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Here we describe the design and the characterization of novel electrode materials consisting of multi-walled carbon nanotubes coated with glyconanoparticles (GNPs) functionalized with anthraquinone sulfonate. The resulting modified electrodes were characterized by scanning electron microscopy and cyclic voltammetry. Their electrochemical behavior reveals a stable pH-dependent redox signal characteristic of anthraquinone sulfonate. Immobilization of bilirubin oxidase on these three-dimensional electrodes leads to the electroenzymatic reduction of O

The non-covalent modification of carbon nanotube electrodes with pyrene derivatives is a versatile approach to enhance the electrical wiring of enzymes for biosensors and biofuel cells. We report here a comparative study of five pyrene derivatives adsorbed at multi-walled carbon nanotube electrodes to shed light on their ability to promote direct electron transfer with horseradish peroxidase (HRP) for H2O2 reduction. In all cases, pyrene-modified electrodes enhanced catalytic reduction compared to the unmodified electrodes. The pyrene N-hydroxysuccinimide (NHS) ester derivative provided access to the highest catalytic current of 1.4 mA cm−2 at 6 mmol L−1 H2O2, high onset potential of 0.61 V vs. Ag/AgCl, insensitivity to parasitic H2O2 oxidation, and a large linear dynamic range that benefits from insensitivity to HRP “suicide inactivation” at 4–6 mmol L−1 H2O2. Pyrene-aliphatic carboxylic acid groups offer better sensor sensitivity and higher catalytic currents at ≤ 1 mmol L−1 H2O2 concentrations. The butyric acid and NHS ester derivatives gave high analytical sensitivities of 5.63 A M−1 cm−2 and 2.96 A M−1 cm−2, respectively, over a wide range (0.25–4 mmol−1) compared to existing carbon-based HRP biosensor electrodes. A bacterial nanocellulose pyrene-NHS HRP bioelectrode was subsequently elaborated via “one-pot” and “layer-by-layer” strategies. The optimised bioelectrode exhibited slightly weaker voltage output, further enhanced catalytic currents, and a major enhancement in 1-week stability with 67% activity remaining compared to 39% at the equivalent electrode without nanocellulose, thus offering excellent prospects for biosensing and biofuel cell applications.

The non-covalent modification of carbon nanotube electrodes with pyrene derivatives is a versatile approach to enhance the electrical wiring of enzymes for biosensors and biofuel cells. We report here a comparative study of five pyrene derivatives adsorbed at multi-walled carbon nanotube electrodes to shed light on their ability to promote direct electron transfer with horseradish peroxidase (HRP) for H

International audience; The electrochemical reduction of aryldiazonium salts is a versatile and direct route to obtain robust covalently-modified electrodes. We report here a comparative study of Azure-A modified carbon nanotube electrodes prepared by diazonium electrografting and by physical adsorption for bioelectrocatalytic glucose oxidation with fungal FAD-glucose dehydrogenase from Aspergillus sp. The electrografted and adsorbed electrodes exhibited different reversible electroactivity consistent with polymer-type and monomer-type phenothiazine surface assemblies, respectively. The electrografted Azure A electrodes exhibited superior mediated bioelectrocatalysis compared to the adsorbed Azure A electrodes. A more than 10-fold higher catalytic current up to 2 mA cm-2 at 0.2 V vs. Ag/AgCl together with a similarly low onset potential of-0.05 V vs. Ag/AgCl was observed at the electrografted electrodes. Faster estimated electron transfer kinetics and a +200 mV potential shift for the polymer-type redox couple vs. the adsorbed monomer-type couple underlines the favourable driving force for mediated electron transfer with the buried FAD active site for the diazonium-derived bioelectrode. Keywords: Phenothiazine redox mediator • FAD dependant glucose dehydrogenase • biofuel cell anode • enzymatic bioelectrode • bioelectrocatalysis 2

International audience; Enzymatic biofuel cells are ecofriendly power sources that can deliver μW−mW outputs from renewable substrates, but their stability is a major issue owing to enzyme fragility. The vast majority of reported biofuel cells can only generate power continuously for relatively short periods of time. Here we report a novel "solubilized enzymatic fuel cell (SEFC)" concept for continuous long-term operation. Avoiding surface immobilization techniques allows bio- catalytic activity to be easily restored or replenished. The biofuel cell exploits freely diffusing enzymes and β-cyclodextrin-coated glycona- noparticles with entrapped quinone and thiazoline redox mediators, for mediated glucose and oxygen conversion. The cell was designed with permselective membranes to enable substrate and proton diffusion while trapping the enzymes and glyconanoparticles in separate compartments. The SEFC exhibited a peak power loss of only 26.3% after 7 days of continuous charge−discharge cycling at 50 μA; thus, SEFCs may be envisaged to power lab-on-a-chip devices for periods of several weeks.

