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This research aims to improve the output power of self-pumping glucose enzymatic biofuel cell (EBFC) and modifying the anode. Adding a fixed ratio of methyl red-chitosan (MR-CS) can effectively improve the EBFC efficiency and stability. In addition, chitosan can be obtained from discarded crustacean fishery waste objects such as shrimp and oysters, are also significant to the use of environmentally friendly materials. The catalyst was immobilized on pyrenecarboxaldehyde (PCA), polyethyleneimine (PEI) and multi-wall carbon nanotubes (MWCNT) and combined with glucose oxidase (GOx). Finally, the [PCA/GOx]/PEI/Nafion solution/MWCNT/[MR-CS] catalyst was immobilized on the carbon cloth. Experimental analysis was progressed under the preparation of enzyme-supported electrode to observe the feasibility of the anode electrode. Experiment including Fourier transform infrared spectroscopy (FTIR) to analyze the distribution of functional groups after modification of the carbon cloth electrode, and through the comparison of the ultraviolet–visible spectrometer (UV–Vis), it can be known that the concentration ratio of [MR-CS] is 1:5, the glucose oxidase load can be maximized. Electrochemical analysis (Cyclic Voltammetry, CV) measures the activity of the maximum reaction of the anode material and the corresponding redox peak, and scanning electron microscope (SEM) observes the surface morphology of the modified electrode. Self-pumping glucose enzymatic biofuel cell module was assembled and examined, the results showed that the maximum output power density (MPD) was 2.64 mW/cm2.

The electrode materials play extremely important roles in building the interfacial electron communications between the active sites of enzymes and the electrode surface, which significantly affect the performance of an enzymatic biofuel cell (EBFC). Herein, defective porous carbon is rationally designed and prepared using asphalt as the low-cost and high-carbon-yield precursor via a facile catalytic pyrolysis and NH3-etching process. The obtained defective asphalt-derived carbon (D-ADC) is utilized as the electrode material to immobilize enzymes and mediators in EBFC applications. It is found that the morphology and structure of ADC can be regulated by the catalytic pyrolysis and NH3-etching processes, which greatly increase the electroactive sites and specific surface area, thus enhancing the catalytic reaction kinetics. Specifically, the fabricated EBFC using D-ADC as the electrode material exhibits an open circuit voltage of 0.58 V and delivers a maximum output power density of 0.32 mW cm-2 with a short circuit current density of 1.12 mA cm-2, comparable to those using conventional graphene and carbon nanotubes. This work offers guidance for the design of functional carbon materials in the application of EBFCs, which has the potential to improve the sustainability and economic efficiency of waste asphalt. [ABSTRACT FROM AUTHOR]

Glucose oxidase based enzymatic biofuel cell is the promising technology for implantable medical devices' power supply. It can open up opportunities for the long‐term implantation of the medical devices like pacemakers without the necessity for replacement of the batteries. Increasing of the cathode efficiency is one of the issues that should be solved before a practical application of biofuel cells. The high catalytic activity of the cathode provides a significant contribution to the efficiency of biofuel cells operation. The creation of cathodes of implantable biofuel cell with the increased power density could resolve the problem with a slow kinetics of the cathodic oxygen reduction reaction. It is especially urgent in the conditions of implantation in physiological fluids, where the oxygen concentration is relatively low. Enzymes application could be an optimal way to increase an efficiency of the cathodic reaction, but enzymes long‐time stability is still in question. Thus, non‐organic and synthetic organic catalysts are considered. In this study, a new type of a cathode for enzymatic biofuel cells is presented. This cathode combines two catalysts: inorganic with platinum nanoparticles (PtNPs) and organic in the form of poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) cross‐linked by poly(ethylene glycol) diglycidyl ether (PEGDE). The received electrodes were investigated by several electrochemical methods: cyclic voltammetry, chronopotentiometry and linear sweep voltammetry method on a rotating disk electrode. It was shown that the combination of PtNPs and PEDOT:PSS provides the maximum cathodic current, due to the fact that both catalysts contribute to the oxygen reduction reaction. The maximum cathodic current was 7.5 μA for an electrode containing 5 % PEGDE with PtNPs, heat‐treated for one hour at 120 °C. The electrodes without platinum nanoparticles were also investigated. This research showed that PEDOT:PSS provides a significant contribution to the overall catalytic effect demonstrated by the electrode proposed in the study. Scanning electron microscopy and X‐ray fluorescence analysis studies showed that the electrodes with combination of PtNPs and PEDOT:PSS were almost fully covered by catalysts. [ABSTRACT FROM AUTHOR]

We describe an enzymatic fuel cell (EFC) that can electrooxidize glucose completely. The EFC contains the hybrid Ni@Pt-CNT/OxOx bioanode, composed of a bimetallic composite catalyst (Ni@Pt-CNT) and the enzyme oxalate oxidase (OxOx), which can cleave carbon-carbon bonds. Ni@Pt-CNT/OxOx displayed 3-fold higher catalytic activity in the presence than in the absence of glucose (1.3 and 0.4 mA cm−2, respectively), indicating that Ni@Pt-CNT and OxOx acted synergistically. Electrochemical impedance spectroscopy showed that Ni@Pt-CNT/OxOx had higher charge transfer resistance and double layer capacitance than Ni@Pt-CNT. Long-term bulk electrolysis (18 h) revealed that the EFC operating with Ni@Pt-CNT/OxOx presented better current density and stability than the electrochemical cell operating with Ni@Pt-CNT, so deep glucose electrooxidation generated energy. The glucose oxidation products detected by HPLC-UV/RID confirmed that glucose was fully electrooxidized, and that 24 electrons were harvested from it. The hybrid Ni@Pt-CNT/OxOx bioanode developed herein could be used in cascade reactions, to provide an EFC with promising application in self-powered electronic devices.

