Enzymatic Fuel Cell Research Articles

Laccase Spontaneous Adsorption Immobilization: Experimental Studies and Mathematical Modeling at Enzymatic Fuel Cell Cathode Construction

The activity of a bioeletrode is largely determined by the amount of enzyme adsorbed on its active layer, including the distribution of enzyme along thickness in the carrier layer. The distribution of enzyme is also required for calculations of the characteristics of bioelectrocatalysis process using a mathematical model. In the present article, on the basis of conducted experimental research a mathematical model of laccase immobilization by spontaneous adsorption on carbon-based sorbentsof different nature was developed. The model can be used to predict adsorption value and enzyme distribution in the layer of an adsorbent. The model includes the equations of the enzyme concentration changing due to its adsorption on the surface of the carbon material (CM) and the enzyme diffusion over the thickness of CM. The diffusion equation is based on the second Fick’s law and contains fractional derivatives instead of the first oder derivative.

CELLOBIOSE DEHYDROGENASE/ EPOXY- GRAPHITE COMPOSITE WITH ARYL DIAZONIUM REDUCTION FOR LACTOSE DETECTION

Milk is an important ingredient in our day to day diet bacause of the high quality nutrients in it. In the dairy industry including cheese fermentation processes, there is a need to control the release of lactose into wastewater streams. There are methods adopted to recover the lactose and to transform the lactose into energy through renewable energy (RE) pathways. These methods however are expensive and require certain skill to operate them. In this study, in-house electrode, which is simple and can be applied after one day of fabrication were investigated. The method was by using graphite-epoxy composite electrode, surface modified with cellobiose dehydrogenase (CDH) enzyme using aryl diazonium. These designed composite electrodes were tested on its capability as biosensor for sensitivity on detecting the lactose as well as its capability as an anode in enzymatic fuel cell (EFC) on long term electrochemical stability in generating electricity from lactose oxidation. The results showed that the CDH-Aryl diazonium modified on surface of fabricated graphite-epoxy electrodes had Michaelis Menten constant Km for CDH (0.65 – 0.75 mM) comparable to available commercial electrodes reported in the literature (0.7 mM). They are also conductively sensitive with the current intensity 86% more with the above mentioned electrodes when modified with embedded multi-walled carbon nanotube (MWCNT) and gave a high reproducibility signal (63% more than fabricated electrodes without MWCNT). In addition to the above, its performance stability in continuous mode operation for 25 days, recorded almost consistent in current detection (19.2 ± 3.8 µA/ cm2). Hence, these fabricated electrodes give alternative for a sensitive lactose detector which is cheap and simple to fabricate.

Recent developments in high surface area bioelectrodes for enzymatic fuel cells

Enzymatic fuel cells (EFC) function in a similar way to low temperature proton exchange membrane fuel cells (PEMFC) but use enzymes instead of noble metals as catalysts for fuel and oxidant transformation. The need for EFCs that deliver enhanced power has resulted in high surface/volume ratio conductive materials being considered as enzyme host matrices. While the enhanced surface has effectively led to higher catalytic currents, the use of high surface area nanomaterials (HSM) has also induced new issues related to the wiring of enzymes, the role of porosity, and the effect on stability. This review discusses the most important features reported in this area over the past three years, and proposes future directions concerning EFC applications. Recent developments in high surface area bioelectrodes for enzymatic fuel cells. Available from: https://www.researchgate.net/publication/318305120_Recent_developments_in_high_surface_area_bioelectrodes_for_enzymatic_fuel_cells [accessed Jul 19, 2017].

Reticulated vitreous carbon as a scaffold for enzymatic fuel cell designing

Three – dimensional (3D) electrodes are successfully used to overcome the limitations of the low space – time yield and low normalized space velocity obtained in electrochemical processes with two – dimensional electrodes. In this study, we developed a three – dimensional reticulated vitreous carbon – gold (RVC-Au) sponge as a scaffold for enzymatic fuel cells (EFC). The structure of gold and the real electrode surface area can be controlled by the parameters of metal electrodeposition. In particular, a 3D RVC-Au sponge provides a large accessible surface area for immobilization of enzyme and electron mediators, moreover, effective mass diffusion can also take place through the uniform macro – porous scaffold. To efficiently bind the enzyme to the electrode and enhance electron transfer parameters the gold surface was modified with ultrasmall gold nanoparticles stabilized with glutathione. These quantum sized nanoparticles exhibit specific electronic properties and also expand the working surface of the electrode. Significantly, at the steady state of power generation, the EFC device with RVC-Au electrodes provided high volumetric power density of 1.18±0.14mWcm−3 (41.3±3.8µWcm−2) calculated based on the volume of electrode material with OCV 0.741±0.021V. These new 3D RVC-Au electrodes showed great promise for improving the power generation of EFC devices.

