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For the first time, we coupled a microextraction technique using a magnetic ionic liquid with voltammetric determination. A hydrophobic magnetic ionic liquid that contains the tetrachloromanganate(II) anion, namely, aliquat tetrachloromanganate(II), was synthesized and used for the extraction of ascorbic acid from aqueous solutions followed by voltammetric determination. The extraction procedure was carried out using a single drop microextraction technique in which the ascorbic acid containing magnetic ionic liquid was separated with a magnet and then cast onto the surface of a carbon paste electrode modified with TiO2 nanoparticles for the voltammetric quantification of the extracted ascorbic acid. Electrochemical quantification was carried out in a blank phosphate buffer solution. After optimizing different experimental conditions, a linear concentration range of 1.50-40.0 nM with a detection limit of 0.43 nM was obtained for the determination of ascorbic acid. The presented approach was successfully applied to the determination of ascorbic acid in samples of vitamin C effervescent tablets and orange juice. [ABSTRACT FROM AUTHOR]

The authors present a voltammetric immunoassay for the quantification of the prostate specific antigen (PSA), a well-established tumor marker. Biotinylated anti- PSA antibodies were immobilized on the surface of a nano-TiO2-modified carbon paste electrode using specific interaction between streptavidin and biotin. Streptavidin itself was covalently grafted to the electrode surface via 4-aminobenzoic acid film. Signal transduction was then performed using polyclonal antibodies conjugated with horseradish peroxidase (HRP) and thionine. An amplified catalytic reduction current was observed in the presence of HO because more than one polyclonal antibody linked to each antigen. Each step of the preparation of the immunosensor was monitored via electrochemical impedance spectroscopy. The electrode, if operated at a typical potential of 0.3 V vs. Ag/AgCl and using hexacyanoferrate as an electrochemical probe, exhibits linear responses in the 0.10 to 5.0 ng·mL and 5.0 to 100 ng·mL PSA concentration ranges, with a detection limit of 200 pg·mL. The accuracy of the biosensor was confirmed by analyzing a certified human serum sample, and this indicated that the immunosensor is well suited for the quantification of PSA. [ABSTRACT FROM AUTHOR]

A novel conductive polymeric ionic liquid (IL)-Fe3O4 nanocomposite (represented as PIL-Fe3O4) based on inorganic-organic hybrid material was synthesized using two different methods. Nuclear magnetic resonance, Fourier transform infrared, X-ray diffraction, and field emission scanning electron microscopy characterized the structures of IL, Fe3O4 nanoparticles, and PIL-Fe3O4. The electrochemical sensors based on PIL-Fe3O4-modified glassy carbon electrode were fabricated, and each of these nanocomposites was examined for the ability to determine amlodipine besylate (AMD). The electrochemical study of the modified electrodes, as well as its efficiency for the electro-oxidation of AMD, was described in 0.1 M phosphate-buffered solution (pH 7.0) using voltammetric methods. The results exhibit a linear dynamic range from 1 to 500 nM and a detection limit of 0.36 nM. Finally, the modified electrode was used for the determination of AMD in pharmaceutical and biological samples. [ABSTRACT FROM AUTHOR]

Oleuropein (Ole), naturally occurring phenolic compound found in olive products, is well known for its benefits for human health. In the present work, a simple, sensitive and rapid determination of Ole was achieved using a label-free electrochemical DNA biosensor. The application was related to the molecular interaction between Ole and double-stranded DNA (dsDNA). So, the voltammetric behavior of Ole at the surface of a DNA-immobilized chitosan-modified carbon paste electrode was studied using differential pulse voltammetry (DPV) where the oxidation peak current of Ole was measured as an analytical signal. A considerable increase was observed in the oxidation signal of Ole at the DNA-coated electrode compared with the DNA-free electrode, indicating the pre-concentration of Ole due to the interaction with the surface-confined DNA layer. In order to use the proposed sensor for real samples, different parameters affecting Ole signal such as, immobilization time and potential, accumulation time and pH, and stripping pH were optimized. Under optimized experimental conditions, a linear concentration range of 0.30–12 μmol L − 1 with a detection limit of 0.090 μmol L − 1 was obtained for Ole determination. The proposed biosensor was successfully applied to the determination of Ole in olive leaf extract and human serum samples. [ABSTRACT FROM AUTHOR]

A carbon paste electrode was modified with ZnO nanorods and 3-(4′-amino-3′-hydroxy-biphenyl-4-yl)-acrylic acid (3,4′AAZCPE) to cause electrocatalysis of norepinephrine oxidation. It has been found that the oxidation of norepinephrine at the surface of modified electrode occurs at a potential of about 180 mV less positive than that of an unmodified carbon paste electrode. Square wave voltammetry (SWV) exhibits linear dynamic range from 1.0×10−7 to 8.0×10−5 M and a detection limit of 3.9×10−8 M for norepinephrine. In addition, this modified electrode was used for simultaneous determination of norepinephrine, tyrosine and nicotine. [ABSTRACT FROM AUTHOR]