Owing to the high efficiency and specificity in moderate conditions, enzymatic biofuel cells (EBFCs) have gained significant interest as a promising energy source for wearable devices. However, the instability of the bioelectrode and the lack of efficient electrical communication between the enzymes and electrodes are the main obstacles. Herein, defect-enriched 3D graphene nanoribbons (GNRs) frameworks are fabricated by unzipping multiwall carbon nanotubes, followed by thermal annealing. It is found that defective carbon shows stronger adsorption energy towards the polar mediators than the pristine carbon, which is beneficial to improving the stability of the bioelectrodes. Consequently, the EBFCs equipped with the GNRs exhibit a significantly enhanced bioelectrocatalytic performance and operational stability, delivering an open-circuit voltage and power density of 0.62 V, 70.7 μW/cm2, and 0.58 V, 18.6 μW/cm2 in phosphate buffer solution and artificial tear, respectively, which represent the high levels among the reported literature. This work provides a design principle according to which defective carbon materials could be more suitable for the immobilization of biocatalytic components in the application of EBFCs. [ABSTRACT FROM AUTHOR]

For enzyme-based electrochemical devices, an improvement in electron transfer between the enzyme and electrode is important. Thus, we developed a nano-scaled hydrogel that includes an electron mediator and enzyme to realize nano-sized effects that enhance the functions. Three different chain lengths (short, medium, and long) of copolymers composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) and methacrylic acid N -hydroxysuccinimide ester (MNHS; poly(MPC- co -MNHS), PMS) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The PMS nanogels can bind to the amino ferrocene (AFc) of the electron mediator and glucose oxidase (GOD) as a catalyst. The mono-dispersive PMS nanogels approximately 200–250 nm in size bound with AFc were prepared with different polymer chain lengths and amounts of AFc (PMMFc X _ Y %, X = 'degree of polymerization, 50, 75, 100' and Y = 'AFc feeding ratio against the amount of NHS group in the polymer chain, 50 %, 100 %'). The size of PMMFc X _ Y % could be controlled by changing degree of polymerization or AFc feeding ratio. After the modification of GOD to PMMFc X _ Y %, their size increased slightly from the original size (ca. 200–250 nm) to approximately 250–300 nm. The catalytic activity of nanogel in dispersed system was higher than that of microgel, indicating that nanogels could improve glucose transport in hydrogel layer. Compared to the catalytic reaction of the PMMFc 75_50 %-GOD nanogel-modified electrodes with that of microgel modified electrode, the current response was improved by decreasing the nanogel size, as evaluated by electrochemical measurements. These results revealed that the smaller nanogels could improve both glucose transport and electron transfer via mediator by smaller size, resulting higher efficiency of enzyme immobilized electrode. [Display omitted] • Size of the nanogel was controlled by changing chain length or redox unit amount. • Enzyme was modified on the zwitterionic redox nanogel. • Nanogel with enzyme improved glucose transport and electron transfer by smaller size. [ABSTRACT FROM AUTHOR]

• CNT/3DG hybrid is a suitable supporting material for enzyme immobilization. • CNT/3DG/Gox/GCE fabricate a modified bioanode in a glucose/O 2 EBFC. • maximum power density of 253.36 µWcm-2 at 0.65 V is harvested. • The immobilized GOx lifetime was increased to 210 days. Long-lasting, high-performance enzymatic biofuel cells (EBFCs) are among the most promising candidates for renewable and green power generation. There are two main drawbacks to EBFCs: 1) short enzyme lifetime due to the enzyme's (protein) denaturation; and 2) low electron transfer efficiency as the enzyme's active site is deeply buried inside the non-conductive protein structure of the enzyme. In this study, a hybrid of carbon nanotubes (CNT) and three-dimensional graphene (3DG) was used to immobilize the glucose oxidase (GOx) on the surface of a glassy carbon electrode (GCE) to fabricate a modified bioanode in a glucose/O 2 EBFC. This facile and low-cost CNT/3DG hybrid is a solution to the problems of instability, short lifespan, and poor electron transport in EBFCs. The exceptional electrocatalytic activity of the porous CNT/3DG hybrid is demonstrated by its effective immobilization of GOx and ability to collect energy from glucose oxidation by direct electron transfer (DET) while preserving the structure of the enzyme. The CNT acts like a tiny electrical wire that reaches and harvests the electron directly from the flavin adenine dinucleotide (FAD) (the redox center of GOx) and transfers it to the electrode surface, thus enhancing the performance of the EBFC. The immobilized GOx lifetime was increased to 210 days with a maximum power density of 253.36 µWcm-2 at 0.65 V. These results demonstrate the attractive capability of the CNT/3DG hybrid in the development of efficient biofuel cells and biosensors that employ enzymes in their structures. [Display omitted] [ABSTRACT FROM AUTHOR]

Electrochemical biosensors, in which enzymatic biofuel cells simultaneously work as energy power and signal generators, have become a research hotspot. They display the merits of power self-support, a simplified structure, in vivo operational feasibility, online and timely monitoring, etc. Since the concept of enzymatic biofuel cell-powered biosensors (EBFC-SPBs) was first proposed, its applications in health monitoring have scored tremendous achievements. However, the creation and practical application of portable EBFC-SPBs are still impeded by the difficulty in their miniaturization. In recent years, the booming microfluidic technology has powerfully pushed forward the progress made in miniaturized and portable EBFC-SPBs. This brief review recalls and summarizes the achievements and progress made in miniaturized EBFC-SPBs. In addition, we also discuss the advantages and challenges that microfluidic and screen-printing technologies provide to wearable and disposable EBFC-SPBs. [ABSTRACT FROM AUTHOR]

Enzymatic biofuel cells (EBCs) represent a promising technology for biosensors, biodevices, and sustainable green energy applications, thanks to enzymes' high specificity and catalytic efficiency. Nevertheless, drawbacks such as limited output power and short lifetime have to be solved. Nowadays, research is addressed to the use of 3D electrode structures, but the high cost and the industrialization difficulties of such electrodes represent a key issue. The purpose of the paper is thus to describe the use of a low-cost commercial conductive polymer (Sigracell® PV15) as support for the covalent immobilization of glucose oxidase and laccase, for bioanode and biocathode fabrication, respectively. Efficient immobilization protocols were determined for the immobilized enzymes in terms of employed linkers and enzyme concentrations, resulting in significant enzymatic activities for units of area. The analysis focuses specifically on the optimization of the challenging immobilization of laccase and assessing its stability over time. In particular, an optimum activity of 23 mU/cm2 was found by immobilizing 0.18 mg/cm2 of laccase, allowing better performances, as for voltage output and electrochemical stability, and a direct electron transfer mechanism to be revealed for the fabricated biocathode. This study thus poses the basis for the viable development of low-cost functional EBC devices for biomedical applications. [ABSTRACT FROM AUTHOR]

A biofuel cell is an electrochemical device using exoelectrogen or biocatalysts to transfer electrons from redox reactions to the electrodes. While wild-type microbes and natural enzymes are often employed as exoelectrogen and biocatalysts, genetically engineered or modified organisms have been developed to enhance exoelectrogen activity. Here, we demonstrated a redox-enzyme integrated microbial fuel cell (REI-MFC) design based on an exoelectrogen-enhancing strategy that reinforces the electrogenic activity of Shewanella oneidensis MR1 by displaying an extra redox enzyme on the cell surface. We constructed the cell-surface display system for Shewanella oneidensis MR-1 by porting the autotransporter of Escherichia coli into the MR-1 strain. The functionality of the display system was validated by examining the various enzymes displayed on the cell surface of S. oneidensis MR-1. The implementation of the REI-MFC design was accomplished by an engineered MR-1 strain displaying a redox enzyme originating from swine NADH-cytochrome b5 reductase 3 (B5R3). At the polarization test of enhanced exoelectrogen in an operating MFC environment, the current generation (Δ I a , peak: 10.4 ± 1.9 μA) of the MR-1 displaying B5R3 was 4.7-fold higher than that of wild-type MR-1 (2.2 ± 0.3 μA). The maximum charge transfer resistance ( R ct ) under the optimized electrochemical test conditions was 70% lower than the wild-type MR-1. The cell surface display system for S. oneidensis MR-1 exploited in this study facilitated the exoelectrogen activity in the REI-MFC design.

