Effect of Multi-Walled Carbon Nanotubes on Glucose Oxidation by Glucose Oxidase or a Flavin-Dependent Glucose Dehydrogenase in Redox-Polymer-Mediated Enzymatic Fuel Cell Anodes

Enzymatic Glucose-Based Bio-batteries: Bioenergy to Fuel Next-Generation Devices

This article consists of a review of the main concepts and paradigms established in the field of biological fuel cells or biofuel cells. The aim is to provide an overview of the current panorama, basic concepts, and methodologies used in the field of enzymatic biofuel cells, as well as the applications of these bio-systems in flexible electronics and implantable or portable devices. Finally, the challenges needing to be addressed in the development of biofuel cells capable of supplying power to small size devices with applications in areas related to health and well-being or next-generation portable devices are analyzed. The aim of this study is to contribute to biofuel cell technology development; this is a multidisciplinary topic about which review articles related to different scientific areas, from Materials Science to technology applications, can be found. With this article, the authors intend to reach a wide readership in order to spread biofuel cell technology for different scientific profiles and boost new contributions and developments to overcome future challenges.

Enzyme production ofd-gluconic acid and glucose oxidase: successful tales of cascade reactions

This review mainly focuses on the use of glucose oxidase in the production ofd-gluconic acid, which is a reactant of undoubtable interest in different industrial areas. As example of diverse enzymatic cascade reactions.

Glucose biosensor based on open-source wireless microfluidic potentiostat

Wireless potentiostats capable of cyclic voltammetry and amperometry that connect to the Internet are emerging as key attributes of future point-of-care devices. This work presents an "integrated microfluidic electrochemical detector" (iMED) three-electrode multi-potentiostat designed around operational amplifiers connected to a powerful WiFi-based microcontroller as a promising alternative to more expensive and complex strategies reported in the literature. The iMED is integrated with a microfluidic system developed to be controlled by the same microcontroller. The iMED is programmed wirelessly over a standard WiFi network and all electrochemical data is uploaded to an open-source cloud-based server. A wired desktop computer is not necessary for operation or program uploading. This method of integrated microfluidic automation is simple, uses common and inexpensive materials, and is compatible with commercial sample injectors. An integrated biosensor platform contains four screen-printed carbon arrays inside 4 separate microfluidic detection chambers with Pt counter and pseudo Ag/AgCl reference electrodes in situ. The iMED is benchmarked with K3[Fe(CN)6] against a commercial potentiostat and then as a glucose biosensor using glucose-oxidising films of [Os(2,2'-bipyridine)2(polyvinylimidazole)10Cl] prepared on screen-printed electrodes with multi walled carbon nanotubes, poly(ethylene glycol) diglycidyl ether and flavin adenine dinucleotide-dependent glucose dehydrogenase. Potential application of this cost-effective wireless potentiostat approach to modern bioelectronics and point-of-care diagnosis is demonstrated by production of glucose oxidation currents, under pseudo-physiological conditions, using mediating films with lower redox potentials.

Tackling the Challenges of Enzymatic (Bio)Fuel Cells

The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.

Efficient Biomass Fuel Cell Powered by Sugar with Photo- and Thermal-Catalysis by Solar Irradiation

The utilization of biomass sugars has received great interesting recently. Herein, we present a highly efficient hybrid solar biomass fuel cell that utilizes thermal- and photocatalysis of solar irradiation and converts biomass sugars into electricity with high power output. The fuel cell uses polyoxometalates (POMs) as photocatalyst to decompose sugars and capture their electrons. The reduced POMs have strong visible and near-infrared light adsorption, which can significantly increase the temperature of the reaction system and largely promotes the thermal oxidation of sugars by the POM. In addition, the reduced POM functions as charge carrier that can release electrons at the anode in the fuel cell to generate electricity. The electron-transfer rates from glucose to POM under thermal and light-irradiation conditions were investigated in detail. The power outputs of this solar biomass fuel cell are investigated by using different types of sugars as fuels, with the highest power density reaching 45 mW cm^-2 .

Effect of Carbon Nanotubes on Direct Electron Transfer and Electrocatalytic Activity of Immobilized Glucose Oxidase

Carbon nanotubes (CNTs) are excellent supports for electrocatalysts because of their large surface area, excellent electronic conductivity, and high chemical and structural stability. In the present study, the activity of CNTs on direct electron transfer (DET) and on immobilized glucose oxidase (GOX) is studied as a function of number of walls of CNTs. The results indicate that the GOX immobilized by the CNTs maintains its electrocatalytic activity toward glucose; however, the DET and electrocatalytic activity of GOX depend strongly on the number of inner tubes of CNTs. The GOX immobilized on triple-walled CNTs (TWNTs) has the highest electron-transfer rate constant, 1.22 s-1, for DET, the highest sensitivity toward glucose detection, 66.11 ± 5.06 μA mM-1 cm-2, and the lowest apparent Michaelis-Menten constant, 6.53 ± 0.58 mM, as compared to GOX immobilized on single-walled and multiwalled CNTs. The promotion effect of CNTs on the GOX electrocatalytic activity and DET is most likely due to the electron-tunneling effect between the outer wall and inner tubes of TWNTs. The results of this study have general implications for the fundamental understanding of the role of CNT supports in DET processes and can be used for the better design of more effective electrocatalysts for biological processes including biofuel cells and biosensors.

