A symmetric supercapacitor/biofuel cell hybrid device based on enzyme-modified nanoporous gold: An autonomous pulse generator

Enzymatic biofuel cell: A potential power source for self-sustained smart textiles

Self-sustained smart textiles require a miniaturized and flexible power source, while the state-of-the-art lithium-ion battery cannot be seamlessly integrated into smart textiles. Enzymatic biofuel cells (EBFC), utilizing physiological glucose or lactate as fuels to convert chemical energy into electricity, are a potential alternative power source. In comparison to other proposed energy harvesters relying on solar and biomechanical energy, EBFCs feature several key properties, including continuous power generation, biocompatible interfaces without using toxic elements, simple configuration without extra packaging, and biodegradability. There is an urgent need to introduce EBFCs to the researchers working on smart textiles, who typically are not expert on bioelectrochemistry. This minireview first introduces the working principle of EBFC and then summarizes its recent progress on fibers, yarns, and textiles. It's expected that this review can help to bridge the knowledge gap and provide the community of smart textiles with information on both the strengths and limitations of EBFCs.

A Dual-Functional MXene-Based Bioanode for Wearable Self-Charging Biosupercapacitors

As a reliable energy-supply platform for wearable electronics, biosupercapacitors combine the characteristics of biofuel cells and supercapacitors to harvest and store the energy from human's sweat. However, the bulky preparation process and deep embedding of enzyme active sites in bioelectrodes usually limit the energy-harvesting process, retarding the practical power-supply sceneries especially during the complicated in vivo motion. Herein, a MXene/single-walled carbon nanotube/lactate oxidase hierarchical structure as the dual-functional bioanode is designed, which can not only provide a superior 3D catalytic microenvironment for enzyme accommodation to harvest energy from sweat, but also offers sufficient capacitance to store energy via the electrical double-layer capacitor. A wearable biosupercapacitor is fabricated in the "island-bridge" structure with a composite bioanode, active carbon/Pt cathode, polyacrylamide hydrogel substrate, and liquid metal conductor. The device exhibits an open-circuit voltage of 0.48 V and the high power density of 220.9 µW cm-2 at 0.5 mA cm-2 . The compact conformal adhesion with skin is successfully maintained under stretching/bending conditions. After repeatedly stretching the devices, there is no significant power attenuation in pulsed output. The unique bioelectrode structure and attractive energy harvesting/storing properties demonstrate the promising potential of this biosupercapacitor as a micro self-powered platform of wearable electronics.

Self-Powered Biosensing System with Multivariate Signal Amplification for Real-Time Amplified Detection of PDGF-BB

A self-powered biosensing system with multivariate signal amplification is designed for the ultrasensitive, highly efficient, rapid-response, and real-time detection of platelet-derived growth factor-BB (PDGF-BB). The biosensing system is composed of enzymatic biofuel cells (EBFCs), a capacitor, a digital multimeter (DMM), and a computer. Using the hybridization chain reaction (HCR), a few single DNA chains are transformed into abundant double-helix chains, which stimulates the reduction of [Ru(NH3)6]3+ to [Ru(NH3)6]2+ by electrostatic interaction, corresponding to the "on" state for HCR. As a result, the open-circuit voltage (EOCV) is significantly increased in this self-powered biosensing system. When PDGF-BB is present, a binding interaction between the target and the aptamer, i.e., PDGF-BB/Apt, corresponding to the "off" state for HCR, results in a decrease of EOCV. The PDGF-BB concentration is inversely proportional to EOCV, allowing readable, effective, and precise real-time detection of PDGF-BB. The detection limit of the biosensing system is 0.031 pg/mL (S/N = 3). This strategy provides a promising and powerful tool for the early clinical diagnosis of related colorectal cancer markers.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Structural design of anthraquinone bridges in direct electron transfer of fructose dehydrogenase

