Electrocatalytic oxidation of ascorbate by heme-Fe III /heme-Fe II redox couple of the HRP and its effect on the electrochemical behaviour of an L-lactate biosensor

Abstract The measurements of L-lactate using the carbon paste electrode modified with lactate oxidase (LOD), horseradish peroxidase (HRP) and ferrocene (FcH) operating at low working potential in flow injection mode showed that the intensity as well as the shape of peaks were dependent on the concentration of the reducing species present in samples (e.g. ascorbate) even at low operating potentials ( À 200 to 0 mV vs. Ag/AgCl). The mechanism of the electrochemical contribution of ascorbate to the L-lactate response was examined by using cyclic voltammetry, hydrodynamic voltammetry and FIA results. Comparative studies showed that HRP was catalytically active for the oxidation of ascorbate leading to a decrease in the cathodic electrochemical signal of L-lactate. The results of our investigation postulated that the direct electron transfer from the HRP-Fe(III)/HRP-Fe(II) redox couple to the electrode surface was involved in the electrocatalytic oxidation of ascorbate at the electrode surface.

Single Electrochemical Impacts of Shewanella oneidensis MR-1 Bacteria for Living Cells Adsorption onto a Polarized Ultramicroelectrode Surface

Funding Information: This work is supported by Nantes Université and the Région Pays de la Loire (Rising stars program, e-NANOBIO). The authors acknowledge the France-Portugal PHC PESSOA 2022 program for support, project 47857YM. Funding Information: This work is supported by Nantes Université and the Région Pays de la Loire (Rising stars program, NANOBIO). The authors acknowledge the France‐Portugal PHC PESSOA 2022 program for support, project 47857YM. e‐ Publisher Copyright: © 2022 The Authors. ChemElectroChem published by Wiley-VCH GmbH.Single electrochemical impacts of Shewanella oneidensis MR-1 Gram-negative electroactive bacteria onto ultramicroelectrode surfaces are reported and in-depth analysed. Chronoamperometry measurements recorded onto 10 μm-diameter Pt and 7 μm-diameter carbon fibre disk ultramicroelectrodes in a 20 mM potassium ferrocyanide aqueous solution in the presence of living bacteria show an electrostatic attraction of Shewanella cells onto the ultramicroelectrode surface polarized at +0.8 V vs Ag/AgCl. Single current step events analysis and atomic force microscopy experiments confirm the adsorption of living bacteria following the collision onto the ultramicroelectrode surface. The bacteria washing step before the chronoamperometry measurements leads to lower current step events related to the smaller size of the living cells. The electrostatic attraction of the negatively charged bacteria onto the positively charged ultramicroelectrode surface polarized at the oxidation potential of ferrocyanide is clearly demonstrated.publishersversionpublishe

Size dependence of efficiency of PbS quantum dots in NiO-based dye sensitised solar cells and mechanistic charge transfer investigation

Quantum dots (QDs) are very attractive materials for solar cells due to their high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to quantum confinement. Particularly interesting are the PbS QDs owing to their broad spectral absorption until the long wavelengths, their easy processability and low cost. Here, we used control of the PbS QDs size to understand charge transfer processes at the interfaces of NiO semiconductor and explain the optimal QDs size in photovoltaic devices. Towards this goal, we have synthesized a series of PbS QDs with different diameters (2.8 A until 4A) and investigated charge transfer dynamics by time resolved spectroscopy and their ability to act as sensitizers in nanocrystalline NiO based solar cells using the cobalt tris(4,4'-diterbutyl-2,2'-bipyridine) complex as redox mediator. We found that PbS QDs with average diameter of 3.0 nm are optimal size in terms of efficient charge transfers and light harvesting efficiency for photovoltaic performances. Our study showed that an hole injection from PbS QDs to NiO valence band (VB) is an efficient process even with low injection driving force (0.3 eV) and occurs in 6-10 ns. Furthermore we found that the direct electrolyte reduction (photoinduced electron transfer to the cobalt redox mediator) also occurs in parallel to the hole injection with rate constant of similar magnitude (10-20 ns). In spite of its large driving force, the rate constant of the oxidative quenching of PbS by Co(III) diminishes more steeply than hole injection on NiO when the diameter of PbS increases. This is understood as the consequence of increasing the trap states that limit electron shift. We believe that our detailed findings will advance the future design of QD sensitized photocathodes. © 2017, Royal Society of Chemistry. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at / https://doi.org/10.1039/C7NR03698

Electro-catalyzed oxidation of reduced glutathione and 2-mercaptoethanol by cobalt phthalocyanine-containing screen printed graphite electrodes

