A glucose/hydrogen peroxide biofuel cell that uses oxidase and peroxidase as catalysts by composite bulk-modified bioelectrodes based on a solid binding matrix

Bi-enzymatic chemo-mechanical feedback loop for continuous self-sustained actuation of conducting polymers

Artificial actuators have been extensively studied due to their wide range of applications from soft robotics to biomedicine. Herein we introduce an autonomous bi-enzymatic system where reversible motion is triggered by the spontaneous oxidation and reduction of glucose and oxygen, respectively. This chemo-mechanical actuation is completely autonomous and does not require any external trigger to induce self-sustained motion. The device takes advantage of the asymmetric uptake and release of ions on the anisotropic surface of a conducting polymer strip, occurring during the operation of the enzymes glucose oxidase and bilirubin oxidase immobilized on its surface. Both enzymes are connected via a redox polymer at each extremity of the strip, but at the opposite faces of the polymer film. The time-asymmetric consumption of both fuels by the enzymatic reactions produces a double break of symmetry of the film, leading to autonomous actuation. An additional break of symmetry, introduced by the irreversible overoxidation of one extremity of the polymer film, leads to a crawling-type motion of the free-standing polymer film. These reactions occur in a virtually unlimited continuous loop, causing long-term autonomous actuation of the device.

Evaluation of Oxidation Process by Ozonation and Glucose Oxidase Enzyme on the Degradation of Benzoquinone in Wheat Flour

Background:

Wheat flour is an important food ingredient for humans, which is the basic ingredient of bread and other bakery products.

Objective:

This study aimed to assess the effect of adding Glucose Oxidase (GOX), and exposure to ozone gas on methyl-1, 4-benzoquinone (MBQ), and ethyl-1, 4-benzoquinone (EBQ) secreted by Tribolium castaneum in flour.

Methods:

The flour contaminated by MBQ and EBQ was treated with ozone gas at (10, 20, and 40 ppm) with exposure times (15, 30, and 45 min). Similarly, GOX was added to flour at (10, 15, and 20 ppm), leaving the dough for periods between 10 and 45 min after treatments. The MBQ and EBQ determined by HPLC, and the UV-Visible Spectrophotometer and Fourier Transform Infrared Spectroscopy (FTIR) were used to describe the changes that occurred in the main structure of EBQ after ozonation at 40 ppm for 45 min.

Results:

The results indicated that adding GOX enzyme to the flour at level 20 ppm degrade the MBQ to 13.7, 20.23, and 39.6 after 15, 30, and 45 min from mixing time, respectively. On the other hnad, the EBQ degrades to 13.6, 18.9, and 35.9%. In contrast, the percentages of degradation of MBQ and EBQ increases after ozonation at 40 ppm for 45min were 84.1 and 78.8%, respectively. The results obtained by UV–vis spectroscopy and FTIR reflect that many oxidation products formed as aldehydes, ketones, and carboxylic acids.

Conclusion:

In general, ozonation was a reliable treatment for the degradation of benzoquinone in flour.

A novel amperometric biosensor for rapid detection of ethanol utilizing gold nanoparticles and enzyme coupled PVC reaction cell

This research was aimed at the fabrication of an improved enzyme-based amperometric biosensor for rapid quantification of ethanol. Alcohol oxidase (AOX) from Pichia pastoris was covalently immobilized on chemically treated polyvinylchloride (PVC) beaker and subsequently horseradish peroxidase (HRP), nafion (Nf), carboxylated multi-walled carbon nanotubes (c-MWCNTs), chitosan (CHIT) and gold nanoparticles (AuNPs) were immobilized onto Au electrode to fabricate a working electrode. The enzyme-coated PVC surface was analysed morphologically via scanning electron microscopy (SEM). At different stages of construction, the electrochemical properties of working electrode were deciphered by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The biosensor displayed optimal response in a short time span of 12 s at pH 7.5 and 35°C temperature. The working range exhibited by the proposed biosensor was 0.01-42 mM with a limit of detection (LOD) of 0.0001 µM and storage stability of 180 days at 4°C. When level of alcohol was evaluated in commercial samples via standard assay kit and existing biosensor, a good correlation (R²= 0.98) was observed which authenticates its reliability.

