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Artificial transplantation of the human body, which requires high technology, has been an attractive issue in the 4th industrial revolution era. The artificial equipment for human applications could contain a small-scale power supply. Enzyme fuel cells (EFCs) that generate green energy are being researched for use as the power supply for pacemakers, insulin pump, and retinal implant in human body. This study focused on an (EFC) using thin film electrodes-based on enzyme immobilization technology. The performance of this EFC was improved by enzyme immobilization and electron transfer. To improve the electron transfer, the GO/Co/chitosan composite was modified on the surface of thin film electrode. The properties of this modified surface of thin film electrode were confirmed by analysis of field emission gun scanning electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy. The performance of the designed EFC was optimized with immobilized redox enzyme on the modified electrode. The highest power density and voltage are determined as 441.48 µW/cm2 and − 0.443 V by thin film electrode, respectively. The optimum conditions of the EFC were 0.1 M D-glucose, 0.1 g/L glucose oxidase, pH 7.0, and reaction time of 4 h for both two types of thin film-electrodes. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) is an oxido-reductase enzyme that catalyzes glucose into hydrogen peroxide and glucono delta-lactone (GDL). GOx has the potential to be used in the medical field. Numerous research concerning the usage of GOx to create enzymatic biofuel cells have been done, nevertheless the results obtained have not been optimal. This research aims to increase the Km values of GOx in order to increase its potential as a material for an enzymatic fuel cell. The amino acid histidine in position 516 is a residue in the active site that plays an important part in the process of glucose oxidation. In this research we mutated H516 by in silico twice resulting in the mutants R516 and D516. The mutations resulted in a change of the docking area for both mutants and in the docking affinity for H516D resulting in higher Km values. This shows that the H516 residue plays an important part in the functions of glucose oxidase and mutation into aspartate could improve glucose oxidase based enzymatic fuel cells.

Activation of methane in low-temperature fuel cells has been a challenge due to its thermodynamic stability. In this study, we demonstrate the feasibility of using a pure culture of Methylococcus capsulatus microbial fuel cell in a proton exchange membrane (PEM) fuel cell in whole-cell and crude enzymatic modes. The impact of time and mediators of the microbial fuel cells (MFCs) was studied. Additionally, a mathematical model was used to predict and explain the fuel cell's electrochemical performance and mechanic details. The fuel cell generated an open-circuit voltage of 378.91 mV and a power density of 438.57 μW/m2 in the whole-cell mode, whereas an OCV of 125.62 mV and a power density of 117.94 μW/m2 in the enzymatic mode without the use of an external mediator. Although the cell was stable throughout the test duration of ten days in the whole-cell mode, the stability declined within minutes in the enzymatic mode. This work demonstrates the feasibility of generating electricity via a proton exchange membrane (PEM) fuel cell in microbial and enzymatic modes using methane as the only carbon source at room temperature with a pure culture of M. capsulatus as a direct electron-transporting biocatalyst. [ABSTRACT FROM AUTHOR]

The article briefly outlines the principle of curricular innovation research before illustrating it with the enzymatic fuel cell: First, the choice of topic is justified. Then, based on a system for enzymatic fuel cells with β‐glucose oxidase and laccase presented in the literature, individual stages of optimization or new development of an analogous school experiment with lactase are presented and an outlook on existing implementations is given. The article concludes with an assessment of the suitability of the school experiment of the enzymatic fuel cell with lactase. [ABSTRACT FROM AUTHOR]

Different cathode configurations with carbon paper (CP) and carbon cloth (CC) gas diffusion layer (GDL) are combined with Nafion® 115 for GOx enzyme fuel cells. Catalyst‐coated Nafion membrane (without a GDL) has resulted with highest impedance and lowest polarization response. Hot pressing of cathode gas diffusion electrode (GDE) onto the Nafion or physical placement onto the alternative chitosan membrane has reduced interface resistance 10 times compared with no‐GDL case. The best performance for the Nafion membrane is 2.1 mA cm−2 current density with hot‐pressed CC‐GDE. Smallest high‐frequency electrolyte (0.55 ohm) and charge transfer resistances (0.15 ohm) were measured with physically placed CC‐GDE on the alternative chitosan membrane resulting in maximum short current density of 3 mA cm−2 with a 4‐cm2 single enzyme fuel cell. [ABSTRACT FROM AUTHOR]

Direct electron transfer (DET), which requires no mediator to shuttle electrons from enzyme active site to the electrode surface, minimizes complexity caused by the mediator and can further enable miniaturization for biocompatible and implantable devices. However, because the redox cofactors are typically deeply embedded in the protein matrix of the enzymes, electrons generated from oxidation reaction cannot easily transfer to the electrode surface. In this review, methods to improve the DET rate for enhancement of enzymatic fuel cell performances are summarized, with a focus on the more recent works (past 10 years). Finally, progress on the application of DET-enabled EFC to some biomedical and implantable devices are reported.