Enzymatic biofuel cells (EBFCs) are a subgroup of fuel cells that use enzymes as catalysts. EBFCs that utilize physiological substrates such as glucose or lactate are of great interest as implantable or wearable power sources to activate medical devices. This contribution introduces the working principles of EBFCs and summarizes recent progress in EBFC-enabled biosensors, pulse generators, and therapy. Biosensors with self-powered characteristic enjoy high selectivity, leading to potential “instrument-free” or “expensive-instrument-free” measurement. Autonomous pulse generation is based on the hybrid of EBFC and supercapacitor, which is promising for the application in medical related electrostimulation. By providing the direct electrical stimulation, or controllably releasing drug, EBFCs can also be used for self-powered therapeutic system. The further combination of self-powered sensing and treating enables EBFC as a possible platform of diagnostics and therapeutics. Future efforts can be focused on resolving the limited power density and lifetime of EBFC.

This study describes the development of an ethylene glycol (EG) biofuel cell that combines the organic catalyst 4‐amino‐TEMPO (TEMPO‐NH2) and the enzyme oxalate oxidase (OxOx) in solution for complete EG oxidation. Cyclic voltammetric curves recorded in the presence of EG showed that the hybrid TEMPO‐NH2/OxOx catalyst provided 1.2 higher current density than the TEMPO‐NH2 catalyst. Chronoamperometric assays after successive EG injections and long‐term electrolysis at a fixed potential of 0.75 V (vs Ag/AgCl) showed that the hybrid TEMPO‐NH2/OxOx catalyst in the presence of EG promoted 14 % and 58 % increase in the current obtained with the TEMPO‐NH2 catalyst, respectively. High‐performance liquid chromatography (HPLC) results confirmed that TEMPO‐NH2 and OxOx respectively acted on EG oxidation and C−C bond cleavage, leading to complete EG oxidation, harvesting all 10 of the EG electrons and high catalytic activity. [ABSTRACT FROM AUTHOR]

Enzymatic Biofuel Cell (EBC) represents a promising green source since it is capable of harvesting electricity from renewable and abundantly available biofuels using enzymes as catalysts. Nevertheless, nowadays long-term stability and low power output are currently the main concerns. To this end, several research studies focus on using complex tridimensional and highly expensive nanostructures as electrode support for enzymes. This increases cell performance whilst drastically reducing the economic feasibility needed for industrial viability. Thus, this paper analyzes a novel flow-based EBC consisting of covalent immobilized GOx (bioanode) and Laccase (biocathode) on a commercial flat conductive polymer. A suitable immobilization technique based on covalent ligands is carried out to enhance EBC durability. The experimental characterization demonstrates that the cell generates power over three weeks, reaching 590 mV and 2.41 µW cm−2 as maximum open circuit voltage and power density, respectively. The most significant contributions of this configuration are definitely ease of implementation, low cost, high scalability, and reproducibility. Therefore, such a design can be considered a step forward in the viable EBC industrialization process for a wide range of applications. [ABSTRACT FROM AUTHOR]

Abstract Background Diaphorase (DI) has received wide attention as the key anodic enzyme mediating the electron transfer and electric energy generation in enzymatic biofuel cells (EBFCs). Lowering the anodic pH may be a useful strategy for constructing high-performance in EBFCs. However, most DI suffered from the poor activity at low pHs. Therefore, it is necessary to modify the activity and its acidic tolerance to further improve the performance of the EBFC. Results This paper attempts to improve the enzyme activity of DI originated from Geobacillus stearothermophilus under acidic conditions through directed evolution. Three rounds of random mutagenesis by error-prone PCR of the GsDI gene followed by high-throughput screening allowed the identification of the mutant 3–8 (H37Q, S73T, F105L, S68T, G61S, D74V) exhibiting a 4- or 7-fold increase in the catalytic activity at pH 5.4 or 4.5 compared to that of the wild type. And the pH stability of mutant 3–8 was significantly better than that of wild type and showed a 1.3 times higher in the stability at pH 5.4. The EBFC anode equipped with 0.5 mg of mutant 3–8 achieved a maximum current of 40 μA at pH 5.4, much higher than that with the same loading of the wild type enzyme. Conclusion The GsDI has been improved in the specific activity and pH stability by directed evolution which leads to the improvement of the EBFC performance. Also, the enlarged catalytic channel of mutant and decreased B-factor may be beneficial for the activity and stability. These results suggest that this engineered DI will be a useful candidate for the construction of enhanced EBFCs.

A mathematical model describing the reduction of Hydrogen peroxide (H2O2) to water in a metal dispersed conducting polymer film is discussed. The model is based on a system of reaction-diffusion equations containing a non-linear term related to Michaelis-Menten kinetics of the enzymatic reaction. The approximate analytical expressions corresponding to the concentration of substrate and product for steady and non-steady state conditions have been obtained using a new approach to homotopy perturbation method (HPM). Approximate analytical expressions of the electrochemical oxidation current are also presented for steady and non-steady state conditions. The numerical simulation (Matlab program) response for concentration profiles was carried out and compared with the analytical results of this work and are found to be in good agreement. The influence of initial substrate concentration, the thickness of the film as well as the diffusion layer and kinetic parameters on the current response were investigated. A graphical procedure for estimating the kinetic parameters from the expression of the current response is also proposed.