Enzymatic electrosynthesis of formate from CO2 reduction in a hybrid biofuel cell system

To seek a sustainable way of CO2 sequestration and conversion, enzymatic electrosynthesis (EES) of formate from CO2 reduction has been investigated in a hybrid biofuel cell system. In an enzymatic fuel cell (EFC), waste CO2 species are specifically reduced to energy-rich product of formate under mild biological conditions. Efficient formate production can be achieved at lowered electrode potential owing to the electrochemically active participation of formate dehydrogenase (CbFDH) as a biocatalyst. Electropolymerized neutral red (PolyNR) is proven to be a promising modifier to enhance the electrochemical behavior of enzymatic electrode, as well as a reducing reagent to regenerate mediator of NADH in enzymatic CO2 reduction. Electrons for EES are extracted from the organic pollutants in wastewater by microbial fuel cell (MFC) stacks arranged in series and/or parallel with different unit numbers (n = 1, 2 and 3). The maximum formate production rate reaches around 60 mg L−1 h−1 with a Faraday efficiency of 70% in the EFC powered by a three-MFC stacked in series. In view of practical applications, the hybrid MFC-EFC system has been demonstrated to be advantageous in both product specificity and energy sustainability.

Bioelectrochemical Haber-Bosch Process: An Ammonia-Producing H2 /N2 Fuel Cell.

Nitrogenases are the only enzymes known to reduce molecular nitrogen (N2 ) to ammonia (NH3 ). By using methyl viologen (N,N'-dimethyl-4,4'-bipyridinium) to shuttle electrons to nitrogenase, N2 reduction to NH3 can be mediated at an electrode surface. The coupling of this nitrogenase cathode with a bioanode that utilizes the enzyme hydrogenase to oxidize molecular hydrogen (H2 ) results in an enzymatic fuel cell (EFC) that is able to produce NH3 from H2 and N2 while simultaneously producing an electrical current. To demonstrate this, a charge of 60 mC was passed across H2 /N2 EFCs, which resulted in the formation of 286 nmol NH3 mg-1 MoFe protein, corresponding to a Faradaic efficiency of 26.4 %.

Bioelectrochemical Haber–Bosch Process: An Ammonia‐Producing H2/N2 Fuel Cell

AbstractNitrogenases are the only enzymes known to reduce molecular nitrogen (N2) to ammonia (NH3). By using methyl viologen (N,N′‐dimethyl‐4,4′‐bipyridinium) to shuttle electrons to nitrogenase, N2 reduction to NH3 can be mediated at an electrode surface. The coupling of this nitrogenase cathode with a bioanode that utilizes the enzyme hydrogenase to oxidize molecular hydrogen (H2) results in an enzymatic fuel cell (EFC) that is able to produce NH3 from H2 and N2 while simultaneously producing an electrical current. To demonstrate this, a charge of 60 mC was passed across H2 /N2 EFCs, which resulted in the formation of 286 nmol NH3 mg−1 MoFe protein, corresponding to a Faradaic efficiency of 26.4 %.