This short review summarizes the improvements on biological fuel cells (BioFCs) with or without ionomer separation membrane. After a general introduction about the main challenges of modern energy management, BioFCs are presented including microbial fuel cells (MFCs) and enzymatic fuel cells (EFCs). The benefits of BioFCs include the capability to derive energy from waste-water and organic matter, the possibility to use bacteria or enzymes to replace expensive catalysts such as platinum, the high selectivity of the electrode reactions that allow working with less complicated systems, without the need for high purification, and the lower environmental impact. In comparison with classical FCs and given their lower electrochemical performances, BioFCs have, up to now, only found niche applications with low power needs, but they could become a green solution in the perspective of sustainable development and the circular economy. Ion exchange membranes for utilization in BioFCs are discussed in the final section of the review: they include perfluorinated proton exchange membranes but also aromatic polymers grafted with proton or anion exchange groups.

Considerably stable enzymatic fuel‐cells (single cell and 5‐cells stack) were prepared by using chitosan based membranes along with glucose oxidase attached bioanode. Continuous operation of fuel‐cells were monitored under short circuit conditions reaching half‐life over a week. Detailed analysis for the effects of pH, temperature, buffer types and concentration on different type of in‐house produced chitosan membranes were performed by electrochemical impedance spectroscopy (EIS). EIS was utilized to observe, total electrolyte resistance, charge transfer properties, mass transfer and double layer effects on integrated fuel cells (single cell and 5‐cells stack). Performance of the fuel cells was also analyzed by the polarization experiments. Current density of the fuel cell increased at higher operation temperatures not only due to better enzyme kinetics, but also due to increase in electrolyte (membrane+buffer solution) conductivity. Buffer concentration in the fuel (glucose) solution was found as an important parameter. Under optimum fuel cell operation conditions (i. e. 30–40 °C, pH 5 0.3 M buffer solution), maximum current densities of 3.0–3.2 mA cm−2 were reached. Low‐power devices (i. e. a calculator, step motor) were powered with 5‐cell stack producing 3 mW at 1.3 V. [ABSTRACT FROM AUTHOR]

Chitosan based reasonably stable membranes were prepared as polymeric electrolyte and separator for enzymatic fuel cell applications. Glucose oxidase (GOx) bioanode centered biofuel cell with the developed chitosan membranes performed much better in stability with high current densities than that of the biofuel cell utilizing a 125 μ‐thick perfluorosulfonic acid‐type membrane (i. e. Nafion® 115). Proposed chitosan membrane structural stability was enhanced by employing cellulosic support materials and chemical crosslinking. The effects of pH, buffer type, buffer concentration, temperature on the manufactured chitosan membranes along with the biofuel cell system were investigated. The biofuel cell operation parameters were optimized for the current density and stability aspects and more than 3 mA cm−2 current density was acquired from the cell at optimum conditions. Operational half‐life of the chitosan membrane was found as higher than the half‐life of the GOx immobilized bioanode. Therefore, this result indicates that chitosan membrane structural stability was not a limiting issue for the biofuel cell lifespan. [ABSTRACT FROM AUTHOR]

A high power enzymatic fuel‐cell was anticipated by using a recently developed glucose oxidase (GOx) immobilized bio‐anode, a conventional platinum−carbon based cathode and a popular high performance 125 μ‐thick perfluorosulfonic acid‐type proton exchange membrane (i. e. Nafion® 115). Unexpected current density decay from 2.13 mA cm−2 to 0.28 mA cm−2 was observed within 2 hours. Polarization measurements and AC impedance analysis indicated that loss of performance was linked to the membrane behavior. Ion exchange between buffer solution and membrane was perceived as the main cause for the fast performance loss. Saturation of the membrane with the cation in the buffer solution diminished proton transfer needed for cathode reaction. Charge transfer resistances, obtained from AC impedance data, increased with time substantially due to cation exchange within membrane. Replacement of membrane with the same enzyme electrode and cathode has resulted 100 % current density recovery on the fuel cell performance. It was concluded that a membrane, not affected by the buffer cations, was required for successful enzymatic fuel cell applications. [ABSTRACT FROM AUTHOR]