Summary: Hollow cobalt nitrogen‐doped carbon (H‐CoNC) is suggested for use in the membraneless hydrogen peroxide fuel cell (HPFC) and enzymatic biofuel cell (EBC) as anodic catalyst boosting hydrogen peroxide oxidation reaction (HPOR). For fabricating H‐CoNCs, a facile spray pyrolysis‐assisted process is used, and such produced H‐CoNCs show a porous and hollow‐shell structure, while they include a large amount of isolated Co atoms and coordinate bonds with Co and nitrogen (CoN4). This structure promotes mass transfer to the active site and excellent catalytic activity for HPOR. With these benefits of H‐CoNCs, the current density of the bioanode consisting of H‐CoNC, carbon nanotube, and glucose oxidase (H‐CoNC/CNT/GOx) observed at 0.3 V under 150 mM glucose is 315.5 μA cm−2, which is 2.1 times higher than that of a conventionally synthesized catalyst using Co‐doped carbon nanoparticles (CoNC‐NPs) (CoNC‐NPs/CNT/GOx, 146.2 μA cm−2). With this superior catalytic activity for HPOR, maximum power density (MPD) of membraneless EBC using H‐CoNC/CNT/GOx is 33.8 ± 4.52 μW cm−2, which is 52% higher than that of CoNP‐NPs/CNT/GOx. In addition, a membraneless HPFC using H‐CoNC/CNT demonstrates 4.87 times higher MPD (231.3 ± 11.3 μW cm−2) than that using CoNC‐NPs/CNT, proving that H‐CoNC improves the performance of fuel cells by its excellent catalytic activity. [ABSTRACT FROM AUTHOR]

The electrode material is a pivotal component in achieving efficient electron transfer in an enzymatic biofuel cell (EBFC). Herein, novel hydrophilic carbon fibers (HCFs) with a helical structure are synthesized through chemical vapor deposition and are used as an electrode material for the immobilization of biocatalysts to fabricate bioelectrodes, where glucose dehydrogenase, serving as the anodic enzyme, is co‐immobilized with 1,4‐naphthoquinone on the HCFs for the catalysis of the glucose oxidation reaction (GOR), and bilirubin oxidase, as the cathodic enzyme, is co‐immobilized with protoporphyrin IX for the catalysis of the oxygen reduction reaction (ORR). It is found that thermal annealing the HCFs improves the bioelectrocatalytic performances of the as‐fabricated bioanode for the GOR and biocathode for the ORR, owing to the enhanced electron transfer kinetics. Subsequently, a membraneless glucose/O2 EBFC assembled by using the as‐synthesized bioelectrodes is able to generate a high open circuit voltage of 0.8 V and a maximum power density of 0.7 mW cm−2 at 0.44 V with good operational stability. The practicability in fabricating membraneless EBFCs makes the synthesized HCFs promising in miniature bioenergy devices. [ABSTRACT FROM AUTHOR]

Electrochemical biosensors, in which enzymatic biofuel cells simultaneously work as energy power and signal generators, have become a research hotspot. They display the merits of power self-support, a simplified structure, in vivo operational feasibility, online and timely monitoring, etc. Since the concept of enzymatic biofuel cell-powered biosensors (EBFC-SPBs) was first proposed, its applications in health monitoring have scored tremendous achievements. However, the creation and practical application of portable EBFC-SPBs are still impeded by the difficulty in their miniaturization. In recent years, the booming microfluidic technology has powerfully pushed forward the progress made in miniaturized and portable EBFC-SPBs. This brief review recalls and summarizes the achievements and progress made in miniaturized EBFC-SPBs. In addition, we also discuss the advantages and challenges that microfluidic and screen-printing technologies provide to wearable and disposable EBFC-SPBs.

Enzymatic biofuel cells (EBCs) represent a promising technology for biosensors, biodevices, and sustainable green energy applications, thanks to enzymes’ high specificity and catalytic efficiency. Nevertheless, drawbacks such as limited output power and short lifetime have to be solved. Nowadays, research is addressed to the use of 3D electrode structures, but the high cost and the industrialization difficulties of such electrodes represent a key issue. The purpose of the paper is thus to describe the use of a low-cost commercial conductive polymer (Sigracell® PV15) as support for the covalent immobilization of glucose oxidase and laccase, for bioanode and biocathode fabrication, respectively. Efficient immobilization protocols were determined for the immobilized enzymes in terms of employed linkers and enzyme concentrations, resulting in significant enzymatic activities for units of area. The analysis focuses specifically on the optimization of the challenging immobilization of laccase and assessing its stability over time. In particular, an optimum activity of 23 mU/cm2 was found by immobilizing 0.18 mg/cm2 of laccase, allowing better performances, as for voltage output and electrochemical stability, and a direct electron transfer mechanism to be revealed for the fabricated biocathode. This study thus poses the basis for the viable development of low-cost functional EBC devices for biomedical applications.

Membraneless microfluidic enzymatic biofuel cells (μEBFCs) operated under the co-laminar flow of fuel and oxidant often face cross-mixing issues, especially at low flow rates. In this work, we propose a new approach to design the single-stream μEBFC based on the investigation of relative positions of the electrodes at the top and bottom of the microchannel. To achieve this, a μEBFC was fabricated with multiwalled carbon nanotube (MWCNT) electrodes via a stencil method. The bioanode and biocathode were modified with glucose dehydrogenase and laccase via direct covalent bonding, respectively. The best results were attained by placing the cathode at the top and anode at the bottom of the microchannel in a Y-shaped two streamflow μEBFC. When a single electrolyte stream was used to achieve more practicality and ease of use, the performance was reduced by 40%. However, with the new design of electrodes in single-stream μEBFC, i.e. cathode at the top and anode at the bottom facing each other in the microchannel, the performance was recovered by 20%. This corresponds to maximum current and power density of 216 ± 12 μA cm−2 and 69.2 ± 9.2 μW cm−2, respectively. The stacking ability of the device was realized by connecting the two cells in series and parallel. The maximum power density delivered by the two single-stream μEBFCs' stack reached 160 μW cm−2 at 0.3 V. Thus, this study validates the viability of using single-stream μEBFCs in large stacks to power microelectronics more simply and practically. • The effect of electrode positions in microfluidic enzymatic biofuel cell (μEBFC) is studied. • The performance is improved by placing the cathode at the top of the microchannel. • A simplified single-stream device is designed to achieve more practicality. • With the new design of electrodes, the performance is enhanced by 20%. • Such a device demonstrates viability to easily stack in large numbers to produce the targeted power. [ABSTRACT FROM AUTHOR]

• AuNPs@GDY is synthesized by leveraging the properties of AuNPs and graphdiyne; • Superior bioelectrocatalysis is achieved on the bio-abiotic interface of AuNPs@GDY; • π-π interaction between enzyme and AuNPs@GDY facilitate electron transfer. The main challenges (sluggish electron transfer, low energy density) hinder the future application of enzymatic biofuel cells (EBFCs), which urgent to take effective measures to solve these issues. In this work, a composite of Au nanoparticles decorated graphdiyne (AuNPs@GDY) is fabricated and employed as the carrier of enzyme (G6PDH), and a mechanism based on π-π interaction of electron transfer is proposed to understand bioelectrocatalysis processes. The results show that the AuNPs@GDY composite exhibits the highest current density among the three materials (GDY, AuNPs, and AuNPs@GDY), which is 3.4 times higher than that of GDY and 2.5 times higher than that of AuNPs. Furthermore, the results reveal that the AuNPs could increase the loading of enzymes and provide more active site for reaction, while GDY provides highly π-conjugated structure and unique sp/sp2-hybridized linkages interface. This work provides new insights to explore a theoretical basis for the development of more efficient bioelectrocatalytic systems. [ABSTRACT FROM AUTHOR]