Study of Electrode Structures and Redox Kinetics in Biofuel Cells

Selection of the anode-cathode electrodes materials and structure is one of the critical challenges of bio fuel cell application. They can affect the power density and columbic efficiency. Two types of bio fuel cell were studied, the Microbial Fuel Cell (MFC) and the Enzymatic Fuel Cell (EFC), where the electrode structure and kinetics are similar except for the rates of redox reaction. The electrochemical characteristics of the In the MFC the anode was inoculated with MRS broth containing Lactobacillus Cesai Shirota. Complete characterisation and optimisation of the redox kinetics will be presented. Mediators will be used to enhance electron transfer between the fuel, bacteria and electrodes to improve electrode kinetics. A fast and convenient bacterial immobilization method will be proposed as an attempt to improve the anode efficiency of a microbial fuel cell, in which bacteria will be entrapped. The electron transfer characteristics with the mediators and immobilizers shall be studied by cyclic voltammetry and SEM imaging. Enzymatic Fuel Cell is a specific type of bio fuel cell that uses enzymes as a catalyst to oxidize its fuel, instead of precious metals. Enzymatic glucose biofuel cells convert chemical energy stored in glucose into electricity. Enzymatic oxidation from complex sugar is carried out by glucose selective enzymes such as glucose oxidase (Gox) and oxygen reducing enzyme namely laccase. These reactions are highly enzyme specific and occur at relatively mild conditions (Neutral pH and ambient temperature). The specific materials and structure for the electrodes used in enzymatic fuel cell can affect the power density and columbic efficiency. This glucose EFC cell features a 3-D porous carbon anode and cathode, for high surface area for the reaction, a suitable immobilizer for the enzyme immobilization and mediators like ferrocene for optimal electron transfer. The achievable cell potential is between 0.7- 0.8V. The achieved power density is still below theoretical value. The EFC will be optimized for enzyme loading; conductive loss minimization, both electronic and ionic, direct charge transfer for improving charge transfer efficiency, and pore channel and size profile.

Rational Combination of Promiscuous Enzymes Yields a Versatile Enzymatic Fuel Cell with Improved Coulombic Efficiency

Enzymatic fuel cells (EFCs) utilize enzymatic catalysts to convert chemical energy to electrical energy, typically by performing a 2e− oxidation of saccharides. In the case of sugars, a single 2e− oxidation does not fully exploit this energy-dense fuel that is capable of producing 24e− from its complete oxidation to CO2. Here, we propose an efficient approach to design a versatile EFC that can produce electrical energy from 12 (oligo)saccharides by combining two enzymes that possess diverse substrate specificities: pyranose dehydrogenase (PDH) and a broad glucose oxidase (bGOx). Additionally, PDH is able to perform single or two sequential oxidations of glucose (at C2 and/or C3) yielding up to 4e−, whereas bGOx only performs a single 2e− oxidation at the anomeric (C1) position. By combining PDH and bGOx, we demonstrate the ability to achieve deep oxidation of glucose and xylose, whereby each is able to undergo sequential oxidations by PDH and bGOx. Additionally, we demonstrate that this deep oxidation can yield improved performances of EFCs. For example, an EFC comprised of a bi-enzymatic PDH/bGOx bioanode using xylose as a fuel yields a maximum current density of 586 ± 3 μAcm−2 whereas mono-enzymatic PDH or bGOx EFC bioanodes result in current densities of 440 ± 4 μAcm−2 and 120 ± 1 μAcm−2, respectively.

Cholesterol as a Promising Alternative Energy Source: Bioelectrocatalytic Oxidation Using NAD-Dependent Cholesterol Dehydrogenase in Human Serum

Cholesterol is an essential structural component of mammalian cells, although elevated concentrations of cholesterol in the human body are linked to atherosclerotic disease. In this context, monitoring physiological cholesterol concentrations is of great interest in medical fields and the concept of producing electrical energy from cholesterol is interesting. In this work, we report the bioelectrocatalytic oxidation of cholesterol with the use of nicotinamide adenine dinucleotide-(NAD) dependent cholesterol dehydrogenase (ChDH) as an alternative enzyme to the commonly-used cholesterol oxidase (ChOx) in bioelectronic applications. To achieve bioelectrocatalytic cholesterol oxidation, ChDH was combined with diaphorase (DH) in a bilayer fashion, whereby DH acts as an intermediary enzyme to facilitate NADH oxidation at a ferrocene redox polymer. Characterization of the resulting bioanode identifies a linear cholesterol response range from 5 μM to 200 μM, with an associated sensitivity of 60.12 mA cm−2 M−1. Furthermore, an O2-reducing biocathode incorporating bilirubin oxidase (BOx) was combined with the cholesterol bioanode into a complete cholesterol/O2 membrane-less enzymatic fuel cell (EFC).

