Matthieu Picot

Surface modification of polymers by reduction of diazonium salts: polymethylmethacrylate as an example

This paper describes the grafting of diazonium salts on polymethylmethacrylate (PMMA), a polymer of wide use. Diazonium salts have been grafted by reduction with hypophosphorous acid, or by thermal decomposition. The nanometer thick films have been characterized by IR, XPS and water contact angle and the thickness of the film estimated. With long chain perfluoroalkyl substitutents on the aryldiazonium group a water contact angle of 108° can be obtained on the smooth polymer, highlighting a hydrophobic surface. This process could be useful for modifying the PMMA surface when used as a glass substitute or as a substrate for microfluidic devices.

Enzymatic versus Microbial Bio‐Catalyzed Electrodes in Bio‐Electrochemical Systems

Catalyses of electrode reactions by oxidoreductases or living electroactive bacteria are compared and recent advances reviewed. The relation between the biological and nevertheless inert nature of enzymes and the living machinery of electroactive microbes is discussed. The way these biocatalysts may be electrically contacted to anodes or cathodes is considered with a focus on their immobilization at electrodes and on the issue of time stability of these assemblies. Recent improvements in power output of biofuel cells are reviewed together with applications that have appeared in the literature. This account also reviews new approaches for combining enzymes and living microbes in bioelectrochemical systems such as reproducing microbial metabolisms with enzyme cascades and expressing oxidoreductases on genetically engineered microbes. Finally, the use of surface chemistry for studying the microbe-electrode interface and bioelectrodes with cell organelles, such as mitochondria, or with higher organisms, such as yeasts, are discussed. Some perspectives for future research to extend this field are offered as conclusions.

Monophyletic group of unclassified γ-Proteobacteria dominates in mixed culture biofilm of high-performing oxygen reducing biocathode

Several mixed microbial communities have been reported to show robust bioelectrocatalysis of oxygen reduction over time at applicable operation conditions. However, clarification of electron transfer mechanism(s) and identification of essential micro-organisms have not been realised. Therefore, the objective of this study was to shape oxygen reducing biocathodes with different microbial communities by means of surface modification using the electrochemical reduction of two different diazonium salts in order to discuss the relation of microbial composition and performance. The resulting oxygen reducing mixed culture biocathodes had complex bacterial biofilms variable in size and shape as observed by confocal and electron microscopy. Sequence analysis of ribosomal 16S rDNA revealed a putative correlation between the abundance of certain microbiota and biocathode performance. The best performing biocathode developed on the unmodified graphite electrode and reached a high current density for oxygen reducing biocathodes at neutral pH (0.9 A/m(2)). This correlated with the highest domination (60.7%) of a monophyletic group of unclassified γ-Proteobacteria. These results corroborate earlier reports by other groups, however, higher current densities and higher presence of these unclassified bacteria were observed in this work. Therefore, members of this group are likely key-players for highly performing oxygen reducing biocathodes.