Multi-functional small molecules attached to an electrode surface can bind non-covalently to the redox enzyme fructose dehydrogenase (FDH) to ensure efficient electrochemical electron transfer (ET) and electrocatalysis of the enzyme in both mediated (MET) and direct (DET) ET modes. The present work investigates the potential of exploiting secondary, electrostatic and hydrophobic interactions between substituents on a small molecular bridge and the local FDH surfaces. Such interactions ensure alignment of the enzyme in an orientation favourable for both MET and DET. We have used a group of novel synthesized anthraquinones as the small molecule bridge, functionalised with electrostatically neutral, anionic, or cationic substituents. Particularly, we investigated the immobilisation of FDH on a nanoporous gold (NPG) electrode decorated with the novel synthesised anthraquinones using electrochemical methods. The best DET-capable fraction out of four anthraquinone derivatives tested is achieved for an anthraquinone functionalised with an anionic sulphonate group. Our study demonstrates, how the combination of chemical design and bioelectrochemistry can be brought to control alignment of enzymes in productive orientations on electrodes, a paradigm for thiol modified surfaces in biosensors and bioelectronics.

Precipitation-based microscale enzyme reactors coupled with porous and adhesive elastomer for effective bacterial decontamination and membrane antifouling on-demand

Bacterial contamination of water environments can cause various troubles in various areas. As one of potential solutions, we develop enzyme-immobilized elastomer, and demonstrate the uses of enzyme reactions on-demand for effective microbial decontamination and antifouling. Asymmetrically-structured elastomer is prepared by combining two polydimethylsiloxane (PDMS) layers with different degrees of crosslinking: highly-crosslinked and lightly-crosslinked PDMS layers. At the surface of highly-crosslinked PDMS layer, porous structure with average diameter of 842 nm is formed by dissolving pre-packed and entrapped latex beads. Lightly-crosslinked PDMS on the other side, due to its adhesive nature, enables iterative attachments on various materials under either dry or wet condition. Glucose oxidase (GOx) is immobilized by using the pores at the surface of highly-crosslinked PDMS matrix via a ship-in-a-bottle protocol of precipitation-based microscale enzyme reactor (p-MER), which consists of GOx adsorption, precipitation and chemical crosslinking (EAPC). As a result, crosslinked enzyme aggregates (CLEAs) of GOx not only are well entrapped within many pores of highly-crosslinked PDMS layer (ship-in-bottle) but also cover the external surface of matrix, both of which are well connected together. Highly-interconnected network of CLEAs themselves effectively prevents enzyme leaching, which shows the 25% residual activity of GOx under shaking at 200 rpm for 156 days after 48% initial drop of loosely-bound p-MER after 4 days. In presence of glucose, the underwater attachment of biocatalytic elastomer demonstrates the generation of hydrogen peroxide via p-MER-catalyzed glucose oxidation, exhibiting effective biocidal activities against both gram-positive S. aureus and gram-negative E. coli. Adhesion-induced GOx-catalyzed reaction also alleviates the biofouling of membrane, suggesting its extendibility to various engineering systems being suffered by biofouling. This study of biocatalytic elastomer has demonstrated its new opportunities for the facile and on-demand enzyme-catalyzed reactions in various environmental applications, such as bactericidal treatment, water treatment/purification, and pollutant degradation.

Engineering bio-interfaces for the direct electron transfer of Myriococcum thermophilum cellobiose dehydrogenase: Towards a mediator-less biosupercapacitor/biofuel cell hybrid

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 (MtCDH) 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 MtCDH surface. The resulting MtCDH 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 MtCDH surface orientation. A dual, entirely DET-based enzymatic biofuel cell (EBFC) was constructed with a MtCDH bioanode and a Myrothecium verrucaria bilirubin oxidase (MvBOD) 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.

Supercapacitive biofuel cells

Supercapacitive biofuel cells' (SBFCs) most recent advancements are herein disclosed. In conventional SBFCs the biocomponent is employed as the pseudocapacitive component, while in self-charging biodevices it also works as the biocatalyst. The performance of different types of SBFCs are summarized according to the categorization based on the biocatalyst employed: supercapacitive microbial fuel cells (s-MFCs), supercapacitive biophotovoltaics (SBPV) and supercapacitive enzymatic fuel cells (s-EFCs). SBFCs could be considered as promising 'alternative' energy devices (low-cost, environmentally friendly, and technically undemanding electric power sources etc.) being suitable for powering a new generation of miniaturized electronic applications.

