39 to 34.56?Bq?kg^?1 with an average value of 16.58?Bq?kg^?1 and a standard deviation of 7.16. The mass and surface exhalation rate has been found to vary from 0.41?×?10^?6 to 2.64?×?10^?6?Bq?kg^?1?d^?1 and 1.41?×?10^?6 to 9.10?×?10^?6?Bq?m^?2?d^?1, respectively. All the values of radium content in soil samples of study area were found to be quite lower than the permissible value of 370?Bq?kg^?1 recommended by Organization for Economic Cooperation and Development.     

A multivariate calibration procedure for the tensammetric determination of detergents

A multivariate calibration procedure based on singular value decomposition (SVD) and the Ho-Kashyap algorithm is used for the tensammetric determination of the cationic detergents Hyamine 1622, benzalkonium chloride (BACl), N-cetyl-N,N,N-trimethylammonium bromide (CTABr) and mixtures of CTABr and BACl. The sensitivity and accuracy depend strongly on the nature of the detergent. Acceptable accuracy is obtained with a two-step calculation procedure in which calibration constants for the total concentration range of interest are used to guide the choice of a more specific set of calibration constants which are valid for a much smaller concentration span. For Hyamine 1622, concentrations in the range 5 × 10^?6?2 × 10^?4 M could be determined with an accuracy of ± 10^?6 M. For CTABr, these numbers were 3 × 10^?6?2 × 10^?4 M and ± 5 × 10^?7 M; for BACl, they were 2 × 10^?3?9 × 10^?2 g l^?1 and ± 1 × 10^?3 g l^?1. In the mixtures of CTABr and BACl, the accuracies were ± 3 × 10^?6 M and × 1 × 10^?3 g l^?1, respectively.     

Rapid voltammetric determination of maltol in some foods and beverages using a poly(methylene blue)/graphene-modified glassy carbon electrode

A novel poly(methylene blue)/graphene composite glassy carbon electrode was fabricated and the electrochemical behavior of maltol at the modified electrode was studied by cyclic voltammetry. In phosphate-buffered solution, the modified electrode exhibited excellent electrocatalytic activity towards the electrochemical oxidation of maltol. Under optimized conditions, the oxidation peak current showed a linear relationship with the concentrations of maltol in the ranges of 8.00?×?10^?7 to 4.00?×?10^?5 and 4.00?×?10^?5 to 5.40?×?10^?4 mol L^?1, with a detection limit of 6.50?×?10^?8 mol L^?1. The performance of the developed method was validated in terms of linearity (r?=?0.9981 and 0.9955), recovery (97.0?99.3 %), reproducibility (relative standard deviations?≤?3.1 %, n?=?6), and robustness. The method shows excellent sensitivity, selectivity, and reproducibility and has been successfully applied to analyzing maltol in a wide variety of food products.     

A novel and simple biosensor based on poly(indoleacetic acid) film and its application for simultaneous electrochemical determination of dopamine and epinephrine in the presence of ascorbic acid

A novel and simple biosensor based on poly(indoleacetic acid) film-modified electrode (PIAA/CPE) was fabricated by electrochemical polymerization of indoleacetic acid on a carbon paste electrode (CPE) through cyclic voltammetry. The resulting electrode was characterized by scanning electron microscopy, and the electrochemical behaviors of dopamine (DA) and epinephrine (EP) at the electrode were studied. It was illustrated that PIAA/CPE had excellent electrochemical catalytic activities toward DA and EP. The anodic peak currents (I _pa) were dramatically enhanced by about seven-fold for DA and ten times for EP at PIAA/CPE. Thus, the determinations of DA and EP were carried out using PIAA/CPE successfully. The linear responses were obtained in the range of 3.0?×?10^?7～7.0?×?10^?4 and 1.0?×?10^?6 ～8.0?×?10^?4 mol L^?1 with the detection limits (3σ) of 1?×?10^?7 and 4?×?10^?7 mol L^?1 corresponding with DA and EP, respectively. Moreover, the cathodic peaks of DA and EP were well-separated with a potential difference about 325 mV in pH 5.3 phosphate-buffered saline, so simultaneous determination of DA and EP was carried out in this paper. Additionally, the interference studies showed that the PIAA/CPE exhibited excellent selectivity in the presence of ascorbic acid (AA). With good selectivity and sensitivity, the present method has been successfully applied to the determination of DA and EP in pharmaceutical samples.     