Sandwich-Type Enzymatic Fuel Cell Based on a New Electro-Conductive Material - Ion Jelly

In the present work, Ion Jelly films based on 1-ethyl-3-methylimidazolium ethylsulfate, with incorporated redox proteins and enzymes were deposited on carbon screen-printed electrodes (SPEs), and their electrochemical characterization was attained. Ion Jelly synthesis was carried out simultaneously with protein incorporation in its structure, followed by a maturation step under controlled atmosphere (4 days at 4 °C and water activity (aw) of 0.76). The electrochemical response of the material was characterized, and a sandwich-type fuel cell configuration was subsequently built, consisting of two SPEs containing two independent Ion Jelly discs in the middle; one disc incorporated Desulfovibrio gigas cytochrome c3 and [NiFe]-hydrogenase, while the other disc contained aldehyde oxidoreductase, constituting the biocathode and bioanode of the cell, respectively. Cell voltage increased with time in the presence of benzaldehyde, in agreement with a successful electronic pathway across the cell and the concomitant aldehyde oxidoreductase enzymatic activity. In the cathodic side assays, hydrogenase showed catalytic activity towards H+ reduction to H2.

Enzymatic versus Electrocatalytic Oxidation of NADH at Carbon‐Nanotube Electrodes Modified with Glucose Dehydrogenases: Application in a Bucky‐Paper‐Based Glucose Enzymatic Fuel Cell

AbstractIn this work, we have designed and compared functionalized carbon‐nanotube‐based electrodes for the electrocatalytic oxidation of NADH. We show that oxidation of NADH at neutral pH values can be performed by pristine multi‐walled carbon nanotubes (MWCNT) and directly wired diaphorase or ruthenium phenanthrolinequinone molecular catalysts. Glucose dehydrogenase was immobilized on these MWCNT electrodes by an activated‐ester‐modified pyrene linker. Glucose‐oxidizing bioelectrodes were compared and integrated into a bucky‐paper‐based glucose/O2 biofuel cell, using a bilirubin‐oxidase‐modified bucky‐paper cathode. The best configuration was obtained using a NADH‐oxidizing molecular catalyst at the anode. The biofuel cell exhibits an open‐circuit voltage of 0.62 V and delivers a power output of 0.47 mW cm−2.

Harvesting Energy using Biocatalysts

<i>Harvesting Energy using Biocatalysts</i>

Application of Hydroxyethyl Methacrylate and Ethylene Glycol Methacrylate Phosphate Copolymer as Hydrogel Electrolyte in Enzymatic Fuel Cell

AbstractA composite polymer electrolyte is developed to improve the properties of electrochemical devices, such as lithium‐ion batteries, supercapacitors and fuel cells. Here we report the application of poly(2‐hydroxyethyl methacrylate) and ethylene glycol methacrylate phosphate copolymer as a pseudo solid state electrolyte for an enzymatic fuel cell. The phosphate groups present in the polymer chains ensure the stability of pH during fuel cell work and enable retaining water molecules in the polymer matrix through hydrogen bond formation. After optimization of synthesis conditions the maximum ionic conductivity of the hydrogel reached 0.028 S cm−1 and maximum loading of entrapped water was 50 % of hydrogel total mass. The hydrogel was employed as the electrolyte in electrochemical measurements of the enzymatic electrodes. The current density of fructose oxidation on the anode covered with single walled carbon nanotubes derivatized with amine groups and fructose dehydrogenase reached 5.2 mA cm−2 in 100 mM fructose concentration in the hydrogel and the current onset potential was −0.12 V vs Ag/AgCl. The cathode covered with multiwalled carbon nanotubes modified with naphthalene groups and laccase gave current density 0.56 mA cm−2 with onset potential of 0.6 V vs Ag/AgCl. Fully enzymatic fuel cell with hydrogel electrolyte exhibited maximum power density 0.2 mW cm−2 and higher stability in time than the cell with the same electrodes stored in water solution.