Glucose oxidase was covalently immobilized to a porous electrode, which was developed by using ferrocene functionalized polyethyleneimine, multiwall carbon nanotubes, and carbon cloth for biofuel cell applications in our recent studies. The kinetics parameters (i.e. kM, Vmax) and other parameters required for the modeling study were determined experimentally. Fuel cell flow channel geometry was analyzed by a computational fluid dynamics modeling approach. Substrate flow rate and mass transfer for each proposed channel type were considered in the simulations. The results showed that serpentine type flow channels are advantageous over pin type or parallel flow channels to acquire sufficient performance from the immobilized enzyme electrode at lower substrate flow rates. On the other hand, a disadvantage of using serpentine type channels was observed as higher pressure drops. However, such pressure drops were accepted as reasonable for the considered flow rates for suitable biofuel cell performance. [ABSTRACT FROM AUTHOR]

We report on a hybrid bioelectrochemical system that integrates an energy converting part, viz. a glucose/oxygen enzymatic fuel cell, with a charge-storing component, in which the redox features of the immobilized redox protein cytochrome c (cyt c) were utilized. Bilirubin oxidase and pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) were employed as the biocatalysts for dioxygen reduction and glucose oxidation, respectively. A bi-protein PQQ-GDH/cyt c signal chain was created that facilitates electron transfer between the enzyme and the electrode surface. The assembled supercapacitor/biofuel cell hybrid biodevice displays a 15 times higher power density tested in the pulse mode compared to the performance achieved from the continuously operating regime (4.5 and 0.3 μW cm−2, respectively) with an 80% residual activity after 50 charge/discharge pulses. This can be considered as a notable step forward in the field of glucose/oxygen membrane-free, biocompatible hybrid power sources. • The device employing biomolecules for energy conversion and storage was developed. • PQQ-GDH and BOx were utilized as anodic and cathodic bioelements, respectively. • Cyt c was used as an anodic mediator and as a redox active charge-storing unit. • The main characteristics were comparable to those for analogous systems. [ABSTRACT FROM AUTHOR]

Objective: The construction of a novel bioanode based on l-proline oxidation using a cascade reaction pathway comprised of thermostable dehydrogenases. Results: A novel multi-enzymatic cascade pathway, containing four kinds of dehydrogenases from thermophiles (dye-linked l-proline dehydrogenase, nicotinamide adenine dinucleotide (NAD)-dependent Δ1-pyrroline-5-carboxylate dehydrogenase, NAD-dependent l-glutamate dehydrogenase and dye-linked NADH dehydrogenase), was designed for the generation of six-electrons from one molecule of l-proline. The current density of the four-dehydrogenase-immobilized electrode, with a voltage of + 450 mV (relative to that of Ag/AgCl), was 226.8 μA/cm2 in the presence of 10 mM l-proline and 0.5 mM ferrocene carboxylate at 50 °C. This value was 4.2-fold higher than that of a similar electrode containing a single dehydrogenase. In addition, about 54% of the initial current in the multi-enzyme cascade bioanode was maintained even after 15 days. Conclusions: Efficient deep oxidation of l-proline by multiple-enzyme cascade reactions was achieved in our designed electrode. The multi-enzyme cascade bioanode, which was built using thermophilic dehydrogenases, showed high durability at room temperature. The long-term stability of the bioanode indicates that it shows great potential for applications as a long-lived enzymatic fuel cell. [ABSTRACT FROM AUTHOR]

Abstract Microfluidic biofuel cell (micro-BFC) stacking is a strategy to improve the power output of micro-BFC. There are limited reports on micro-BFC stacking, although they usually study either series or parallel configurations. Here we report on a micro-BFC stack comprising four cells connected with various configurations, e.g., individually, series, parallel and series/parallel. Electrodes modified with glucose dehydrogenase and bilirubin oxidase were used as bioanode and biocathode, respectively. A single cell generated an open circuit potential (OCP) of 0.78 V with a current density and power density of 1.37 mA cm−2 and 0.36 mW cm−2, respectively. The OCP voltage enhanced further to 1.27 V when the four cells were connected in series and a density current of 0.78 mA cm−2. When the four cells were connected in parallel, the current density and power output increased to 2.0 mA cm−2 and 0.58 mW cm−2. A combined series/parallel configuration was also evaluated, yielding a maximum OCP of 1.23 V, although the current density and power output remained unchanged around to 0.95 mA cm−2 and 0.42 mWcm−2, respectively. This type of micro-BFC stacking presents a new strategy for obtaining improved voltages and power outputs without the requirement of any external electronic device. Highlights • Microfluidic biofuel cell stack is constructed to improve the power output. • Stack consist 4 cells connected individually, series or parallel or combined. • Biocatalyst consisted in glucose dehydrogenase and bilirubin oxidase enzymes. • A combined series/parallel configuration yielding 0.42 mWcm−2 of power density. • The stacking is a new strategy for improved voltages and power outputs. [ABSTRACT FROM AUTHOR]