Nanoparticles have become omnipresent as they have distinctively diverse properties from their bulk counterparts. They find a considerable research interest in numerous biological, biomedical, biopharmaceutical, and biochemical applications. The productivity and structure of nanoparticles are deeply reliant on the method used for their synthesis. The classical hydrothermal method needs massive and expensive temperature controller instruments, a huge amount of reagents, and specific autoclaves for their synthesis. With this motivation, herein, an automated, integrated, and miniaturized thermal monitoring system has been designed and developed for producing nanoparticle-on-chip (NoC) in a microfluidic platform. Herein, Zinc oxide (ZnO) nanoparticles were synthesized. The device comprises a microcontroller, self-designed switching circuit, cartridge heater, and thermocouple. The device, with dimensions $78 \times 75 \times 40$ mm3, has benefits such as portability, easy-to-use, amenability to geotagged data logging, and inexpensive. The device showcased the temperature sensitivity of ± 0.5 °C. A polymethyl methacrylate (PMMA)-based microfluidic device, with a suitable microreactor, was fabricated using the CO2 laser ablation technique. ZnO nanoparticles were successfully synthesized at 95 °C within 60 min and were subjected to several characterization techniques to manifest their crystographic, elemental, morphologic, and spectroscopic properties. As a proof-of-principle, the produced ZnO nanoparticles were validated for electrocatalytic sensing of hydrazine and uric acid, and as a catalyst in an enzymatic glucose biofuel cell (EBFC) to test its efficiency. The proposed microfluidic thermal system can be utilized for carrying out numerous temperature-based reactions and analyses. [ABSTRACT FROM AUTHOR]

The prospective of this work is to synthesize a new nanocomposite that serves as an electrode material for the immobilization of biomolecules. In this work surface-functionalized single-walled carbon nanotubes (f–COOH–SWCNTs), and hydrothermally synthesized surface defected 2D nanoplates wrapped by polpyrrole matrix was developed. The developed nanocomposite was utilized as the anode material for the immobilization of enzymes. Nanocomposite f-SWCNTs@Ppy@NiMoSe 2 was characterized by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the electrochemical methods including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). The electrochemically controlled bioanode reached to the open circuit potential (OCV) of 0.35 V and delivered the maximum current density of 9.01 mA cm−2 in 50 mM glucose concentration prepared in phosphate buffer solution (PBS) (pH 7.0) as the testing solution at 100 mVs−1 scan rates. • Nickel doped 2 D nanoplates synthesized by hydrothermal routes. • Improved wiring of enzyme and mediator. • Mediated electron transfer using biocompatible mediator. • Bioanode deliver a high current density of 9.01 mA cm−2. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) is one of the most frequently used enzymes in a design of enzymatic biosensors and biofuel cells, which are novel electrical energy generation systems. Therefore, a better understanding of the mode of action of this enzyme is very important for further development of GOx-based sensors. In this research fluorescence properties of GOx in different acidic media have been estimated by the evaluation of redox states of active center that is flavine adenine dinucleotide (FAD). Steady-state fluorescence spectroscopy was applied to monitor the activity of GOx. A variation of pH has been invoked to gain a better understanding in the variations of GOx activity. The tendency of GOx activity to decrease over the time was determined, while increased intensity of the fluorescence band of GOx at 530 nm was associated with a decreased activity of the enzyme. The changes in fluorescence intensity of this band are caused by the dissociation of FAD from the enzyme. This process is not reversible, therefore, the decrease in the fluorescence intensity can be also associated with structural changes of the FAD during its reduction. Unlabelled Image • Fluorescence properties of glucose oxidase (GOx) in different acidic medium have been estimated. • Steady-state spectroscopy was applied to monitor the activity of glucose oxidase. • Evaluation of redox states of active center – FAD – has been performed. • The tendency of GOx activity decrease over the time was determined. • The changes of fluorescence intensity band have been associated with dissociation of FAD from the protein pat of enzyme. [ABSTRACT FROM AUTHOR]

Development of bioelectrodes with multiple virtues, such as biocompatibility, flexibility, versatility and cost-effectiveness, remains a huge area of research for multiple applications. Here, we delve upon fabricating carbon electrodes using a desktop PCB printer in a cost-and-time efficient manner (less than 2 min). Such printed carbon paste electrodes have been incorporated to develop an enzyme-based glucose biofuel cell to power various low-power biomedical devices and for biosensing. The bioelectrodes were prepared by electrodepositing gold nanorods followed by the immobilization of suitable enzymes. These bioelectrodes were tested for their electrochemical behavior and was setup as a Direct Electron Transfer (DET)-based enzymatic biofuel to be amenable for various physiological fluids, like tears, human saliva, whole blood and blood serum, due to its biocompatibility and efficiency. It delivered maximum energy of 3.18 µW/cm2 and 8.8 µW/cm2 from tears and human serum, respectively. These fabricated electrodes have huge potential to be incorporated in miniaturized devices as a renewable energy source for implantable and self-powered bioelectronics. [ABSTRACT FROM AUTHOR]

Background: Diaphorase (DI) has received wide attention as the key anodic enzyme mediating the electron transfer and electric energy generation in enzymatic biofuel cells (EBFCs). Lowering the anodic pH may be a useful strategy for constructing high-performance in EBFCs. However, most DI suffered from the poor activity at low pHs. Therefore, it is necessary to modify the activity and its acidic tolerance to further improve the performance of the EBFC. Results: This paper attempts to improve the enzyme activity of DI originated from Geobacillus stearothermophilus under acidic conditions through directed evolution. Three rounds of random mutagenesis by error-prone PCR of the GsDI gene followed by high-throughput screening allowed the identification of the mutant 3–8 (H37Q, S73T, F105L, S68T, G61S, D74V) exhibiting a 4- or 7-fold increase in the catalytic activity at pH 5.4 or 4.5 compared to that of the wild type. And the pH stability of mutant 3–8 was significantly better than that of wild type and showed a 1.3 times higher in the stability at pH 5.4. The EBFC anode equipped with 0.5 mg of mutant 3–8 achieved a maximum current of 40 μA at pH 5.4, much higher than that with the same loading of the wild type enzyme. Conclusion: The GsDI has been improved in the specific activity and pH stability by directed evolution which leads to the improvement of the EBFC performance. Also, the enlarged catalytic channel of mutant and decreased B-factor may be beneficial for the activity and stability. These results suggest that this engineered DI will be a useful candidate for the construction of enhanced EBFCs. [ABSTRACT FROM AUTHOR]

