Pierre Gros | Université de Toulouse III Paul Sabatier (original) (raw)

Papers by Pierre Gros

Journal of Electroanalytical Chemistry, 2010

International Journal of Electrochemical Science, 2013

The electrochemical reduction of dioxygen (O₂) has been studied on bulk gold (Au) and glassy carb... more The electrochemical reduction of dioxygen (O₂) has been studied on bulk gold (Au) and glassy carbon (GC) electrodes in aqueous neutral solution close to blood ionic composition. The mechanism was found to involve two successive bielectronic steps with hydrogen peroxide (H₂O₂) as the reaction intermediate whatever the electrode material used. On Au, O₂ and H₂O₂ were reduced at close potentials. The determination of the kinetic parameters of O₂ electroreduction was thus achieved after removing the cathodic current corresponding to H₂O₂ reduction. Cyclic voltammograms exhibited one cathodic peak whose both current density (jp) and potential (Ep) evolution as a function of potential scan rate (r) was in accordance with Randles Sevcik and Nicholson-Shain equations, respectively. Rotating disk electrode (RDE) voltammetry was also performed and the data were analyzed using the Koutecky-Levich relationship. The effective number of electrons (n) was found to be roughly independent of the pot...

Oxidative stress is associated to the massive generation of reactive oxygen species inducing fast... more Oxidative stress is associated to the massive generation of reactive oxygen species inducing fast oxidative reactions in chain. To overcome this problem, reasonable supplementations of antioxidants are widely practiced, mostly based on empirical protocols. An electrochemical process is proposed to choose the best molecules association inducing the greatest antioxidant capacity, by coupling homogeneous or heterogeneous catalytic reactions involving antioxidants with an electrochemical step. Cyclic voltammetry and constant potential electrolysis experiments were used to highlight regeneration reactions induced by specific associations of hydrophilic and lipophilic antioxidants in homogeneous medium or at liquid/liquid interface. Results showed that N-Acetyl-L-Cysteine (NAC) was effectively regenerated by both ascorbic acid (AA) and ascorbyl glucoside (AA-2G) but not by ascorbyl phosphate magnesium (AA-2P). The antioxidant properties of alpha-tocopherol also increased to 40% when assoc...

Electroanalysis

A gold electrode surface was functionalized by means of an electropolymerized conductive poly(3,4... more A gold electrode surface was functionalized by means of an electropolymerized conductive poly(3,4ethylenedioxythiophene) (PEDOT) organic layer. This modified electrode was used for the electrochemical detection of ascorbic (AA) and uric (UA) acids in an aqueous mixture with a selectivity around 340 mV. The electrochemical reactions kinetics were limited by AA diffusion and UA adsorption at the electrode surface, respectively. Following a previous study ([Electrochem Comm. 2011, 13, 423-425]) cyclic voltammetry was used to provide a better understanding of the EC' mechanism of regeneration of UA by AA. Experiments particularly showed that allantoin (i. e. the final product of UA oxidation) is not actually involved in the synergic mechanism but rather the oxidized UA product diimine which is adsorbed at the electrode surface.

Journal of Electroanalytical Chemistry, 2016

A new route for the integration of a graphene-based electrode on a silicon substrate was studied ... more A new route for the integration of a graphene-based electrode on a silicon substrate was studied for the simultaneous detection and assay of ascorbic (AA) and uric (UA) acids. Graphene was synthesized by catalytic chemical vapour deposition (CVD) from methane as carbon feedstock onto both platinum foils and supported thin platinum films on silicon wafers which were used as catalyst. Graphene was characterized by Raman spectroscopy and electron microscopies. The resulting electrodes were further functionalized by successive electrodeposition of a stabilizing diazonium layer and a poly(3,4-ethylenedioxythiophene) (PEDOT) conductive film. AA and UA determination on such modified electrode was performed either by cyclic voltammetry or by differential pulse voltammetry. In the latter case, the selectivity was about 380 mV and the sensitivity was 2.40 and 2.75 μA cm −2 μM −1 for AA and UA, respectively. The present study shows that monolayer graphene allows a greater sensitivity of AA and UA detection than that observed with modified glassy carbon electrode.

Irbm, 2008

Potentiometry and cyclic voltammetry were proposed as simple, reliable and non invasive methods f... more Potentiometry and cyclic voltammetry were proposed as simple, reliable and non invasive methods for the simultaneous determination of pH and antioxidant properties of skin. Experiments were performed with microelectrodes just deposited on skin surface without any gel or water added. pH was measured by means of the zero current potential of a tungsten W/WO3 sensor. A nerstian response was recorded

ABSTRACT Voltammetric sensors for the determination of antioxidant properties in dermatology and ... more ABSTRACT Voltammetric sensors for the determination of antioxidant properties in dermatology and cosmetics

