Benoît Limoges

A disposable Protein A-based immunosensor for flow-injection assay with electrochemical detection

Abstract Low-cost disposable immunosensors were produced by covalent binding of Protein A or G on graphite-polystyrene screen-printed electrodes, and they were used in a fully automated flow-injection analysis (FIA) system, allowing the kinetics of IgG binding to Protein A or G to be improved by forced convection. The displacement of rabbit IgG bound to Protein A or G by mouse IgG isotypes (IgG 1 or IgG 2a ) was studied. A FIA immunoassay of mouse IgG 2a was performed at a Protein A-based immunosensor with a good sensibility (down to 0.02xa0μgxa0ml −1 ) and a total assay time of 19xa0min. It was shown that the immunosensor combines the advantages of being reusable for more than 30 assay cycles in flow-injection analysis, and disposable when necessary.

Redox cationic or procationic labeled drugs detected at a perfluorosulfonated ionomer film-coated electrode

With the aim of developing a new type of immunoassay with electrochemical detection, a Nafion® film-modified electrode was used as an amplifying sensor to detect redox cationic labeled drugs by square-wave voltammetry. A series of amino drugs was labeled with three model redox labels, i.e. cationic cobaltocenium and procationic ferrocene and nitroxide groups. Several parameters were involved in the optimization of the analytical properties of the sensor, i.e. film processing and film thickness, accumulation time, ionic strength and ethanol content. The preconcentration of the labeled drugs was impeded by the competitive accumulation of hydrophobic amines. The accumulation process of the procationic labeled drugs was influenced significantly by the potential applied during accumulation, and their strong non-specific binding with proteins was observed in the presence of serum. Therefore the choice of cobaltocenium as a label was preferred. Optimized conditions were defined, which took into account these various aspects. The avidin-biotin system was proposed as an applicable extension of this approach.

Determination of alkaline phosphatase using a Nafion®-modified electrode

Abstract Alkaline phosphatase (AP) assays were performed at pH 7.5 with [ N -ferrocenoyl], -6-amino-2,4-dimethylphenyl phosphate ( 3 ) as substrate and a Nafion®-modified glassy carbon (GC + Nafion®) electrode as sensor. At this pH value, the substrate was dianionic and therefore was repulsed by the GC + Nafion® electrode, whereas the corresponding alcohol 4 generated enzymatically was entrapped within the Nafion® film as a ferricinium salt by applying a potential of 0.6 V vs. Ag|AgCl during an accumulation step that followed incubation and preceded the electrochemical determination of 4. In a typical experiment, enzymatic hydrolysis of 3 to the corresponding alcohol 4 was carried out for 15 min in Tris buffer solution at pH 10.2. The pH value was then lowered to 7.5 and the solution was transferred to an electrochemical cell. The accumulation occurred for 5 min at a rotating GC + Nafion® electrode, prior to the determination of 4 by square-wave voltammetry at stationary GC + Nafion® electrode. The AP detection limit was 0.02 U l −1 (signal/residual current = 2). The accumulation of [ N -ferrocenoyl]-4-aminophenol ( 2 ) within the Nafion® film was also examined. It was observed that, at low concentrations, the dimethylated alcohol 4 accumulated more readily in the Nafion® film than 2 , which is consistent with the more hydrophobic character of the former alcohol. Therefore the use of [ N -ferrocenoyl]-4-aminophenyl phosphate as substrate for very sensitive AP assays at the Nafion® electrode is not recommended.

Competitive assay of 2,4-dichlorophenoxyacetic acid using a polymer imprinted with an electrochemically active tracer closely related to the analyte

2-Chloro-4-hydroxyphenoxyacetic acid was used as an nelectroactive tracer in a ligand displacement assay involving molecularly nimprinted polymer particles for the analysis of the herbicide n2,4-dichlorophenoxyacetic acid by means of linear scan voltammetry at a ndisposable screen-printed electrode.

Electrocatalytic oxidation of hydrogen peroxide by nitroxyl radicals

Abstract A series of nitroxyl radicals have been used as efficient organic catalysts for the mediated oxidation of hydrogen peroxide at a carbon paste electrode immersed in aqueous media. Second order catalytic rate constants were measured and indicate an efficient inner sphere catalytic process. A nitroxide-loaded carbon paste electrode was prepared and used as a sensitive reagentless hydrogen peroxide sensor. The sensitivity of the resulting H 2 O 2 anode was 0.23 A cm −2 M −1 at 0.6 V and a detection limit of 5 × 10 −8 M was obtained.

Redox Labeling of Two Antiepileptic Drugs with Metallocenes and Their Simultaneous Detection by a Nafion-modified Electrode

Two different cationic redox labels, i.e. a ferroceneammonium ion and a cobaltocenium ion, were covalently attached to two antiepileptics, phenytoin and phenobarbital, respectively. The two labeled drugs possess distinct standard redox potentials of 0.3 9V for the phenytoin derivative and 20.9 2V for phenobarbital derivative (vs Ag/AgCl, Cl 2 0.0 5M) at a carbon paste electrode. After preconcentration in a polyanionic Nafionloaded carbon paste electrode the positively charged labeled phenytoin and phenobarbital derivatives could be simultaneously detected in concentration ranges which were relevant to the therapeutic ranges of the antiepileptics, with a view to a future dual-analyte immunoassay. Square-wave voltammetry permitted detection limits of 5 310 28 M(for the phenytoin derivative) and 2.5 310 28 M (for the phenobarbital derivative) for non-simultaneous detection.