Biofuel cells are an attractive alternative to conventional fuel cells, because they use biological catalysts. We report in this article the construction of an ethanol/O2 enzymatic biofuel cell. In the first time, the performance comparison with different methods for ethanol/O2 biofuel cell has been study. Alcohol dehydrogenase, a nicotinamide adenine dinucleotide (NAD)-dependent enzyme, is immobilized with NAD+, diaphorase, and vitamin K3 (VK3) on the electrode. The oxygen is reduced at the cathode with laccase and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS). The performances of the electrodes are improved thanks to addition of carbon powder (KS6 and Super P® carbon). The benefit of the carbon particles with higher surface porosity was explained by the high-porous structure that offered a closer proximity to the reactive species and improved diffusion of ethanol and oxygen within the enzyme films. Efficiency of immobilization of NAD+ cofactor has been also demonstrated. We have shown the effect of multi-enzymatic reaction at the anode on the storage and operational stability. A high open-circuit potential has been recorded 1.02 V, demonstrating the benefit of NAD+ immobilization with maximal power density of 300 μW cm−2. Chronoamperometric measurements show a current density of 90 μA cm−2 during 20 h demonstrating the operational stability of the ethanol biofuel cell based on NAD+ cofactor immobilization. [ABSTRACT FROM AUTHOR]

In this study, a self-powered biosensor based on an enzymatic biofuel cell was proposed for the first time for the ultrasensitive detection of soluble CD44 protein. The as-prepared biosensor was composed of the co-exist aptamer and glucose oxidase bioanode and bilirubin oxidase modified biocathode. Initially, the electron transfer from bioanode to biocathode was hindered due to the presence of the aptamer with high insulation, generating a low open-circuit voltage (EOCV). Once the target CD44 protein was present, it was recognized and captured by the aptamer at the bioanode, thus the interaction between the target CD44 protein and the immobilized aptamer caused the structural change at the surface of the electrode, which facilitated the transfer of electrons. The EOCV showed a good linear relationship with the logarithm of the CD44 protein concentrations in the range of 0.5–1000 ng mL−1 and the detection limit was 0.052 ng mL−1 (S/N = 3). The sensing platform showed excellent anti-interference performance and outstanding stability that maintained over 97% of original EOCV after 15 days. In addition, the relative standard deviation (1.40–1.96%) and recovery (100.23–101.31%) obtained from detecting CD44 protein in real-life blood samples without special pre-treatment indicated that the constructed biosensor had great potential for early cancer diagnosis. [Display omitted] • An EBFC-SPB was proposed firstly for the ultrasensitive CD44 protein sensing. • The CD44 protein detected by the aptamer at bioanode caused the positive response. • The wide logarithm linear relationship was in the range of 0.5–1000 ng mL−1. • The detection limit was as low as 0.052 ng mL−1 (S/N = 3). • It showed excellent anti-interference performance and recovery for real sample. [ABSTRACT FROM AUTHOR]

[Display omitted] • HEDs combining EBFCs and SCs are suggested as power source of wearable and implantable devices. • HEDs exhibit exceptional fuel reactivity achieving 0.91 and 0.51 mA/cm2 in GOR and ORR. • HEDs produce power and specific storage capacitance of 0.93 mW/cm2 and 307 mF/cm2 like SCs. • Self-charging of HEDs is observed by unique design using enzyme and mediator in each electrode. • By self-charging effect, OCV of HEDs is well preserved and HEDs can discharge even wiothout fuels. Enzymatic biofuel cells (EBFCs) are promising as a biocompatible power source for implantable and wearable devices, converting chemical energy of body fluids into electricity. However, they have intrinsic limitations, such as low power density and requirement for continuous fuel supply. To overcome the difficulties, hybrid energy devices (HEDs) that are combinative device of supercapacitor (SC) and EBFC are suggested in this study. They consist of anode and cathode including (i) enzymes reacting with respective fuels and (ii) mediators promoting transfer and storage of electrons. As EBFCs, HEDs exhibit exceptional fuel reactivity, achieving 0.91 and 0.51 mA/cm2 in glucose oxidation reaction and oxygen reduction reaction, while they play as SCs with excellent power and specific storage capacitance of 0.93 mW/cm2 and 307 mF/cm2. Moreover, HEDs show self-charging property that is uniquely observed in devices operated by the collaboration of enzyme and mediator. By this benefit, their open circuit voltage is well preserved in absent of fuels, while they can discharge even without supply of fuel. These features are obvious evidence that HEDs can be considered as advanced power sources for implantable and wearable devices. [ABSTRACT FROM AUTHOR]

The appearance and evolution of biofuel cells can be categorized into three groups: microbial biofuel cells (MBFCs), enzymatic biofuel cells (EBFCs), and enzyme-like nanomaterial (nanozyme)-based biofuel cells (NBFCs). MBFCs can produce electricity from waste; however, they have significantly low power output as well as difficulty in controlling electron transfer and microbial growth. EBFCs are more productive in generating electricity with the assistance of natural enzymes, but their vulnerability under diverse environmental conditions has critically hindered practical applications. In contrast, because of the intrinsic advantages of nanozymes, such as high stability and robustness even in harsh conditions, low synthesis cost through facile scale-up, and tunable catalytic activity, NBFCs have attracted attention, particularly for developing wearable and implantable devices to generate electricity from glucose in the physiological fluids of plants, animals, and humans. In this review, recent studies on NBFCs, including the synthetic strategies and catalytic activities of metal and metal oxide-based nanozymes, the mechanism of electricity generation from glucose, and representative studies are reviewed and discussed. Current challenges and prospects for the utilization of nanozymes in glucose biofuel cells are also discussed.

