Khalid R. Temsamani

Voltammetric determination of trace mercury at a sonogel-carbon electrode modified with poly-3-methylthiophene.

The sonogel-carbon electrode is a new class of sol-gel electrode that exhibit favourable mechanics and electrics properties to be used as electrochemical sensor. In this paper, a modified sonogel-carbon electrode is proposed to determine mercury at trace levels. The modified electrode is obtained by electropolymerization of 3-methylthiophene on the surface of a bare sonogel-carbon electrode. This electrode shows high selectivity and sensitivity and linear response towards Hg(II), with a detection limit of 1.4x10(-3)mgl(-1). The electrode is reusable by a simple chemical cleaning procedure. No deterioration was observed in the electrode response during at least 1 week of successive measurements.

Electrochemical control of solid phase micro-extraction: conducting polymer coated film material applicable for preconcentration/analysis of neutral species

Exploitation of the physical, chemical and electrically conductive properties of poly(3-dodecylthiophene) (P3DDT) for the preconcentration and release in solid phase microextraction (SPME) of organometallic arsenobetaine (AsB) from aqueous media was investigated. Hydrophobic interactions between this neutral arsenic species and an undoped polythiophene (no applied potential) with n-substituted alkyl groups (n=12) in the three position were used for the diffusion-controlled preconcentration. After absorption into the polymer matrix, the chemical properties of this conductive polymer were changed by applying an external potential. This potential provides a sufficient driving force for desorption of the analyte from the extraction phase into an aqueous solution for subsequent analysis. The applied positive potential oxidizes the polymer to its charged hydrophilic state, which releases the neutral analyte. The concentration and speciation of the analyte from the sample matrix was analyzed by HPLC coupled to an ICP-MS. The diffusion-controlled uptake was fast (equilibrium attained within minutes) and did not require pretreatment of the analyte. The electrochemically-controlled release of the analyte is also very rapid (within minutes). This conducting polymer film system, therefore, can offer analytical applications for the convenient preconcentration and subsequent analysis of neutral environmental species.

Phenol biosensor based on Sonogel-Carbon transducer with tyrosinase alumina sol–gel immobilization

A new biosensor for detection of phenols, based on tyrosinase immobilization with alumina sol-gel on Sonogel-Carbon transducer, has been developed. The electrode was prepared using high energy ultrasounds directly applied to the precursors. The alumina sol-gel provided a microenvironment for retaining the native structure and activity of the entrapped enzyme and a very low mass transport barrier to the enzyme substrates. Phenols are oxidized by tyrosinase biosensor to form a detectable product, which was determined at -300 mV vs. Ag/AgCl reference electrode. For phenol, the sensor exhibited a fast response which resulted from the porous structure and high enzyme loading of the sol-gel matrix. The linear range was from 5 x 10(-7)M to 3 x 10(-5)M, with a detection limit of 3 x 10(-7)M. The stability of the biosensor was also evaluated.

Stripping voltammetry of silver ions at polythiophene-modified platinum electrodes.

The present work describes the development of a modified platinum electrode for stripping voltammetric determination of silver. The deposition of films based on electropolymerisation of the monomer thiophene was carried out by cycling the potential towards positive values between 0 and 1.6V. The preconcentration process of silver ions was initiated on the surface of the modified electrode by complexing silver with polythiophene (PTH) when a negative potential (-0.5V) was applied; then the reduced products was oxidized by means of differential pulse stripping voltammetry and the peak was observed at 0.17V. Parameters such as pH, supporting electrolyte and number of electropolymerisation cycles were studied. A linear relation between current peak and concentration of Ag(I) was obtained in the range 0.07-1.0mgL(-1). The detection limit for Ag(I) was evaluated to be 0.06mgL(-1). The reproducibility was tested carrying out 11 measurements at different electrodes and the relative standard deviation was 1.5%. The interference of several metals was investigated and showed negligible effect on the electrode response.

Electrosynthesis and analytical performances of functionalized poly (pyrrole/β-cyclodextrin) films

The supramolecular complexing properties of cyclodextrins (CDs) have been investigated inside a conducting polymer environment. In this work, we report the synthesis and characterization of a polypyrrole/beta-cyclodextrin (Ppy/beta-CD) film at a glassy carbon (GC) electrode surface. The polypyrrole/beta-cyclodextrin (Ppy/beta-CD) film was prepared by a simple electropolymerization of a 20:1 mixture of the CD and the pyrrole monomer LiClO(4) supporting electrolyte. The resulting functionalized polymer film features interesting electrochemical properties such as selective, simultaneous and quantitative detection of some organic compounds of interest such as polyhydroxyphenyls and neurotransmitters derived from pyrogallol and catechol. The fabricated electrochemical sensor exhibits a fast and reversible linear response toward catechol within the concentration range of 1.5x10(-7) to 8x10(-6)M and towards pyrogallol within the concentration range of 1x10(-6) to 1x10(-5)M. The detection limit was 4x10(-7) and 1.8x10(-6)M for catechol and pyrogallol, respectively. Studies of neurotransmitters such as epinephrine, metanephrine and l-dopa (l-3,4-dihydroxyphenylalanine), showed better response toward epinephrine and l-dopa than for metanephrine. Calibration curves for these two neurotransmitters were linear over the concentration range of 1x10(-6) to 1x10(-5)M. The detection limit was 4x10(-6) and 1x10(-6), respectively. The complexation capability of the Ppy/beta-CD system is addressed here in terms of structure-electrochemical activity relationship. The mechanical stability of the film is also discussed. Measurements were performed using cyclic voltammetry (CV), scanning electron microscopy (SEM) coupled to energy dispersive analysis of X-ray (EDAX) and electrochemical impedance spectroscopy (EIS).

