Implantable Biofuel Cells Research Articles

A pacemaker powered by an implantable biofuel cell operating under conditions mimicking the human blood circulatory system – battery not included

Biocatalytic electrodes made of buckypaper were modified with PQQ-dependent glucose dehydrogenase on the anode and with laccase on the cathode and were assembled in a flow biofuel cell filled with serum solution mimicking the human blood circulatory system. The biofuel cell generated an open circuitry voltage, Voc, of ca. 470 mV and a short circuitry current, Isc, of ca. 5 mA (a current density of 0.83 mA cm(-2)). The power generated by the implantable biofuel cell was used to activate a pacemaker connected to the cell via a charge pump and a DC-DC converter interface circuit to adjust the voltage produced by the biofuel cell to the value required by the pacemaker. The voltage-current dependencies were analyzed for the biofuel cell connected to an Ohmic load and to the electronic loads composed of the interface circuit, or the power converter, and the pacemaker to study their operation. The correct pacemaker operation was confirmed using a medical device - an implantable loop recorder. Sustainable operation of the pacemaker was achieved with the system closely mimicking human physiological conditions using a single biofuel cell. This first demonstration of the pacemaker activated by the physiologically produced electrical energy shows promise for future electronic implantable medical devices powered by electricity harvested from the human body.

A highly efficient O2 cathode based on bilirubin oxidase from Bacillus pumilus operating in serum

Here we report, for the first time, the efficient reduction of O2 in serum using a glassy carbon electrode modified with a new bilirubin oxidase from Bacillus pumilus and a polycationic redox polymer, without coating the electrode with any protective membrane. After 3.3h of continuous operation in serum, the new cathode only lost 9% of its current density while an electrode made with Trachyderma tsunodae lost more than 38% within the same period of time. This result, in combination with the high thermostability, low sensitivity to chloride anions and high activity, makes the new BOD a promising candidate for the development of cathodes for implanted biofuel cells.

Snails with implanted biofuel cells produce electricity

Snails with implanted biofuel cells produce electricity

Implanted Biofuel Cell Operating in a Living Snail

Implantable biofuel cells have been suggested as sustainable micropower sources operating in living organisms, but such bioelectronic systems are still exotic and very challenging to design. Very few examples of abiotic and enzyme-based biofuel cells operating in animals in vivo have been reported. Implantation of biocatalytic electrodes and extraction of electrical power from small living creatures is even more difficult and has not been achieved to date. Here we report on the first implanted biofuel cell continuously operating in a snail and producing electrical power over a long period of time using physiologically produced glucose as a fuel. The "electrified" snail, being a biotechnological living "device", was able to regenerate glucose consumed by biocatalytic electrodes, upon appropriate feeding and relaxing, and then produce a new "portion" of electrical energy. The snail with the implanted biofuel cell will be able to operate in a natural environment, producing sustainable electrical micropower for activating various bioelectronic devices.

A chloride tolerant laccase from the plant pathogen ascomycete Botrytis aclada expressed at high levels in Pichia pastoris

Fungal laccases from basidiomycetous fungi are thoroughly investigated in respect of catalytic mechanism and industrial applications, but the number of reported and well characterized ascomycetous laccases is much smaller although they exhibit interesting catalytic properties. We report on a highly chloride tolerant laccase produced by the plant pathogen ascomycete Botrytis aclada, which was recombinantly expressed in Pichia pastoris with an extremely high yield and purified to homogeneity. In a fed-batch fermentation, 495 mg L(-1) of laccase was measured in the medium, which is the highest concentration obtained for a laccase by a yeast expression system. The recombinant B. aclada laccase has a typical molecular mass of 61,565 Da for the amino acid chain. The pI is approximately 2.4, a very low value for a laccase. Glycosyl residues attached to the recombinant protein make up for approximately 27% of the total protein mass. B. aclada laccase exhibits very low K(M) values and high substrate turnover numbers for phenolic and non-phenolic substrates at acidic and near neutral pH. The enzyme's stability increases in the presence of chloride ions and, even more important, its substrate turnover is only weakly inhibited by chloride ions (I(50)=1.4M), which is in sharp contrast to most other described laccases. This high chloride tolerance is mandatory for some applications such as implantable biofuel cells and laccase catalyzed reactions, which suffer from the presence of chloride ions. The high expression yield permits fast and easy production for further basic and applied research.