Utilization of FAD-Glucose Dehydrogenase from T. emersonii for Amperometric Biosensing and Biofuel Cell Devices

Flavin-dependent glucose dehydrogenases (FAD-GDH) are oxygen-independent enzymes with high potential to be used as biocatalysts in glucose biosensing applications. Here, we present the construction of an amperometric biosensor and a biofuel cell device, which are based on a thermophilic variant of the enzyme originated from Talaromyces emersonii. The enzyme overexpression in Escherichia coli and its isolation and performance in terms of maximal bioelectrocatalytic currents were evaluated. We examined the biosensor's bioelectrocatalytic activity in 2,6-dichlorophenolindophenol-, thionine-, and dichloro-naphthoquinone-mediated electron transfer configurations or in a direct electron transfer one. We showed a negligible interference effect and good stability for at least 20 h for the dichloro-naphthoquinone configuration. The constructed biosensor was also tested in interstitial fluid-like solutions to show high bioelectrocatalytic current responses. The bioanode was coupled with a bilirubin oxidase-based biocathode to generate 270 μW/cm2 in a biofuel cell device.

Miniature microbial solar cells to power wireless sensor networks

Conventional wireless sensor networks (WSNs) powered by traditional batteries or energy storage devices such as lithium-ion batteries and supercapacitors have challenges providing long-term and self-sustaining operation due to their limited energy budgets. Emerging energy harvesting technologies can achieve the longstanding vision of self-powered, long-lived sensors. In particular, miniature microbial solar cells (MSCs) can be the most feasible power source for small and low-power sensor nodes in unattended working environments because they continuously scavenge power from microbial photosynthesis by using the most abundant resources on Earth; solar energy and water. Even with low illumination, the MSC can harvest electricity from microbial respiration. Despite the vast potential and promise of miniature MSCs, their power and lifetime remain insufficient to power potential WSN applications. In this overview, we will introduce the field of miniature MSCs, from early breakthroughs to current achievements, with a focus on emerging techniques to improve their performance. Finally, challenges and perspectives for the future direction of miniature MSCs to self-sustainably power WSN applications will be given.

Antimicrobial enzymatic biofuel cells

A compact antibiotic delivery system based on enzymatic biofuel cells was prepared, in which ampicillin was released when discharged in the presence of glucose and O₂. The release of ampicillin was effective in inhibiting the growth of bacterium Escherichia coli as confirmed by ex situ and in situ release studies in culture media.

Bilirubin oxidase oriented on novel type three-dimensional biocathodes with reduced graphene aggregation for biocathode

Aggregation of reduced graphene oxide (RGO) due to π-π stacking is a recurrent problem in graphene-based electrochemistry, decreasing the effective working area and therefore the performance of the RGO electrodes. Dispersing RGO on three-dimensional (3D) carbon paper electrodes is one strategy towards overcoming this challenge, with partial relief aggregation. In this report, we describe the grafting of negatively charged 4-aminobenzoic acid (4-ABA) onto a graphene functionalized carbon paper electrode surface. 4-ABA functionalization induces separation of the RGO layers, at the same time leading to favorable orientation of the blue multi-copper enzyme Myrothecium verrucaria bilirubin oxidase (MvBOD) for direct electron transfer (DET) in the dioxygen reduction reaction (ORR) at neutral pH. Simultaneous electroreduction of graphene oxide to RGO and covalent attachment of 4-ABA are achieved by applying alternating cathodic and anodic electrochemical potential pulses, leading to a high catalytic current density (Δj_cat:193 ± 4 μA cm^-2) under static conditions. Electrochemically grafted 4-ABA not only leads to a favorable orientation of BOD as validated by fitting a kinetic model to the electrocatalytic data, but also acts to alleviate RGO aggregation as disclosed by scanning electron microscopy, most likely due to the electrostatic repulsion between 4-ABA-grafted graphene layers. With a half-lifetime of 55 h, the bioelectrode also shows the highest operational stability for DET-type MvBOD-based bioelectrodes reported to date. The bioelectrode was finally shown to work well as a biocathode of a membrane-less glucose/O₂ enzymatic biofuel cell with a maximum power density of 22 μW cm^-2 and an open circuit voltage of 0.51 V.