A significant problem still exists with the low power output and durability of the bioelectrochemical fuel cells. We constructed a fuel cell with an enzymatic cascade at the anode for efficient energy conversion. The construction involved fabrication of the flow-through cell by three-dimensional printing. Gold nanoparticles with covalently bound naphthoquinone moieties deposited on cellulose/polypyrrole (CPPy) paper allowed us to significantly improve the catalysis rate, both at the anode and cathode of the fuel cell. The enzymatic cascade on the anode consisted of invertase, mutarotase, Flavine Adenine Dinucleotide (FAD)-dependent glucose dehydrogenase and fructose dehydrogenase. The multi-substrate anode utilized glucose, fructose, sucrose, or a combination of them, as the anode fuel and molecular oxygen were the oxidant at the laccase-based cathode. Laccase was adsorbed on the same type of naphthoquinone modified gold nanoparticles. Interestingly, the naphthoquinone modified gold nanoparticles acted as the enzyme orienting units and not as mediators since the catalyzed oxygen reduction occurred at the potential where direct electron transfer takes place. Thanks to the good catalytic and capacitive properties of the modified electrodes, the power density of the sucrose/oxygen enzymatic fuel cells (EFC) reached 0.81 mW cm−2, which is beneficial for a cell composed of a single cathode and anode.

This study is focused on the utilization of waste microalgal sludge (MS) from microalgal extraction and its potential as an electrode material. The MS was activated under N 2 at high temperature for conversion to biochar (MSB). In addition, cobalt (Co; metal hydroxide) and chitosan were used as a mediator for electron transfer by immobilization on MSB (MSB/Co/chitosan). Through analysis of the surface and components of the MSB/Co/chitosan, it was shown that Co and chitosan were properly synthesized with MSB. The enzymatic fuel cell (EFC) system successfully obtained a power density of 3.1 mW cm −2 and a current density of 9.7 mA cm −2 . In addition, the glucose biosensors applied with the developed electron transfer mediator showed a sensitivity of 0.488 mA mM −1  cm −2 . [ABSTRACT FROM AUTHOR]

We present a novel concept of an air-breathing enzymatic biofuel cell cathode combined with continuous supply of unpurified laccase-containing supernatant of the white-rot fungus Trametes versicolor for extended lifetime. The air-breathing cathode design obviates the need for energy-intensive active aeration. In a corresponding long-term experiment at a constant current density of 50 µA cm −2 , we demonstrated an increased lifetime of 33 days (cathode potential above 0.430 V vs. SCE), independent of enzyme degradation. The obtained data suggest that theoretically a longer lifetime is feasible. However, further engineering efforts are required to prevent clogging and fouling of the supply tubes. These results represent an important step towards the realization of enzymatic biofuel cell cathodes with extended lifetime and enhanced performance. [ABSTRACT FROM AUTHOR]

The kinetics and isotherms of adsorption of Myrothecium verrucaria bilirubin oxidase ( Mv BOD) on nanoporous carbons (CNP) and carbon nanofibers (CNF) were studied by the solution depletion method. The kinetics of adsorption of Mv BOD on both carbons are very fast, reaching equilibrium within 10 min and 30 min for CNP and CNF, respectively. The adsorption isotherms reveal a strong affinity between Mv BOD and both carbons. An original flow-through device based on electrodes filled with CNP and CNF connected to an UV–vis spectrophotometer was used to correlate the dioxygen catalytic current reduction to the amount of Mv BOD adsorbed on the carbons. It was shown that although the amount of BOD adsorbed on CNP is much lower than the amount adsorbed on CNF, the currents are comparable, suggesting that the Mv BOD orientation is more favourable for direct electron transfer in the case of CNP. Chronoamperometry experiments showed that the catalytic current is stable for a few days (70 h). It was emphasized by stop and flow experiments that the current is limited by mass transport inside the column. [ABSTRACT FROM AUTHOR]