Bifunctional Trehalose Anode Incorporating Two Covalently Linked Enzymes Acting in Series

A bienzymatic electrode incorporating trehalase (Tre) and glucose oxidase (GOx) covalently bound to the surface of Pt through a functionalized thiol linker (Tre|GOx|Pt) has been designed and assembled and its catalytic properties examined by chemical and electrochemical methods in aqueous phosphate buffer solutions (PBS, pH 7.4). Exposure of Tre|GOx|Pt to PBS containing trehalose (Tr) and subsequent polarization at 0.6 V versus Ag/AgCl yielded after a few minutes well-defined steady-state currents ascribed to the oxidation of hydrogen peroxide generated by the GOx-mediated oxidation of glucose (Gl) produced by the Tre-mediated dissociation of Tr. Plots of the steady-state currents versus [Tr] over the range examined, i.e., 5-25 mM, were found to be linear. Implications of these results toward the development of an implantable biofuel cell as an autonomous energy conversion device for insects are discussed.

Design of highly electrocatalytically active carbon sphere chains/Au architectures

An advanced carbon paper (CP) macro-substrate (current collector)/submicro-carbon sphere chains, CSCs (catalyst support)/Au (nanocatalyst) architecture was designed and constructed. Gold was deposited onto the surface of CSCs (several microns in length) through pulsed laser deposition to produce a porous ultra-thin film. In sulfuric acid solution, the CSC/Au electrode exhibited a high real surface area of about 36 times higher than that exhibited by a Au wire electrode. The potential utility of the CSC/Au electrode was demonstrated by investigating the electrocatalytic oxidation of glucose, an important clinical biomolecule for both biosensors and implantable biofuel cells. The CSC/Au electrode displayed a prominent response towards the electrocatalytic oxidation of glucose with a peak current of about 676 times superior to that delivered by a Au wire electrode.

Conducting Polymer Enzyme Alloys: Electromaterials Exhibiting Direct Electron Transfer

Glucose oxidase (GOx) is an important enzyme with great potential application for enzymatic sensing of glucose, in implantable biofuel cells for powering of medical devices in vivo and for large-scale biofuel cells for distributed energy generation. For these applications, immobilisation of GOx and direct transfer of electrons from the enzyme to an electrode material is required. This paper describes synthesis of conducting polymer (CP) structures in which GOx has been entrained such that direct electron transfer is possible between GOx and the CP. CP/enzyme composites prepared by other means show no evidence of such "wiring". These materials therefore show promise for mediator-less electronic connection of GOx into easily produced electrodes for biosensing or biofuel cell applications.

Biofuel Cells Controlled by Logically Processed Biochemical Signals: Towards Physiologically Regulated Bioelectronic Devices

Biofuel cells with a switchable power release controlled by biochemical signals, which can be logically processed by biomolecular computing systems, have been designed. The switchable properties of the biofuel cells were based on the polymer-brush-modified electrodes with the activity dependent on the solution pH value. The pH changes generated in situ by biocatalytic reactions allowed the reversible activation-inactivation of the bioelectrocatalytic interfaces-thus affecting the activity of the entire biofuel cells. Boolean logic operations performed by either enzyme- or immune-based systems were functionally integrated with the switchable biocatalytic process allowing logic control over them. Scaling up the complexity of the biocomputing systems to complex multi-component logic networks with a built-in "program" resulted in the control of the bioelectronic systems by multi-signal patterns of biochemical inputs. Future implantable biofuel cells producing electrical power on-demand depending on physiological conditions are feasible, as the result of the present research.

