Search

Abstract In this study, a novel carbon tube was prepared by carbonizing a rectangular polypyrrole (RPPy) tube at a high temperature for the construction of enzymatic biofuel cells with high performance. SEM and TEM images clearly showed that the initial PPy presented a rectangular tube shape, while the carbonized PPy became a shriveled rectangular tube with a concave surface, which might be beneficial for enzyme immobilization and electrochemical applications. The glucose oxidase (GOx)- or laccase (Lac)-modified electrodes based on carbonized RPPy exhibited excellent bioelectrochemical performance. In addition, a biofuel cell (GOx, glucose/O 2 , Lac) was assembled, and the open-circuit voltage reached 1.16 V. The maximum power density was measured to 0.350 mW cm−2, which correlated to the gravimetric power density of 0.265 mW mg−1 (per mg of GOx) at 0.85 V. The constant-current discharge method was used to further evaluate the continuous discharge capacity. The discharge time reached 49.9 h at a discharge current of 0.2 mA before the voltage was lower than 0.8 V. Furthermore, three of the fabricated biofuel cells in series were able to continually light up a white light-emitting diode (LED) whose turn-on voltage was ca. 2.4 V for more than 48 h. This study suggests that carbonized conducting polymers may become a useful electrode material for the development of enzymatic biofuel cells. Highlights • A shriveled rectangular carbon tube with the concave surface was prepared for enhanced enzymatic biofuel cell. • The unit of power density, mW mg−1 (per mg of enzyme), was adopted for characterization of EBFCs. • The constant-current discharge method was used for further evaluating the EBFCs on continuous discharge capacity. [ABSTRACT FROM AUTHOR]

Abstract MWCNT-COOH, TEMPO-modified linear poly(ethylenimine), and alcohol (ADH) and aldehyde (AldDH) dehydrogenase immobilization on electrode surfaces yields a hybrid, tri-catalytic architecture that can catalyze complete ethanol electro-oxidation. The chromatographic results obtained for the tri-catalytic hybrid electrode system show that ethanol is totally oxidized to CO 2 after 12 h of electrolysis, confirming that organic oxidation catalysts combined with enzymatic catalysts enable collection of up to 12 electrons from ethanol. The Faradaic efficiency lies above 60% for all of the electrode systems investigated herein. Overall, this study illustrates that surface-immobilized, polymer hydrogel-based hybrid multi-catalytic systems exhibit high oxidation rates and constitute a simple methodology with useful application in the development of enzymatic biofuel cells. Graphical abstract fx1 Highlights • The hybrid catalytic system is able to ethanol C-C bond. • The tri-catalytic hybrid electrode showed only CO 2 from ethanol oxidation. • The prepared bioelectrode enable collection of up to 12 electrons from etanol. [ABSTRACT FROM AUTHOR]

Enzymatic biofuel cells can generate electricity directly from the chemical energy of biofuels in physiological fluids, but their power density is significantly limited by the performance of the cathode which is based on oxygen reduction for in vivo applications. An oxygen-independent and membrane-less glucose biobattery was prepared that consists of a dealloyed nanoporous gold (NPG) supported glucose dehydrogenase (GDH) bioanode, immobilised with the assistance of conductive polymer/Os redox polymer composites, and a solid-state NPG/MnO 2 cathode. In a solution containing 10 mM glucose, a maximum power density of 2.3 µW cm −2 at 0.21 V and an open circuit voltage (OCV) of 0.49 V were registered as a biobattery. The potential of the discharged MnO 2 could be recovered, enabling a proof-of-concept biobattery/supercapacitor hybrid device. The resulting device exhibited a stable performance for 50 cycles of self-recovery and galvanostatic discharge as a supercapacitor at 0.1 mA cm −2 over a period of 25 h. The device could be discharged at current densities up to 2 mA cm −2 supplying a maximum instantaneous power density of 676 μW cm −2 , which is 294 times higher than that from the biobattery alone. A mechanism for the recovery of the potential of the cathode, analogous to that of RuO 2 (Electrochim. Acta 42(23), 3541–3552) is described. [ABSTRACT FROM AUTHOR]