Enzymatic Biofuel Cells for Self-Powered, Controlled Drug Release

Self-powered drug-delivery systems based on conductive polymers (CPs) that eliminate the need for external power sources are of significant interest for use in clinical applications. Osmium redox polymer-mediated glucose/O₂ enzymatic biofuel cells (EBFCs) were prepared with an additional CP-drug layer on the cathode. On discharging the EBFCs in the presence of glucose and dioxygen, model drug compounds incorporated in the CP layer were rapidly released with negligible amounts released when the EBFCs were held at open circuit. Controlled and ex situ release of three model compounds, ibuprofen (IBU), fluorescein (FLU), and 4',6-diamidino-2-phenylindole (DAPI), was achieved with this self-powered drug-release system. DAPI released in situ in cell culture media was incorporated into retinal pigment epithelium (RPE) cells. This work demonstrates a proof-of-concept responsive drug-release system that may be used in implantable devices.

Development of graphene-based enzymatic biofuel cells: A minireview

Enzymatic biofuel cells (EBFCs) have attracted increasing attention due to their potential to harvest energy from a wide range of fuels under mild conditions. Fabrication of effective bioelectrodes is essential for the practical application of EBFCs. Graphene possesses unique physiochemical properties making it an attractive material for the construction of EBFCs. Despite these promising properties, graphene has not been used for EBFCs as frequently as carbon nanotubes, another nanoscale carbon allotrope. This review focuses on current research progress in graphene-based electrodes, including electrodes modified with graphene derivatives and graphene composites, as well as free-standing graphene electrodes. Particular features of graphene-based electrodes such as high conductivity, mechanical flexibility and high porosity for bioelectrochemical applications are highlighted. Reports on graphene-based EBFCs from the last five years are summarized, and perspectives for graphene-based EBFCs are offered.

Porous Gold: A New Frontier for Enzyme-Based Electrodes

Porous gold (PG) layers modified electrodes have emerged as valuable enzyme support to realize multiple enzyme-based bioelectrochemical devices like biosensors, enzymatic fuel cells (EFCs), smart drug delivery devices triggered by enzyme catalyzed reactions, etc. PG films can be synthesized by using different methods such as dealloying, electrochemical (e.g., templated electrochemical deposition, self-templated electrochemical deposition, etc.) self-assembly and sputter deposition. This review aims to summarize the recent findings about PG synthesis and electrosynthesis, its characterization and application for enzyme-based electrodes used for biosensors and enzymatic fuel cells (EFCs) development.

The emerging science of electrosynbionics

Dramatic changes in electricity generation, use and storage are needed to keep pace with increasing demand while reducing carbon dioxide emissions. There is great potential for application of bioengineering in this area. We have the tools to re-engineer biological molecules and systems, and a significant amount of research and development is being carried out on technologies such as biophotovoltaics, biocapacitors, biofuel cells and biobatteries. However, there does not seem to be a satisfactory overarching term to describe this area, and I propose a new word-'electrosynbionics'. This is to be defined as: the creation of engineered devices that use components derived from or inspired by biology to perform a useful electrical function. Here, the phrase 'electrical function' is taken to mean the generation, use and storage of electricity, where the primary charge carriers may be either electrons or ions. 'Electrosynbionics' is distinct from 'bioelectronics', which normally relates to applications in sensing, computing or electroceuticals. Electrosynbionic devices have the potential to solve challenges in electricity generation, use and storage by exploiting or mimicking some of the desirable attributes of biological systems, including high efficiency, benign operating conditions and intricate molecular structures.

Tackling the Challenges of Enzymatic (Bio)Fuel Cells

The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.

A self-charging cyanobacterial supercapacitor

Microliter-scale photosynthetic microbial fuel cells (micro-PMFC) can be the most suitable power source for unattended environmental sensors because the technique can continuously generate electricity from microbial photosynthesis and respiration through day-night cycles, offering a clean and renewable power source with self-sustaining potential. However, the promise of this technology has not been translated into practical applications because of its relatively low performance. By creating an innovative supercapacitive micro-PMFC device with maximized bacterial photoelectrochemical activities in a well-controlled, tightly enclosed micro-chamber, this work established innovative strategies to revolutionize micro-PMFC performance to attain stable high power and current density (38 μW/cm² and 120 μA/cm²) that then potentially provides a practical and sustainable power supply for the environmental sensing applications. The proposed technique is based on a 3-D double-functional bio-anode concurrently exhibiting bio-electrocatalytic energy harvesting and charge storing. It offers the high-energy harvesting functionality of micro-PMFCs with the high-power operation of an internal supercapacitor for charging and discharging. The performance of the supercapacitive micro-PMFC improved significantly through miniaturizing innovative device architectures and connecting multiple miniature devices in series.