A simple and sensitive label-free electrochemical DNA biosensor was proposed for the rapid determination of uric acid (UA) using a carbon nano tube paste electrode (CNTPE) modified with salmon sperm dsDNA. At first, the interaction between UA and the DNA was studied using differential pulse voltammetry (DPV). The addition of the DNA to UA solution resulted in a decrease in the peak current of UA and at the same time, a positive shift in the peak potential indicating an intercalative interaction. Then, the voltammetric response of a DNA-immobilized CNTPE was investigated for the determination of UA. The immobilization of the DNA was carried out using acid-functionalized carbon nanotubes and studied using Fe(CN)6 3−/Fe(CN)6 4− redox indicator. Compared with unmodified CNTPE, the oxidation signal of UA showed a significant increase at the DNA-coated electrode, and shifted to more positive potentials attributed to the pre-concentration of UA at the electrode surface due to interaction with the surface-confined DNA layer. This interaction was used for the fabrication of a simple and sensitive biosensor for determining UA. After the optimization of operational parameters, a linear dependence of the peak current on the UA concentration was observed in the range of 7.0×10−7 to 1.1×10−4 molL−1, with the detection and quantification limits of 1.8×10−7 and 5.8×10−7 molL−1, respectively. The proposed biosensor was successfully applied to validate its capability for the analysis of UA in human serum and urine samples. [ABSTRACT FROM AUTHOR]

In this study, a carbon paste electrode modified with TiO2 nanoparticles and ferrocene monocarboxylic acid (FM) was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for the detection of methyldopa in the presence of folic acid and glycine. The peak potentials recorded in a phosphate buffer solution (PBS) of pH7.0 were 325, 750 and 880mV vs. Ag/AgCl/KCl (3.0M) for methyldopa, folic acid and glycine, respectively. Under the optimum pH of 7.0, the oxidation of methyldopa occurred at a potential about 160mV less positive than that of the unmodified carbon paste electrode (CPE). The response of catalytic current with methyldopa concentration showed a linear relation in the range from 2.0×10−7 to 1.0×10−4 M with a detection limit of 8.0 (±0.2)×10−8 M. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of Ag-4-ATP-MWCNT nanocomposite and its use as a modifier of working electrode. The surface of the electrochemical Ag-4-ATP-MWCNT electrode was modified with a double-stranded DNA (dsDNA) to detect daunorubicin-DNA interactions. Differential pulse voltammetry was applied to develop an electroanalytical procedure for the determination of daunorubicin and evaluate its interaction with dsDNA immobilized on the electrode surface. After the optimization of operational parameters, the linear dependence of the peak current on the daunorubicin concentration was observed in the range of 0.10 × 10 − 8 to 1.00 × 10 − 5 mol L − 1 , with the detection and quantification limits of 3.00 × 10 − 10 and 1.00 × 10 − 9 mol L − 1 , respectively. The proposed biosensor was successfully applied to validate its capability for the determination of daunorubicin in human serum and urine samples. [ABSTRACT FROM AUTHOR]

Extra concentrations of hemin are toxic since it may intercalate in lipid membranes and catalyze the formation of hydroxyl radicals resulted in the lysis and death of the cell. So, we have proposed a novel green approach for the determination of hemin in biological samples. Due to the complexity of the matrix of these samples, an efficient extraction procedure has been also involved in the approach. An ammonium-based task-specific ionic liquid containing salicylate anion was synthesized and used for the extraction and pre-concentration of hemin trough a dispersive liquid phase microextraction. Hemin was extracted into a few micro liters of the ionic liquid and so, separated from the sample matrix. Differential pulse voltammetry followed the extraction process for the quantification of hemin in the IL-rich phase separated from the sample and placed on the surface of a glassy carbon electrode. In the presented approach, the ionic liquid was used as both the extracting solvent (due to its polarity and water-immiscibility) and the electrode modifying agent (due to its ionic structure). The peak current obtained from the electrochemical reduction of hemin was used as the analytical signal correlated to the concentration of hemin. Different experimental parameters affecting both the extraction and electrochemical processes were optimized. Under the optimized conditions, a linear concentration range of 0.020–2.60 μM with a detection limit of 3.16 × 10 − 3 μM was obtained. The proposed methodology was successfully applied to the determination of hemin in a mouse serum sample indicating its applicability to complex media. [ABSTRACT FROM AUTHOR]

Abstract: A highly selective and sensitive carbon paste electrode modified with multi-walled carbon nanotubes and 4-[1-(4-methoxyphenyl) methylidene]-3-methyl-5-isoxazolone was used for accumulation and determination of trace amounts of bismuth using the differential pulse anodic stripping voltammetric method. The analytical procedure consisted of a closed-circuit accumulation step onto the modified carbon paste electrode. An anodic peak related to the oxidation of accumulated Bi(0) on the electrode surface was observed at about −0.05V. The calibration curve was linear in the range of 1–400μgL−1. The limit of detection was 0.2μgL−1 and the relative standard deviations for seven replicated determinations at 30, 100 and 300μgL−1 of bismuth were 3.6, 2.4 and 1.6%, respectively. The modified electrode was applied for the determination of bismuth in pharmaceutical, biological and several water samples. The accuracy and precision of results were comparable to those obtained by the graphite furnace atomic absorption spectroscopy method. [Copyright &y& Elsevier]

In the present study, a carbon paste electrode chemically modified with gold nanoparticles was used as a sensitive electrochemical sensor for determination of eugenol. The differential pulse voltammetric method was employed to study the behavior of eugenol on this modified electrode. The effect of variables such as percent of gold nanoparticles, pH of solution, accumulation potential and time on voltammogram peak current were optimized. The proposed electrode showed good oxidation response for eugenol in 0.1 mol L − 1 phosphate buffer solution (pH 8) and the peak potential was about + 285 mV (vs. Ag/AgCl). The peak current increased linearly with the eugenol concentration in the range of 5–250 μmol L − 1 . The detection limit was found to be 2.0 μmol L − 1 and the relative standard deviation was 1.2% (n = 7). The effect of interferences on the eugenol peak current was studied. The method has been applied to the determination of eugenol in different real samples, spiked recoveries were in the range of 96%–99%. [ABSTRACT FROM AUTHOR]