The purpose of this study is to generate power by using the waste hydrolysate from microalgal extracts (AH), substrates of enzymatic fuel cell (EFC), and analyze the effects of microalgal hydrolysate containing a neutralizing agent on EFC. The effect of different dilute acids on extraction of microalgae was also investigated. The maximum concentration (∼5 g/L) of extraction was achieved for Chlorella pyrenoiudosa under the optimum conditions (2% hydrochloric acid and 100 g/L biomass loading). In order to investigate the effects of various neutralization agents used for AH on the EFC system, CV and EIS were investigated. Higher current and lower resistance values appeared during the neutralization using KOH. Maximum power density of 3637 μW/cm 2 was obtained for the EFC system, 6.59 folds higher than the control. The result implies that AH used as a substrate has a significant influence on the power generation in the EFC system. [ABSTRACT FROM AUTHOR]

Heteroatom-doping of pristine graphene is an effective route for tailoring new characteristics in terms of catalytic performance which opens up potentials for new applications in energy conversion and storage devices. Nitrogen-doped graphene (N-graphene), for instance, has shown excellent performance in many electrochemical systems involving oxygen reduction reaction (ORR), and more recently glucose oxidation. Owing to the excellent H2O2 sensitivity of N-graphene, the development of highly sensitive and fast-response enzymatic biosensors is made possible. However, a question that needs to be addressed is whether or not improving the anodic response to glucose detection leads to a higher overall performance of enzymatic biofuel cell (eBFC). Thus, here we first synthesized N-graphene via a catalyst-free single-step thermal process, and made use of it as the biocatalyst support in a membraneless eBFC to identify its role in altering the performance characteristics. Our findings demonstrate that the electron accepting nitrogen sites in the graphene structure enhances the electron transfer efficiency between the mediator (redox polymer), redox active site of the enzymes, and electrode surface. Moreover, the best performance in terms of power output and current density of eBFCs was observed when the bioanode was modified with highly doped N-graphene. [ABSTRACT FROM AUTHOR]

The wide use of portable electronics urgently requires better batteries featuring high energy density, good safety, and biodegradability. Although sugar-powered enzymatic fuel cells (EFCs) could be next-generation, environmentally friendly, micropower sources, they suffer from incomplete oxidation of the sugar fuels and an inability to utilize mixed sugars, which causes the low efficiency of fuel utilization and limits the choice of fuels. In this study, we designed an in vitro 15-enzyme pathway that can co-utilize sucrose, glucose, and fructose in the anodic compartment of EFCs. The EFCs achieved Faraday efficiencies of approximately 95% for these three sugars, suggesting that the fuels were completely oxidized, and yielded a maximum power density of 0.80–1.08 mW cm −2 . In addition, EFCs based on this versatile enzymatic pathway were capable of running on mixed sugars, such as commercial soft drinks. These results offer a possible solution for the extraction of the maximum energy stored in mixed sugar fuels and the achievement of high energy densities for EFCs; these EFCs offer good substrate flexibility and commercial potential. [ABSTRACT FROM AUTHOR]

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±0.14 mW cm −3 (41.3±3.8 µW cm −2 ) calculated based on the volume of electrode material with OCV 0.741±0.021 V. These new 3D RVC-Au electrodes showed great promise for improving the power generation of EFC devices. [ABSTRACT FROM AUTHOR]

We report a paper-based self-powered sensor patch for prevention and management of exercise-induced hypoglycemia. The article describes the fabrication, in vitro, and in vivo characterization of the sensor for glucose monitoring in human sweat. This wearable, non-invasive, single-use biosensor integrates a vertically stacked, paper-based glucose/oxygen enzymatic fuel cell into a standard Band-Aid adhesive patch. The paper-based device attaches directly to skin, wicks sweat by using capillary forces to a reservoir where chemical energy is converted to electrical energy, and monitors glucose without external power and sophisticated readout instruments. The device utilizes (1) a 3-D paper-based fuel cell configuration, (2) an electrically conducting microfluidic reservoir for a high anode surface area and efficient mass transfer, and (3) a direct electron transfer between glucose oxidase and anodes for enhanced electron discharge properties. The developed sensor shows a high linearity of current at 0.02-1.0 mg/mL glucose centration (R² = 0.989) with a high sensitivity of 1.35 μA/mM. [ABSTRACT FROM AUTHOR]

To seek a sustainable way of CO 2 sequestration and conversion, enzymatic electrosynthesis (EES) of formate from CO 2 reduction has been investigated in a hybrid biofuel cell system. In an enzymatic fuel cell (EFC), waste CO 2 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 ( Cb FDH) 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 CO 2 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. [ABSTRACT FROM AUTHOR]