International audience; Enzymatic biofuel cells generate electrical energy from renewable sources with high selectivity and environmental benefits compared to lithium batteries and traditional fuel cells. For enzymatic fuel cells to become competitive, major improvements in electrode design are required to enhance power density, voltage output, and stability. Here we have developed a freestanding paper biofuel cell comprising redox molecule embedded multiwalled carbon nanotube papers for electrical wiring of enzymes. The drop-coat and one-pot fabrication methods provide flexibility and permit easy scalability of functionalized bioelectrodes via commercially available materials. Buckypaper functionalized with 1,10-phenanthroline-5,6-dione (PLQ) as an efficient electron mediator for fungal-derived FAD-dependent glucose dehydrogenase (FADGDH) shows very high steady-state current densities for glucose oxidation of Imax = 5.38 ± 0.54 mA cm–2 at 0.15 V vs SCE at neutral pH. When coupled with a bioinspired protoporphyrin IX buckypaper cathode, the resulting glucose/O2 fuel cell delivered a power density of 0.65 ± 0.10 mW cm–2 or 24.1 ± 4.7 mW cm–3 at a cell voltage of 0.5 V, limited by the cathode. Galvanostatic and current discharge experiments confirm robust short-term operational performance.

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Cubic Pd nanoparticles (PdNPs) were synthesized using ascorbic acid as a reducing agent and were evaluated for the catalytic oxygen reduction reaction. PdNPs were confined with multiwalled carbon nanotube (MWCNT) dispersions to form black suspensions and these inks were dropcast onto glassy carbon electrodes. Different nanoparticle sizes were synthesized and investigated upon oxygen reduction capacities (onset potential and electrocatalytic current densities) under O2 saturated conditions at varying pH values. Strong evidence of O2 diffusion limitation was demonstrated. In order to overcome oxygen concentration and diffusion limitations in solution, we used a gas diffusion layer to create a PdNP-based air-breathing cathode, which delivered -1.5 mA cm(-2) at 0.0 V with an onset potential of 0.4 V. This air-breathing cathode was combined with a specially designed phenanthrolinequinone/glucose dehydrogenase-based anode to form a complete glucose/O2 hybrid bio-fuel cell providing an open circuit voltage of 0.554 V and delivering a maximal power output of 184 ± 21 μW cm(-2) at 0.19 V and pH 7.0.

After a short comparison of biofuel cells based on enzymes and microorganisms, several important developments and applications of enzymatic fuel cells (EFCs) are discussed. This discussion emphasizes how to evaluate the performance of EFCs, and highlights the influence of temperature and how it must be carefully considered for practical use of EFCs as power sources. Some of the latest and most important innovations in EFC design using buckypapers and redox nanoparticles are briefly reviewed.

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An elegant method to perform bioelectocatalysis with different oxidoreductases at the cathode and at the anode of an enzymatic biofuel cell is presented. Noncovalent functionalization of multiwalled carbon nanotubes (MWCNTs) was accomplished via π–π interactions of pyrene derivatives. 1-[Bis(2-naphthoquinonyl)aminomethyl]pyrene was synthesized and successfully immobilized on MWCNTs. The incorporation of the quinone-modified MWCNTs within enzymatic bioelectrocatalytic applications was evaluated. The hydrophobic nature of the naphthoquinone aided orientation of laccase and bilirubin oxidase toward the electrode, which enhanced their ability to undergo the direct bioelectrocatalysis of oxygen. In contrast, the electrochemical properties of the quinone were used at the bioanode to mediate electrons from the bioelectrocatalytic oxidation of glucose by pyrroloquinoline quinone-dependent glucose dehydrogenase. This method demonstrates how the smart modification of MWCNTs can develop materials, which can be used ...