One-step construction of an electrode modified with electrodeposited Au/SiO2 nanoparticles, and its application to the determination of NADH and ethanol

A new electrode was developed by one-step potentiostatic electrodeposition (at ?2.0 V for 20 s) of Au/SiO₂ nanoparticles on a glassy carbon electrode. The resulting electrode (nano-Au/SiO₂/GCE) was characterized by scanning electronic microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) at the nano-Au/SiO₂/GCE were thoroughly investigated. Compared to the unmodified electrode, the overpotential decreased by about 300 mV, and the current response significantly increased. These changes indicated that the modified electrode showed excellent catalytic activity in the oxidation of NADH. A linear relationship was obtained in the NADH concentration range from 1.0?×?10^?6 to 1.0?×?10^?4 mol?L^?1. In addition, amperometric sensing of ethanol at the nano-Au/SiO₂/GCE in combination with alcohol dehydrogenase and nicotinamide adenine dinucleotide was successfully demonstrated. A wide linear response was also found for ethanol in the range from 5.0?×?10^?5 to 1.0?×?10^?3 mol?L^?1 and 1.0?×?10^?3 to 1.0?×?10^?2 mol?L^?1, respectively. The method was successfully applied to determine ethanol in beer and biological samples.     

Analysis of Nitrification in Agricultural Soil and Improvement of Nitrogen Circulation with Autotrophic Ammonia-Oxidizing Bacteria

Accumulations of inorganic nitrogen (NH₄ ⁺, NO₂ ^?, and NO₃ ^?) were analyzed to evaluate the nitrogen circulation activity in 76 agricultural soils. Accumulation of NH₄ ⁺ was observed, and the reaction of NH₄ ⁺?→?NO₂ ^? appeared to be slower than that of NO₂ ^??→?NO₃ ^? in agricultural soil. Two autotrophic and five heterotrophic ammonia-oxidizing bacteria (AOB) were isolated and identified from the soils, and the ammonia-oxidizing activities of the autotrophic AOB were 1.0?×?10³–1.0?×?10⁶ times higher than those of heterotrophic AOB. The relationship between AOB number, soil bacterial number, and ammonia-oxidizing activity was investigated with 30 agricultural soils. The ratio of autotrophic AOB number was 0.00032–0.26 % of the total soil bacterial number. The soil samples rich in autotrophic AOB (>1.0?×?10⁴ cells/g soil) had a high nitrogen circulation activity, and additionally, the nitrogen circulation in the agricultural soil was improved by controlling the autotrophic AOBs.     

Molecular imprinting polymer electrosensor based on gold nanoparticles for theophylline recognition and determination

An electrochemical sensor for theophylline (ThPh) was prepared by electropolymerizing o-phenylenediamine on a glassy carbon electrode in the presence of ThPh via cyclic voltammetry, followed by deposition of gold nanoparticles using a potentiostatic method. The effects of pH, ratio between template molecule and monomer, number of cycles for electropolymerization, and of the solution for extraction were optimized. The current of the electro-active model system hexacyanoferrate(III) and hexacyanoferrate(IV) decreased linearly with successive addition of ThPh in the concentration range between 4.0?×?10^?7?~?1.5?×?10^?5 mol·L^?1 and 2.4?×?10^?4?~?3.4?×?10^?3 mol·L^?1, with a detection limit of 1.0?×?10^?7 mol·L^?1. The sensor has an excellent recognition capability for ThPh compared to structurally related molecules, can be regenerated and is stable.

Electrochemical determination of norepinephrine on the membrane of silver nanoparticles doped poly-glycine eliminating the interference of ascorbic acid

The silver nanoparticles doped poly-glycine composite membrane was prepared by cyclic voltammetry on the surface of the glassy carbon electrode (GCE). The morphology and electrochemical properties were characterized by scanning electron microscopy and cyclic voltammetry, respectively, and in detail, the electrochemical behaviors of the norepinephrine (NE) on this membrane were studied. The results showed that the membrane had good catalytic properties for the oxidative–reductive reaction of NE. NE had a couple of sensitive oxidative-reductive current peaks. The reductive peak currents were linearly with its concentration in the range of 1.90?×?10^?7 to 7.00?×?10^?6 and 7.00?×?10^?6 to 1.00?×?10^?4?mol l^?1, and the linear regressive equations were i _pc (A)?=?3.73?×?10^?6?+?0.70C (mol l^?1), i _pc (A)?=?9.83?×?10^?5?+?0.12C (mol l^?1), respectively, with the relate coefficient (r) of 0.9926 and 0.9944. The detection limit was 1.2?×?10^?7?mol l^?1 (S/N?=?3), which could be used to determine the content of NE and at the same time, eliminate the interference of the ascorbic acid (AA). The proposed method had high sensitivity, good selectivity and stability.     

