An enzyme-based biofuel cell with a pH-switchable oxygen electrode, controlled by enzyme logic operations processing in situ biochemical input signals, has been developed. Two Boolean logic gates (AND/OR) were assembled from enzyme systems to process biochemical signals and to convert them logically into pH-changes of the solution. The cathode used in the biofuel cell was modified with a polymer-brush functionalized with Os-complex redox species operating as relay units to mediate electron transport between the conductive support and soluble laccase biocatalyzing oxygen reduction. The electrochemical activity of the modified electrode was switchable by alteration of the solution pH value. The electrode was electrochemically mute at pH > 5.5, and it was activated for the bioelectrocatalytic oxygen reduction at pH < 4.5. The sharp transition between the inactive and active states was used to control the electrode activity by external enzymatic systems operating as logic switches in the system. The enzyme logic systems were decreasing the pH value upon appropriate combinations of the biochemical signals corresponding to the AND/OR Boolean logic. Then the pH-switchable electrode was activated for the oxygen reduction, and the entire biofuel cell was switched ON. The biofuel cell was also switched OFF by another biochemical signal which resets the pH value to the original neutral value. The present biofuel cell is the first prototype of a future implantable biofuel cell controlled by complex biochemical reactions to deliver power on-demand responding in a logical way to the physiological needs.

Gehaltsabhängig: Die Reaktion von Polycyclooctadien (Poly(COD)) und [RhCl(C2H4)2]2 ergab wohldefinierte π‐gebundene Hybridpolymere, deren Größe vom Rhodiumgehalt abhängig war (siehe Bild). Die Reaktion dieser Polymere mit einem Phosphinaldehyd führte zur Regenerierung der ursprünglichen Polymere und beweist damit die Zugänglichkeit des Metalls.

The generation of a current through interaction between bacteria and electrodes has been explored by various methods. We demonstrate the attachment of living bacteria through a surface displayed redox enzyme, alcohol dehydrogenase II. The unnatural amino acid para-azido-L-phenylalanine was incorporated into a specific site of the displayed enzyme, facilitating electron transfer between the enzyme and an electrode. In order to attach the bacteria carrying the surface displayed enzyme to a surface, a linker containing an alkyne and a thiol moiety on opposite ends was synthesized and attached to the dehydrogenase site specifically through a copper(I)-catalyzed azide-alkyne cycloaddition reaction. Using this approach we were able to covalently link bacteria to gold-coated surfaces and to gold nanoparticles, while maintaining viability and catalytic activity. We show the performance of a biofuel cell using these modified bacteria at the anode, which resulted in site-specific dependent fuel cell performance for at least a week. This is the first example of site-specific attachment of a true living biohybrid to inorganic material.

A novel concept for a biofuel cell is presented. Enzyme based fuel cells suffer from enzyme instability when a long time of operation is required. Hence, a system that will continuously produce the biocatalyst needed for the system is necessary. A hybrid of an enzyme-based microbial fuel cell was developed. The redox enzyme glucose oxidase from Aspergillus niger was displayed on the surface of Saccharomyces cerevisiae using the Yeast Surface Display System in a high copy number and as an active enzyme. We have demonstrated its activity both biochemically and electrochemically and observed much higher activity over yeast cells not displaying glucose oxidase as well as over purified glucose oxidase from Aspergillus niger. Further, we were able to construct a biofuel cell, where the anode was comprised of the yeast cells displaying glucose oxidase in the presence of a mediator (methylene blue) and the cathode compartment was comprised of the oxygen reducing enzyme laccase from Trametes versicolor and a redox mediator. Our constructed biofuel cell displayed higher power outputs and current densities than those observed for unmodified yeast and a much longer time of operation in comparison with a similar cell where the anode is comprised of purified glucose oxidase.

A microbial fuel cell (MFC) was designed in which fuel is generated in the cell by the enzyme glucoamylase, which is displayed on the surface of yeast. The enzyme digests starch specifically into monomeric glucose units and as a consequence enables further glucose oxidation by microorganisms present in the MFC anode. The oxidative enzyme glucose oxidase was coupled to the glucoamylase digestive enzyme. When both enzymes were displayed on the surface of yeast cells in a mixed culture, superior fuel-cell performance was observed in comparison with other combinations of yeast cells, unmodified yeast, or pure enzymes. The feasibility of the use of the green macroalgae Ulva lactuca in such a genetically modified MFC was also demonstrated. Herein, we report the performance of such fuel cells as a proof of concept for the enzymatic digestion of complex organic fuels in the anode of MFCs to render the fuel more available to microorganisms.

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