A three-dimensional architecture of PANI@GO hybrid was synthesized via in-situ polymerization of aniline monomers on the surface of graphene oxide (GO) and carbonized at 1600 °C. The SEM images showed that surfaces of planar GO were covered by a compact nanofiber-like polyaniline (PANI) layer which presented an interconnected network. Nanofiber-like PANI on the GO surface was mostly preserved and became the carbon nanofibers (CNFs) after carbonization. The TEM images showed that the carbonized PANI grew seamlessly on the GO surface and served as conductive “network” between interlayers of GO. The carbonized PANI@GO hybrid was used to modify a glassy carbon electrode (GCE) based on GOx, resulting in efficient direct electron transfer (DET) and excellent bio-catalytic performance. In addition, a glucose/O 2 fuel cell constructed using Nafion/GOx/PANI 1600 @GO/GCE as the anode and an E-TEK Pt/C modified GCE as the cathode generated a maximum power density of 0.756 mW cm −2 at 0.42 V. Findings in this study may be helpful for exploiting novel materials for immobilization of enzymes through carbonizing conducting polymers or their composites with inorganic materials at high temperature for applications in enzymatic biofuel cells or biosensors. [ABSTRACT FROM AUTHOR]

It is essential to construct a biofuel cell-based sensor and develop an effective strategy to detect glucose without any potentiostat circuitry in order to create a simple and miniaturized device. In this report, an enzymatic biofuel cell (EBFC) is fabricated by the facile design of an anode and cathode on a screen-printed carbon electrode (SPCE). To construct the anode, thionine and flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) are covalently immobilized via a crosslinker to make a cross-linked redox network. As a cathode, the Pt-free oxygen reduction carbon catalyst is employed alternative to the commonly used bilirubin oxidase. We proposed the importance of EBFC-based sensors through the connection of anode and cathode; they can identify a short-circuit current by means of applied zero external voltage, thereby capable of glucose detection without under the operation of the potentiostat. The result shows that the EBFC-based sensor could be able to detect based on a short-circuit current with a wide range of glucose concentrations from 0.28 to 30 mM. Further, an EBFC is employed as a one-compartment model energy harvester with a maximum power density of (36 ± 3) μW cm− 2 in sample volume 5 μL. In addition, the constructed EBFC-based sensor demonstrates that the physiological range of ascorbic acid and uric acid shows no significant effect on the short-circuit current generation. Moreover, this EBFC can be used as a sensor in artificial plasma without losing its performance and thereby used as a disposable test strip in real blood sample analysis. [ABSTRACT FROM AUTHOR]

Recent advances in enzymatic biofuel cells (EBFCs) have resulted in great progress in health monitoring and supplying power to medical applications, such as drug delivery. On the other hand, to enhance the electric field-assisted transdermal permeation for facial mask application, an external power source is usually required. Herein, we attempted to combine an EBFC with a facial mask so that the microcurrent generated can boost the transdermal permeability of target molecules in the facial mask essence. When screen-printed onto a polypropylene-based non-woven fabric, the three-layered flexible EBFC could produce a voltage of ∼0.4 V and a maximum power density of 23.3 μW cm−2, leading to an approximately 2–3-fold increase in permeated nicotinamide, arbutin, and aspirin levels within 15 min compared to non-iontophoretic transdermal drug delivery. Both cell viability and animal experiments further demonstrated that the EBFC-powered iontophoresis worked well in living animals with good biocompatibility. These results suggest that the EBFC-powered iontophoretic facial mask can effectively improve the permeation of drugs and holds a promise for the possible cosmetic application. [ABSTRACT FROM AUTHOR]