Alumina sol-gel/sonogel-carbon electrode based on acetylcholinesterase for detection of organophosphorus pesticides.

Two new amperometric biosensors based on immobilization of acetylcholinesterase on a sonogel-carbon electrode for detection of organophosphorous compounds are proposed. The electrodes were prepared applying high-energy ultrasounds directly to the precursors. The first biosensor was obtained by simple entrapping acetylcholinesterase in Al(2)O(3) sol-gel matrix on the sonogel-carbon. The second biosensor was produced in a sandwich configuration. Its preparation involved adsorption of the enzyme and modification via a polymeric membrane such as polyethylene glycol and the ion-exchanger Nafion. The optimal enzyme loading was found to be 0.7 mIU. Both biosensors showed optimal activity in 0.2 M phosphate buffer, pH 7.0, at an operating potential of 210 mV. The detection limit achieved for chlorpyriphos-ethyl-oxon was 2.5x10(-10)M at a 10-min incubation time.

Electrochemical behaviour of epinephrine and uric acid at a Sonogel―Carbon L-Cysteine modified electrode

The Sonogel-Carbon electrode is a special class of sol-gel electrode that exhibits favourable mechanic and electric properties to be used as electrochemical sensor. In this study, Sonogel-Carbon modified with L-Cysteine was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for detection of epinephrine in the presence of uric acid. The response of catalytic current with epinephrine concentration shows a linear relation in the range from 1 x 10(-7) to 5 x 10(-4)M with a correlation coefficient of 0.998, and a detection limit of 8.7 x 10(-8)M. The modified electrode had also been applied to the determination of epinephrine and uric acid in biological samples with satisfactory results. A surface characterisation of this modified electrode was carried out helped by scanning electron microscopy (SEM) and X-Ray energy dispersive spectroscopy (EDS).

Investigation of biosensor signal bioamplification: comparison of direct electrochemistry phenomena of individual Laccase, and dual Laccase-Tyrosinase copper enzymes, at a Sonogel-Carbon electrode.

Direct electrochemistry of Trametes versicolor Laccase (LAC) was found at a Sonogel-Carbon electrode. The bioamplification, performed by dual immobilization of this enzyme and Mushroom Tyrosinase (TYR), of the bio-electrocatalytic reduction of O(2) was investigated. The calculated alpha transfer coefficients were 0.64 and 0.67, and the heterogeneous electron-transfer rate constants were 6.19 and 8.52 s(-1), respectively, for the individual LAC and dual LAC-TYR-based Nafion/Sonogel-Carbon bio-electrodes. The responses of the dual enzymes electrode to polyphenols were stronger than those of the individual LAC or TYR biosensors. Hypotheses are offered about the mechanism of bioamplification. The surfaces of the biosensors were also characterized by AFM.

A simple conducting polymer-based biosensor for the detection of atrazine

Abstract In this paper, we present preliminary results for the preparation and application of a biosensor intended to detect photosynthetic inhibiting herbicides such as atrazine. Our approach is based on the preparation of a glassy carbon electrodes operating at open‐circuit and serving for the immobilization of the enzyme polyphenol oxidase (PPO) during the anodic electropolymerization of polypyrrole (PPy). The enzyme is trapped at the electrode surface during the electrochemical synthesis process. A biological reactor can then be realized. Once the biological reactor (the film at the electrode surface) is prepared, another electrode is used as a redox product detector of PPO catalytic activity. The concentration of atrazine in aqueous solution can be determined, thanks to its inhibitory power toward the catalytic activity of PPO represented by the produced quinone concentration. A long electrode lifetime is achieved, thanks to the well‐known high mechanical stability of the conducting polymer PPy and to the absence of polarization of the first electrode (open‐circuit conditions). The interesting analytical performances and simplicity of fabrication of our biosensor suggests its possible application for photosynthetic inhibiting herbicide monitoring.

The Electrochemical Behavior of Neurotransmitters at a Poly (Pyrrole‐ β‐Cyclodextrin) Modified Glassy Carbon Electrode

Abstract A glassy carbon electrode surface was modified with an electropolymerized film made of pyrrole and β‐cyclodextrin 1∶1, in a 0.1 M LiClO4 solution using cyclic voltammetry. The resulting modified electrode (Ppy/β‐CD) exhibits interesting electrocatalytic activity toward the electrochemical oxidation of neurotransmitters such as dopamine (DA) and norepinephrine (NE). Well‐resolved and reversible cyclic voltammograms (CVs) were obtained for these organic compounds in a 0.1 M H2SO4 solution. The effect of the pH on the voltammetric response of DA and NE was also investigated inside the range of pH 2.8–8.4. The oxidation current of norepinephrine increase linearly with the concentration inside the range of 4×10−7 M–2×10−6 M. The oxidation current of dopamine also followed the same trend range of 2×10−6 M–10−5 M. The detection limit was 6×10−6 M for (DA) and 8×10−7 M for (NE). As an example, the relative standard deviation for 1×10−5 M of DA was 2.056%. The diffusion coefficients D for the molecules studied were determined by means of the measurement of the effect of the scan rate on the CVs of the neurotransmitters. All the results showed that the electron transfer was predominantly diffusion controlled at the conducting polymer/solution interface. Interference phenomenon due to ascorbic acid (AA) toward the neurotransmitters was also investigated. The novel modified electrodes presented capability to resolve perfectly the AA and neurotransmitters oxidation peaks. This performance could be achieved even at a concentration 20 times higher than the neurotransmitters. Finally, the newly fabricated Ppy/β‐CD film exhibits interesting analytical performances compared with other systems in the literature, such as higher sensitivity, rapid response, good mechanical stability and reproducibility.