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There is a growing interest in the technological transfer of highly performing electrochemical sensors within portable analytical devices for the in situ monitoring of environmental contaminants, such as perfluorooctanesulfonic acid (PFOS). In the redesign of biomimetic sensors, many parameters should be taken into account from the working conditions to the electrode surface roughness. A complete characterization of the surface modifiers can help to avoid time-consuming optimizations and better interpret the sensor responses. In the present study, a molecularly imprinted polymer electrochemical sensor (MIP) for PFOS optimized on gold disk electrodes was redesigned on commercial gold screen-printed electrodes. However, its performance investigated by differential pulse voltammetry was found to be poor. Before proceeding with further optimization, a morphological study of the bare and modified electrode surfaces was carried out by scanning electron microscopy&ndash, energy-dispersive X-ray spectrometry (SEM&ndash, EDS), atomic force microscopy (AFM) and profilometry revealing an heterogeneous distribution of the polymer strongly influenced by the electrode roughness. The high content of fluorine of the target-template molecule allowed to map the distribution of the molecularly imprinted polymer before the template removal and to define a characterization protocol. This case study shows the importance of a multi-analytical characterization approach and identify significant parameters to be considered in similar redesigning studies.

The addition of the ortho-phenylenediamine (OPDA) to aniline solution resulted in a slower polymer synthesis rate and in the modified PANI structural change. The interaction of both monomers produced the change in PANI morphology, which was confirmed by atomic force microscope (AFM). The stainless steel (SS) corrosion protective properties of PANI and modified PANI coatings were examined in chloride (Cl−) media by open circuit potential (Eo.c. vs. t) monitoring. The presence of Cl− in supporting electrolyte resulted in two different Eo.c. vs. t potential regions. The different Eo.c. “drop” in two specific potential regions was attributed to the facilitated and hindered Cl− flux through PANI towards the SS surface. The Cl− flux was found to be governed by the potentially dependant “pump” and “barrier” effects, which were explained to be governed by the PANI anion exchange property. It has been found that the polymer structure has a significant influence on the electroactive behavior of the modified PANI. The influence of the polymer structure on the “barrier” and “pump” effects was additionally investigated by adding OPDA. The denser polymer structure obtained by addition of OPDA resulted in “weakened pump” and “enhanced barrier” effects, which produced hindered Cl− flux. The anion exchange process detected by electrochemical impedance spectroscopy (EIS) in the low frequency region and the PANI anion exchange property were found to be under the influence of the OPDA additions. An increase in OPDA addition resulted in a lower polymer ability to replace the anions, which consequently hindered the process detected in the low frequency region. The method proposed in this paper offers the possibility to predict the modified PANI corrosive protective properties of SS in Cl− media using EIS measurement, which is less time consuming than the long-lasting Eo.c. vs. t measurements.

Silica sulfuric acid is found to catalyze efficiently the condensation of o-phenylenediamines with various linear and cyclic ketones to afford the corresponding 1,5-benzodiazepines in quantitative yields under solvent-free conditions at room temperature

The aim of this work is to study the sulfite oxidation mediated by glassy carbon electrodes modified with copolymers formed by ortho-phenylenediamine (OPD) and Co(II)-tetrakis(para-aminophenyl)porphyrin (CoTAPP). The copolymer was obtained through continuous cycling of potential of a glassy carbon electrode in acid medium containing each respective homopolymer in 1:1 feeding volume, in which the ortho-phenylenediamine concentration was 1·10-1 M and the CoTAPP concentration was 1·10-4 M. The film obtained is thin, stable and contains a low amount of porphyrin in comparison to the amount in orthophenylenediamine. Its electrocatalytic activity was tested toward the sulfite oxidation. In this case, this film is more electrocatalytic than the modified electrode modified with the CoTAPP electropolymer, even though ortho-phenylenediamine is inactive in this reaction. In this work the electrocatalysis process, the morphology of the film, and the difference of electrocatalytic behavior between the ortho-phenylenediamine and cobalt porphyrin homopolymers and the orthophenylenediamine-porphyrin copolymer were studied. The morphologic studies were done using Au electrodes since the electrocatalytic activity on Au and on glassy carbon are quite similar.

