Optical Algal Biosensor using Alkaline Phosphatase for Determination of Heavy Metals

International audienceA biosensor is constructed to detect heavy metals from inhibition of alkaline phosphatase (AP) present on the external membrane of Chlorella vulgaris microalgae. The microalgal cells are immobilized on removable membranes placed in front of the tip of an optical fiber bundle inside a homemade microcell. C. vulgaris was cultivated in the laboratory and its alkaline phosphatase activity is strongly inhibited in the presence of heavy metals. This property has been used for the determination of those toxic compounds

Biosensor using immobilized Chlorella microalgae for determination of volatile organic compounds.

International audienceA biosensor using Chlorella microalgae immobilized on the membrane of an oxygen electrode has been designed to determine volatile organic compounds (VOC) in the form of aerosols. A homemade controlled atmosphere chamber is constructed for perchloroethylene detection. Monitoring of perchloroethylene is obtained by the measurement of the oxygen production during the algae photosynthetic process

Transfert et génération des gaz par les membranes. Application aux oxygénateurs et aux capteurs

No english abstractDans l'optique de la séparation de l'hydrogène pour les piles à combustibles, nous avons étudié successivement le transfert des gaz à travers les membranes poreuses, non-poreuses et élastiques. Nos membranes en caoutchouc minces et étirées ont réussi à concilier sélectivité et perméabilité. L'étirement, sous forme sphérique de ces membranes, permet de déterminer, en une seule opération, les variations continues de perméabilité et de contrainte appliquée à la membrane. Afin d'améliorer les vitesses de transfert des gaz dissous à travers les membranes, nous avons étudié d'une part le transport physique de ces gaz, d'autre part celui accompagné de réactions chimiques à travers les membranes. Nous avons adopté trois méthodes de mesure des flux de gaz : En régime stationnaire, en régime d'évolution, avec écoulement de la phase liquide dans de longs conduits. Ces méthodes nous ont permis de déterminer la perméabilité globale du système et de montrer que cette perméabilité ainsi que l'épaisseur de la couche-limite de diffusion équivalente sont indépendantes du gradient de pression. Nous avons montré que l'efficacité du transport (dans le cas d'une réaction chimique lors du passage du gaz dans le liquide) est amélioré par l'augmentation des vitesses de retour à l 'équilibre chimique grâce à un catalyseur tel que l'anhydrase carbonique. Dans le cas particulier des membranes oxygénatrices de sang, nous avons réduit la barrière de l'oxygène en le faisant traverser sans forme d'eau oxygénée et en le régénérant grâce à la catalase fixée au niveau de l'interface membrane-solution à oxygéner. Afin de mesurer les concentrations en métabolites, nous avons transposé les réactions enzymatiques obtenues en solution, en réactions uniquement localisées au niveau d'une électrode, grâce à l'emploi d'enzymes fixées. Ces modèles de capteurs utilisent des enzymes capables de transformer les concentrations intéressant certains phénomènes physiologiques en produits sensibles aux électrodes de mesure. Ils offrent ainsi la possibilité de mesure in vivo en continu et permettent des contrôles et des régulations à distance

Fluorescent biosensor using whole cells in an inorganic translucent matrix

8 pagesInternational audienceAn optical biosensor based on vegetal cells entrapped in an inorganic translucent matrix and fluorescence detection has been developed. The biosensor uses Chlorella vulgaris immobilized in a translucent support produced from sol-gel technology. The translucence of the structure enables the algal active layer to be placed directly in contact with the optical fibers for fluorescence detection. This configuration has many advantages over the use of an opaque support because no space between the optical fibers and the active layer is required to collect fluorescence. This reagentless biosensor allows determination of diuron as an anti-PSII herbicide and its long term activity is assessed

Sol-gel process for vegetal-cells encapsulation

International audienceA sol-gel process was carried out at room temperature to obtain porous silica matrixes for entrapment of vegetal cells. The process uses sodium silicate as a precursor rather than alkoxides to avoid generation of by-products that is detrimental to Chlorella vulgaris cells. The influence of several factors influencing the gelification was explored to optimize the encapsulation process. The technique produces a transparent matrix and is then very suitable for vegetal cells entrapment since they require light for their photosynthetic activity. Activity of the algal cells was determined by measurement of the intensity of fluorescence emission at 682 nm. This measurement also allowed to evaluate the efficiency of the immobilization technique and assess the long term activity of the encapsulated whole-cells