Production and characterization of cellobiose dehydrogenase from Phanerochaete chrysosporium KCCM 60256 and its application for an enzymatic fuel cell

The enzyme cellobiose dehydrogenase (CDH), with high ability of electron transport, has been widely used in enzymatic fuel cells or biosensors. In this study, the cellobiose dehydrogenase gene from Phanerochaete chrysosporium KCCM 60256 was amplified and expressed in the methylotrophic yeast Pichia pastoris X-33. The recombinant enzyme (PcCDH) was purified using a metal affinity chromatography under non-denaturing conditions. The purified enzyme was analyzed by SDS-PAGE, confirming a corresponding band about 100 kDa. The enzyme activity of this purified PcCDH was determined as 1,845U/L (65mg/L protein). The enzyme showed the maximum activity at pH 4.5 and high activity in broad ranges of temperature from 30°C to 60°C. Moreover, the application of PcCDH to enzymatic fuel cell (EFC) was demonstrated. Lactose was used as the substrate in the EFC system; anode and cathode were immobilized with PcCDH and laccase, respectively. The cell’s open circuit voltage and maximum power density of the EFC system were, respectively, determined as 0.435 V and 314 μW/cm2 (at 0.247 V) with 10 mM lactose.

Development and Characterization of Cellulolytic Enzymatic Fuel Cells with DNA-Organized Multi-Enzyme Cascade

As fossil fuel is depleting, an alternative source of energy to accommodate the current standard of living is of great interest in research. Out of many methods that have been studied, fuel cells have been shown to be both environmentally friendly and flexible in types of fuels, such as hydrogen and alcohols. Enzymatic fuel cells (EFCs), more specifically, use isolated enzymes as a catalyst to redox reactions instead of noble metal catalysts commonly used in other fuel cells, which are nonrenewable. EFCs are also attractive because they can operate under mild conditions such as room temperature, atmospheric pressure, and neutral pH.1Along with microbial fuel cells (MFCs), EFCs are the only type of fuel cell that can use biologically derived materials – such as glucose – as fuels. This eliminates the additional steps to obtain pure hydrogen typically used as fuel. Early works with enzymatic fuel cells only involved a single enzyme as biocatalyst, usually glucose oxidase (GOx) to convert glucose to electricity via glucose-oxygen redox reactions.2This results in incomplete oxidation of fuel and thus a lower power density output. We plan to mimic the structured multi-enzyme scaffold in anaerobic bacteria called cellulosome to develop a biological approach for fuel cell applications via enzyme organization to create multi-enzyme cascade for cellulose hydrolysis and glucose oxidation. We hypothesized that the substrate channeling effect of organized enzyme cascade can enhance the efficiency in power generation. Previously, protein scaffolds have been used as scaffold to organize cellulases, but the problem of scaffold truncation occurred when the scaffold size increased.3 On the other hand, the length of DNA can be increased easily by technique such as rolling circle amplification.4 It also provides high binding specificity and affinity with flexible design.5DNA was therefore selected as scaffolds and immobilization tags in our design. In the fully assembled cellulolytic biofuel cell, the anode was fabricated by simple method of electrospinning a nanofiber mat of nickel coated with a few monolayers of gold via galvanic displacement. The main DNA scaffold was modified with a thiol group for high gold-binding affinity to maximize the density of the multi-enzyme scaffold on the anode. Three cellulases - endoglucanase, exoglucanase, and β-glucosidase -, which synergistically break down cellulose, a cellulose-binding domain (CBD), glucose oxidase, and a mediator were site-specifically bound to the DNA scaffold in an appropriate order for efficient conversion of cellulose to electricity (Fig 1). The cellulases and the CBD were expressed in E. coli. The purification was based on the thermally induced reversible inverse phase transition property of the fusion partner, elastin-like polypeptide (ELP), and conjugation with DNA was enabled by its fusion partner, HaloTag. The glassy carbon cathode was functionalized with oxygen reducing agent, bilirubin oxidase, adsorbed onto a carbon nanotube. Binding of each enzyme on DNA scaffolds was confirmed and the surface density of electrode surface was quantified by Quartz Crystal Microbalance (QCM). Cyclic voltammetry and electrochemical impedance spectroscopy were performed to characterize the electrochemical properties of the assembled enzymatic fuel cell. Acknowledgements This work was made possible by the catalysis and biocatalysis division of the National Science Foundation (NSF). References Minteer, S. D.; Liaw, B. Y.; Cooney, M. J. Enzyme-based biofuel cells. Energy Biotech. 2007, 18, 228-234. Ivnitski, D.; Branch, B.; Atanassov, P.; Apblet, C. Glucose oxidase anode for biofuel cell based on direct electron transfer. Electrochem. Comm. 2006, 8, 1204-1210. Moraïs, S.; Morag, E.; Barak, Y. Deconstruction of Lignocellulose into Soluble Sugars by Native and Designer Cellulosomes. MBio 2012, 3, 1–11. Ali, M. M.; Li, F.; Zhang, Z.; Zhang, K.; Kang, D.-K.; Ankrum, J. a; Le, X. C.; Zhao, W. Rolling circle amplification: a versatile tool for chemical biology, materials science and medicine. Chem. Soc. Rev. 2014, 43, 3324–3341. Pinheiro, A. V; Han, D.; Shih, W. M.; Yan, H. Challenges and opportunities for structural DNA nanotechnology. Nat. Nanotechnol. 2011, 6, 763–772. Figure 1