It is important to develop effective strategies to construct enzymatic biofuel cell based self-powered biosensors. We report here the facile regulation of enzymatic loading capacity on the bioanode by utilizing a concatenated catalytic hairpin assembly (CHA)/hybridization chain reaction (HCR) and its application for self-powered microRNA-141 (miRNA-141) detection. To construct the bioanode, a concatenated CHA/HCR process triggered by miRNA-141 was conducted on the three-dimensional macroporous gold (3DMG) electrode to generate long double-stranded DNA nanowires for glucose oxidase immobilization. Quartz crystal microbalance study reveals that the enzymatic loading capacity on the bioanode increases at an increasing miRNA-141 concentration, leading to enhanced catalytic performance for glucose oxidation. The short-circuit currents of the assembled glucose/O 2 biofuel cells increase at increasing miRNA-141 concentrations, enabling ultrasensitive detection of miRNA-141. The self-powered biosensor features a wide dynamic range for detecting miRNA-141 from 10−17 to 10−11 M, with an ultralow detection limit of 1.3 aM. This work provides a highly sensitive self-powered biosensing platform for miRNA detection. [ABSTRACT FROM AUTHOR]

A novel “ON–OFF” switchable enzymatic biofuel cell (EBFC), controlled by in situ thermal-stimuli signal, has been consciously designed. Poly ( N -isopropylacrylamide) (PNIPAm) chains were used to act as “ON” and “OFF” channels. Consecutively switching of temperature below and above the lower critical solution temperature (LCST), the reversible conformation changing of the PNIPAm chains between superhydrophilicity and superhydrophobicity was achieved, which constructed the “ON” and “OFF” channel for the transfer of the electrochemical probe to the underlying electrode correspondingly. Gold nanoparticles (AuNPs) protected glucose oxidase and laccase were successfully entrapped into the intelligent thermal-sensitive PNIPAm chains, and performed as the catalysts for the oxidation of glucose and the reduction of O 2 , respectively. Below the LCST, the fuels and the mediator could access to the catalytic centers of enzymes (set as “ON” state); while above the LCST, the reaction was impeded because the process of reactant transmission was blocked (set as “OFF” state). By switching the “valve” of mass transfer, the fabricated EBFC displayed the obvious “ON–OFF” controllable behavior. At the “ON” state, the open circuit voltage ( E cell ocv ) and maximal power output density ( P max ) could reach to 0.70 V and 20.52 μW cm −2 , respectively; while at the “OFF” state, the E cell ocv and P max were only 0.30 V and 3.28 μW cm −2 correspondingly. The switchable process was repeatable, and the response time was only several minutes. [ABSTRACT FROM AUTHOR]

A contact lens biofuel cell was fabricated using buckypaper electrodes cured on a silicone elastomer soft contact lens. The buckypaper anode consisted of poly(methylene green) and a hydrogel matrix containing lactate dehydrogenase and nicotinamide adenine dinucleotide hydrate (NAD + ). The buckypaper cathode was modified with 1-pyrenemethyl anthracene-2-carboxylate, and then bilirubin oxidase was immobilized within a polymer. Contact lens biofuel cell testing was performed in a synthetic tear solution at 35 °C. The open circuit voltage was 0.413±0.06 V and the maximum current and power density were 61.3±2.9 µA cm −2 and 8.01±1.4 µW cm −2 , respectively. Continuous operation for 17 h revealed anode instability as output current rapidly decreased in the first 4 h and then stabilized for the next 13 h. The contact lens biofuel cell presented here is a step toward achieving self-powered electronic contact lenses and ocular devices with an integrated power source. [ABSTRACT FROM AUTHOR]