We demonstrate self-assembly, characterization and bioelectrocatalysis of redox-active cyclodextrin-coated nanoparticles. The nanoparticles with host–guest functionality are easy to assemble and permit entrapment of hydrophobic redox molecules in aqueous solution. Bis-pyrene-ABTS encapsulated nanoparticles were investigated electrochemically and spectroscopically. Their use as electron shuttles is demonstrated via an intraelectron transfer chain between neighboring redox units of clustered particles (Dh,DLS = 195 nm) and the mono- and trinuclear Cu sites of bilirubin oxidases. Enhanced current densities for mediated O2 reduction are observed with the redox nanoparticle system compared to equivalent bioelectrode cells with dissolved mediator. Improved catalytic stability over 2 days was also observed with the redox nanoparticles, highlighting a stabilizing effect of the polymeric architecture. Bioinspired nanoparticles as mediators for bioelectrocatalysis promises to be valuable for future biofuel cells an...

We report the functionalization of multi-walled carbon nanotubes (MWCNTs) electrodes by a bifunctional nitroaromatic molecule accomplished via π-π interactions of a pyrene derivative. DTNB (5,5'-dithiobis(2-nitrobenzoic acid)) has the particularity to possess both electroactivable nitro groups and negatively charged carboxylic groups. The integration of the DTNB-modified MWCNTs was evaluated for different bioelectrocatalytic systems. The immobilized DTNB-based electrodes showed electrocatalytic activity toward the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) with low overpotential of -0.09V vs Ag/AgCl at neutral pH. Glucose dehydrogenase was successfully immobilized at the surface of DTNB-based electrodes and, in the presence of NAD+, the resulting bioelectrode achieved efficient glucose oxidation with high current densities of 2.03mAcm-2. On the other hand, the aromatic structure and the negatively charged nature of the DTNB provoked orientation of both laccase and bilirubin oxidase onto the electrode, which enhanced their ability to undergo a direct electron transfer for oxygen reduction. Due to the proper orientation, low overpotentials were obtained (ca. 0.6V vs Ag/AgCl) and high electrocatalytic currents of about 3.5mAcm-2 were recorded at neutral pH in O2 saturated conditions for bilirubin oxidase electrodes. The combination of these bioanodes and bilirubin oxidase biocathodes provided glucose/O2 enzymatic biofuel cells (EBFC) exhibiting an open-circuit potential of 0.640V, with an associated maximum current density of 2.10mAcm-2. Moreover, the fuel cell delivered a maximum power density of 0.50mWcm-2 at 0.36 V.

The regeneration of the enzymatic cofactor nicotinamide adenine dinucleotide (NADH) by rhodium-based catalysts such as [Rh(Cp∗)(bpy)Cl]+ (Cp∗ = pentamethylcyclopentadienyl, bpy = 2,2� -bipyridine) and derivatives have previously been studied extensively in solution. In this work, we report a synthetic route of a rhodium complex with a pyrene-substituted phenanthroline ligand (pyr-Rh). The immobilization of the pyr-Rh complex was accomplished on multi-walled carbon nanotubes (MWCNTs) via π-π stacking to obtain effective and durable indirect electrochemical regeneration of NADH. Cyclic voltammetry and amperometry were used to demonstrate the electrochemical activity of the surface-confined pyr-Rh complex. The loading quantity of the pyr-Rh complex was found to be 47 ± 2 nmol/mg of MWCNTs. The reusability of the electrodes modified with the pyr-Rh complex was investigated and an average turnover frequency of 3.6 ± 0.1 s −1 over ten cycles in the presence of 2 mM nicotinamide adenine dinucleotide (NAD + ) was observed. Lastly, malate dehydrogenase (MDH), a NADH-dependent enzyme, was evaluated in the presence of the immobilized pyr-Rh complex to confirm the catalyst’s capability to regenerate biologically active NADH for biocatalysis. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any

Enzymatic biological fuel cells (E-BFCs) were prepared using glucose oxidase (GOx) or FAD-dependent glucose dehydrogenase (FAD-GDH) as the anodic enzyme, coupled with direct electrocatalytic bilirubin oxidase (BOd) biocathodes obtained via incorporation of anthracene-modified multi-walled carbon nanotubes (Ac-MWCNTs). For GOx/BOd E-BFCs operating at pH 6.5 (200 mM glucose), open-circuit potentials, maximum current densities and maximum power densities of 0.47 ± 0.02 V, 332.7 ± 19.6 μA cm, and 46.5 ± 2.8 μW cm were observed. For FAD-GDH/BOd E-BFCs operating in the same conditions, open-circuit potentials, maximum current densities and maximum power densities of 0.40 ± 0.01 V, 226.6 ± 8.0 μA cm, and 35.9 ± 1.3 μW cm were observed. The effect of HO (as produced by the enzymatic side-reaction of GOx) on BOd bioelectrocatalytic cathodes in E-BFCs was also investigated. Short-term testing (steady state) revealed that GOx did not produce significant quantities of HO to affect BOd biocathodes. However, long-term testing (steady state, 24 hours) revealed that the quantity of HO produced by GOx is large enough to have detrimental effects on the performance of the E-BFCs. © 2014.