Electro-catalytic behavior of screen printed graphite electrodes modified with cobalt phthalocyanine (CoPc) towards the oxidation of reduced glutathione (GSH) and 2-mercaptoethanol (2-ME) is reported. We find, by using cyclic voltammetry, that the oxidation of 2-ME occurs at 0.2 V vs Ag/AgCl and − 0.3 vs Ag/AgCl V at pH = 7 and pH = 13, respectively and that of GSH occurs at 0.4 V vs Ag/AgCl and 0.0 V vs Ag/AgCl at pH = 7 and 13, respectively. The electro-catalytic activity depends on the method of electrode modification and the amount of catalyst incorporated in the ink used to fabricate the SPCEs. The highest activity was obtained with electrodes prepared with 2.5% (w:w) of CoPc

Size dependence of efficiency of PbS quantum dots in NiO-based dye sensitised solar cells and mechanistic charge transfer investigation

ANR is gratefully acknowledged for the financial support of these researches through the QuePhelec project (n° ANR-13-BS10-0011-01). Région des Pays de la Loire and Nantes University for the project LUMOMAT are also acknowledged. We acknowledge support from the European Research Council (grant number 321305) and the EPSRC (grant number EP/L017008/1). IDWS is a Royal Society Wolfson Research Merit award holder. The research data supporting this publication can be accessed at http://dx.doi.org/10.17630/ddaebfb9-e127-43cb-9048-966a572b50ac.Quantum dots (QDs) are very attractive materials for solar cells due to their high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to quantum confinement. Particularly interesting are the PbS QDs owing to their broad spectral absorption until the long wavelengths, their easy processability and low cost. Here, we used control of the PbS QDs size to understand charge transfer processes at the interfaces of NiO semiconductor and explain the optimal QDs size in photovoltaic devices. Towards this goal, we have synthesized a series of PbS QDs with different diameters (2.8 A until 4A) and investigated charge transfer dynamics by time resolved spectroscopy and their ability to act as sensitizers in nanocrystalline NiO based solar cells using the cobalt tris(4,4'-diterbutyl-2,2'-bipyridine) complex as redox mediator. We found that PbS QDs with average diameter of 3.0 nm are optimal size in terms of efficient charge transfers and light harvesting efficiency for photovoltaic performances. Our study showed that an hole injection from PbS QDs to NiO valence band (VB) is an efficient process even with low injection driving force (0.3 eV) and occurs in 6-10 ns. Furthermore we found that the direct electrolyte reduction (photoinduced electron transfer to the cobalt redox mediator) also occurs in parallel to the hole injection with rate constant of similar magnitude (10-20 ns). In spite of its large driving force, the rate constant of the oxidative quenching of PbS by Co(III) diminishes more steeply than hole injection on NiO when the diameter of PbS increases. This is understood as the consequence of increasing the trap states that limit electron shift. We believe that our detailed findings will advance the future design of QD sensitized photocathodes.PostprintPeer reviewe

Electrodes enzymatiques pour le dosage de l'ethanol et des lactates dans les produits agroalimentaires

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 84757 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Relation formulation / propriétés électrochimiques dans le développement d'un biocapteur sérigraphié basé sur le transfert direct d'électrons

Ce travail porte sur la préparation et l'étude d'électrodes sérigraphiées modifées dans leur masse par la HRP (peroxidase de raifort). Une première étude par voltampérométrie cyclique et impédance électrochimique a mis en évidence un rôle important de la nature et la proportion des différents composants de l'encre dans le biomateriau sur les cinétiques de transfert d'électrons et la diffusion à la surface des électrodes. L'électrode sérigraphiée ainsi obtenue en une seule étape a été optimisée pour la détection ampérométrique en analyse par injection en flux continu du peroxyde d'hydrogène entre 0 et 100 mV vs. Ag/AgCl. Ce biocapteur utilise le transfert direct d'électrons entre la HRP et la surface de l'électrode. L'influence d'une modification chimique de la HRP ainsi que de la nature et proportion du liant sur la stabilité, la linéarité et la stabilité a été étudiée. Enfin, un biocapteur bienzymatique permettant le dosage du lactate a été mis au point sur le même modèle.The preparation and performances of screen-printed carbon electrodes modified in their bulk with HRP is reported. In a first study using cyclic voltametry and electrochemical impedance spectroscopy techniques, we showed that both the electron transfer kinetics and the diffusion toward electrode surface were dependent on the different components of the ink. The resulting modified HRP-SPCE was prepared in a one-step procedure, and was optimised as an amperometric biosensor operating at [0 - 100] mV vs Ag/AgCl in flow injection mode for hydrogen peroxide. The amperometric response was due to direct electron transfer between HRP and SPCE surface. Factors such as chemical modifications of the enzyme or the nature and rate of the binder were investigated regards to their influence on the sensitivity, linear range and operational stability. This configuration was finally extended to the preparation of a bienzymatic screen-printed biosensor for the determination of L-lactate in food samples.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Advances in the Electrochemical Simulation of Oxidation Reactions Mediated by Cytochrome P450