Biofuel Cell Controlled by Enzyme Logic Systems

An enzyme-based biofuel cell with a pH-switchable oxygen electrode, controlled by enzyme logic operations processing in situ biochemical input signals, has been developed. Two Boolean logic gates (AND/OR) were assembled from enzyme systems to process biochemical signals and to convert them logically into pH-changes of the solution. The cathode used in the biofuel cell was modified with a polymer-brush functionalized with Os-complex redox species operating as relay units to mediate electron transport between the conductive support and soluble laccase biocatalyzing oxygen reduction. The electrochemical activity of the modified electrode was switchable by alteration of the solution pH value. The electrode was electrochemically mute at pH > 5.5, and it was activated for the bioelectrocatalytic oxygen reduction at pH < 4.5. The sharp transition between the inactive and active states was used to control the electrode activity by external enzymatic systems operating as logic switches in the system. The enzyme logic systems were decreasing the pH value upon appropriate combinations of the biochemical signals corresponding to the AND/OR Boolean logic. Then the pH-switchable electrode was activated for the oxygen reduction, and the entire biofuel cell was switched ON. The biofuel cell was also switched OFF by another biochemical signal which resets the pH value to the original neutral value. The present biofuel cell is the first prototype of a future implantable biofuel cell controlled by complex biochemical reactions to deliver power on-demand responding in a logical way to the physiological needs.

Highly Efficient and Versatile Anodes for Biofuel Cells Based on Cellobiose Dehydrogenase from Myriococcum thermophilum

A powerful alternative to glucose oxidase as anode material in implantable biofuel cells is presented: Cellobiose dehydrogenase (CDH) from the ascomycete Myriococcum thermophilum (MtCDH) catalyzes the electrochemical oxidation of glucose, lactose, and cellobiose over a broad pH range. Current densities of more than 1 mA·cm−2 can be reached when MtCDH is wired to an Os redox polymer in the presence of single-walled carbon nanotubes and when lactose is used as a substrate at pH 8. In contrast to CDHs from basidiomycete fungi, which oxidize only β-1,4-linked di- and oligosaccharides efficiently, MtCDH is also able to oxidize glucose and other monosaccharides at relatively high turnover rates. The current density toward oxidation of 5 mM glucose under physiological conditions was about 100 μA·cm−2. Outstanding properties of MtCDH are high-temperature stability; a strong discrimination of oxygen turnover (and therefore no H2O2 production) in the presence of alternative electron acceptors; an ability to oxidize a range of carbohydrates, and a working pH from 3 to 10, which allows for combination with a variety of enzyme-based cathodes for oxygen reduction. The performance and stability of a membraneless glucose biofuel cell consisting of an MtCDH-modified anode and a Pt black cathode working under physiological conditions (PBS buffer, pH 7.4, 37 °C) were investigated over a period of 3 days. A maximum voltage of 500 mV, a maximum current density of almost 700 μA·cm−2, and a maximum power density of 157 μW·cm−2 at an operating voltage of 280 mV (under oxygen purging/nonquiescent conditions) could be obtained with glucose (100 mM) as the substrate. Furthermore, the direct and mediated electron-transfer properties of MtCDH are compared in this work. The electrocatalytic current detected for mediated electron transfer (MET) is much higher and starts at a less positive potential than that for direct electron transfer (DET). The reason is that, in MET, the Os redox polymer is able to collect the electrons from the catalytically active flavin domain, whereas DET requires the oxidation of the heme domain, which has a more positive redox potential. The electrocatalytic current densities for DET and MET are significantly increased in the presence of single-walled carbon nanotubes.

A special type of raney-alloy catalyst used in compact biofuel cells

In developing implantable biofuel cells to generate higher power it is essential to prepare very thin and highly active electrodes in order to produce the required energy in as small a volume as possible. A method has been developed for glucose electrodes which enables us to produce firmly adhering active layers on very thin foils (up to 50 μn) of homogeneous alloys, containing platinum and a ferrous metal, by controlled anodic dissolution of the non-noble metal. Such electrodes are roughly 10 to 20 times more active than conventional glucose anodes. The activity is remarkably increased by the addition of tungsten and tantalum to the alloy. So far it has been possible to transfer 17 out of the 24 available electrons of the glucose molecule.