The utilization of carbon felt as the conductive material for the construction of a monosaccharide-based coin-cell biobattery is explored. Anthracene-modified carbon nanotubes were used at the positive electrode to preferentially orientate laccase for direct electron transfer during O2 reduction. A ferrocene-modified poly(ethylenimine) redox polymer was used to electrically communicate with either glucose oxidase or fructose dehydrogenase at the negative electrode. The use of carbon felt helped in the immobilization of a larger quantity of enzyme. Cathodic and anodic currents with carbon felt electrodes showed a three-fold and twofold increase, respectively, relative to the currents obtained with Toray paper materials. Bioelectrodes were assembled in a commercial coin-cell battery casing and were tested as possible biobatteries. This work presents the first time in which a traditional battery design is used for the performance evaluation of different biobatteries.

The increasing interest in producing electrical energy from renewable resources has caused the field of biofuel cells to flourish. Enzymatic biofuel cell systems are capable of producing energy from renewable fuels. Basically, enzymatic biofuel cells (EBFC) generate electricityfromtheoxidationofthefuelattheanodeandthereduction of the oxidant at the cathode using biological catalysts (enzymes) instead of traditional metal catalysts. More detailed descriptions of

The employment of multi-enzyme cascades as catalysts is a promising strategy to improve performance of enzymatic biofuel cells, as it allows for the conversion of more chemical energy stored in complex fuels. However, the performance of these enzyme systems is often limited by the mass transport of intermediate substrates between enzymes. Nature addresses this issue by organizing metabolic enzymes in a sequential and proximal manner to enhance the efficiency of metabolic pathways. In this work, we investigate the utilization of DNA as a structural scaffold for assembly of the invertase/glucose oxidase enzyme cascade to improve sucrose bioelectrocatalytic activity. It has been found that the DNA-assembled enzyme cascade has higher activity than the free cascade, both in solution and in the immobilized state on an electrode surface. The organization of the enzyme cascade on the DNA scaffold leads to a 100% increase in the current density in amperometric measurements and a 75% increase in the power density of the biofuel cell. This is the first evidence of the advantages of utilizing DNA scaffords for improved bioelectrocatalysis.

The clean production of electrical energy from renewable resources has received recently a growing attention from the research community. A way to achieve this goal is the use of biological catalysts to catalyze the oxidation of renewable fuels. One of the streamlines on the research dealing with green electrical energy production is represented by oxidoreductase enzymes as the biocatalysts. Thanks to their specificity towards their respective substrates and activity in relatively mild conditions (pH, temperature, etc…), they are ideal candidates to replace noble metals regularly found in fuel cells. However, due to low power densities achieved utilizing these redox proteins and their limited stability; enzymatic fuel cells (EFCs) are so far only envisioned to power small and disposable electronic devices. In most literature reports, the redox enzymes are essentially immobilized on chemically modified electrode surfaces. There, they harvest and convert the chemical energy stored in fuels and turn it into electrical energy. The growing field in bioelectrocatalysis is beneficial not only for the biofuel cell technology but also for the design of efficient biosensing or bioreactor devices. In this presentation, we will focus on two different approaches for the design of EFCs currently studied in our laboratory. The rationalization of the electrode surface requirement to achieve efficient bioelectrocatalysis (mediated or direct electron transfer) [1] allowed for the synthesis of redox active gold nanoparticles (AuNPs) bearing electroactivable nitro groups and negatively charged groups. The obtained hydroxylamine-modified AuNPs are catalytically active for nicotinamide adenine dinucleotide (NADH) oxidation and for NAD+ regeneration in bioelectrocatalysis (with NAD-dependent glucose dehydrogenase). In contrast, the same particles possessing also negatively charged carboxylic groups had been shown to favorably orientate some multi-copper oxidases having their T1 copper center facing the metallic particles and consequently enhancing oxygen electroreduction. On the other hand, we will also present our recent strategy to design solubilized enzymatic fuel cell (SEFC). The entrapment of different redox mediator is accomplished by host-guest interaction with β-cyclodextrin-coated glyconanoparticles for the mediated glucose and oxygen conversion [2,3]. Hence, the cell was designed with permselective membranes to enable substrate and proton diffusion while trapping the enzymes and redox glyconanoparticles in separate compartments. The SEFC suffered a limited power loss of about 25% after 7 days of continuous charge-discharge cycling at 50 µA [3]. References [1] F. Giroud, K. Sawada, M. Taya, S. Cosnier, Biosens. Bioelectron., 2017, 87, 957-963. [2] A. J. Gross, X. Chen, F. Giroud, C. Travelet, R. Borsali, S. Cosnier, J. Am. Chem. Soc., 2017, 139, 16076-16079. [3] J. L. Hammond, A. J. Gross, F. Giroud, C. Travelet, R. Borsali, S. Cosnier, ACS Energy Lett., 2019, 4, 142-148.