Amperometric tyrosinase based biosensor using an electrogenerated polythiophene film as an entrapment support

International audienceAn amperometric enzyme sensor using tyrosinase, also called polyphenol oxidase (PPO), was constructed for determination of phenolic compounds and herbicides. The enzyme was entrapped in a conducting polymer, poly 3,4-ethylenedioxythiophene (PEDT), electrochemically generated on a glassy carbon electrode. Several experimental parameters in the electropolymerisation process and working conditions were determined to optimise biosensor performances. Mono-phenol and di-phenol were tested in oxygenated solutions, by amperometric measurements at −200 mV (vs. SCE) in a batch system. The limit of detection of these molecules ranges from 5 to 500 nM. Detection of herbicides was obtained from the inhibition of tyrosinase electrode responses. The limit of detection for atrazine and diuron was 1 and 0.5 mg l−1 respectively. These data suggest that PEDT film is a promising PPO immobilisation method

Synchronous-scan fluorescence of algal cells for toxicity assessment of heavy metals and herbicides.

International audienceSynchronous-scan spectrofluorometry was applied to Chlorella vulgaris cells to assess the toxicity of heavy metals and herbicides in water. Simultaneous scan of both the excitation and emission spectra was done at a constant wavelength difference Deltalambda (20-140 nm) between the emission and excitation wavelengths in the range of 420-700 nm emission, where a peak of fluorescence was observed. Its position depends on Deltalambda. Fluorescence measurements were conducted with algal cells in suspension in water and immobilized in a translucent silica matrix. The influence of toxic chemicals was tested with cadmium as a heavy metal and with atrazine, diuron, DNOC and paraquat as herbicides. The toxic effect of those chemicals mainly results in a quenching of algal cells fluorescence by reducing their photosynthetic activity

Simulation of several CNT based macrostructures using slip-link model and discrete element method

The CNT macrostructures including membranes start by forming web on which CNT fibers are oriented along the web axis, some of them are parallel and others are poorly aligned or coiled. Since the CNT web impacts on the properties of derived macrostructures, the simulation of CNT membranes attracted significant attentions. The scanning electron microscopy analysis of CNT webs showed that CNT fibers entangle together. This entanglement is a key factor for the formation of CNT macrostructures because it allows the array of parallel fibers to unfold continuously into CNT networks. The work focuses on modelling the interconnection between CNT fibers within membranes and also other macro-structures and then analyzing mechanical properties of them

A glucose biosensor based on modified-enzyme incorporated within electropolymerised poly(3,4-ethylenedioxythiophene) (PEDT) films

International audienceWe have constructed and characterised a glucose sensor using glucose oxidase (GOD) covalently attached to carboxylic acid polyethyleneglycol (PEG), called (PEG–GOD). This modified enzyme was entrapped afterwards within poly(3,4-ethylenedioxythiophene) (PEDT) films electrogenerated on glassy carbon (GC) electrodes. The composite (PEG–GOD/PEDT) film is more porous than the film without enzyme (PEDT+PEG). Data from electrochemical quartz microbalance (ECQM) and pH-stat experiments indicate a good relative activity of the modified enzyme, ca. 12–15%. Amperometric measurements, using ferrocenemethanol as the redox mediator, confirms that the modified enzyme is catalytically active. The effect of film thickness was also investigated. The sensitivities were quite similar for modified-GOD electrodes (ca. 3 mA cm−2 M−1) and unmodified-GOD electrodes (ca. 2.7 mA cm−2 M−1) but a better stability was obtained with modified PEG–GOD electrodes

Immobilization of biocatalysts on solid supports for analytical applications

International audienceEnzyme sensors for diagnostic and environmental applications have developed by immobilizing biocatalysts onto the active solid surface of physico-chemical sensors. The performances of a biosensor are mainly related to the properties of the bioreceptor material and the techniques used for its immobilization onto the transducer. Different enzyme immobilization techniques will be presented: immersion, direct binding, reinforced membranes and finally aerosol vaporisation that combines adsorption and covalent binding of proteins to obtain ultrathin bioactive films