This study describes construction of an enzymatic fuel cell comprised of poly(caprolactone- g -ethylene glycol) coated novel glucose oxidase anode and laccase cathode. Rationally designed poly(caprolactone- g -ethylene glycol) containing various poly(ethylene glycol) percentages ranging between 2.67 and 15.04% were synthesized chemically and tested separately for operation of the fuel cell system to achieve the best energy generation. The maximum power density was found to be 80.55 μW cm − 2 at 0.91 V (vs. Ag/AgCl) in pH 5, 100 mM citrate buffer (20 °C) by the addition of 30 mM of glucose from the electrodes coated with 11.34% poly(ethylene glycol) containing polymer with a quantity of 600 μg. High poly(ethylene glycol) percentages with more numbers of long poly(ethylene glycol) brushes lead to the creation of a complexity in the polymer morphology and steric hindrance effect for electron transport. The graft copolymer was easily used for the fuel cell system owing to its biocompatible and microporous film morphology. The grafted polymer was able to facilitate enzymatic glucose oxidation and oxygen reduction while simultaneously producing high catalytic electrical currents. [ABSTRACT FROM AUTHOR]

Enzymatic biobatteries can be implanted in living organisms to exploit the chemical energy stored in physiological fluids. Generally, commonly-used electron donors (such as sugars) are ubiquitous in physiological environments, while electron acceptors such as oxygen are limited due to many factors including solubility, temperature, and pressure. The wide range of solid-state cathodes, however, may replace the need for oxygen breathing electrodes and serve in enzymatic biobatteries for implantable devices. Here, we have fabricated a glucose biobattery suitable for in vivo applications employing a glucose oxidase (GOx) anode coupled to a solid-state Prussian Blue (PB) thin-film cathode. PB is a non-toxic material and its electrochemistry enables fast regeneration if used in a secondary cell. This novel biobattery can effectively operate in a membraneless architecture as PB can reduce the peroxide produced by some oxidase enzymes. The resulting biobattery delivers a maximum power and current density of 44 μW cm − 2 and 0.9 mA cm − 2 , respectively, which is ca. 37% and 180% higher than an equivalent enzymatic fuel cell equipped with a bilirubin oxidase cathode. Moreover, the biobattery demonstrated a stable performance over 20 cycles of charging and discharging periods with only ca. 3% loss of operating voltage. [ABSTRACT FROM AUTHOR]

Enzymatic electrodes over-coated by thin film of nano-composite made up of polymer and functionalized nano-gold particle was prepared. Glucose/O 2 membrane-free enzymatic fuel cell based on nano-composite based electrodes with incorporated glucose oxidase and laccase was assembled. This enzymatic fuel cell exhibited high energy out-put density even when applied in human serum. Catalytic cycle involved in enzymatic fuel cell was limited by oxidation of glucose occurred on bioanode resulting from impact of sophisticated interaction between active site in glucose oxidase and nano-gold particle on configuration of redox center of enzyme molecule which crippled catalytic efficiency of redox protein. [ABSTRACT FROM AUTHOR]

Serious brain disorders, such as the Alzheimer's Disease (AD), are associated with a marked drop in the levels of important neurotransmitters, such as acetylcholine (ACh). Real time monitoring of such biomarkers can therefore play a critical role in enhancing AD therapies by allowing timely diagnosis, verifications of treatment effectiveness, and developments of new medicines. In this study, we present the first acetylcholine/oxygen hybrid enzymatic fuel cell for the self-powered on site detection of ACh in plasma, which is based on the combination of an enzymatic anode with a Pt cathode. Firstly, an effective acetylcholinesterase immobilized electrode was developed and its electrochemical performance evaluated. Highly porous gold was used as the electrode material, and the enzyme was immobilized via a one step rapid and simple procedure that does not require the use of harsh chemicals or any electrode/enzyme pre-treatments. The resulting enzymatic electrode was subsequently used as the anode of a miniature flow-through membrane-less fuel cell and showed excellent response to varying concentrations of ACh. The peak power generated by the fuel cell was 4 nW at a voltage of 260 mV and with a current density of 9 μA cm −2 . The limit of detection of the fuel cell sensor was 10 μM, with an average response time as short as 3 min. These exciting results open new horizons for point-of-care Alzheimer diagnosis and provide an attractive potential alternative to established methods that require laborious and time-consuming sample treatments and expensive instruments. [ABSTRACT FROM AUTHOR]

Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron-sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from Density Functional Theory (DFT) calculations. The distal cubane FeS-cluster has a three-cysteine and one-histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and an all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron-sulfur cluster is realized by a fine-tuned protein environment, which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering. [ABSTRACT FROM AUTHOR]