Although mitochondria have been used for bio-electrochemistry for over 5 years, little is known about their direct electrochemistry mechanism. This paper focuses on developing a better understanding of the electron transfer mechanism of mitochondria from three different organisms at carbon electrodes. Yeast, potato and bovine mitochondria have been successfully isolated and immobilized onto Toray paper electrodes via vapor deposited silica. Organelle-modified electrodes were first characterized using cyclic voltammetry. Similar electrochemical signals were obtained for all organisms. Direct electron transfer was observed when a metabolite of the Krebs cycle was present in the buffer solution. Control experiments based on the immobilization of two electron carriers contained in mitochondria, cytochrome c and a quinone (coenzyme Q 10 ), tend to show the electron transfer mechanism to the carbon material comes from the quinone pool of the organelles. As quinones are known to be pH-dependent, we further investigated the response of the electrochemical signal of the three isolated mitochondria and the two electron carriers separately. The half wave potentials obtained from the organelles appeared to be pH-dependent and their variations are comparable to coenzyme Q 10 rather than cytochrome c. Finally, extraction of both the cytochrome c and the quinone pool from intact mitochondria was performed to validate our hypothesis that direct electrochemistry of mitochondria happens via the quinone pool. Electrochemistry of immobilized quinone-depleted mitochondria validated the hypothesis that the mitochondria are communicating with the electrodes through the quinone pool.

This paper describes the design and testing of a microfluidic biofuel cell that uses a flow-through bioanode and an air-breathing cathode. The bioanode is Toray carbon paper with glucose dehydrogenase (GDH), multi-walled carbon nanotubes (MWCNTs), and methylene green immobilized within a hydrogel. The cathode consists of a commercially available air-breathing platinum cathode hot pressed to a Nafion membrane. All remaining biofuel cell components were laser-cut from poly(methyl methacrylate) (PMMA) and silicone sheets. Half-cell experiments indicate that cathode variability limits the biofuel cell. An examination of flow rate effects on the biofuel cell showed that the current density increased sharply up to about 1 mL/min. Tested at this flow rate, the flow-through biofuel cell achieved a maximum current and power density of 705 μA/cm 2 and 146 μW/cm 2 . This was a 6% and 29% improvement in the current and power density, respectively, compared to the previously demonstrated bioanode without flow. Fuel utilization was calculated based on the measured current and by measuring UV-Vis absorbance of the reduced form of hydroxybenzhydrazide. The maximum fuel utilization was 5.8% at a flow rate of 0.05 mL/min. Finally, a numerical model of the biofuel cell was designed and its results compare favorably to actual data.

We report the functionalization of multi-walled carbon nanotubes (MWCNTs) electrodes by a bifunctional nitroaromatic molecule accomplished via π-π interactions of a pyrene derivative. DTNB (5,5'-dithiobis(2-nitrobenzoic acid)) has the particularity to possess both electroactivable nitro groups and negatively charged carboxylic groups. The integration of the DTNB-modified MWCNTs was evaluated for different bioelectrocatalytic systems. The immobilized DTNB-based electrodes showed electrocatalytic activity toward the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) with low overpotential of -0.09V vs Ag/AgCl at neutral pH. Glucose dehydrogenase was successfully immobilized at the surface of DTNB-based electrodes and, in the presence of NAD

