Development of alcohol/O2 biofuel cells using salt-extracted tetrabutylammonium bromide/Nafion membranes to immobilize dehydrogenase enzymes

Facilitation of high-rate NADH electrocatalysis using electrochemically activated carbon materials

Electrochemical activation of glassy carbon, carbon paper and functionalized carbon nanotubes via high-applied-potential cyclic voltammetry leads to the formation of adsorbed, redox active functional groups and increased active surface area. Electrochemically activated carbon electrodes display enhanced activity toward nicotinamide adenine dinucleotide (NADH) oxidation, and more importantly, dramatically improved adsorption of bioelectrochemically active azine dyes. Adsorption of methylene green on an electroactivated carbon electrode yields a catalyst layer that is 1.8-fold more active toward NADH oxidation than an electrode prepared using electropolymerized methylene green. Stability studies using cyclic voltammetry indicate 70% activity retention after 4000 cycles. This work further facilitates the electrocatalysis of NADH oxidation for bioconversion, biosensor and bioenergy processes.

The spatial and sequential immobilisation of cytochrome c at adjacent electrodes

Two adjacent electrode surfaces were modified in a sequential manner with self-assembled thiol layers from the same solution using conditions (aqueous buffer at neutral pH) suitable for applications with proteins. A faradaic response was obtained from the redox protein, cytochrome c, independently immobilised at each surface.

Biofuel cells for biomedical applications: colonizing the animal kingdom

Interdisciplinary research has combined the efforts of many scientists and engineers to gain an understanding of biotic and abiotic electrochemical processes, materials properties, biomedical, and engineering approaches for the development of alternative power-generating and/or energy-harvesting devices, aiming to solve health-related issues and to improve the quality of human life. This review intends to recapitulate the principles of biofuel cell development and the progress over the years, thanks to the contribution of cross-disciplinary researchers that have combined knowledge and innovative ideas to the field. The emergence of biofuel cells, as a response to the demand of electrical power devices that can operate under physiological conditions, are reviewed. Implantable biofuel cells operating inside living organisms have been envisioned for over fifty years, but few reports of implanted devices have existed up until very recently. The very first report of an implanted biofuel cell (implanted in a grape) was published only in 2003 by Adam Heller and his coworkers. This work was a result of earlier scientific efforts of this group to "wire" enzymes to the electrode surface. The last couple of years have, however, seen a multitude of biofuel cells being implanted and operating in different living organisms, including mammals. Herein, the evolution of the biofuel concept, the understanding and employment of catalyst and biocatalyst processes to mimic biological processes, are explored. These potentially green technology biodevices are designed to be applied for biomedical applications to power nano- and microelectronic devices, drug delivery systems, biosensors, and many more.

Cell-free Biosystems in the Production of Electricity and Bioenergy

: Increasing needs of green energy and concerns of climate change are motivating intensive R&D efforts toward the low-cost production of electricity and bioenergy, such as hydrogen, alcohols, and jet fuel, from renewable sugars. Cell-free biosystems for biomanufacturing (CFB2) have been suggested as an emerging platform to replace mainstream microbial fermentation for the cost-effective production of some biocommodities. As compared to whole-cell factories, cell-free biosystems comprised of synthetic enzymatic pathways have numerous advantages, such as high product yield, fast reaction rate, broad reaction condition, easy process control and regulation, tolerance of toxic compound/product, and an unmatched capability of performing unnatural reactions. However, issues pertaining to high costs and low stabilities of enzymes and cofactors as well as compromised optimal conditions for different source enzymes need to be solved before cell-free biosystems are scaled up for biomanufacturing. Here, we review the current status of cell-free technology, update recent advances, and focus on its applications in the production of electricity and bioenergy.

Grafted Azure A modified electrodes as disposable β-nicotinamide adenine dinucleotide sensors

We report the in situ generation of aryl diazonium cations of Azure A, a redox-active phenothiazine dye, by reaction between the corresponding aromatic aminophenyl group and sodium nitrite in 0.1 M HCl. The subsequent electrochemical reduction of these dye diazonium salts gives rise to conductive electrografted films onto screen-printed carbon (SPC) electrodes. The resulting Azure A films have a very stable and reversible electrochemical response and exhibit potent and persistent electrocatalytic behavior toward NADH oxidation. We have optimized the electrografting conditions in order to obtain SPC modified electrodes with high and stable electrocatalytic response. The kinetic of the reaction between the NADH and the redox active centers in the Azure A film has been characterized using cyclic voltammetry and single step chronoamperometry. The catalytic currents were proportional to the concentration of NADH giving rise to linear calibration plots up to a concentration of 0.5 mM with a detection limit of 0.57±0.03 μM and a sensitivity of 9.48 A mol cm(-2) μM(-1). The precision of chronoamperometric determinations was found to be 2.3% for five replicate determinations of 3.95 μM NADH. The great stability of such modified electrodes makes them ideal for their application in the development of biosensing platforms based on dehydrogenases.

