Editorial: Women in Science: Chemistry

Following UNESCO’s official celebration of the International Day of Women and Girls in Science, Frontiers in Chemistry decided to run a special issue “Women in Science: Chemistry”. Indeed, although science and gender equality are essential to ensure sustainable development, less than 30% of researchers worldwide are women

Light-induced reactivation of O2-tolerant membrane-bound [Ni-Fe] hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus under turnover conditions.

International audienceWe report the effect of UV-Vis light on the membrane-bound [Ni-Fe] hydrogenase from Aquifex aeolicus under turnover conditions. Using electrochemistry, we show a potential dependent light sensitivity and propose that a light-induced structural change of the [Ni-Fe] active site is related to an enhanced reactivation of the hydrogenase under illumination at high potentials

Hydrogen bioelectrooxidation on gold nanoparticle-based electrodes modified by Aquifex aeolicus hydrogenase: Application to hydrogen/oxygen enzymatic biofuel cells

International audienceFor the first time, gold nanoparticle-based electrodes have been used as platforms for efficient immobilization of the [NiFe] hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus. AuNPs were characterized by electronic microscopy, dynamic light scattering and UV-Vis spectroscopy. Two sizes around 20.0 ± 5.3 nm and 37.2 ± 4.3 nm nm were synthesized. After thiol-based functionalization, the AuNPs were proved to allow direct H2 oxidn. over a large range of temps. A high c.d. up to 1.85 ± 0.15 mA·cm- 2 was reached at the smallest AuNPs, which is 170 times higher than the one recorded at the bare gold electrode. The catalytic current was esp. studied as a function of the AuNP size and amt., and procedure for deposition. A synergetic effect between the AuNP porous deposit and the increase surface area was shown. Compared to previously used nanomaterials such as carbon nanofibers, the covalent grafting of the enzyme on the thiol-modified gold nanoparticles was shown to enhance the stability of the hydrogenase. This bioanode was finally coupled to a biocathode where BOD from Myrothecium verrucaria was immobilized on AuNP-based film. The performance of the so-mounted H2/O2 biofuel cell was evaluated, and a power d. of 0.25 mW·cm- 2 was recorded. [on SciFinder(R)

Development of an enzymatic amperometric biosensor using cytochromes C3 for the fast quantification of chromate bio-availability in the environment.

International audienceThe presence of toxic Heavy Metals and Metalloids (HMM) in the environment greatly affects the quality of water, soil and chain-food. The toxicity of the HMM depends on metal availability. Many analytical methods, such as sequential extraction or mathematical modelling, have been used for a long time for the assessment of HMM bioavailability. However, these techniques are very often difficult, expensive and long. The biosensors, like analytical tools, have advantages while bringing in addition to specificity, fast and quantitative measurement of a metal that reacts with the biomaterial. This principle is applied to detect the presence of bio-available concentrations of certain metals. The biosensor presented in this study is an amperometric one and its sensitive part is a hemo-protein, the cytochrome c3 from Desulfomicrobium norvegicum. The cytochrome c3 has been chosen for its better properties as a reducing agent of chromate (CrO42-). This study required instrumental developments or adaptations: the development of glassy carbon electrode with immobilized cytochrome c3 and the implementation of electrochemical methods for the study of redox systems, i.e. cyclic voltammetry (CV) and chronoamperometry (CA). The performances of various configurations of biosensors, according to the mode of immobilization of the enzyme, are studied for the qualitative and quantitative determination of chromate. These tools made it possible to identify and follow the redox reactions taking place during the contact of the electrode without and with chromate in solution. The tests on the various configurations of electrode allowed us, for the moment, to choose two promising configurations: The first one is an immobilization of the enzyme with a dialysis membrane and the second is an immobilization with a cellulose nitrate filter. Chromate concentrations from 0.2 to 6.8 mg/L can be detected by the biosensors that were designed

Electrochemical studies on small electron transfer proteins using membrane electrodes