This work presents a first approach towards the development of a cost-effective enzymatic paper-based glucose/O2 microfluidic fuel cell in which fluid transport is based on capillary action. A first fuel cell configuration consists of a Y-shaped paper device with the fuel and the oxidant flowing in parallel over carbon paper electrodes modified with bioelectrocatalytic enzymes. The anode consists of a ferrocenium-based polyethyleneimine polymer linked to glucose oxidase (GOx/Fc-C6-LPEI), while the cathode contains a mixture of laccase, anthracene-modified multiwall carbon nanotubes, and tetrabutylammonium bromide-modified Nafion (MWCNTs/laccase/TBAB-Nafion). Subsequently, the Y-shaped configuration is improved to use a single solution containing both, the anolyte and the catholyte. Thus, the electrolytes pHs of the fuel and the oxidant solutions are adapted to an intermediate pH of 5.5. Finally, the fuel cell is run with this single solution obtaining a maximum open circuit of 0.55 ± 0.04 V and a maximum current and power density of 225 ± 17 μA cm−2 and 24 ± 5 μW cm−2, respectively. Hence, a power source closer to a commercial application (similar to conventional lateral flow test strips) is developed and successfully operated. This system can be used to supply the energy required to power microelectronics demanding low power consumption., F. Javier del Campo acknowledges funding from the Spanish Ministry of Economy through the DADDi2 project (TEC2013-48506-C3). Juan Pablo Esquivel would like to thank the support from Marie Curie International Outgoing Fellowship (APPOCS-328144) within the 7th European Community Framework Programme. Shelley D. Minteer and Fabien Giroud would like to thank the National Science Foundation (CHE-1057597) for funding. Neus Sabaté acknowledges funding from the European H2020 Framework Programme (Grant Agreement 648518 - SUPERCELL - ERC 2014 CoG).

International audience; This paper reports the development and optimisation of a glucose/O-2 biofuel cell. At the anode, the glucose oxidation was performed by glucose oxidase (GOx) co-immobilised with a phenanthrenequinone mediator. At the cathode, the catalysis of O-2 using tetrathiafulvalene and polyphenol oxidase (PPO) has been demonstrated for the first time. The open circuit voltage (OCV) of the optimised biofuel cell reached 0.32 V, and the maximum power density achieved was 40.811 mu W cm(-2) at 0.2 V. This original new GBFC showed quasi-stability in both OCV and power density for more than 25 days.

The development of new, efficient bioelectrodes is important to the improvement of biosensor and biofuel cell technology. NAD-dependent dehydrogenase enzymes represent a diverse field of oxidoreductase enzymes that can be used to create unique biosensors and biofuel cells, but require electrocatalysts to oxidize NADH in order to harvest the electrons efficiently from fuel oxidation. This study presents a new methodology for the co-immobilization of dehydrogenase enzymes, azine-based NADH electrocatalysts, carbon nanotubes, and polymer hydrogels. The easy “one-pot” mixing and casting procedure is shown to produce electrodes that can electro-oxidize NADH at low potentials. In situ electropolymerization of the azine dyes within the composites is shown to improve NADH sensitivity, but harms enzyme activity. Biosensors and biofuel cells are constructed with a model enzyme, glucose dehydrogenase, to show the application of this system in a glucose biosensor and biofuel cell. Glucose biosensors produced limiting current densities of 400 μA/cm2 and glucose/air-breathing biofuel cells produced power densities slightly greater than 100 μW/cm2.

International audience; We report on an alternative concept of biofuelcell functioning based on the unconventional use of enzymes to create apH difference generating a potential difference between electrodes soaked in quinhydrone solutions. The electrode and quinhydrone solution were confined in a dialysis bag placed into a compartment containing either glucose oxidase and catalase for the biocathode or urease for the bioanode. In presence of 0.4 mol L−1 glucose and urea, the enzyme reactions generate apH difference of 3.55, both compartments being separated by an agar-agar wall. The resulting biofuelcell exhibits an open-circuit voltage and maximum power of 208 mV and 30.6 μW, respectively, without immobilization and electrical connection of the involved enzymes. In addition, this biofuelcell was able to provide continuously10 μA during 23 h, producing 0.133 J and 0.828 C. A similar biofuelcell configuration based only on dialysis bags was also developed. A graphite disk electrode elaborated by mechanical compression of graphite particles and quinhydrone, was placed in a dialysis bag itself confined into another dialysis bag containing enzyme solution. The resulting power and open-circuit voltage at saturating substrate conditions are 7.6 μW and 157 mV, respectively.