Selectivity and Sustainability of Electroenzymatic Process for Glucose Conversion to Gluconic Acid

Electroenzymatic processes are interesting solutions for the development of new processes based on renewable feedstocks, renewable energies, and green catalysts. High-selectivity and sustainability of these processes are usually assumed. In this contribution, these two aspects were studied in more detail. In a membrane-less electroenzymatic reactor, 97% product selectivity at 80% glucose conversion to gluconic acid was determined. With the help of nuclear magnetic resonance spectroscopy, two main side products were identified. The yields of D-arabinose and formic acid can be controlled by the flow rate and the electroenzymatic reactor mode of operation (fuel cell or ion-pumping). The possible pathways for the side product formation have been discussed. The electroenzymatic cathode was found to be responsible for a decrease in selectivity. The choice of the enzymatic catalyst on the cathode side led to 100% selectivity of gluconic acid at somewhat reduced conversion. Furthermore, sustainability of the electroenzymatic process is estimated based on several sustainability indicators. Although some indicators (like Space Time Yield) are favorable for electroenzymatic process, the E-factor of electroenzymatic process has to improve significantly in order to compete with the fermentation process. This can be achieved by an increase of a cycle time and/or enzyme utilization which is currently low.

Artificial Muscles Powered by Glucose

Untethered actuation is important for robotic devices to achieve autonomous motion, which is typically enabled by using batteries. Using enzymes to provide the required electrical charge is particularly interesting as it will enable direct harvesting of fuel components from a surrounding fluid. Here, a soft artificial muscle is presented, which uses the biofuel glucose in the presence of oxygen. Glucose oxidase and laccase enzymes integrated in the actuator catalytically convert glucose and oxygen into electrical power that in turn is converted into movement by the electroactive polymer polypyrrole causing the actuator to bend. The integrated bioelectrode pair shows a maximum open-circuit voltage of 0.70 ± 0.04 V at room temperature and a maximum power density of 0.27 µW cm^-2 at 0.50 V, sufficient to drive an external polypyrrole-based trilayer artificial muscle. Next, the enzymes are fully integrated into the artificial muscle, resulting in an autonomously powered actuator that can bend reversibly in both directions driven by glucose and O₂ only. This autonomously powered artificial muscle can be of great interest for soft (micro-)robotics and implantable or ingestible medical devices manoeuvring throughout the body, for devices in regenerative medicine, wearables, and environmental monitoring devices operating autonomously in aqueous environments.

Switchable aerobic/anaerobic multi-substrate biofuel cell operating on anodic and cathodic enzymatic cascade assemblies

Enzymatic fuel cells may become more accessible for applications powering portable electronic devices by broadening the range of potentially usable fuels and oxidizers. In this work we demonstrate the operation of an integrated, yet versatile multi-substrate biofuel cell utilizing either glucose, fructose, sucrose or combinations of thereof as biofuels, and molecular oxygen originating from solution phase and/or an internal chemical source, as the oxidizer. In order to achieve this goal we designed an enzymatic cascade-functionalized anode consisting of invertase (INV), mutarotase (MUT), glucose oxidase (GOX), and fructose dehydrogenase (FDH), deposited on top of a mesoporous carbon nanoparticle matrix, in which electron relay molecules had been entrapped. The anode was then conjugated to a compatible enzymatic cathode that employs a cascade of catalase (CAT) and bilirubin oxidase (BOD), allowing the cell to operate in an aerobic environment and/or to utilize, under anaerobic conditions for instance, hydrogen peroxide as a source for the oxygen oxidizer. While operated in the presence of the sugar mixture and hydrogen peroxide, the power output of the dually cascaded biofuel cell reaches a peak power density of 0.25 mW cm^-2 and demonstrates an open circuit potential of 0.65 V. To our knowledge this is the first reported biofuel cell that discharges with both anodic and cathodic enzymatic cascade architectures and the first biofuel cell that is repeatedly switched between aerobic and anaerobic conditions without any significant decrease in the discharge performance.

Iron–nickel hexacyanoferrate bilayer as an advanced electrocatalyst for H2O2 reduction

An advanced electrocatalyst for H₂O₂ reduction synthesized via the deposition of an iron- and nickel hexacyanoferrate bilayer displays similar to Prussian Blue electrocatalytic activity (≈0.01 cm s⁻¹) with 100-fold improved operational stability.