Http Www Theses Fr, 1996

Les syntheses biochimiques de produits a haute valeur ajoutee basees sur des reactions d'oxyd... more Les syntheses biochimiques de produits a haute valeur ajoutee basees sur des reactions d'oxydoreduction sont generalement realisees par des procedes fermentaires, qui pechent par leur manque de selectivite. Leur substitution par des procedes bioelectrochimiques exploitant la selectivite des catalyses enzymatiques n'est economiquement envisageable que si l'enzyme est confinee au voisinage de l'electrode. L'objectif du travail est de mettre au point et d'extrapoler a l'echelle d'un reacteur de laboratoire une interface electrode/enzyme, en immobilisant le biocatalyseur dans un film de polypyrrole electroforme. Une etude experimentale et theorique du couplage entre reaction electrochimique, reaction enzymatique et transfert de matiere dans le polymere est menee avec la glucose oxydase. Le modele a permis de souligner la forte concentration de l'enzyme dans le film et de mettre en evidence la diffusion restreinte des substrats. Quels que soient les parametres d'electropolymerisation du pyrrole choisis, le film presente une permeabilite relativement faible. Celle-ci a ete augmentee par un facteur dix en reduisant fortement l'epaisseur du polymere et en introduisant des molecules de polyethylene glycol dans la solution de monomere. Les performances d'un reacteur electroenzymatique concu autour de cette interface ont ete evaluees en mettant en uvre deux reactions biochimiques: la reduction du coenzyme pyridinique catalysee par une hydrogenase, et la production d'acide gluconique catalysee par la glucose oxydase. Le rendement de la premiere reaction est limite par l'inhibition de l'hydrogenase dans le polymere. Les resultats obtenus dans le second cas demontrent en revanche toutes les potentialites de l'edifice electrode/enzyme/polymere dans le domaine de la synthese et mettent en evidence l'amelioration de l'efficacite du procede grace a l'assistance electrochimique

Journal of Electroanalytical Chemistry, 1995

The behaviour of an electrode modified by entrapment of glucose oxidase in an insulating polypyrr... more The behaviour of an electrode modified by entrapment of glucose oxidase in an insulating polypyrrole film is examined using both an experimental study and a theoretical model. Although adsorption of glucose oxidase at the electrode surface and at the polymer ]solution interface was shown experimentally, more than 90% of the amperometric responsc due to the glucose oxidation was generated by the enzyme confined inside the polymeric matrix. The maximum amperomctric response was obtained with a polypyrrole film of thickness 250 nm; the global process rate was governed by the kinetics of the catalysed reaction for thin films and by the mass transport of the species in the polymer for thicker films. All the experimental results were tilted correctly by a complete model using the same values of the physicochemical parameters in all cases. In particular, the theoretical results agreed well with the enzyme location determined experimentally; furthermore, they permitted the prediction that the amperometric response decreased when solution stirring increased. The simulation of the theoretical concentration profiles confirmed that the external mass transport of all species in the solution had to be taken into account and showed that the enzymatic reaction occurred preferentially near the polymer ]solution interface. This last result suggested some improvements in the design of the electrode.

AIChE Journal, 2005

ABSTRACT A bioelectrochemical interface was designed by entrapping glucose oxidase (GOx) in a pol... more ABSTRACT A bioelectrochemical interface was designed by entrapping glucose oxidase (GOx) in a polypyrrole film electrosynthesized on a platinum electrode. The efficiency of the modified electrodes for synthesis was evaluated with the reaction of glucose oxidation into gluconic acid by oxygen. Glucose transformation was carried out with or without the electrochemical step. The electrochemical step led to the regeneration of oxygen, which also ensured the oxidation of the hydrogen peroxide produced as a by-product, thus protecting GOx against denaturing. The experimental results were first analyzed according to the “effectiveness factor/Thiele modulus” classic approach. They were confirmed theoretically by a model based on the resolution of glucose mass balance equation. Second, the simulation of the concentration profiles of oxygen and hydrogen peroxide inside the polymer film explained the experimental data, highlighting the protection of the enzyme by the electrochemical step. The maximum conversion yield was obtained with a 500-nm-thick polymer. As a consequence of the combined effects of oxygen regeneration and enzyme protection, the electrochemical step increased by a factor of 2 the transformation ratios obtained with immobilized GOx. Furthermore, the electrochemically enhanced process was 50% more efficient than the equivalent homogeneous process carried out for 24 h with the same amount of enzyme.

Journal of Pharmaceutical and Biomedical Analysis, 2006

OATAO is an open access repository that collects the work of Toulouse researchers and makes it fr... more OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID : 3078 To link to this article : URL : http://dx.( 2006) Exploration of the global antioxidant capacity of the stratum corneum by cyclic voltammetry.

An electrochemical microsensor has been developed for the simultaneous assay of ascorbate (AA) an... more An electrochemical microsensor has been developed for the simultaneous assay of ascorbate (AA) and urate (UA) antioxidants in human blood serum. The electrode surface was modified by means of electropolymerized conductive poly(3,4-ethylenedioxythiophene) PEDOT organic films. Highly selective responses (detection potential difference more than 250 mV) were obtained for both biomarkers by optimizing the PEDOT thickness. Contrary to most previous studies the analytical performances were recorded by testing the microsensor directly in blood serum without any pretreatment of the samples. Using differential pulse voltammetry (DPV) the sensitivity and detection limit were 0.481 μA μM(-1) cm(-2) and 4.2 μmol L(-1) for AA and 1.815 μA μM(-1) cm(-2) and 2.0 μmol L(-1) for UA. The calibration curves were linear in the concentration range 5-200 μmol L(-1) for AA and 3-700 μmol L-1 for UA. The accuracy of the sensor was satisfactorily compared with the reference analytical methods provided that the synergic effect between both antioxidants was considered. The sensor response was unmodified in the presence of the major biochemical interfering species.

Comprehensive Analytical Chemistry, 2007