This paper describes the construction of an impedimetric immunosensor for the label-free detection of ciprofloxacin, an antibiotic belonging to synthetic fluoroquinolones. A poly(pyrrole-N-hydroxysuccinimide) film was electrogenerated onto electrodes and then used for the reagentless covalent binding of a fluoroquinolone model bearing an amino group. The resulting electrodes were utilized to immobilize a layer of anticiprofloxacin antibody onto the polymer surface by immunoreaction. In presence of ciprofloxacin, the antibody was displaced in solution inducing marked changes in the impedance of the sensor electrodes. These phenomena were detected and characterized by electrochemical impedance spectroscopy allowing the selective detection of extremely low ciprofloxacin concentration, namely, 1 x 10(-12) g mL(-1) or 3 pmol L(-1). Sensors exposed to ciprofloxacin showed a decrease in the sum of the interfacial resistances with the increase in ciprofloxacin concentration from 1 x 10(-12) to 1 x 10(-6) g mL(-1).

Mediator-less, direct electro-catalytic reduction of oxygen to water by bilirubin oxidase (Myrothecium sp.) was obtained on anthracene-modified, multi-walled carbon nanotubes. H2O2 was found to significantly and irreversibly affect the electro-catalytic activity of bilirubin oxidase, whereas similar electrodes comprised of laccase (Trametes versicolor) were reversibly inhibited.

5 pages; International audience; We describe the first implanted glucose biofuel cell (GBFC) that is capable of generating sufficient power from a mammal's body fluids to act as the sole power source for electronic devices. This GBFC is based on carbon nanotube/enzyme electrodes, which utilize glucose oxidase for glucose oxidation and laccase for dioxygen reduction. The GBFC, implanted in the abdominal cavity of a rat, produces an average open-circuit voltage of 0.57 V. This implanted GBFC delivered a power output of 38.7 μW, which corresponded to a power density of 193.5 μW cm(-2) and a volumetric power of 161 μW mL(-1). We demonstrate that one single implanted enzymatic GBFC can power a light-emitting diode (LED), or a digital thermometer. In addition, no signs of rejection or inflammation were observed after 110 days implantation in the rat.

International audience; Powering future generations of implanted medical devices will require cumbersome transcutaneous energy transfer or harvesting energy from the human body. No functional solution that harvests power from the body is currently available, despite attempts to use the Seebeck thermoelectric effect, vibrations or body movements. Glucose fuel cells appear more promising, since they produce electrical energy from glucose and dioxygen, two substrates present in physiological fluids. The most powerful ones, Glucose BioFuel Cells (GBFCs), are based on enzymes electrically wired by redox mediators. However, GBFCs cannot be implanted in animals, mainly because the enzymes they rely on either require low pH or are inhibited by chloride or urate anions, present in the Extra Cellular Fluid (ECF). Here we present the first functional implantable GBFC, working in the retroperitoneal space of freely moving rats. The breakthrough relies on the design of a new family of GBFCs, characterized by an innovative and simple mechanical confinement of various enzymes and redox mediators: enzymes are no longer covalently bound to the surface of the electron collectors, which enables use of a wide variety of enzymes and redox mediators, augments the quantity of active enzymes, and simplifies GBFC construction. Our most efficient GBFC was based on composite graphite discs containing glucose oxidase and ubiquinone at the anode, polyphenol oxidase (PPO) and quinone at the cathode. PPO reduces dioxygen into water, at pH 7 and in the presence of chloride ions and urates at physiological concentrations. This GBFC, with electrodes of 0.133 mL, produced a peak specific power of 24.4 microW mL(-1), which is better than pacemakers' requirements and paves the way for the development of a new generation of implantable artificial organs, covering a wide range of medical applications.

There has been a significant interest lately in the complete oxidation of biofuels to CO2. The use of multiple biocatalysts allows for deeper biofuel oxidation and thus maximizes the energy density that can be extracted per molecule of biofuel. However, there are still many biofuels for which a suitable biocatalyst is not known. We have recently taken an alternative approach to combine the high catalytic activity of enzymatic biocatalysts with the promiscuous nature of small molecule organic catalysts. We demonstrate the complete electrochemical oxidation of the biofuel glycerol to CO2 using a hybrid enzymatic and small-molecule catalytic system. Combining an enzyme, oxalate oxidase, and an organic oxidation catalyst, 4-amino-TEMPO, we are able to electrochemically oxidize glycerol at a carbon electrode, while collecting as many as 16 e-s per molecule of fuel. Additionally, we investigate the anomalous electrocatalytic properties that allow 4-amino-TEMPO to be active under the acidic conditions required for oxalate oxidase to function.