Printing of Enzyme Electrodes on Nonwoven Fabric for Flexible Biofuel Cells

Enzymatic biofuel cells (EBFCs) are lightweight and eco-friendly power sources that employ enzymes as catalysts and sugar as fuel for redox reactions at ambient temperatures. Due to their lightness and biocompatibility, EBFCs recently attract a great deal of attention and have been applied to a wide range of medical, implantable, and wearable devices [1-5]. We previously developed an iontophoresis skin patch with a built-in EBFC for enhancing drug delivery through skin by ionic current generated by the EBFC. The electrodes of the EBFC in the skin patch were made by multi-step fabrication. Carbon fabric was immersed in the dispersion of carbon nanotubes (CNTs) to make electrodes, followed by immobilization of enzymes onto them. Fructose dehydrogenase (FDH) was immobilized on an anode, and bilirubin oxidase (BOD) on a cathode to form a complete EBFC. In this study, we developed ink of CNTs and enzyme that can be printed onto nonwoven fabric that works as a flexible substrate. This material simplifies the fabrication process of CNT/enzyme electrodes, and enables patterning of the electrode with an arbitrary shape. To prepare the CNT/enzyme ink, CNT and additives of different roles were first mixed in aqueous solution and dispersed by sonication: CNTs as a highly-conductive scaffold for enzyme immobilization, polyvinylimidazole (PVI) as a binder, trehalose as a stabilizer of enzymes during freeze-drying, and 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBSE) for non-covalent immobilization of enzymes to CNTs. Next, FDH as an enzyme catalyst for an anode was added to the mixture above to complete the CNT/enzyme ink. The CNT/enzyme ink was cast on nonwoven fabric in 1 cm2 size to form an anode. Finally, the cast electrode was freeze-dried for 6 hours. After freeze-drying, the fabricated FDH anode had highly porous structures as observed by scanning electron microscopy, and it could be preserved for longer time after freeze-drying because of trehalose. The performance of the printed FDH anode and the effects of the additives were evaluated. The FDH anode was immersed in a stirred buffer solution containing 200 mM fructose and measured by typical cyclic voltammetry (CV) at 10 mV/s. The FDH anode generated current density of 2 mA cm-2 with fructose as fuel. Though the printed ink was originally aqueous dispersion, the printed shape was kept intact after rehydration, while without PVI the printed electrode readily dissolved in buffer solution. CV of the anode in the presence and absence of PBSE indicated that PBSE was essential for high power density. [1] Enzymatic Fuel Cells from Fundamental to Applications (Eds: H. R. L uckarift, P. Atanassov, G. R. Johnson), Wiley, New Jersey, 2014 [2] W. Gellett, et al., Electroanalysis., 22, 727, (2010) [3] G. Valdés-Ramírez, et al., Electrochem. Commun., 47, 58, (2014) [4] S. Cosnier, et al., Electrochem. Commun., 38, 19, (2014) [5] Y. Ogawa, et al., Adv. Healthc. Mater., 4, 506, (2015) Figure 1