We prepared robust bioanodes by immobilizing the alcohol dehydrogenase (ADH) enzyme onto a one-pot electropolymerized film consisting of methylene green and pyrrole. The enzymatic film containing immobilized ADH furnished power densities as high as 183 ± 10 μW cm−2; addition of carbon nanotubes (MWCNTs) increased the bioanode power density to 275 ± 12 μW cm−2. The bioanode was very stable, with a mean decay of 36% of its initial power density after 20 weeks of storage. Long-term ethanol electrolysis (12h) followed by HPLC-UV/RID confirmed that the system was highly selective and generated a two-electron product. MWNCT introduction provided five times higher acetaldehyde production. Compared to literature data, results were promising and showed that the system can be used to construct biofuel cells. In addition, the film obtained by simultaneous methylene green and pyrrole electropolymerization afforded interesting results and can be applied in other systems, such as biosensors. Unlabelled Image • One-pot electropolymerized methylene green and pyrrole can catalyze ethanol oxidation. • Poly-(MG-PYR)ADH film bioanode has good stability. • HPLC confirms two electrons per ethanol molecule after 12 h of electrolysis. • MWCNT addition to the bioanode increases acetaldehyde production. [ABSTRACT FROM AUTHOR]

We designed an enzymatic biofuel cell (EFC) that utilizes indium tin oxide (ITO) electrodes, and sequential deposition of single-walled carbon nanotube (SWCNT) and gold nanoparticle (AuNP) layers on the electrodes to enhance their electron transfer. Cyclic voltammograms of the SWCNT-modified ITO electrodes showed higher peak currents compared to those of the bare ITO electrodes. Immobilization of glucose oxidase (GOD) on SWCNT-modi-fied ITO electrodes increased their electron transfer resistance by a factor of ten, which could be mitigated by incorporating an AuNP layer between the GOD and SWCNT layers. The single-layer GOD generated higher current than the doubled-layer GOD, with higher specific activity. The assembled EFC featured SWCNT-modified ITO electrodes with sequential layers of immobilized AuNPs and GOD (anode), and with a single layer of immobilized bilirubin oxidase (BOD) (cathode). The cathode performance was further improved by the presence of AuNPs between the BOD and SWCNTs on cathode. The enhanced electron transfer kinetics and enzymatic activity observed for SWCNT/AuNP-modified ITO electrodes resulted in a maximum power density of 38.2±2.0 µW/cm2 at 0.57±0.03 V of a cell voltage. [ABSTRACT FROM AUTHOR]

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]

Enzymatic biofuel cells promise green power generation from a variety of natural resources, yet these systems all suffer from time-dependent degradation effects, in particular progressing inactivation of enzymes, which severely limit the operational lifetimes of such power sources. To extend operational lifetimes, we introduce a method to magnetically exchange exhausted enzymes for fresh ones. To this end, anodic and cathodic enzymes or enzyme cascades are immobilized on carbon coated magnetic nanoparticles. Under the action of suitable magnetic field gradients, these nanoparticles are assembled on the respective stationary electrodes, or released from the electrodes for collection and subsequent exchange. We demonstrate this method on a fructose/oxygen consuming biofuel cell employing fructose dehydrogenase and bilirubin oxidase as well as on anodic and cathodic cascades employing fructose dehydrogenase/invertase and bilirubin oxidase/catalase, respectively. The enzyme-modified nanoparticles support direct electron transfer bioelectrocatalytic currents by wiring the redox active cofactors to the carbonaceous coating and from there to the electrode surfaces. The facile injection, assembly, and removal of enzyme-modified magnetic nanoparticles along with fuel solution provides a promising approach to extend the operational lifetime of enzymatic biofuel cells without the need for exchanging entire systems including chambers and electrodes. [ABSTRACT FROM AUTHOR]

Escherichia coli's copper efflux oxidase (CueO) has rarely been employed in the cathodic compartment of enzymatic biofuel cells (EBFCs) due to its low redox potential (0.36 V vs. Ag/AgCl, pH 5.5) towards O2 reduction. Herein, directed evolution of CueO towards a more positive onset potential was performed in an electrochemical screening system. An improved CueO variant (D439T/L502K) was obtained with a significantly increased onset potential (0.54 V), comparable to that of high‐redox‐potential fungal laccases. Upon coupling with an anodic compartment, the EBFC exhibited an open‐circuit voltage (Voc) of 0.56 V. Directed enzyme evolution by tailoring enzymes to application conditions in EBFCs has been validated and might, in combination with molecular understanding, enable future breakthroughs in EBFC performance Directed CueO evolution via electrochemical screening found that the substitutions at the second sphere of T1 Cu led to a dramatic overpotential decrease of 0.12 V, making CueO competitive to fungal laccases and applicable in enzymatic biofuel cells. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) and four different quinone derivatives (p-benzoquinone (BQ), naphthoquinone (NQ), anthraquinone (AQ) and 1,5-Dihydroxyanthraquinone (15DHAQ)) based biocomposites were embedded in polyethyleneimine (PEI) and then immobilized on carbon nanotube (CNT) substrate (CNT/PEI/Quinone/GOx). These catalysts were then used as the anodic biocatalysts for the enzymatic biofuel cell (EBC). According to the performance investigations of catalysts, the catalytic activity for glucose oxidation reaction (GOR) representing the electron transfer rate between GOx and glucose fuel is mostly enhanced in CNT/PEI/NQ/GOx. It is because two benzene rings of NQ play a role in attracting and releasing electrons effectively, increasing the catalytic activity for GOR, while other quinones have problems about attracting electrons (AQ and 15DHAQ) and wrong position of the reactive site for electron transfer (BQ). Excellent electron transfer rate constant (1.1 s-1) and Michaelis-Menten constant (0.99mM) are outstanding evidence for that. Furthermore, when the catalyst is utilized for EBC, high power density (57.4 μWcm-2) and high open circuit voltage (0.64 V) are accomplished. [ABSTRACT FROM AUTHOR]

Because of environmental concerns, there is a growing interest in new ways to produce green energy. Among the several studied applications, enzymatic biofuel cells can be considered as a promising solution to generate electricity from biological catalytic reactions. Indeed, enzymes show very good results as biocatalysts thanks to their excellent intrinsic properties, such as specificity toward substrate, high catalytic activity with low overvoltage for substrate conversion, mild operating conditions like ambient temperature and near-neutral pH. Furthermore, enzymes present low cost, renewability and biodegradability. The wide range of applications moves from miniaturized portable electronic equipment and sensors to integrated lab-on-chip power supplies, advanced in vivo diagnostic medical devices to wearable devices. Nevertheless, enzymatic biofuel cells show great concerns in terms of long-term stability and high power output nowadays, highlighting that this particular technology is still at early stage of development. The main aim of this review concerns the performance assessment of enzymatic biofuel cells based on flow designs, considered to be of great interest for powering biosensors and wearable devices. Different enzymatic flow cell designs are presented and analyzed highlighting the achieved performances in terms of power output and long-term stability and emphasizing new promising fabrication methods both for electrodes and cells.

In this article, we describe an enzyme-based, membraneless, microfluidic biofuel cell for the continuous determination of glucose using electrochemical power generation as a transducing signal. Enzymes were immobilized on multi-walled carbon nanotube (MWCNT) electrodes placed parallel to the co-laminar flow in a Y-shaped microchannel. The microchannel was produced with polydimethylsiloxane (PDMS) using soft lithography, while the MWCNT electrodes were replicated via a PDMS stencil on indium tin oxide (ITO) glass. Moreover, the electrodes were modified with glucose oxidase and laccase by direct covalent bonding. The device was studied at different MWCNT deposition amounts and electrolyte flow rates to achieve optimum settings. The experimental results demonstrated that glucose could be determined linearly up to a concentration of 4 mM at a sensitivity of 31 mV∙mM−1cm−2.