L’objectif principal de ce projet de recherche est d’étudier l’efficacité de la microencapsulation, technique d’immobilisation d’enzymes utilisée pour la réalisation des nouveaux biocapteurs électrochimiques. Généralement, l’analyte d’intérêt produit ou consomme des électrons, et la réponse électrochimique est mesurée, afin d’identifier ou quantifier l’analyte. Dans le développement d’un biocapteur, il est désirable de quantifier la conversion du substrat (analyte) et/ou la formation de produit de réaction enzymatique. Les similarités structurales entre le substrat et le produit de réaction dans les réactions redox demandent que la technique utilisée pour les identifier soit très sélective. Le haut pouvoir de résolution de l’électrophorèse capillaire (EC) pour des séparations rapides de produits similaires en fait une méthode de choix, spécialement quand le substrat et le produit peuvent être suivis pendant et après la réaction catalysée par l’enzyme immobilisée. Un choix judicieux du substrat, compte tenu de son comportement en EC peut fournir des informations autant sur l’activité de l’enzyme que sur l’efficacité de la microencapsulation. Pour cette raison, nous avons choisi le substrat o-phenylènediamine qui est oxydé par la laccase, pour former le produit 2,3-diaminophenazine, tout en réduisant l’oxygène en eau. Pour commencer, nous avons préparé les microcapsules et évalué l’impact de la microencapsulation sur le comportement de l’enzyme. Ensuite, nous avons développé une méthode de séparation en EC afin de quantifier la conversion de l’OPD en DAP par la laccase libre. La même méthode d’analyse a été utilisée pour caractériser la laccase immobilisée dans les microcapsules. Par la suite, afin de suivre la réaction enzymatique, un microréacteur à base d’enzyme microencapsulée a été couplé hors ligne au système d’EC. Finalement, nous avons essayé l’implémentation du système en ligne et les résultats préliminaires seront présentés., The principal objective of this research project is to study the efficiency of microencapsulation, technique used for enzyme immobilization in order to create new types of electrochemical biosensors. Generally, the target analyte involved either produces or consumes electrons and the electrochemical response is measured to identify or quantify the analyte. In the development of a biosensor, it is desirable to quantify the conversion of substrate (analyte) and/or the formation of product of the enzymatic reaction. The structural similarity between substrate and product in redox reactions means that the technique used to determine these species must be very selective. The high resolving power of capillary electrophoresis (CE) for rapidly separating similar compounds is thus an attractive method, particularly if substrate and product can both be monitored during or following the reaction catalyzed by microencapsulated enzyme. A judicious choice of substrate with respect to its behaviour in CE separations can help provide information on enzyme activity as well as microencapsulation efficiency. To achieve this, we chose the substrate o-phenylenediamine (OPD), which is oxidized by laccase to form the product 2,3-diaminophenazine (DAP) concomitant with the reduction of molecular oxygen to water. We firstly prepared the microcapsules and evaluate the impact of microencapsulation on the behaviour of the enzyme. After that, we developed a CE based separation method to quantify the conversion of OPD to DAP by free laccase. We also used the CE method to characterize laccase immobilized in microcapsules. Subsequent, the microencapsulated laccase was packed into a microreactor format permitting its off-line coupling with CE as a means to follow the enzymatic reaction. Finally, we tried to implement the on-line system and the preliminaries results are presented., Réalisé en codirection avec Karen C. Waldron et Dominic Rochefort.

The influence of adding ortho-phenylenediamine (OPDA) during the polymerization of aniline on the characteristics of the resulting polymer film was examined. When using a platinum electrode, the deposits were obtained from solutions containing 0.1 mol dm−3 aniline and 1, 5, or 10 mmol dm−3 OPDA. The deposits were also prepared from solutions containing 0.5 mol dm−3 aniline and 5, 10, or 50 mmol dm−3 OPDA. In both cases, 3 mol dm−3 phosphoric acid solution was used as a supporting electrolyte. The characteristics of the obtained layers were investigated through the catalytic effect of different polymer layers on hydroquinone/quinone (H2Q/Q) test redox system. The results obtained confirm the earlier established catalytic effect on the potential of the redox reaction by shifting it to more reversible values. However, as the concentration of OPDA was increased, the resulting limiting current decreased, thus indicating in the presence of OPDA a lower population of the available active centers necessary for the catalytic reaction to proceed. The influence of OPDA on polymer characteristics was also studied by using scanning electron microscopy as well as electrochemical impedance spectroscopy. The polymer was synthesized on a stainless steel electrode (13% Cr) from a solution containing 0.5 mol dm−3 aniline and 5, 10, or 50 mmol dm−3 OPDA. The layers were tested in chloride-containing solutions by monitoring the open circuit potential. The results obtained suggest that, by increasing the concentration of OPDA, the time of OCP in the passive region of stainless steel is prolonged. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