Hierarchical bi-continuous Pt decorated nanoporous Au-Sn alloy on carbon fiber paper for ascorbic acid, dopamine and uric acid simultaneous sensing

In this work, Pt nanoparticles modified nanoporous AuSn(Pt@NP-AuSn) alloy on Ni buffered flexible carbon fiber paper (CFP) is fabricated by a simple replacement reaction in which NP-AuSn is fabricated by controllable dealloy of electrodeposited Au-Sn alloy films. The as prepared Pt@NP-AuSn/Ni/CFP possesses hierarchical pore structure, high specific surface area and excellent catalytic activity. Due to the bi-functions of both the large surface area of nanoporous metal and macroporous of carbon fiber paper facilitating mass transfer, the Pt@NP-AuSn/Ni/CFP shows high sensitivity of detecting ascorbic acid (AA), dopamine (DA) and uric acid (UA), with sensitivities of 0.14 μA μM^-1 cm^-2, 15.23 μA μM^-1 cm^-2, 0.28 μA μM^-1 cm^-2 under the concentration ranging from 200 to 2000 μM, 1-10 μM, and 25-800 μM for AA, DA and UA, respectively. Further, the Pt@NP-AuSn/Ni/CFP possesses long-term stability of sensing AA, DA and UA and presents great anti-interference towards a variety of common compounds in body fluid. All of these results manifest the Pt@NP-AuSn/Ni/CFP can be a promising candidate for the application of the electrochemical sensor for simultaneous detection of AA, DA and UA.

Wearable biofuel cells based on the classification of enzyme for high power outputs and lifetimes

Wearable enzymatic biofuel cells would be the most prospective fuel cells for wearable devices because of their low cost, compactness and flexibility. As the high specificity and catalytic properties of enzymes, enzymatic biofuel cells (EBFCs) catalyze the fuel associated with the redox reaction and get electrical energy. Available biofuels such as glucose, lactate and pyruvate can be harvested from biofluids of sweat, tears and blood, which afford cells a favorable use in implantable and wearable devices. However, the development of wearable enzymatic biofuel cells requires significant improvements on the power density and enzymes lifetime. In this paper, some new advances in improving the performance of wearable enzymatic biofuel cells are reviewed based on the bioanode and biocathode by classifying single-enzyme and multi-enzyme catalysis system. Thereinto, the bioanode usually contains oxidases and dehydrogenases as catalyst, and the biocathode utilizes the catalysis of multi-copper oxidases (MCOs) in the single system. For further enhancing the power density, efforts to develop multi-enzyme catalysis strategies are discussed in bioanode and biocathode respectively. Moreover, some potential technologies in recent years, such as carbon nanodots, CNT sponges and mixed operational/storage electrode are summarized owing to notable efficiency and the capability of enhancing electron transfer on the electrode. Finally, major challenges and future prospects are discussed for the high power output, stable and practical wearable enzymatic biofuel cells.

Nanoporous Gold-Based Biofuel Cells on Contact Lenses

A lactate/O₂ enzymatic biofuel cell (EBFC) was prepared as a potential power source for wearable microelectronic devices. Mechanically stable and flexible nanoporous gold (NPG) electrodes were prepared using an electrochemical dealloying method consisting of a pre-anodization process and a subsequent electrochemical cleaning step. Bioanodes were prepared by the electrodeposition of an Os polymer and Pediococcus sp. lactate oxidase onto the NPG electrode. The electrocatalytic response to lactate could be tuned by adjusting the deposition time. Bilirubin oxidase from Myrothecium verrucaria was covalently attached to a diazonium-modified NPG surface. A flexible EBFC was prepared by placing the electrodes between two commercially available contact lenses to avoid direct contact with the eye. When tested in air-equilibrated artificial tear solutions (3 mM lactate), a maximum power density of 1.7 ± 0.1 μW cm^-2 and an open-circuit voltage of 380 ± 28 mV were obtained, values slightly lower than those obtained in phosphate buffer solution (2.4 ± 0.2 μW cm^-2 and 455 ± 21 mV, respectively). The decrease was mainly attributed to interference from ascorbate. After 5.5 h of operation, the EBFC retained 20% of the initial power output.