The direct generation of electricity from the most abundant renewable sugar, glucose, is an appealing alternative to the production of liquid biofuels and biohydrogen. However, enzyme-catalyzed bioelectricity generation from glucose suffers from low yields due to the incomplete oxidation of the six-carbon compound glucose via one or few enzymes. Here, we demonstrate a synthetic ATP- and CoA-free 12-enzyme pathway to implement the complete oxidation of glucose in vitro . This pathway is comprised of glucose phosphorylation via polyphosphate glucokinase, NADH generation catalyzed by glucose 6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), electron transfer from NADH to the anode, and glucose 6-phosphate regeneration via the non-oxidative pentose phosphate pathway and gluconeogenesis. The faraday efficiency from glucose to electrons via this pathway was as high as 98.8%, suggesting the generation of nearly 24 electrons per molecule of glucose. The generated current density was greatly increased from 2.8 to 6.9 mA cm −2 by replacing a low-activity G6PDH with a high-activity G6PDH and introducing a new enzyme, 6-phosphogluconolactonase, between G6PDH and 6PGDH. These results suggest the great potential of high-yield bioelectricity generation through in vitro metabolic engineering. [ABSTRACT FROM AUTHOR]

For the first time, a paper based enzymatic fuel cell is used as self-recharged supercapacitor. In this supercapacitive enzymatic fuel cell (SC-EFC), the supercapacitive features of the electrodes are exploited to demonstrate high power output under pulse operation. Glucose dehydrogenase-based anode and bilirubin oxidase-based cathode were assembled to a quasi-2D capillary-driven microfluidic system. Capillary flow guarantees the continuous supply of glucose, cofactor and electrolytes to the anodic enzyme and the gas-diffusional cathode design provides the passive supply of oxygen to the catalytic layer of the electrode. The paper-based cell was self-recharged under rest and discharged by high current pulses up to 4 mA cm −2 . The supercapacitive behavior and low equivalent series resistance of the cell permitted to achieve up to a maximum power of 0.87 mW cm −2 (10.6 mW) for pulses of 0.01 s at 4 mA cm −2 . This operation mode allowed the system to achieve at least one order of magnitude higher current/power generation compared to the steady state operation. [ABSTRACT FROM AUTHOR]

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/cm (at 0.247 V) with 10 mM lactose. [ABSTRACT FROM AUTHOR]

A 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. [ABSTRACT FROM AUTHOR]

Neutron imaging provides a route for studying the effect of environmental conditions on enzymatic electrochemical cell (EEC) performance. Here, the application of 2D and 3D neutron imaging is demonstrated as a means to investigate effects of environmental conditions on EEC performance. Changes in aqueous solutions that are vital to the operation of EECs have been directly observed in real time using neutron radiography (NR). These changes include uptake of aqueous solutions in electrode materials and in situ observation of water content during operation. The EEC structure has also been observed using ex situ neutron tomography. Initially samples constructed to simulate EEC geometry were imaged, and aqueous buffer solution uptake behavior was observed in carbon paper cell components. In follow-on studies neutron tomography was used to map regions of enzyme catalyst inks, defining active regions within the EEC electrode. The higher neutron attenuation of polymeric ink components enables this observation. Finally, in situ imaging of a prototype EEC pouch cell was performed using a standard chronoamperometry arrangement while performing real time neutron radiography. Neutron radiographs acquired during operation show a clear variation in transmission behavior, primarily due to drying. Together these studies demonstrate the applicability and attendant challenges of neutron imaging for the study of EEC performance and reliability. [ABSTRACT FROM AUTHOR]

A carboxylated poly(styrene-b-isoprene-b-styrene) triblock copolymer was synthesized for the construction of an enzymatic fuel cell. Glucose oxidase and bilirubin oxidase were chemically immobilized via the carboxylated functional groups of the polymer. The enzymatic fuel cell working electrodes were modified with graphene to accelerate the electron transfer rate of the system. Essential design and operational parameters were carefully optimized for improving the power of the enzymatic fuel cell. A power density of 20 µW cm−2with only 4 µg of immobilized bilirubin oxidase was generated from 30 mM glucose at 0.72 V. The improved enzymatic fuel cell was tested in a plant leaf. A power density of 14 nW cm−2was generated with glucose produced by photosynthesis reactions conducted during 30 min in the leaf. [ABSTRACT FROM AUTHOR]