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.

Deep oxidation of glucose in enzymatic fuel cells through a synthetic enzymatic pathway containing a cascade of two thermostable dehydrogenases

A synthetic enzymatic pathway was designed for the deep oxidation of glucose in enzymatic fuel cells (EFCs). Polyphosphate glucokinase converts glucose to glucose-6-phosphate using low-cost, stable polyphosphate rather than costly ATP. Two NAD-dependent dehydrogenases (glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) that were immobilized on the bioanode were responsible for generating two NADH per glucose-6-phosphate (i.e., four electrons were generated per glucose via a diaphorase-vitamin K(3) electron shuttle system at the anode). Additionally, to prolong the enzyme lifetime and increase the power output, all of the recombinant enzymes that originated from thermophiles were expressed in Escherichia coli and purified to homogeneity. The maximum power density of the EFC with two dehydrogenases was 0.0203 mW cm(-2) in 10 mM glucose at room temperature, which was 32% higher than that of an EFC with one dehydrogenase, suggesting that the deep oxidation of glucose had occurred. When the temperature was increased to 50°C, the maximum power density increased to 0.322 mW cm(-2), which was approximately eight times higher than that based on mesophilic enzymes at the same temperature. Our results suggest that the deep oxidation of glucose could be achieved by using multiple dehydrogenases in synthetic cascade pathways and that high power output could be achieved by using thermostable enzymes at elevated temperatures.

Biofuel cells: enhanced enzymatic bioelectrocatalysis

Enzymatic biofuel cells represent an emerging technology that can create electrical energy from biologically renewable catalysts and fuels. A wide variety of redox enzymes have been employed to create unique biofuel cells that can be used in applications such as implantable power sources, energy sources for small electronic devices, self-powered sensors, and bioelectrocatalytic logic gates. This review addresses the fundamental concepts necessary to understand the operating principles of biofuel cells, as well as recent advances in mediated electron transfer- and direct electron transfer-based biofuel cells, which have been developed to create bioelectrical devices that can produce significant power and remain stable for long periods.

Enzymatic biofuel cells utilizing a biomimetic cofactor

The performance of immobilized enzyme systems is often limited by cofactor diffusion and regeneration. Here, we demonstrate an engineered enzyme capable of utilizing the minimal cofactor nicotinamide mononucleotide (NMN(+)) to address these limitations. Significant gains in performance are observed with NMN(+) in immobilized systems, despite a decreased turnover rate with the minimal cofactor.

Bioelectrochemistry of non-covalent immobilized alcohol dehydrogenase on oxidized diamond nanoparticles

Diamond nanoparticles are considered a biocompatible material mainly due to their non-cytotoxicity and remarkable cellular uptake. Model proteins such as cytochrome c and lysozyme have been physically adsorbed onto diamond nanoparticles, proving it to be a suitable surface for high protein loading. Herein, we explore the non-covalent immobilization of the redox enzyme alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae (E.C.1.1.1.1) onto oxidized diamond nanoparticles for bioelectrochemical applications. Diamond nanoparticles were first oxidized and physically characterized by X-ray diffraction (XRD), FT-IR and TEM. Langmuir isotherms were constructed to investigate the ADH adsorption onto the diamond nanoparticles as a function of pH. It was found that a higher packing density is achieved at the isoelectric point of the enzyme. Moreover, the relative activity of the immobilized enzyme on diamond nanoparticles was addressed under optimum pH conditions able to retain up to 70% of its initial activity. Thereafter, an ethanol bioelectrochemical cell was constructed by employing the immobilized alcohol dehydrogenase onto diamond nanoparticles, this being able to provide a current increment of 72% when compared to the blank solution. The results of this investigation suggest that this technology may be useful for the construction of alcohol biosensors or biofuel cells in the near future.

Automatic, sequential power generation for prolonging the net lifetime of a miniature biofuel cell stack

A sequential power generation system for prolonging the net lifetime of a miniature biofuel cell stack has been developed. The system consists of layered chambers of enzyme fuel cells designed to be exposed sequentially to fuel solution by automatically switched fuel flow. The cell chambers were initially separated by magnetized plastic covers sealed with a degradable glue, poly(lactic-co-glycolic acid) (PLGA). The time that the cover was opened by attraction with an external magnet, thereby activating the following cell, was adjustable from a few hours to a few weeks by controlling the weight ratio of Fe(3)O(4) in the covers and the molecular weight of PLGA. By using sequential power generation in this way, the power output of the system was stable for longer periods, and therefore the net lifetime of the stack has been extended as compared with that of a single biofuel cell.