We report an Enzymatic Fuel Cell (EFC) combining an enzyme that can cleave carbon-carbon bonds (oxalate oxidase (OxOx)) with an organic catalyst (Pyrene-TEMPO (TEMPO = 2,2,6,6-tetramethyl piperidinyl-N-oxyl)) immobilized on the surface of modified carboxylated multi-walled carbon nanotubes (MWCNT-COOH). This combination gave a hybrid bi-catalyst electrode for complete ethylene glycol (EG) oxidation. The hybrid electrode provided ninefold enhanced catalytic activity (0.17 ± 6 × 10−3 mA cm−2) in the presence of EG as compared to the electrode in the absence of EG (0.018 ± 3 × 10−5 mA cm−2), indicating that the enzyme combined with the organic catalyst improved energy generation through deep EG electrooxidation. Electrochemical impedance spectroscopy reveals that the addition of the enzyme in the electrode containing MWCNT–COOH–Pyrene-TEMPO increased the charge transfer resistance (R c t ) and the capacitance of the double layer. Long-term electrolysis for 15 h showed that the hybrid electrode presented outstanding current density and stability. The EG oxidation products were identified and quantified by high-performance liquid chromatography (HPLC-UV/RID). The results confirmed complete EG oxidation in the presence of CO 2 in the solution, allowing 10 electrons to be collected from the fuel. Overall, this study illustrates the development of a simple and improved hybrid bi-catalyst electrode for promising applications in small electronic devices. [ABSTRACT FROM AUTHOR]

We report here an alcohol oxidase (AOx) based third generation bioanode for generating power from methanol substrate in a fuel cell setup using air breathed laccase biocathode. A composite three dimensional microporous matrix containing multiwalled carbon nanotubes, carbon paste and nafion was used as electroactive support for immobilization of the enzymes on toray carbon paper as supporting electrode in the fabrication of the bioelectrodes. Polyethylenimine was used to electrostatically stabilize the AOx (pI 4.3) on the anode operating on direct electrochemistry principle. Osmium tetroxide on poly (4-vinylpyridine) was used to wire the laccase for electron transfer in the biocathode. The enzymatic biofuel cell (EFC) generated an open circuit potential of 0.61 (±0.02) V with a maximum power density of 46 (±0.002)µWcm−2 at an optimum of 1M methanol, 25°C and an internal resistance of 0.024µΩ. The operation and storage half life (t 1/2) of the EFC were 17.22h and 52 days, respectively at a fixed load of 1.85Ω. The findings have demonstrated the feasibility of developing EFC using AOx based bioanode and laccase based biocathode without applying any toxic free mediator and metal electrode supports for generating electricity. [ABSTRACT FROM AUTHOR]

Direct electron transfer (DET) of enzymes on electrode surfaces is highly desirable both for fundamental mechanistic studies and to achieve membrane- and mediator-less bioenergy harvesting. In this report, we describe the preparation and comprehensive structural and electrochemical characterization of a three-dimensional (3D) graphene-based carbon electrode, onto which the two-domain redox enzyme Myriococcum thermophilum cellobiose dehydrogenase (Mt CDH) is immobilized. The electrode is prepared by an entirely novel method, which combines in a single step electrochemical reduction of graphene oxide (GO) and simultaneous electrodeposition of positively charged polyethylenimine (PEI), resulting in a well dispersed Mt CDH surface. The resulting Mt CDH bio-interface was characterized structurally in detail, optimized, and found to exhibit a DET maximum current density of 7.7 ± 0.9 μA cm−2 and a half-lifetime of 48 h for glucose oxidation, attributed to favorable Mt CDH surface orientation. A dual, entirely DET-based enzymatic biofuel cell (EBFC) was constructed with a Mt CDH bioanode and a Myrothecium verrucaria bilirubin oxidase (Mv BOD) biocathode. The EBFC delivers a maximum power density (P max) of 7.6 ± 1.3 μW cm−2, an open-circuit voltage (OCV) of 0.60 V, and an operational lifetime over seven days, which exceeds most reported CDH based DET-type EBFCs. A biosupercapacitor/EBFC hybrid was also constructed and found to register maximum power densities 62 and 43 times higher than single glucose/air and lactose/air EBFCs, respectively. This hybrid also shows excellent operational stability with self-charging/discharging over at least 500 cycles. [ABSTRACT FROM AUTHOR]

Enzymatic biofuel cell (EBFC)-based self-powered biochemical sensors obviate the need for external power sources thus enabling device miniaturization. While recent efforts driven by experimentalists illustrate the potential of EBFC-based sensors for real-time monitoring of physiologically relevant biochemicals, a robust mathematical model that quantifies the contributions of sensor components and empowers experimentalists to predict sensor performance is missing. In this paper, we provide an elegant yet simple equivalent circuit model that captures the complex, three-dimensional interplay among coupled catalytic redox reactions occurring in an EBFC-based sensor and predicts its output signal with high correlations to experimental observations. The model explains the trade-off among chemical design parameters such as the surface density of enzymes, various reaction constants as well as electrical parameters in the Butler–Volmer relationship. The model shows that the linear dynamic range and sensitivity of the EBFC-based sensor can be independently fine-tuned by changing the surface density of enzymes and electron mediators at the anode and by enhancing reductant concentrations at the cathode. The mathematical model derived in this work can be easily adapted to understand a wide range of two-electrode systems, including sensors, fuel cells, and energy storage devices. • This work provides an elegant yet simple model for EBFC-based sensor. • An equivalent circuit method self-consistently includes the role of cathode reactions. • The oxygen starvation effect should be carefully handled for EBFC-based sensor applications. • The theoretical approach can be adapted to a wide range of two-electrode systems. [ABSTRACT FROM AUTHOR]

To realize direct power generation from biofuels in natural organisms, we demonstrate a needle-type biofuel cell (BFC) using enzyme/mediator/carbon nanotube (CNT) composite fibers with the structure Osmium-based polymer/CNT/glucose oxidase/Os-based polymer/CNT. The composite fibers performed a high current density (10 mA/cm2) in 5 mM artificial blood glucose. Owing to their hydrophilicity, they also provided sufficient ionic conductivity between the needle-type anode and the gas-diffusion cathode. When the tip of the anodic needle was inserted into natural specimens of grape, kiwifruit, and apple, the assembled BFC generated powers of 55, 44, and 33 μW from glucose, respectively. In addition, the power generated from the blood glucose in mouse heart was 16.3 μW at 0.29 V. The lifetime of the BFC was improved by coating an anti-fouling polymer 2-methacryloyloxyethyl phosphorylcholine (MPC) on the anodic electrode, and sealing the cathodic hydrogel chamber with medical tape to minimize the water evaporation without compromising the oxygen permeability. • Needle –type biofuel cell (BFC) was developed with flexible enzyme/mediator/CNT fibers for direct power generation from glucose in natural organisms. • The bioanode for glucose oxidation and oxygen-diffusion biocathode fibers are prepared through modification with glucose oxidase and bilirubin oxidase, respectively, on CNT decorated carbon fibers. • Both biofibers are assembled to the needle BFC and generate a power (55 μW, 44 μW, 33 μW, 8.5 μW, and 16.3 μW) from glucose in grape, kiwifruit, apple, mouse abdominal cavity, and its heart, respectively. [ABSTRACT FROM AUTHOR]

The work presented herein demonstrates a hybrid bi-catalytic architecture for the complete electrochemical oxidation of ethanol. The new catalytic system contains pyrene-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidinyl-N-oxyl) immobilized on the surface of carboxylated multi-walled carbon nanotubes (MWCNT-COOH), and oxalate decarboxylase enzyme (OxDc) immobilized onto a carbon cloth electrode. Electrolysis revealed a stable amperometric curve and an excellent current density value over a duration of 10 h. In addition, the hybrid system immobilized on the carbon electrode exhibits outstanding stability after electrolysis. Nuclear magnetic resonance (NMR) and gas chromatography (GC) demonstrate that the hybrid electrode system is able to oxidize ethanol to CO 2 after 10 h of electrolysis. Overall, this study illustrates the enhancement of an enzymatic biofuel cell through the hybrid multi-catalytic systems, which exhibit high oxidation rates for all substrates involved in complete ethanol oxidation, enabling the collection of up to 12 electrons per molecule of ethanol. Image 1 • This bi-catalytic architecture system showed excellent electrocatalytic performance. • The hybrid system exhibit good stability during long term electrolysis. • The enzymatic/organic system allows for the enhancement of complete ethanol oxidation. • The multi-catalytic electrode enable collection of up to 12 electrons from ethanol. • The new system represents a promising advancement in the bioelectrochemistry. [ABSTRACT FROM AUTHOR]