The development of 3D structures exploring the properties of nano-materials and biological molecules has been shown through the years as an effective path forward for the design of advanced bio-nano architectures for enzymatic fuel cells, photo-bio energy harvesting devices, nano-biosensors and bio-actuators and other bio-nano-interfacial architectures. In this study we demonstrate a scaffold design utilizing carbon nanotubes, deoxyribose nucleic acid (DNA) and a specific DNA binding transcription factor that allows for directed immobilization of a single enzyme. Functionalized carbon nanotubes were covalently bonded to a diazonium salt modified gold surface through carbodiimide chemistry creating a brush-type nanotube alignment. The aligned nanotubes created a highly ordered structure with high surface area that allowed for the attachment of a protein assembly through a designed DNA scaffold. The enzyme immobilization was controlled by a zinc finger (ZNF) protein domain that binds to a specific dsDNA sequence. ZNF 268 was genetically fused to the small laccase (SLAC) from Streptomyces coelicolor , an enzyme belonging to the family of multi-copper oxidases, and used to demonstrate the applicability of the developed approach. Analytical techniques such as X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and enzymatic activity analysis, allowed characterization at each stage of development of the bio-nano architecture. This article is part of a Special Issue entitled Biodesign for Bioenergetics — the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson. [ABSTRACT FROM AUTHOR]

The development of self-powered wearable biodevices is highly attractive for a number of applications, such as health monitoring and drug delivery. Enzymatic fuel cells (EFCs) hold great potential as power sources for such devices, since they can generate power from physiological fluids and operate at body temperature. In this study, we present a cascade of three EFCs embedded in a compact and handy single channel device and we demonstrate for the first time power generation from iontophoresis extracts obtained from pig skin. The EFCs implement non-toxic highly-porous gold electrodes; an easy-to-reproduce procedure is adopted for the immobilization of glucose oxidase and laccase at the anode and cathode respectively; no external mediators are used; and the system design can easily be further miniaturized. When electrically connected in parallel, the EFCs generated a power output close to the sum of the power generated by each unit, with peak values of 0.7 µW (flow-through mode) and 0.4 µW (batch mode), at a glucose concentration of 27 mM. When the device was fed with transdermal extracts, containing only 30 μM of glucose, the average peak power was proportionally lower (0.004 µW). [ABSTRACT FROM AUTHOR]

The waste hydrolysate after dilute acid pretreatment (DAP) of lignocellulosic biomass was utilized to generate electricity using an enzymatic fuel cell (EFC) system. During DAP, the components of biomass containing hemicellulose and other compounds are hydrolyzed, and glucose is solubilized into the dilute acid solution, called as the hydrolysate liquid. Glucose oxidase (GOD) and laccase (Lac) were assembled on the electrode of the anode and cathode, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were measured, and the maximum power density was found to be 1.254 × 10 3 μW/cm 2 . The results indicate that the hydrolysate from DAP is a reliable electrolyte containing the fuel of EFC. Moreover, the impurities in the hydrolysate such as phenols and furans slightly affected the charge transfer on the surface of the electrode, but did not affect the power generation of the EFC system in principal. [ABSTRACT FROM AUTHOR]

Mathematical model describing the oxidation of glucose in a multiscale porous biocatalytic electrode is discussed. The model considers herein is composed of two nonlinear differential equations accounting for reaction and diffusion within the hydrogel film. In this letter, approximate analytical expressions for the concentration of mediator, substrate and current have been obtained using the Adomian decomposition method (ADM). Furthermore, a comparison confirmed that our analytical result fitted very well with the numerical solution (Matlab). Sensitivity analysis of the parameters is also reported. [ABSTRACT FROM AUTHOR]

The present work reported a compartment-less enzymatic fuel cell (EFC) based on newly synthesized Poly(pyrrole-2-carboxylic acid-co-3-thiophene acetic acid) film containing glucose oxidase and laccase effectively wired byp-benzoquinone incorporated into the copolymer structure. The resulting system generated a power density of 18.8 µW/cm2with 30 mM of glucose addition at +0.94 V at room temperature. Improvements to maximize the power output were ensured with step-by-step optimization of electrode fabrication design and operational parameters for operating the system with renewable fuel sources. We demonstrated that the improved fuel cell could easily harvest glucose produced during photosynthesis to produce electrical energy in a simple, renewable and sustainable way by generating a power density of 10 nW/cm2in the plant leaf within 2 min. An EFC for the first time was successfully operated in municipal wastewater which contained glycolytic substances to generate electrical energy with a power output of 3.3 µW/cm2. [ABSTRACT FROM PUBLISHER]