Combining electrochemistry with mass spectrometry constitutes an increasingly useful approach' for simulating reactions catalyzed by cytochrom P450 (CYP450). In this review, we discuss the ability of the electrochemical cell to act as a reliable tool to mimic CYP450. The electrochemical oxidation process and CYP450 catalyzed reactions are compared in terms of mechanistic pathways chemical structures of reactive intermediate metabolites, and final chemical structures of oxidation products. The oxidation reactions mediated by CYP450 are known to occur by either a single electron transfer (SET) or a hydrogen atom transfer (HAT) mechanism. The similarities between the reactions mediated electrochemically or by CYP450 are discussed in terms of SET and HAT mechanisms

Développement de méthodes rapides pour une estimation du taux des composés phénoliques dans les produits fumés (capteur et biocapteur)

Ce travail porte sur la préparation et l étude d électrodes modifiées de type sérigraphié pour le dosage des composés phénoliques. L objectif principal de cette thèse était le développement de biocapteurs de type jetable pour une détection rapide des composés phénoliques dans des matrices complexes. Pour ce faire deux configurations ont été donc examinées et étudiées pour le développement de biocapteurs pour la détection du phénol et certains de ses dérivés. En première temps une électrode de carbone de type sérigraphiée modifié en surface par la tyrosinase (SPCE-Tyr/Paa/Glut) a été élaboré. La composition de l électrode Tyr/Paa/ Glut a été optimisée pour un fonctionnement en mode d analyse par injection en flux continu (FIA) à 0 V vs. Ag/AgCl. Le dosage des composés phénoliques dans les extraits de produits fumés telles que le jambon, le bacon, le poulet, le saumon fumés a été effectué. Les résultats obtenus avec le biocapteur en mode FIA ont été comparés avec les résultats obtenus par la méthode chromatographie en phase gazeuse. En deuxième temps nous avons développé une autre électrode sérigraphiée basée sur une détection photoélectrochimique. Dans cette deuxième configuration il s agit d une électrode transparente à base du ITO recouvert par du TiO2. Cette électrode a été examinée pour développer un capteur pour la détection photoélectrochimique des dérivés phénoliques.This work deals with the preparation and the study of modified screen-printed carbon electrodes to detect phenolic compounds. The main objective was to develop disposable biosensors for a rapid detection of phenolic compounds in complex matrix. For this purpose, two configurations were examined and studied to prepare biosensors to detect phenolic compounds. The first configuration is based on screen-printed carbon electrode modified on its surface by tyrosinase as biorecognising element. The formulation of the biorecognising layer was then optimised for flow injection analysis mode. The resulting modified screen-printed carbon electrode operates at 0 V vs Ag/Ag,Cl. A series of measurement were carried out in various smoked samples as chicken, bacon, salmon and ham. The results of the measurements obtained with the optimised biosensors were then compared with those obtained with gas chromatography. In the second configuration, we examined transparent and conductive electrodes operating on photoelectrochemical detection. For this purpose, ITO covered with TiO2 layer was examined towards the preparation of a sensor for phenolic compounds detection.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Caractérisation de films composites à base de carbone/polymère de type sérigraphié (influence de la composition de la surface sur la réactivité électrochimique)

Dans le cadre de ce travail, des électrodes à base de carbone/graphite de type sérigraphié ont été étudiées et examinées en terme de réactivité électrochimique. L étude électrochimique par voltamétrie cyclique, et la caractérisation de la surface des électrodes sérigraphiées par imagerie MEB et spectroscopie XPS ont révélé une relation entre la composition chimique de la surface et les performances électrochimiques des électrodes utilisées. Le matériau étudié et mis au point a été utilisé comme cathode pour la régénération d une cellule solaire hybride organique-inorganique de type Grätzel. Par ailleurs, nous avons exploré deux nouvelles approches de modification et d activation des électrodes. La première approche était basée sur une modification en surface par un dépôt de couche mince de carbone amorphe nitruré (a-CNx) par pulvérisation cathodique magnétron, La deuxième approche consistait en un traitement de surface par plasma. Les deux approches ont conduit à des changements chimiques et morphologiques importants, accompagnés d une augmentation significative de la réactivité électrochimique des électrodes. Ces nouveaux procédés ont été ensuite utilisés pour améliorer la réponse électro-catalytique de biocapteurs à peroxyde d hydrogène et pour dérivés phénoliquesThe study of screen printed carbon/graphite electrodes in term of electrochemical reactivity was reported in this manuscript. Cyclic voltammetric study and surface characterisation by both SEM and XPS techniques demonstrated that the electrochemical performance of the electrodes has significantly found related to the electrode surface chemistry. The resulting carbon/graphite material was then successfully used as cathode for the regeneration of Grätzel solar cell. On the other hand, two modification approaches were examined to enhance the electron transfer at the screen-printed carbon electrode surface. The first approach consisted in the deposition of a thin nitride carbon film by using a reactive magnetron sputtering process, whereas in the second one we examined the effect of a series of plasma treatment on the electrochemical reactivity of the electrode surface. Both approaches were then used to improve the sensitivity of some electrochemical biosensorsNANTES-BU Sciences (441092104) / SudocSudocFranceF