Investigation of photocurrents resulting from a living unicellular algae suspension with quinones over time

International audiencePlants, algae, and some bacteria convert solar energy into chemical energy by using photosynthesis. In light of the current energy environment, many research strategies try to benefit from photosynthesis in order to generate usable photobioelectricity. Among all the strategies developed for transferring electrons from the photosynthetic chain to an outer collecting electrode, we recently implemented a method on a preparative scale (high surface electrode) based on a Chlamydomonas reinhardtii green algae suspension in the presence of exogenous quinones as redox mediators. While giving rise to an interesting performance (10-60 mA cm À2) in the course of one hour, this device appears to cause a slow decrease of the recorded photocurrent. In this paper, we wish to analyze and understand this gradual fall in performance in order to limit this issue in future applications. We thus first show that this kind of degradation could be related to over-irradiation conditions or side-effects of quinones depending on experimental conditions. We therefore built an empirical model involving a kinetic quenching induced by incubation with quinones, which is globally consistent with the experimental data provided by fluorescence measurements achieved after dark incubation of algae in the presence of quinones

FRAP to Characterize Molecular Diffusion and Interaction in Various Membrane Environments

Fluorescence recovery after photobleaching (FRAP) is a standard method used to study the dynamics of lipids and proteins in artificial and cellular membrane systems. The advent of confocal microscopy two decades ago has made quantitative FRAP easily available to most laboratories. Usually, a single bleaching pattern/area is used and the corresponding recovery time is assumed to directly provide a diffusion coefficient, although this is only true in the case of unrestricted Brownian motion. Here, we propose some general guidelines to perform FRAP experiments under a confocal microscope with different bleaching patterns and area, allowing the experimentalist to establish whether the molecules undergo Brownian motion (free diffusion) or whether they have restricted or directed movements. Using in silico simulations of FRAP measurements, we further indicate the data acquisition criteria that have to be verified in order to obtain accurate values for the diffusion coefficient and to be able to distinguish between different diffusive species. Using this approach, we compare the behavior of lipids in three different membrane platforms (supported lipid bilayers, giant liposomes and sponge phases), and we demonstrate that FRAP measurements are consistent with results obtained using other techniques such as Fluorescence Correlation Spectroscopy (FCS) or Single Particle Tracking (SPT). Finally, we apply this method to show that the presence of the synaptic protein Munc18-1 inhibits the interaction between the synaptic vesicle SNARE protein, VAMP2, and its partner from the plasma membrane, Syn1A

Rôle des interfaces et du confinement dans les films liquides minces

Interfaces properties and confinement effects of complex fluids are involved in stabilization of foams. This question is also related to micro-fluidics and nano-fluidics, which have been developed during recent years.Mixed solutions made of polyelectrolytes and surfactants have been used to study the influence of both confinement and surfactant in ultra-thin films (< 100 nm). Dissipation in these films was probed by using a thin film pressure balance as a rheometer and an hydrodynamics model. An effective viscosity can be extracted, which is higher for thinner films and affected by the nature of the surfactant.Generation of thicker films (a few microns) by dip coating of a solid plate enables to rule out the confinement. Several surfactants with different solubilities were used. A dynamic transition of thickening was found out and quantitatively explained. Furthermore, in the frame of a collaboration, an hydrodynamic model was developed to take into account surface viscosity in the thickening phenomenon. We could characterize the regime in which interfacial rheology is driven by pure surface viscosity. This model could be the first step toward a model taking into account both surface elasticity and surface viscosity.La compréhension de la stabilisation des mousses impose de prendre en compte les effets liés au confinement des fluides complexes, ainsi que le rôle des propriétés des interfaces. Ces problèmes se retrouvent également dans les domaines de la microfluiuidique et de la nanofluidique.Le confinement et l'influence des tensioactifs sur l'amincissement de films ultra-minces (< 100 nm ) ont été étudiés sur des systèmes mixtes de tensioactifs et de polyélectrolytes. L'étude expérimentale de ces films ultra-minces à l'aide d'une balance à films, utilisée comme un rhéomètre et couplée à un modèle hydrodynamique a permis d'accéder à la dissipation dans les films à travers une viscosité effetive. Celle-ci est plus élevée dans les flms plus minces. De plus elle est aussi affectée par la nature des interfaces qui confinent le polyélectrolyte.La formation de films plus épais ( ∼ 10 μm ) entraînés sur une plaque solide permet d'isoler le rôle de l'interface. L'utilisation de tensioactifs de solubilités différentes a permis de mettre en évidence quantitativement une nouvelle transition dynamique d'épaississement et de retrouver une transition déjà observée dans une autre géométrie (fibre). Par ailleurs, dans le cadre d'une collaboration, un modèle a été développé pour prendre en compte l'effet de la viscosité de surface dans l'épaississement. Nous avons pu caractériser le régime de concentration dans lequel la rhéologie interfaiale est régie par la viscosité seule. Ce modèle pourrait constituer la première étape vers un modèle prenant en compte la visco-élasticité de surface

Rôle des interfaces et du confinement dans les films minces liquides

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Vesicular Exocytosis and Microdevices – Microelectrode Arrays