In Vitro and In Vivo Characterization of Plant Growth Promoting Bacillus Strains Isolated from Extreme Environments of Eastern Algeria

This report is to our knowledge the first to study plant growth promotion and biocontrol characteristics of Bacillus isolates from extreme environments of Eastern Algeria. Seven isolates of 14 (50 %) were screened for their ability to inhibit growth of some phytopathogenic fungi on PDA and some roots exudates. The bacteria identification based on 16S r-RNA and gyrase-A gene sequence analysis showed that 71 % of the screened isolates belonged to Bacillus amyloliquefaciens and the rest were closely related to B. atrophaeus and B. mojavensis. Most of them had high spore yields (22?×?10⁸–27?×?10⁸ spores/ml). They produced protease and cellulase cell wall-degrading enzymes while the chitinase activity was only observed in the B. atrophaeus (6SEL). A wide variety of lipopeptides homologous was detected by liquid chromatography–electrospray ionization–mass spectrometry analysis. Interestingly, some additional peaks with new masses were characterized, which may correspond to new fengycin classes. The isolates produced siderophores and indole-3- acetic acid phytohormone. The greenhouse experiment using a naturally infested soil with Sclerotonia sclerotiorum showed that the B. atrophaeus (6SEL) significantly increased the size of the chickpea plants and reduced the stem rot disease (P?<?0.05). These results suggest that these isolates may be used further as bio-inoculants to improve crop systems.     

Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis

Hemoglobin (Hb) and silver–silver oxide (Ag–Ag₂O) nanoparticles were co-immobilized on a bare silver electrode surface by cyclic voltammetry, and were characterized by UV–vis reflection spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The immobilized Hb was shown to maintain its biological activity well. Direct electron transfer between Hb and the resulting electrode was achieved without the aid of any electron mediator. The reduction currents to hydrogen peroxide (H₂O₂) at co-immobilized electrodes showed a linear relationship with H₂O₂ concentration over a concentration range from 6.0?×?10^?6 to 5.0?×?10^?2 mol L^?1, and a detection limit of 2.0?×?10^?6 mol L^?1 (S/N?=?3).     

Detection of flagellin by interaction with human recombinant TLR5 immobilized in liposomes

Digestive diseases caused by flagellated bacteria are a huge public health problem worldwide and rapid detection methods are needed for contaminated environments. In this study, we propose a method to detect patterns associated with pathogens based on the properties of the innate immune system. Specifically, we use Toll-like receptor 5 (TLR5), a transmembrane protein that specifically recognizes flagellin (the structural protein of bacterial flagella). TLR5, which was obtained by recombinant production in insect cells, was immobilized into liposomes to form TLR5-proteoliposomes. Through surface plasmon resonance (SPR) and competition flow cytometry assays, the sensitivity of proteoliposomes to recognize Escherichia coli and Salmonella typhimurium flagellin was evaluated. In addition, we compared the results obtained by immobilizing anti-flagellin antibodies into liposomes. The results of the flagellin-affinity tests, expressed as an SPR kinetic rate constant ratio in the equilibrium equation K _D?=?k _d/k _a, showed values of 13.8?×?10^?9 and 7.73?×?10^?9?M for the TLR5-proteoliposomes and anti-flagellin antibodies, respectively, against S. typhimurium. The anti-flagellin affinity results for E. coli showed K _D of 84.1?×?10^?8?M for SPR assays and K _D of 3.5?×?10^?8?M for competitive flow cytometry, which was used as a detection system without the immobilization of proteoliposomes. This research demonstrates the practical possibility of using proteoliposomes as recognition elements in the generation of systems for the rapid detection of flagellated bacteria, which could help avoid consumption of contaminated food by humans and thereby prevent intestinal infections.     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

Impact of Nitrate Dose on Toluene Degradation under Denitrifying Condition

In this study, we investigated the impact of nitrate dose on toluene degradation by Pseudomonas putida to elucidate the upper limit of nitrate concentration and whether an optimum ratio of nitrate to toluene concentration exists. Batch microcosm studies were conducted in order to monitor toluene degradation for various ratios (2–20) of nitrate to toluene with nitrate concentrations ranging from 0 to 700 mg?L^?1 for a given toluene concentration of 50 and 25 mg?L^?1 during 4-day (short term) and 14-day (long term) incubation time, respectively. The short-term study revealed that nitrate concentration of 500 mg?L^?1 was toxic to bacteria and the optimum concentration was 300 mg?L^?1 yielding the highest toluene degradation rate (0.083 mg?L^?1?h^?1). In the batch study of long term, toluene degradation was limited to 6 days after which the nitrate at 50 mg?L^?1 was depleted, indicating that nitrate was a necessary electron acceptor. For both batch studies, an optimum ratio of 6 was found yielding the highest toluene degradation rate. This indicates that an appropriate nitrate dose is essential for efficient degradation of toluene when bioremediation of groundwater contaminated with toluene is under consideration.     