Journal of Electroanalytical Chemistry 541 (2003) 153-162Membrane electrodes (ME) were constructed using gold, glassy carbon and pyrolytic graphite supports and a dialysis membrane, and used to study the electrochemical behavior of small size electron transfer proteins: monohemic cytochrome c522 from Pseudomonas nautica and cytochrome c533 as well as rubredoxin from Desulfovibrio vulgaris . Different electrochemical techniques were used including cyclic voltammetry (CV), square wave voltammetry (SW) and differential pulse voltammetry (DP). A direct electrochemical response was obtained in all cases except with rubredoxin where a facilitator was added to the protein solution entrapped between the membrane and the electrode surface. Formal potentials and heterogeneous charge transfer rate constants were determined from the voltammetric data. The influence of the ionic strength and the pH of the medium on the electrochemical response at the ME were analyzed. The benefits from the use of the ME in protein electrochemistry and its role in modulating the redox behavior are analyzed. A critical comparison is presented with data obtained at non-MEs. Finally, the interactions that must be established between the proteins and the electrode surfaces are discussed, thereby modeling molecular interactions that occur in biological systems

Electrostatic-Driven Activity, Loading, Dynamics, and Stability of a Redox Enzyme on Functionalized-Gold Electrodes for Bioelectrocatalysis

The oxygen reduction reaction is the limiting step in fuel cells, and many works are in progress to find efficient cathode catalysts. Among them, bilirubin oxidases are copper-based enzymes that reduce oxygen into water with low overpotentials. The factors that ensure electrocatalytic efficiency of the enzyme in the immobilized state are not well understood, however. In this work, we use a multiple methodological approach on a wide range of pH values for protein adsorption and electrocatalysis to demonstrate the effect of electrostatic interactions on the electrical wiring, dynamics, and stability of a bilirubin oxidase adsorbed on self-assembled-monolayers on gold. We show on one hand that the global charge of the enzyme controls the loading on the interface and that the specific activity of the immobilized enzyme decreases with the enzyme coverage. On the other hand, we show that the dipole moment of the protein and the charge in the vicinity of the Cu site acting as the entry point of electrons drive the enzyme orientation. In case of weak electrostatic interactions, we demonstrate that local pH variation affects the electron transfer rate as a result of protein mobility on the surface. On the contrary, stronger electrostatic interactions destabilize the protein structure and affect the stability of the catalytic signal. These data illustrate the interplay between immobilized protein dynamics and local environment that control the efficiency of bioelectrocatalysis

Electron transfer in an acidophilic bacterium: interaction between a diheme cytochrome and a cupredoxin

Acidithiobacillus ferrooxidans, a chemolithoautotrophic Gram-negative bacterium, has a remarkable ability to obtain energy from ferrous iron oxidation at pH 2. Several metalloproteins have been described as being involved in this respiratory chain coupling iron oxidation with oxygen reduction. However, their properties and physiological functions remain largely unknown, preventing a clear understanding of the global mechanism. In this work, we focus on two metalloproteins of this respiratory pathway, a diheme cytochrome c4 (Cyt c4) and a green copper protein (AcoP) of unknown function. We first demonstrate the formation of a complex between these two purified proteins, which allows homogeneous intermolecular electron-transfer in solution. We then mimic the physiological interaction between the two partners by replacing one at a time with electrodes displaying different chemical functionalities. From the electrochemical behavior of individual proteins, we show that, while electron transfer on AcoP requires weak electrostatic interaction, electron transfer on Cyt c4 tolerates different charge and hydrophobicity conditions, suggesting a pivotal role of this protein in the metabolic chain. The electrochemical study of the proteins incubated together demonstrates an intermolecular electron transfer involving the protein complex, in which AcoP is reduced through the high potential heme of Cyt c4. Modelling of the electrochemical signals at different scan rates allows us to estimate the rate constant of this intermolecular electron transfer in the range of a few s−1. Possible routes for electron transfer in the acidophilic bacterium are deduced

Nitrite Biosensing via Selective Enzymes—A Long but Promising Route

The last decades have witnessed a steady increase of the social and political awareness for the need of monitoring and controlling environmental and industrial processes. In the case of nitrite ion, due to its potential toxicity for human health, the European Union has recently implemented a number of rules to restrict its level in drinking waters and food products. Although several analytical protocols have been proposed for nitrite quantification, none of them enable a reliable and quick analysis of complex samples. An alternative approach relies on the construction of biosensing devices using stable enzymes, with both high activity and specificity for nitrite. In this paper we review the current state-of-the-art in the field of electrochemical and optical biosensors using nitrite reducing enzymes as biorecognition elements and discuss the opportunities and challenges in this emerging market

Photonic hydrogel sensors

Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This Review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified