Pascal Mailley

Development of amperometric biosensors based on the immobilization of enzymes in polymer films electrogenerated from a series of amphiphilic pyrrole derivatives

Abstract A series of amphiphilic pyrrolyl-alkylammonium ions differing in the size of their ammonium heads has been used for the immobilization at the electrode surface of horseradish peroxidase, galactose oxidase, polyphenol oxidase, glucose oxidase and xanthine oxidase in polypyrrolic films electrogenerated from adsorbed amphiphilic pyrrole-enzyme mixtures. The enzyme retention properties of the different polymers have been determined indicating that the less hydrophobic monomer has the best immobilization efficiency. The electrochemical assays performed for galactose, glucose and hypoxanthine detection show clearly that the bioelectrode sensitivity is related to the permeability of the host polymer. The selectivity of the glucose oxidase electrodes towards interfering agents like ascorbate, urate and acetaminophen has also been examined, these agents interfering to some extent when present at physiological concentrations.

Electrochemical and structural characterizations of electrodeposited iridium oxide thin-film electrodes applied to neurostimulating electrical signal

Abstract Thin-film technology takes more and more importance in the development of biomedical devices dedicated to functional neurostimulation. Our research about the design of implantable neurostimulating electrode is oriented toward thin-film cuff electrodes based on PTFE substrate covered by a gold/iridium oxide film. A gold-sputtered film serves as adhesion layer and current collector whereas iridium oxide acts as an electrochemical actuator. The latter is obtained under galvanostatic oxidation and for various electrodeposited charge densities (from 11 to 116 mC/cm2). This paper deals with the design and the characterization of the iridium oxide interfaces and their in vitro application in model nonproteic electrolyte. Microstructural characterization was developed using SEM and AFM. The optimal microstructural organisation was obtained for electrodeposition charge densities from 46 to 70 mC/cm2. The analysis of the interface electrochemical behaviour was carried out by cyclic voltammetry, impedance spectroscopy and square-wave signal. The electrode material shows redox reversible system at 0.5 V/SCE, enabling low-resistance interface and facilitating charge transfer. The optimum electrochemical properties and the optimum microstructure, regarding a biocompatible electrical stimulation, were recorded for electrodeposition charges from 46 to 70 mC/cm2.

Polypyrrole based DNA hybridization assays: study of label free detection processes versus fluorescence on microchips.

In this paper, we present different ways to detect DNA hybridization on a solid support. The grafting chemistry is based on the electro-controlled copolymerization of a pyrrole-modified oligonucleotide and pyrrole. This process allows an easy functionalization of conducting materials. Three kind of devices were studied: silicon chips bearing an array of addressable 50 or 4 microm microelectrodes, quartz crystal microbalance (QCM) and a non patterned gold/glass slide bearing 500 microm spots. Each device is compatible with a specific detection process: a classical indirect fluorescence detection for the microchips, a microgravimetric measurement for the QCM and a surface plasmon resonance imaging process (SPRi) for the gold slides. Both QCM and SPRi are a label-free real time detection process whereas the fluorescence methodology gives end-point data but only the fluorescence and the SPRi give multiparametric results. Although the hybridization experiments show that the detection limit for an oligonucleotide is better for the fluorescence (1-10 pM) than that found for SPRi (10 nM) and QCM (250 nM), the information content of real time measurement techniques such as SPRi is of interest for many biological studies.

A comparison of amperometric screen-printed, carbon electrodes and their application to the analysis of phenolic compounds present in beers.

In this paper a comparison between three commercially-available, screen-printable graphite inks for the construction of phenolic biosensors is made. The enzyme tyrosinase was immobilised within a polymer matrix and the substrate catechol was used to characterise the bio-electroanalytical response of each electrode. Biosensors fabricated from Gwent graphite inks exhibited the greatest sensitivity (5740 mA mol cm(-2)) compared to Dupont and Acheson graphite-based inks. This difference in sensitivity was attributed to a combination of a larger electroactive surface area, and thus a greater number of immobilised enzyme molecules. However, the dynamic range was considerably smaller (0.025-14 muM) indicating that the enzyme molecules were easily accessible to the substrate catechol. The surface properties of the biosensors were characterised using ac impedance, which indicated that the presence of the polymer on the electrode surface not only increased the charge-transfer kinetics of the three biosensors, but also increased the surface roughness of biosensors fabricated from Gwent inks. On the basis of these results Gwent graphite-based inks were used for analysis of phenolic compounds in lager beers by flow-injection analysis. The biosensor displayed favourable response characteristics, but cannot differentiate between the various phenolic compounds present in the samples. Nevertheless, the biosensor maybe suitable for indicating the phenolic status of beer or brew samples compared to time-consuming traditional methods, e.g. colorimetric or chromatographic methods.