Glucose oxidase (GOx) is commonly incorporated into glucose-oxidising/oxygen-reducing enzymatic biological fuel cells (EBFCs), as the anodic biocatalyst. The flavin adenine dinucleotide (FAD) cofactor of GOx is tightly bound, and possesses an associated favourable low redox potential allowing the use of a wide range of electron mediators, which in turn increases the theoretical maximum open-circuit potential (OCP) of EBFCs. Furthermore, GOx is highly specific to glucose and offers high catalytic activity, making it a good choice for futuristic implantable EBFCs. GOx-based anodes do, however, exhibit a major significant drawback; electron transfer to the electrode following the enzymatic oxidation of glucose competes with the natural electron acceptor of GOx: oxygen. The reduction of oxygen by GOx can dramatically lower the dissolved oxygen concentration of a solution, whilst simultaneously producing hydrogen peroxide. Laccase and bilirubin oxidase (BOd) can undergo the enzymatic 4-electron reduction of dissolved oxygen to water, and efficient direct electron transfer (DET) has been established for both enzymes. The inhibition of laccase and BOd by halides (primarily fluoride and chloride ions) is well documented; it is reported that BOd exhibits greater resistance to halide inhibition. Nevertheless, DET can also instil a degree of resistance to chloride inhibition. Lastly, BOd can efficiently reduce oxygen to water at near-neutral and physiological pH, making it a favourable choice of biocatalyst in implantable devices. The research presented within this paper investigates the effect of the parasitic reduction of oxygen to hydrogen peroxide by GOx, on laccase and BOd direct bioelectrocatalytic cathodes. We report that GOx can produce significant quantities of hydrogen peroxide and thereby significantly affect laccase and BOd cathodes (albeit by different mechanisms), even when DET is established (a mode previously used to remediate chloride inhibition). Furthermore, we compare and contrast the performance of laccase and BOd when GOx is replaced with “oxygen-insensitive” FAD-dependent glucose dehydrogenase (FAD-GDH). This research has implications for the future design of EBFCs. This research is funded by the UK SuperGen Biological Fuel Cells Consortium (Contract: EP/H019480/1), National Science Foundation Grant #105797 and the Air Force Office of Scientific Research (AFOSR).

Biofuel cells provide a safe and renewable means of powering small electronic devices. We have recently demonstrated a bioanode that is capable of extracting four electrons from a single molecule of sucrose by way of a three-enzyme cascade. Invertase, fructose dehydrogenase and glucose oxidase are immobilized in a ferrocene-modified linear poly(ethylenimine) (LPEI) hydrogel onto the surface of a carbon electrode. Fuel sources are generated in the polymer film by (1) hydrolyzing sucrose into fructose and glucose, and then (2) electroenzymatically oxidizing fructose and glucose to produce a current response. A previously unreported synergistic effect is observed between glucose oxidase and fructose dehydrogenase that results in a current response that is considerably higher than expected. The newly described enzyme cascade generated 302 ± 57 μA/cm2 at 25 oC and 602 ± 62 μA/cm2 at 37 oC and when poised against an air breathing platinum cathode in a biofuel cell, the multienzyme-containing film generated 42 ± 15 μW/cm2 at 172 mV with a maximum current density of 344 ± 25 μA/cm2 in 100 mmol/L sucrose at 25 oC.

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Biofuel cells typically yield lower power and are more difficult to fabricate than conventional fuel cells using inorganic catalysts. This work presents a glucose/O2 microfluidic biofuel cell (MBFC) featuring pyrolyzed photoresist film (PPF) electrodes made on silicon wafers using a rapid thermal process, and subsequently encapsulated by rapid prototyping techniques into a double-Y-shaped microchannel made entirely of plastic. A ferrocenium-based polyethyleneimine polymer linked to glucose oxidase (GOx/Fc-C6-LPEI) was used in the anode, while the cathode contained a mixture of laccase, anthracene-modified multi-walled carbon nanotubes, and tetrabutylammonium bromide-modified Nafion (MWCNTs/laccase/TBAB-Nafion). The cell performance was studied under different flow-rates, obtaining a maximum open circuit voltage of 0.54 ± 0.04 V and a maximum current density of 290 ± 28 μA cm(-2) at room temperature under a flow rate of 70 μL min(-1) representing a maximum power density of 64 ± 5 μW cm(-2). Although there is room for improvement, this is the best performance reported to date for a bioelectrode-based microfluidic enzymatic biofuel cell, and its materials and fabrication are amenable to mass production.