In this work the influence of ortho-phenylenediamine (OPDA) addition in the process of aniline polymerisation has been examined. The electrochemical polymerisation of the layer was carried out by means of cyclic voltammetry. The study of PANI layer characteristics were carried out on two substrates: Pt- and stainless steel electrode. The investigations on Pt-electrode were carried out for the layer obtained from 0.1M aniline with the addition of 1 and 5 mM of OPDA, all in 3 M phosphoric acid solution. The characteristics of the obtained layer were investigated by examining the catalytic effect of the different layers on H2Q/Q test redox system by means of RDE voltammetry. It was found that there is present a catalytic effect on the potential of H2Q/Q redox reaction, but the resulting limiting current decreases as the addition of OPDA increases, indicating that lower density of active centres, necessary for the catalytic oxidation, is available. The investigations on steel electrode (13% Cr) were carried out on a layer resulting from the polymerisation of 0.5M aniline with the addition of 5, 10 and 50 mM of OPDA. The layer was tested in Cl- solution by monitoring the open circuit potential (OCP). It was shown that, with the increase of OPDA addition, the time at OPC is prolonged. The AFM micrographs show the difference in morphology when OPDA is added, suggesting that OPDA additions cause the increased compactness of the polymer layer.

It is known that the addition of ortho-phenylenediamine (OPDA) to aniline solutions for the electrochemical polymerisation, results in layers with the change in morphology compared to the morphology of pure polyaniline (PANI) layers. That change is accompanied by other changed properties of the layer lika catalyses and corrosion protection. In the test of catalytic activity it is shown that the catalytic current of H2Q/Q reaction decreases with the increase of OPDA in the solution of synthesis, but as long as aniline is part of the layer there is a catalytic decrease of H2Q/Q reaction potential difference (Ep). In case of pure POPDA layer there is no catalytic activity whatsoever. The images taken from optic microscope indicate that at higher content of OPDA there is an independent growth of different polymers, presumably, PANI and PODPA., indicating that the actual copolymerisation is not taking place in a sense of incorporating different monomers into the same polymer. The images taken by AFM confirm quite different morphology of the regions of different colours.

In recent yeras it has been recognized that conductive polymer coatings on steel surface stabilise the potential of the substrate in the passive region and thus protect it from corrosion. This work investigates the corrosion protection of stainless steel by electrochemically deposited polyaniline (PANI) and polyaniline modified by addition of o-phenylenediamine in 3M H2SO4. The efficieny of PANI coatings in corrosion protection was tested by monitoring the open circuit potential. It is shown that the time of maintaining the potential in the passive region increases with the increase of PANI layer thickness and especially with the inrease of o-PDA addition.

The electrochemical synthesis of polyaniline has been carried out with the addituion of ortho-phenylenediamine by means of cyclic voltammetry. Reaction mechanisms are suggested in which o-PDA molecules influence the polymerisation path and result in very dense "closed" morphology.

In recent years it has been recognized that conductive polymer coatings on steel surface (1-4) stabilize the potential of the substrate in the passivation region and thus protect it from corrosion. This work investigates the corrosion protection of stainless steel by electrochemically deposited polyaniline (PANI) and modified polyaniline coatings. PANI coatings on stainless steel (13% Cr) were synthesized from 0.5 M solutions of aniline in 3 M H2SO4, and in 3M H3PO4, and from 0.5 M aniline with additions of 5, 10 and 25 mM of ortho-phenilenediamine (OPDA1, OPDA2, OPDA5) in 3 M H2SO4. The composition of the solution for coatings influences the rate of PANI deposition. It is found that in sulfuric acid solutions the rate of PANI coating growth decreases with the increase of OPDA addition. The decrease in PANI growth rate can be attributed to the change in polymerization mechanism due to the OPDA additions. The presence of OPDA can influence the appearance of the ladder-like structure, the branching of the polymer chains via amino- groups in ortho&#8211 ; ; position, as well as the earlier termination of the chain growth. The change in the polymerization mechanism leads also to the different morphology what is observed on SEM micrographs. The efficiency of PANI coatings in stainless steel corrosion protection was tested by observing the open circuit potential (Eoc) of the coated sample immersed in pure supporting electrolyte. As shown in Fig. 2 the time of maintaining the potential in the passive region increases with the increase in the thickness of PANI layer (PANI1: Q=18 mC, PANI2: Q=80 mC) and with the increase of OPDA addition. From earlier work it is known that PANI coatings, synthesized from phosphoric acid solutions, offer corrosion protection superior to PANI coatings from sulfuric acid solutions (4). In this work, therefore, coatings of different thickness were tested. Since the earlier investigated PANIPO4 thickness proved to offer long time corrosion protection, the tests were carried out for thinner layers of PANIPO4 coatings. For all the tested coatings of the thickness higher than 1 mC cm-2 Eoc during the time of observation (150&#8211 ; ; 200 hours) was maintained in the passive potential region.