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

A new view of electrochemistry at highly oriented pyrolytic graphite

Major new insights on electrochemical processes at graphite electrodes are reported, following extensive investigations of two of the most studied redox couples, Fe(CN)64–/3– and Ru(NH3)63+/2+. Experiments have been carried out on five different grades of highly oriented pyrolytic graphite (HOPG) that vary in step-edge height and surface coverage. Significantly, the same electrochemical characteristic is observed on all surfaces, independent of surface quality: initial cyclic voltammetry (CV) is close to reversible on freshly cleaved surfaces (>400 measurements for Fe(CN)64–/3– and >100 for Ru(NH3)63+/2+), in marked contrast to previous studies that have found very slow electron transfer (ET) kinetics, with an interpretation that ET only occurs at step edges. Significantly, high spatial resolution electrochemical imaging with scanning electrochemical cell microscopy, on the highest quality mechanically cleaved HOPG, demonstrates definitively that the pristine basal surface supports fast ET, and that ET is not confined to step edges. However, the history of the HOPG surface strongly influences the electrochemical behavior. Thus, Fe(CN)64–/3– shows markedly diminished ET kinetics with either extended exposure of the HOPG surface to the ambient environment or repeated CV measurements. In situ atomic force microscopy (AFM) reveals that the deterioration in apparent ET kinetics is coupled with the deposition of material on the HOPG electrode, while conducting-AFM highlights that, after cleaving, the local surface conductivity of HOPG deteriorates significantly with time. These observations and new insights are not only important for graphite, but have significant implications for electrochemistry at related carbon materials such as graphene and carbon nanotubes

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

Electrochemical Harvesting of Photosynthetic Electrons from Unicellular Algae Population at the Preparative Scale by Using 2,6-dichlorobenzoquinone

International audienceOxygenic photosynthesis is the process used by plants, cyanobacteria or algae to convert the solar energy into a chemical one from the carbon dioxide reduction and water oxidation. In the past years, many strategies were implemented to take benefits from the overall low yield of this process to extract photosynthetic electrons and thus produce a sustainable photocurrent. In practice, electrochemical tools were involved and the principle of electrons harvestings was related to the step of electron transfer between the photosynthetic organism and a collecting electrode. In this context, works involving an algae population in suspension were rather scarce and rather focus on the grafting of the photosynthetic machinery at the electrode surface. Based on our previous works, we report here the implementation of an electrochemical set-up at the preparative scale to produce photocurrents. An algae suspension, i.e. an intact biological system to ensure culture and growth, was involved in presence of a centimeter-sized carbon gauze as the collecting electrode. The spectroelectrochemical cell contains 16 mL of suspension of a Chlamydomonas reinhardtii mutant with an appropriate mediator (2,6-DCBQ). Under these conditions, stable photocurrents were recorded over 1 h whose magnitude depends on the quinone concentration and the light illumination

Simultaneous Electrochemical Detection of Primary Reactive Oxygen and Nitrogen Species Released by Cell Populations in Integrated Microdevices

International audienceInnovative microdevices were designed to monitor electrochemically primary reactive oxygen (ROS) and reactive nitrogen species (RNS) released by populations of aerobic cells. Taking advantage of the space confinement and microelectrodes properties, only few experiments were sufficient to provide significant statistical data relative to the average behavior of cells during oxidative stress bursts. In this study, platinum-black coated platinum (Pt/Pt-black) electrodes were first microfabricated and optimized to reach optimal performances during the electrochemical detection of four primary species H2O2, NO•, ONOO-and NO2 −. The results demonstrated that relative ROS/RNS contents in synthetic mixtures could be easily assessed at selected detection potentials. Under given experimental conditions, the Pt/Pt-black electrodes allowed detection limits down to 10 nM with high sensitivities and long-term stability of the electrode responses. The electrochemical detection of ROS/RNS released by cell populations was then implemented with Pt/Pt-black microelectrodes integrated into a multi-wells microdevice and a microfluidic device. As an important cell type, macrophages secretion triggered by calcium ionophore was chosen for assessing the performances, sensitivity and specificity of the detections. In comparison to some previous evaluations obtained from single-cell measurements, reproducible and relevant determinations were achieved. However, separating emitting cells from the detection area in the microfluidic device seems a better approach to avoid any perturbations of cell behaviors by electrode operations. Furthermore, the investigation of any biological effects during oxidative stress of living cells is facilitated. As a proof of concept, we reported the analysis of the influence of a NO synthase inhibitor during the perfusion culture

Highly Sensitive Platinum-Black Coated Platinum Electrodes for Electrochemical Detection of Hydrogen Peroxide and Nitrite in Microchannel

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Astrocyte-derived adenosine is central to the hypnogenic effect of glucose

International audienceSleep has been hypothesised to maintain a close relationship with metabolism. Here we focus on the brain structure that triggers slow-wave sleep, the ventrolateral preoptic nucleus (VLPO), to explore the cellular and molecular signalling pathways recruited by an increase in glucose concentration. We used infrared videomicroscopy on ex vivo brain slices to establish that glucose induces vasodilations specifically in the VLPO via the astrocytic release of adenosine. Real-time detection by in situ purine biosensors further revealed that the adenosine level doubles in response to glucose, and triples during the wakefulness period. Finally, patch-clamp recordings uncovered the depolarizing effect of adenosine and its A2A receptor agonist, CGS-21680, on sleep-promoting VLPO neurons. Altogether, our results provide new insights into the metabolically driven release of adenosine. We hypothesise that adenosine adjusts the local energy supply to local neuronal activity in response to glucose. This pathway could contribute to sleep-wake transition and sleep intensity

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