Kinetic determination of hexacyanoferrates by their inhibition of an oscillating chemical reaction

A method for the kinetic determination of traces of hexacyanoferrate based on an oscillating chemical reaction is presented. In a Belousov-Zhabotinskii reaction system, by using a bromide ion-selective electrode, the amplitude decrease of the potentiometric oscillation is linearly proportional to the concentration of Fe(CN)^3?₆ [or Fe(CN)^4?₆] in the range 7 × 10^?8?5 × 10^?6 M. The relative standard deviation for 1 × 10^?6 M Fe(CN)^3?₆ is 2.7% (n = 6). Cyclic voltammetry was applied to study the mechanism of the proposed system. The procedure was utilized to determine hexacyanoferrates in silver plating and photographic solutions.     

Simultaneous determination of dopamine and serotonin by use of covalent modification of 5-hydroxytryptophan on glassy carbon electrode

An electrochemical biosensor was fabricated by covalent modification of 5-hydroxytryptophan (5-HTP) on the surface of glassy carbon electrode (GCE). The electrode, denoted as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry. For comparison, tryptophan modified GCE (TRP/GCE) and serotonin modified GCE (5-HT/GCE) were prepared by the same method. It was found that electrocatalytic ability of these electrodes was in the order of 5-HTP/GCE?>?TRP/GCE?>?5-HT/GCE for the oxidation of dopamine (DA) and 5-HT. The sensor was effective to simultaneously determine DA and 5-HT in a mixture. It can resolve the overlapping anodic peaks into two well-defined voltammetric peaks at 0.24 and 0.39 V (versus SCE). The linear response is in the range of 5.0?×?10^?7–3.5?×?10^?5 mol L^?1 with a detection limit of 3.1?×?10^?7 mol L^?1 for DA, and in the range of 5.0?×?10^?6–3.5?×?10^?5 mol L^?1 with a detection limit of 1.7?×?10^?6 mol L^?1 for 5-HT (s/n?=?3), respectively.     

Automated determination of carboxylic acids in biological and geochemical samples by means of a chemical reaction detector

Rapid evaluation of carboxylic acids by means of an automated spectrophotometric determination in a continuous-flow system is described. The system was applied to food and soil extracts either as a stand-alone device or as a chemical reaction detector coupled to a chromatographic separation column. Calibration in the automated system was performed with citric acid as a reference standard in the concentration range 4.76 × 10^?5?4.76 × 10^?3 mol l^?1. The molar calibration equation was A=64x ? 6.7 × 10^?5 (x=concentration ) with a correlation coefficient of 0.9997 ( six points). The sample volume was 0.5 ml. In addition to the semi-quantitative evaluation of carboxylic groups, it is shown that the system is also applicable to species analyses.     

Cyclic voltammetry of Tifluadom at a C18-modified carbon-paste electrode

Tifluadom, N-[5-(2-fluorophenyl)-2,3-dihydro-methyl-1H-1,4-benzodiazepine]-2-4-methyl-3-thiophene carboxamide, was determined by using a carbon-paste electrode modified with C₁₈ μBondapak. Adsorption on the electrode served as a preconcentration step which improved the limit of detection. Preconcentration for 5 min (open circuit) gave a linear range of 2.2×10^?7 M?4.5×10^?6 M with a detection limit of 1.3×10^?7 M (%C₁₈=25, w/w) for Tifluadom in Britton-Robinson buffer pH 6. The determination of Tifluadom added to urine required no preliminary treatment; the detection limit was 1.3×10^?6 M.     

Rapid colorimetric detection of Salmonella typhimuriumusing a selective filtration technique combined with antibody–magnetic nanoparticle nanocomposites

Detection of pathogenic bacteria that pose a great risk to human health requires a rapid, convenient, reliable, and sensitive detection method. In this study, we developed a selective filtration method using monoclonal antibody (MAb)–magnetic nanoparticle (MNP) nanocomposites for the rapid and sensitive colorimetric detection of Salmonella typhimurium. The method contains two key steps: the immunomagnetic separation of the bacteria using MAb–MNP nanocomposites and the filtration of the nanocomposite-bound bacteria. Color signals from the nanocomposites remaining on the membrane were measured, which reflected the amount of bacteria in test samples. Immunomagnetic capture efficiencies of 8 to 90 % for various concentrations of the pathogen (2?×?10⁴–2?×?10¹ cells) were obtained. After optimization of the method, 2?×?10¹ cells of S. typhimurium in pure culture solution was detectable as well as in artificially inoculated vegetables (100 cells/g). The method was confirmed to be highly specific to S. typhimurium without cross-reaction to other pathogenic bacteria and could be concluded within 45 min, yielding results in a shorter or similar time period as compared with recently reported antibody immobilized on magnetic-particle-based methods. This study also demonstrated direct application of MAb–MNP nanocomposites without a dissociation step of bacteria from magnetic beads in colorimetric assays in practice.     

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.