NAD-dependent dehydrogenase bioelectrocatalysis: the ability of a naphthoquinone redox polymer to regenerate NAD

Electron mediation between NAD-dependent enzymes using quinone moieties typically requires the use of a diaphorase as an intermediary enzyme. The ability for a naphthoquinone redox polymer to independently oxidize enzymatically-generated NADH is demonstrated for application to glucose/O2 enzymatic fuel cells.

Fully Enzymatic Membraneless Glucose|Oxygen Fuel Cell That Provides 0.275 mA cm(-2) in 5 mM Glucose, Operates in Human Physiological Solutions, and Powers Transmission of Sensing Data

Coimmobilization of pyranose dehydrogenase as an enzyme catalyst, osmium redox polymers [Os(4,4'-dimethoxy-2,2'-bipyridine)2(poly(vinylimidazole))10Cl](+) or [Os(4,4'-dimethyl-2,2'-bipyridine)2(poly(vinylimidazole))10Cl](+) as mediators, and carbon nanotube conductive scaffolds in films on graphite electrodes provides enzyme electrodes for glucose oxidation. The recombinant enzyme and a deglycosylated form, both expressed in Pichia pastoris, are investigated and compared as biocatalysts for glucose oxidation using flow injection amperometry and voltammetry. In the presence of 5 mM glucose in phosphate-buffered saline (PBS) (50 mM phosphate buffer solution, pH 7.4, with 150 mM NaCl), higher glucose oxidation current densities, 0.41 mA cm(-2), are obtained from enzyme electrodes containing the deglycosylated form of the enzyme. The optimized glucose-oxidizing anode, prepared using deglycosylated enzyme coimmobilized with [Os(4,4'-dimethyl-2,2'-bipyridine)2(poly(vinylimidazole))10Cl](+) and carbon nanotubes, was coupled with an oxygen-reducing bilirubin oxidase on gold nanoparticle dispersed on gold electrode as a biocathode to provide a membraneless fully enzymatic fuel cell. A maximum power density of 275 μW cm(-2) is obtained in 5 mM glucose in PBS, the highest to date under these conditions, providing sufficient power to enable wireless transmission of a signal to a data logger. When tested in whole human blood and unstimulated human saliva maximum power densities of 73 and 6 μW cm(-2) are obtained for the same fuel cell configuration, respectively.

Rational design of quinones for high power density biofuel cells

Enzymatic fuel cells (EFCs) are devices that can produce electrical energy by enzymatic oxidation of energy-dense fuels (such as glucose). When considering bioanode construction for EFCs, it is desirable to use a system with a low onset potential and high catalytic current density. While these two properties are typically mutually exclusive, merging these two properties will significantly enhance EFC performance. We present the rational design and preparation of an alternative naphthoquinone-based redox polymer hydrogel that is able to facilitate enzymatic glucose oxidation at low oxidation potentials while simultaneously producing high catalytic current densities. When coupled with an enzymatic biocathode, the resulting glucose/O2 EFC possessed an open-circuit potential of 0.864 ± 0.006 V, with an associated maximum current density of 5.4 ± 0.5 mA cm-2. Moreover, the EFC delivered its maximum power density (2.3 ± 0.2 mW cm-2) at a high operational potential of 0.55 V.

Employing FAD-dependent glucose dehydrogenase within a glucose/oxygen enzymatic fuel cell operating in human serum

Flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) is emerging as an oxygen-insensitive alternative to glucose oxidase (GOx) as the biocatalyst for bioelectrodes and bioanodes in glucose sensing and glucose enzymatic fuel cells (EFCs). Glucose EFCs, which utilize oxygen as the oxidant and final electron acceptor, have the added benefit of being able to be implanted within living hosts. These can then produce electrical energy from physiological glucose concentrations and power internal or external devices. EFCs were prepared with FAD-GDH and bilirubin oxidase (BOx) to evaluate the suitability of FAD-GDH within an implantable setting. Maximum current and power densities of 186.6±7.1 μA cm(-2) and 39.5±1.3 μW cm(-2) were observed when operating in human serum at 21 °C, which increased to 285.7±31.3 μA cm(-2) and 57.5±5.4 μW cm(-2) at 37 °C. Although good stability was observed with continual near-optimal operation of the EFCs in human serum at 21 °C for 24 h, device failure was observed between 13-14 h when continually operated at 37 °C.