Meta-study Focusing on Abiotic Cells for Human Implants

Abstract: Powering implantable devices in human body with a glucose based fuel cell (GFC) offers an alternative to non-rechargeable batteries that typically require routine invasive surgery. There are three main approaches for GFCs to oxidise glucose. Enzymatic Fuel Cells are selective and have a high reaction rate but are unstable as the proteins can denature giving the cell a short lifespan. Microbial Fuel Cells use microbes to break down glucose to produce electrons. However they possess the danger of cell leakages that can introduce the microbes to the patient and risk possible infection. Abiotic Fuel Cells employ inorganic catalysts, typically a noble metal alloy or metallic carbon to oxidise and reduce glucose and oxygen respectively. Abiotic is the safest and most stable of the three but possesses the lowest output due to the electrodes inability to target glucose specifically. This meta-study investigates for Abiotic Glucose Fuel Cell being the most viable candidate of the three for possible use in autonomous medical devices. We will assess current abiotic fuel cells on the thermodynamic parameters of output voltage, current/current density, power density and efficiency. The kinetic parameters of internal resistance and rate at which membranes transport electrons will also be assessed. Operational parameters of lifespan and overall architecture will also be assessed to further understand the conditions and materials these cells were produced.Keywords: Glucose; Fuel Cell; Meta-study; Enzymatic; Microbial; Abiotic; Implantable Devices

Deep Oxidation of Multiple (Poly)Saccharides at a Bi-Enzymatic Bioelectrode

As perhaps the most commonly utilized fuel for enzymatic fuel cells (EFCs), glucose oxidation is largely under-exploited. Theoretically, the oxidation of glucose and its downstream metabolites is able to deliver a maximum of 24e- to a bioanode, however the vast majority of EFCs reported to date only perform a single 2e- oxidation of glucose. Commercially available glucose oxidase (GOx) from Aspergillus sp. oxidizes the anomeric (C1) carbon of glucose. Recently, mediated bioelectrocatalysis of pyranose dehydrogenase from Agaricus meleagris (AmPDH) via an osmium redox hydrogel has been demonstrated, whereby AmPDH is reported to be able to oxidize glucose and other saccharides at combinations of their respective C1/C2/C3 positions.1 Another attractive property of an EFC is the ability to utilize a single biocatalyst to oxidize a range of fuels. We recently reported the use of an engineered commercially-available glucose oxidase with broader substrate specificity at an electrode surface that resulted in an EFC configuration that was able to oxidize multiple (poly)saccharides, including lactose from dairy milk and starch.2 This study reports the ability of a ferrocene redox hydrogel to mediate bioelectrocatalytic saccharide oxidation by AmPDH. Further, AmPDH and broad substrate specificity glucose oxidase were combined to yield an EFC that was able to operate on multiple (poly)saccharides while theoretically increasing the extent of oxidation of each substrate, resulting in a more-versatile EFC with greater efficiency.

Self-Powered Arsenic Biosensor Based on the Inhibition of Laccase By As3+ and As5+

Laccase is a multi-copper center enzyme that is able to oxidize phenolic substrates and undergo a four electron reduction of O2 to H2O. The interaction of laccase with different environmental toxins has been reported, whereby laccase can either oxidize pollutants (polyphenols, polyamines and paradiphenols) as fuels or be inhibited by the toxin (mercury and azide).[1] Laccase is also commonly employed within enzymatic fuel cells (EFCs) yielding a biocathode that bioelectrocatalytically reduces O2 to H2O. Self-powered biosensors are advantageous in terms of portability because they are not reliant on external power sources. In the past, glucose/O2 EFCs have been widely used as self-powered biosensors utilizing laccase as the cathodic biocatalyst.[2] Self-powered biosensors that sense based on enzymatic inhibition by an analyte are an important category of self-powered biosensors and have been extensively studied.[3] This study reports the first experimental evidence on the inhibition of laccase by two arsenic species (arsenite and arsenate). The mechanism for both inhibitors was determined to follow an uncompetitive inhibition model via UV-Vis assays using 2,2'azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as the oxidant/indicator. Enzymatic inhibition was also studied electrochemically via amperometric i-t experiments. Furthermore, laccase cathodes were employed as part of a conceptual self-powered arsenite/arsenate biosensor, demonstrating sensitivities of 0.91 ± 0.07 mV/mM for arsenite and 0.98 ± 0.02 mV/mM for arsenate. [1] S. R. Couto, J. L. T. Herrera, Biotechnology advances 2006, 24, 500-513. [2] E. Katz, A. F. Bückmann, I. Willner, Journal of the American Chemical Society 2001, 123, 10752-10753. [3] D. Wen, L. Deng, S. Guo, S. Dong, Analytical chemistry 2011, 83, 3968-3972. Figure 1