In research on enzyme-based biofuel cells, covalent or noncovalent molecular modifications of carbon-based electrode materials are generally used as a method for immobilizing enzymes and/or mediators. However, the influence of these molecular modifications on the electrochemical properties of electrode materials has not been clarified. In this study, we present the electrochemical properties of chemical vapor deposition (CVD)-grown monolayer graphene electrodes before and after molecular modification. The electrochemical properties of graphene electrodes were evaluated by cyclic voltammetry and electrochemical impedance measurements. A covalently modified graphene electrode showed an approximately 25-fold higher charge transfer resistance than before modification. In comparison, the electrochemical properties of a noncovalently modified graphene electrode were not degraded by the modification.

Herein, a novel, low-cost, and readily available HB pencil graphite (PG), as bioanode for enzymatic biofuel cell, is presented. The surface area of the PG is substantially increased by coating carboxylated multiwalled carbon nanotube through the dipping method followed by its covalent immobilization with glucose oxidase enzyme to fabricate the bioanode. The surface morphology of fabricated bioanode is characterized by scanning electron microscopy, and the electrochemical studies are performed through linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The results reveal that the fabricated bioanode shows good direct electron transfer characteristics between the dynamic site of the enzyme and the terminal surface of electrode. Approximately, $1.23 \times 10^{-11}\,\,\text {mol}\cdot \text {cm}^{-2}$ of glucose oxidase is found to anchor on the fabricated bioanode with significant electron transfer rate of 3.2 s−1. Furthermore, the catalytic activity of fabricated bioanode is enhanced with increase in the glucose concentration, and a hyperbolic Michaelis–Menten kinetics is observed with $K_{\text {m}}$ value of 5.5 mM and maximum current density of 4605 $\mu \text {A}\cdot \text {cm}^{-2}$ at 40-mM saturated glucose concentration. Finally, the fabricated bioanode exhibits stability with reasonably good retention of biocatalytic activity, thus establishing HB PG as promising bioanode material for enzymatic biofuel cell. [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]

Amorphous carbon nitride (a-CNx) thin films were used for the first time as electrode materials in the elaboration of biofuel cell cathodes as a consequence of i) the natural presence of amine type functional groups and ii) the ease to generate carboxylic acid groups on their surface with the help of an anodic treatment. Their rich surface chemistry was exploited to investigate the influence of the orientation of immobilised laccase on their bioelectrocatalytic activity towards oxygen reduction reaction (ORR) in a direct electron transfer configuration. Among four different immobilisation strategies leading to a statistical control of the orientation and tested in this work, spontaneous adsorption of natural laccase on pristine a-CNx provided the smallest current density value (3.5 μA cm −2 ) whereas covalent grafting of oxidised laccase on anodically treated a-CNx via imine and amide bond formation using a coupling agent led to a much higher but still low 44.6 μA cm −2 current density. This substantial improvement of the current density value measured for ORR confirms that the orientation of immobilised laccase exerts a measurable influence on its bioelectrocatalytic activity towards ORR. In parallel, the surface coverage rate of enzymes showing such activity was estimated as a function of the immobilisation method by using four different techniques (current density, activity towards ABTS, XPS and AFM). It was found that only a small fraction (7.1% to the most) of the electrode surface is covered with active enzymes, whatever the immobilisation method, whereas an enzyme population corresponding (almost) to a full enzyme monolayer was actually immobilised. This observation is crucial because it strongly suggests that the development of innovative immobilisation strategies allowing an increase of the active enzyme fraction through a simultaneous optimisation of the bioelectrocatalytic activity of the enzyme and of its electronic communication with the electrode offers much more promising perspectives than the control of the orientation of the immobilised enzyme population on its own. [ABSTRACT FROM AUTHOR]

A bioelectronic device comprising an enzymatic biofuel cell (GBFC) connected to a wireless tele-transmission system was implanted in a rabbit and its function was monitored and controlled in vivo for a period of 2 months. After the 18th day of implantation, the tele-transmission system was used to wirelessly charge and discharge the operational GBFC in vivo through a 100 kΩ load for 30 min each day. For a further 16 days of operation, the GBFC delivered 16 μW mL −1 continuously during each 30 min discharge each day for 16 days. At the end of the 2 month period of implantation the power output had diminished, which was most likely due to an inflammatory process. Our results also indicate that the duration of operational activity is increased by optimizing the interface between the GBFC and the body to minimize inflammatory processes and biofouling. These data provide a significant advance in the achievable output from a GBFC that is implanted in a mammal, and importantly provide a basis upon which to further develop stable implantable biofuel cells. Improving the in vivo performance of an implanted GBFC includes the development of biocompatible diffusing polymers to act as buffering diffusion barriers. [ABSTRACT FROM AUTHOR]

Plastic products have many applications due to their low cost and simple production. However, since their remaining wastes can be a resource of environmental pollution, recycling of plastic waste is significant. In this study, for doing that, tertiary recycling of low-density polyethylenes (LDPEs) that are plastic waste is newly explored. With that, LDPEs are converted into useful carbonized LDPEs (C-LDPEs) used as Supporting material for electrodes of enzymatic biofuel cells (EBFCs) by stabilization and carbonization process. By recycling of LDPEs, their surface area increases, while desirable graphitic structure is produced. Glucose oxidase- and bilirubin oxidase-based catalytic structures are then loaded onto C-LDPEs to complete electrodes. After confirming excellence in their catalytic activity, the performance of membraneless flow-type EBFCs using C-LDPE based electrodes is measured. According to the evaluations, their open circuit voltage and maximum power density are 0.64 ± 0.03 V and 20.5 ± 1.3 μW cm-2. [Display omitted] • Tertiary recycling is a promising method for recycling plastic wastes. • Tertiary recycling of plastic waste LDPEs converts them into useful C-LDPEs. • C-LDPEs have large specific surface area and proper pore size. • C-LDPEs are used as carbon supporter of enzyme-based electrodes for EBFC. • Performance of membraneless EBFCs using C-LDPE-based electrodes is excellent. [ABSTRACT FROM AUTHOR]

The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate the effect of different designs and spatial distributions of the microelectrode arrays on mass transport of fuels, enzymatic reaction rate, open circuit output potential and current density. To optimize the performance of the EBFCs, numerical simulations have been performed for cylindrical electrodes with various electrode heights and well widths. Optimized cell performance was obtained when the well width is half of the height of the 3-D electrode. In addition, semi-elliptical shaped electrode is preferred based on the results from current density and resistive heating simulation.