A New 3-D Finite-Element Model Based on Thin-Film Approximation for Microelectrode Array Recording of Extracellular Action Potential

A transient finite-element model has been developed to simulate an extracellular action potential recording in a tissue slice by a planar microelectrode array. The thin-film approximation of the active neuron membrane allows the simulation within single finite-element software of the intracellular and extracellular potential fields. In comparison with a compartmental neuron model, it is shown that the thin-film approximation-based model is able to properly represent the neuron bioelectrical behavior in terms of transmembrane current and potential. Moreover, the model is able to simulate extracellular action potential recordings with properties similar to those observed in biological experiments. It is demonstrated that an ideal measurement system model can be used to represent the recording microelectrode, provided that the electronic recording system adapts to the electrode-tissue interface impedance. By comparing it with a point source approximated neuron, it is also shown that the neuron three-dimensional volume should be taken into account to simulate the extracellular action potential recording. Finally, the influence of the electrode size on the signal amplitude is evaluated. This parameter, together with the microelectrode noise, should be taken into account in order to optimize future microelectrode designs in terms of the signal-to-noise ratio.

Individual Blood‐Cell Capture and 2D Organization on Microarrays

The image shows living B lymphocytes captured on a microcantilever-arrayed biochip. Antibodies targeting cellular antigens are pyrrole-modified and then electropolymerized into polypyrrole films on a gold surface. The arrayed feature size is close to a lymphocyte size and thus allows efficient cell capture and organization. Gold layers can thus be arrayed in a predetermined manner that gives access to organized blood cells on surfaces. Each line is separated from the other by 50 µm.

Amperometric carbon paste biosensor based on plant tissue for the determination of total flavanol content in beers

Apple tissue containing polyphenol oxidase was incorporated in carbon paste matrix to make a biosensor for the analysis of flavanols in beers. The electrochemical and structural properties of different carbon paste compositions were assessed using ac impedance, other electrochemical techniques and scanning electron microscopy. Results are discussed regarding electroactive surface, mechanical stability, impedance parameters and surface roughness of the carbon pastes. From these results, an optimum graphite/Nujol ratio of 4 was chosen and applied to the construction of apple-based biosensors. The electrochemical, morphological and analytical properties of these sensors were investigated with respect to biomolecule loading. The analytical properties (sensitivity, Imax) of these biosensors increased with plant tissue loading. This result was correlated with ac impedance parameters, electroactive surface and carbon paste morphology. A biosensor using a plant tissue/carbon paste ratio of 0.086 was used to assess sensitivity and selectivity to various flavanols and phenolic compounds.

Multichannel Boron Doped Nanocrystalline Diamond Ultramicroelectrode Arrays: Design, Fabrication and Characterization

We report on the fabrication and characterization of an 8 × 8 multichannel Boron Doped Diamond (BDD) ultramicro-electrode array (UMEA). The device combines both the assets of microelectrodes, resulting from conditions in mass transport from the bulk solution toward the electrode, and of BDDs remarkable intrinsic electrochemical properties. The UMEAs were fabricated using an original approach relying on the selective growth of diamond over pre-processed 4 inches silicon substrates. The prepared UMEAs were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results demonstrated that the electrodes have exhibited a very fast electrode transfer rate (k0) up to 0.05 cm·s−1 (in a fast redox couple) and on average, a steady state limiting current (in a 0.5 M potassium chloride aqueous solution containing 1 mM Fe(CN)64− ion at 100 mV·s−1) of 1.8 nA. The UMEAs are targeted for electrophysiological as well as analytical applications.

Quasi-Real Time Quantification of Uric Acid in Urine Using Boron Doped Diamond Microelectrode with in Situ Cleaning

We report herein an innovative electrochemical (EC) technique based on boron doped diamond (BDD) microelectrodes which enable the fast determination of uric acid (UA) concentrations in urine. On the basis of fast cyclic voltammetry (CV), the technique was assessed in human urine samples and compared successfully using routine spectrophotometric diagnosis. The approach relies on the use of BDDs superior properties such as low background current, low adsorption of species, long-term stability, and antifouling capabilities using electrochemical reactivation. Moreover, the article also describes an in situ activation technique, where the electrodes were reactivated within human urine, thereby opening the way toward automatic quantification of UA with in situ cleaning. The time taken to quantify UA concentration and cleaning remains below 0.5 s. Two analytic models were derived, based on different concentrations of ascorbic acid (AA) and uric acid, consisting of 2 s order calibration curves. Solving the second order equation enables the direct estimation of UA concentration, and values demonstrated good accuracy when compared with spectrophotometric measurements.

Contactless Electrofunctionalization of a Single Pore

Customized pores are smart components that find challenging applications in a variety of fields including purification membranes and biosensing systems. The incorporation of recognition probes within pores is therefore a challenge, due to the technical difficulty of delimiting the area functionalized and obtaining the localized, specific chemical modification of pore walls. An innovative approach, named contactless electrofunctionalization (CLEF), is presented to overcome this problem. CLEF allows easy, one-step modification of the inner surface of a pore etched in a dielectric membrane. The pore wall is coated under the influence of an electric field created by the application of a voltage between two electrodes, located near but not in contact with the pore openings. This specific localization of the deposited material within the pore is extremely rapid. Coatings were reliably and reproducibly obtained using polypyrrole co-polymers bearing oligonucleotides, demonstrating that this technology has a promising future in the design of biosensors. Moreover, the versatility of this process allows the deposition of various electroactive entities such as iridium oxide and therefore indicates a strong potential for diverse applications involving porous materials.