Vertically-aligned sandwich nanowires enhance the photoelectrochemical reduction of hydrogen peroxide: hierarchical formation on carbon nanotubes of cadmium sulfide quantum dots and Prussian blue nanocoatings

We describe a vertically-aligned array of sandwiched nanowires comprising Prussian blue (PB) nanocoating-carbon nanotube (CNT) core-shell structures with CdS particles positioning at the core/shell interface, viz. PB/CdS/CNT. The PB/CdS/CNT electrode thus constructed are noticeable in synchronically harvesting photon-, ionic-, and chemical-energies, respectively, from visible light radiation, K(+) uptaking and releasing, and the reduction of H2O2. In 0.2 M K2SO4 aqueous solution, the photoelectrocatalytic reduction of 1.5 mM H2O2 at PB/CdS/CNT delivered the current density as high as 1.91 mA/cm(2) at reduced overpotential, that is, three times that at the Pt/C. This superb performance is causally linked to the judicious choice of materials and their assembly into defining sandwich nanostructures wherein the three components closely cooperate with each other in the photoelectrocatalytic reduction of H2O2, including photo-induced charge separation in CdS, spontaneous electron injection into PB due to its relatively low Fermi level, and the electrocatalytic reduction of H2O2 by PB via an electrochemical-chemical-electrochemical reaction mechanism. The structural alignment of PB/CdS/CNT ensures the simplest pathway for the mass diffusion and electron shuttle, and a high surface area accessible to the chemical and electrochemical reactions, so as to minimize the concentration- and electrochemical-polarization and thus ensure the fast overall kinetics of the electrode reaction.

Novel method for screening microbes for application in microbial fuel cell

The ability to produce and to transport exo-electrons by microbes either to external acceptors or to electrodes are reported in our study. All investigated microorganisms (exception of Lactobacillus plantarum) exhibited strong iron-reducing capabilities in the absence of mediator meaning production and secretion of exo-electrons to the growth medium. L.plantarum, Saccharomyces cerevisiae and Escherichia coli need an electron shuttle molecule to reduce Fe(3+) ion. Significant correlation was observed between growth and iron-reducing capacity, as well as between initial cell counts and iron-reducing capacity. Changes of bio-current generated in MFC and iron-reduction were experimentally monitored, and a mathematical model was established by regression analysis. Based on these results, a novel and rapid screening method was developed for the selection of microorganisms for potential application in MFC. The method is based on the measurement of absorbance of bacterial and yeast cultures at 460 nm, providing a robust and high sample throughput approach.

A 96-well electrochemical method for the screening of enzymatic activities

The rapid electrochemical screening of enzyme activities in bioelectronics is still a challenging issue. In order to solve this problem, we propose to use a 96-well electrochemical assay. This system is composed of 96 screen-printed electrodes on a printed circuit board adapted from a commercial system (carbon is used as the working electrode and silver chloride as the counter/reference electrode). The associated device allows for the measurements on the 96 electrodes to be performed within a few seconds. In this work, we demonstrate the validity of the screening method with the commercial laccase from the fungus Trametes versicolor. The signal-to-noise ratio (S/N) is found to be the best way to analyze the electrochemical signals. The S/N follows a saturation-like mechanism with a dynamic linear range of two decades ranging from 0.5 to 75 ng of laccase (corresponding to enzymatic activities from 62 × 10(-6) to 9.37 × 10(-3) μmol min(-1)) and a sensitivity of 3027 μg(-1) at +100 mV versus Ag/AgCl. Laccase inhibitors (azide and fluoride anions), pH optima, and interfering molecules could also be identified within a few minutes.

Investigation of a deoxyribozyme as a biofuel cell catalyst

We examined the ability of a previously identified peroxidase deoxyribozyme to be employed as a catalyst in biofuel cells, as a possible replacement for oxidoreductase proteins. We constructed a biocathode using a covalently linked version of the peroxidase deoxyribozyme-hemin complex and successfully paired it with a glucose dehydrogenase-modified bioanode for power production.

Conjugated polymers and an iron complex as electrocatalytic materials for an enzyme-based biofuel cell

Poly-5,2':5',2''-terthiophen-3'-carboxylic acid (polyTTCA) and poly-Fe(III)-[N,N'-bis[4-(5,2':5',2''-terthien-3'-yl)salicyliden]-1,2-ethanediamine] (polyFeTSED) were synthesized and electrochemically polymerized on an Au surface for use as mediators and catalysts for a biofuel cell. The atomic force microscopy (AFM) images of (a) the TTCA homopolymer (polyTTCA) and (b) the TTCA-FeTSED copolymer (poly(TTCA-FeTSED)) layers show a nanoparticle structure. The enzymes (glucose oxidase (GOx) or horseradish peroxidase (HRP)) were immobilized onto the conducting polymer layer through covalent bond formation, which allowed for direct electron transfer processes of the enzymes. A quartz crystal microbalance (QCM) revealed that the surface coverages of GOx and HRP were 4.21 x 10(-12)M and 9.65 x 10(-12)M, respectively. The anode with immobilized GOx and the cathode with immobilized HRP were used as model enzyme systems in biofuel cells for glucose and H(2)O(2) detection, respectively. The biofuel cell composed of the GOx/polyTTCA/Au and the HRP/poly(TTCA-FeTSED)/Au electrodes was assembled and examined for cell performance. The copolymer of polyFeTSED complex with polyTTCA revealed a catalytic activity for the electrochemical reduction of H(2)O(2) and resulted in approximately a sevenfold increase in the power density of the biofuel cell over that of polyTTCA itself. Moreover, the conjugated polymers extend the biofuel cell lifetime to 4 months through the stabilization of immobilized enzymes. The biofuel cell operated in a solution containing glucose and anode-produced H(2)O(2) generated an open-circuit voltage of approximately 366.0 mV, while the maximum electrical power density extracted from the cell was 5.12 microW cm(-2) at an external optimal load of 25.0 k Omega.