International audienceAmong all the analytical techniques capable of monitoring exocytosis in real time at the single cell level, electrochemistry (particularly amperometry at a constant potential) using ultramicroelectrodes has been demonstrated to be an important and convenient tool for more than two decades. Indeed, because the electrochemical sensor is located in the close vicinity of the emitting cell (“artificial synapse” configuration), much data can be gathered from the whole cell activity (secretion frequency) to the individual vesicular release (duration, fluxes or amount of molecules released) with an excellent sensitivity. However, such a single cell analysis and its intrinsic benefits are at the expense of the spatial resolution and/or the number of experiments. The quite recent development of microdevices/microsystems (and mainly the microelectrode arrays (MEAs)) offers in some way a complementary approach either by combining spectroscopy–microscopy or by implementing a multianalysis. Such developments are described and discussed in the present review over the 2005–2014 period

More Transparency in BioAnalysis of Exocytosis: Coupling of Electrochemistry and Fluorescence Microscopy at ITO Electrodes

Vesicular exocytosis is an essential biological mechanism used by cellular organisms to release bioactive molecules (hormones, neurotransmitters…) in their environment. For instance, this is the pathway by which chromaffin cells deliver catecholamines (adrenaline, nor-adrenaline, dopamine…) in blood. During this process, secretory vesicles that initially stored the (bio)chemical messengers dock to the cell membrane. The subsequent fusion of vesicle and cell membranes induces the formation of a fusion pore that initiates the first exchanges between the intravesicular and extracellular media. Its following expansion thus favours a larger release of the vesicular content into the external medium. Several analytical methods have been developed in order to study exocytosis at the single living cell level in real time. Among those techniques, mostly based on electric or optic measurements, amperometry with a carbon-fiber ultramicroelectrode [1], used in the first part of this report, and total internal reflection fluorescence microscopy (TIRFM) appear as the most powerful [2] Practically, physico-chemical properties of ultramicroelectrodes induce a high detection sensitivity and temporal resolution, thus being particularly well adapted to monitor exocytosis of electroactive molecules in real time

More Transparency in BioAnalysis of Exocytosis: Coupling of Electrochemistry and Fluorescence Microscopy at ITO Electrodes

Vesicular exocytosis is an essential biological mechanism used by cellular organisms to release bioactive molecules (hormones, neurotransmitters…) in their environment. For instance, this is the pathway by which chromaffin cells deliver catecholamines (adrenaline, nor-adrenaline, dopamine…) in blood. During this process, secretory vesicles that initially stored the (bio)chemical messengers dock to the cell membrane. The subsequent fusion of vesicle and cell membranes induces the formation of a fusion pore that initiates the first exchanges between the intravesicular and extracellular media. Its following expansion thus favours a larger release of the vesicular content into the external medium. Several analytical methods have been developed in order to study exocytosis at the single living cell level in real time. Among those techniques, mostly based on electric or optic measurements, amperometry with a carbon-fiber ultramicroelectrode [1], used in the first part of this report, and total internal reflection fluorescence microscopy (TIRFM) appear as the most powerful [2] Practically, physico-chemical properties of ultramicroelectrodes induce a high detection sensitivity and temporal resolution, thus being particularly well adapted to monitor exocytosis of electroactive molecules in real time

Plate coating: influence of concentrated surfactants on the film thickness.

International audienceWe present a large range of experimental data concerning the influence of surfactants on the well-known Landau-Levich–Derjaguin experiment where a liquid film is generated by pulling a plate out of a bath. The thickness h of the film was measured as a function of the pulling velocity V for different kinds of surfactants (C12E6, which is a nonionic surfactant, and DeTAB and DTAB, which are ionic) and at various concentrations near and above the critical micellar concentration (cmc). We report the thickening factor α = h/hLLD, where hLLD is the film thickness obtained without a surfactant effect, i.e., as for a pure fluid but with the same viscosity and surface tension as the surfactant solution, over a wide range of capillary numbers (Ca = ηV/γ, with η being the surfactant solution viscosity and γ its surface tension) and identify three regimes: (i) at small Ca α is large due to confinement and surface elasticity (or Marangoni) effects, (ii) for increasing Ca there is an intermediate regime where α decreases as Ca increases, and (iii) at larger (but still small) Ca α is slightly higher than unity due to surface viscosity effects. In the case of nonionic surfactants, the second regime begins at a fixed Ca, independent of the surfactant concentration, while for ionic surfactants the transition depends on the concentration, which we suggest is probably due to the existence of an electrostatic barrier to surface adsorption. Control of the physical chemistry at the interface allowed us to elucidate the nature of the three regimes in terms of surface rheological properties

Finding Adapted Quinones for Harvesting Electrons from Photosynthetic Algae Suspensions

International audienceAmong all the chemical and biotechnological strategies implemented to extract energy from oxygenic photosynthesis, several concern the use of intact photosynthetic organisms (algae, cyanobacteria…). This means rerouting (fully or partially) the electron flow from the photosynthetic chain to an outer collecting electrode thus generating a photocurrent. While diverting photosynthetic electrons from living biological systems is an encouraging approach, this strategy is limited by the need to use an electron shuttle. Redox mediators that are able to interact with an embedded photosynthetic chain are rather scarce. In this respect, exogenous quinones are the most frequently used. Unfortunately, some of them also act as poisoning agents within relatively long timeframes. It thus raises the question of the best quinone. In this work, we use a previously reported electrochemical device to analyze the performance of different quinones. Photocurrents (maximum photocurrent, stability) were measured from suspensions of Chlamydomonas reinhardtii algae/quinones by chronoamperometry and compared to parameters like quinone redox potentials or cytotoxic concentration. From these results, several quinones were synthesized and analyzed in order to find the best compromise between bioelectricity production and toxicity