Biofuel cells--recent advances and applications

In 2006, the journal Biosensors and Bioelectronics published a special issue devoted exclusively to biofuel cells, including several research papers and an extensive review of the field [Bullen, R.A., Arnot, T.C., Lakeman, J.B., Walsh, F.C., 2006. Biosens. Bioelectron.]. Within this review a brief description will firstly be given of the history of biofuel cells together with coverage of some of the major historical advances. The review is intended, however, to largely concentrate on and give an overview of the advances made in recent years in this area together with a discussion surrounding the practical application of biofuel cells. There are several classes of biofuel cells: we shall firstly discuss the recent advances in biofuel cells that convert chemical fuels to produce electrical power by use of catalytic enzymes. This will be followed by a section on similar cells where micro-organisms rather than enzymes are used to convert the fuel to energy. Thirdly we shall consider hybrid biofuel cells that combine the utilisation of photochemical chemistries and biological systems for the generation of electricity. Finally we will discuss some of the proposed uses of biofuel cells together with a short consideration of future research possibilities and applications of these systems.

Biofuel cells and their development

This review considers the literature published since 1994 on microbial and enzymatic biofuel cells. Types of biofuel cell are classified according to the nature of the electrode reaction and the nature of the biochemical reactions. The performance of fuel cells is critically reviewed and a variety of possible applications is considered. The current direction of development of biofuel cells is carefully analysed. While considerable chemical development of enzyme electrodes has occurred, relatively little progress has been made towards the engineering development biofuel cells. The limit of performance of biofuel cells is highlighted and suggestions for future research directions are provided.

Procedure for determining maximum sustainable power generated by microbial fuel cells

Power generated by microbial fuel cells is computed as a product of current passing through an external resistor and voltage drop across this resistor. If the applied resistance is very low, then high instantaneous power generated by the cell is measured, which is not sustainable; the cell cannot deliver that much power for long periods of time. Since using small electrical resistors leads to erroneous assessment of the capabilities of microbial fuel cells, a question arises: what resistor should be used in such measurements? To address this question, we have defined the sustainable power as the steady state of power delivery by a microbial fuel cell under a given set of conditions and the maximum sustainable power as the highest sustainable power that a microbial fuel cell can deliver under a given set of conditions. Selecting the external resistance that is associated with the maximum sustainable power in a microbial fuel cell (MFC) is difficult because the operator has limited influence on the main factors that control power generation: the rate of charge transfer at the current-limiting electrode and the potential established across the fuel cell. The internal electrical resistance of microbial fuel cells varies, and it depends on the operational conditions of the fuel cell. We have designed an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell operated under a given set of conditions. Following the procedure, we change the external resistors incrementally, in steps of 500 omega every 10, 60, or 180 s and measure the anode potential, the cathode potential, and the cell current. Power generated in the microbial fuel cell that we were using was limited by the anodic current. The anodic potential was used to determine the condition where the maximum sustainable power is obtained. The procedure is simple, microbial fuel cells can be characterized within an hour, and the results of the measurements can serve many purposes, such as: (1) estimating power generation in various MFCs, (2) comparing power generation in MFCs using different electroactive reactants, (3) quantifying the effects of the operational regime on the power generation in MFCs, and finally, (4) the purpose for which the procedure was designed, optimizing the performance of existing MFCs.

Challenges in biocatalysis for enzyme-based biofuel cells

Enzyme-based biofuel cells are attracting attention rapidly partially due to the promising advances reported recently. However, there are issues to be addressed before biofuel cells become competitive in practical applications. Two critical issues are short lifetime and poor power density, both of which are related to enzyme stability, electron transfer rate, and enzyme loading. Recent progress in nanobiocatalysis opens the possibility to improve in these aspects. Many nano-structured materials, such as mesoporous media, nanoparticles, nanofibers, and nanotubes, have been demonstrated as efficient hosts of enzyme immobilization. It is evident that, when nanostructure of conductive materials are used, the large surface area of these nanomaterials can increase the enzyme loading and facilitate reaction kinetics, and thus improving the power density of biofuel cells. In addition, research efforts have also been made to improve the activity and stability of immobilized enzymes by using nanostructures. It appears to be reasonable to us to expect that progress in nanostuctured biocatalysts will play a critical role in overcoming the major obstacles in the development of powerful biofuel cells.

A Low-Cost Biofuel Cell with pH-Dependent Power Output Based on Porous Carbon as Matrix

A glucose/O2 biofuel cell (BFC) possessing a pH-dependent power output was fabricated by taking porous carbon (PC) as the matrix to load glucose oxidase or fungi laccase as the catalysts. The electrolytes in the anode and cathode compartments contain ferrocene monocarboxylic acid and 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt as the mediators, respectively. The power of the BFC was enhanced significantly by using PC as the matrix, rather than glassy carbon electrode. Additionally, the power output of the BFC decreases as the pH of the solution increases from 4.0 to 7.0, which provides a simple and efficient method to achieve the required power output. More importantly, the BFC can operate at pH 6.0, and even at pH 7.0, which overcomes the requirement for cathode solutions of pH<5.0 when using fungi laccase as a catalyst. Operation of the BFC at neutral pH may provide a means to power medical devices implanted in physiological systems. The facile and low-cost fabrication of this BFC may enable its development for other applications.

Electricity generation from artificial wastewater using an upflow microbial fuel cell

The upflow microbial fuel cell (UMFC) was developed to generate electricity while simultaneously treating wastewater. During a five-month period of feeding a sucrose solution as the electron donor, the UMFC continuously generated electricity with a maximum power density of 170 mW/m2. To achieve this power density, the artificial electron-mediator hexacyanoferrate was required in the cathode chamber. The power density increased with increasing chemical oxygen demand (COD) loading rates up to 2.0 g COD/ L/day after which no further increases in power density were observed, indicating the presence of limiting factors. The overarching limiting factor for the UMFC in this study was the internal resistance, which was estimated as 84 omega at the maximum power density, and restricted the power output by causing a significant decrease in operating potential. Low Coulombic efficiencies varying from 0.7 to 8.1% implied that the electron-transfer bacteria were incapable of converting all of the available organics into electricity, so the excessive substrate created niches for the growth of methanogens. We found that the soluble COD (SCOD) removal efficiencies remained over 90% throughout the operational period, mainly because of methanogenic activity, which accounted for 35 to 58% of the SCOD removed at a loading rate of 1.0 g COD/L/ day. Additionally, transport limitation due to insufficient substrate diffusion was shown by cyclic voltammetry (CV).

Production of Electrical Energy from Carbohydrates using a Transition Metal-Catalysed Liquid Alkaline Fuel Cell

Biomass may be converted to energy by enzymatic hydrolysis to monomer components and fermentative conversion of those products to ethanol for use as fuel. Both glucose and xylose in aqueous solution were directly converted to electrical energy using a liquid alkaline fuel cell (AFC) at room temperature. Hydrolysis products derived from the action of cellulase and amylase on cellulose and starch, respectively, were also used as fuels in the AFC system. We suggest that this approach may provide a more direct means of accessing some of the energy available from biomass.

Characteristics of a miniature compartment-less glucose-O2 biofuel cell and its operation in a living plant

We report the temperature, pH, glucose concentration, NaCl concentration, and operating atmosphere dependence of the power output of a compartment-less miniature glucose-O(2) biofuel cell, comprised only of two bioelectrocatalyst-coated carbon fibers, each of 7 micro m diameter and 2 cm length (Mano, N.; Mao, F.; Heller, A. J. Am. Chem. Soc. 2002, 124, 12962). The bioelectrocatalyst of the anode consists of glucose oxidase from Aspergillus niger electrically "wired" by polymer I, having a redox potential of -0.19 V vs Ag/AgCl. That of the cathode consists of bilirubin oxidase from Trachyderma tsunodae "wired" by polymer II having a redox potential of +0.36 V vs Ag/AgCl (Mano, N.; Kim, H.-H.; Zhang, Y.; Heller, A. J. Am. Chem. Soc. 2002, 124, 6480. Mano, N.; Kim, H.-H.; Heller, A. J. Phys. Chem. B 2002, 106, 8842). Implantation of the fibers in the grape leads to an operating biofuel cell producing 2.4 micro W at 0.52 V.