Fuel-independent and membrane-less self-charging biosupercapacitor

A fuel-independent self-charging biosupercapacitor consisting of an enzymatic biocathode and a bioelectrode employing supercapacitive features of immobilized myoglobin is described.

A quasi-solid-state and self-powered biosupercapacitor based on flexible nanoporous gold electrodes

A quasi-solid-state and flexible biofuel cell using a hydrogel electrolyte preloaded with sugar as a fuel is described.

Enzyme Immobilization on Nanoporous Gold: A Review

Nanoporous gold (referred to as np-Au or NPG) has emerged over the past 10 years as a new support for enzyme immobilization. The material has appealing features of ease of preparation, tunability of pore size, high surface to volume ratio, and compatibility with multiple strategies for enzyme immobilization. The np-Au material is especially of interest for immobilization of redox enzymes for biosensor and biofuel cell applications given the ability to construct electrodes of high surface area and stability. Adjustment of the pore size of np-Au can yield enhancements in enzyme thermal stability. Glucose oxidase immobilization on np-Au has been a focus for development of glucose sensors. Immobilization of laccase and related enzymes has demonstrated the utility of np-Au for construction of biofuel cells. Np-Au has been used to immobilize other redox enzymes, enzyme conjugates for use in bioassays, and enzymes of interest for industrial processes.

Magnetic Nanoparticle-Reduced Graphene Oxide Nanocomposite as a Novel Bioelectrode for Mediatorless-Membraneless Glucose Enzymatic Biofuel Cells

In this work, an enzymatic biofuel cell (EBC) based on a membraneless and mediatorless glucose enzymatic fuel cell system was constructed for operation in physiological conditions (pH 7.0 and temperature 37 °C). The new platform EBC made of nanocomposite, including magnetic nanoparticles (Fe₃O₄ NPs) and reduced graphene oxide (RGO), was used for the immobilization of glucose oxidase (GOD) as bioanode and bilirubin oxidase (BOD) as biocathode. The EBC bioelectrodes were fabricated without binder or adhesive agents for immobilized enzyme and the first EBC using superparamagnetic properties with Fe₃O₄ NPs has been reported. The performance of the EBC was evaluated with promising results. In EBC tests, the maximum power density of the EBC was 73.7 μW cm⁻² and an open circuit voltage (OCV) as +0.63 V with 5 mM of glucose concentration for the physiological condition of humans. The Fe₃O₄-RGO nanocomposite offers remarkable enhancement in large surface areas, is a favorable environment for enzyme immobilization, and facilitates electron transfer between enzymes and electrode surfaces. Fe₃O₄ and RGO have been implied as new promising composite nanomaterials for immobilizing enzymes and efficient platforms due to their superparamagnetism properties. Thus, glucose EBCs could potentially be used as self-powered biosensors or electric power sources for biomedical device applications.

Effective immobilization of alcohol dehydrogenase on carbon nanoscaffolds for ethanol biofuel cell

An efficient approach for immobilizing alcohol dehydrogenase (ADH) while enhancing its electron transfer ability has been developed using poly(2-(trimethylamino)ethyl methacrylate) (MADQUAT) cationic polymer and carbon nanoscaffolds. The carbon nanoscaffolds were comprised of single-walled carbon nanotubes (SWCNTs) wrapped with reduced graphene oxide (rGO). The ADH entrapped within the MADQUAT that was present on the carbon nanoscaffolds exhibited a high electron exchange capability with the electrode through its cofactor β-nicotinamide adenine dinucleotide hydrate and β-nicotinamide adenine dinucleotide reduced disodium salt hydrate (NAD⁺/NADH) redox reaction. The advantages of the carbon nanoscaffolds used as the support matrix and the MADQUAT employed for the entrapment of ADH versus physisorption were demonstrated via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Our experimental results showed a higher electron transfer, electrocatalytic activity, and rate constant for MADQUAT entrapped ADH on the carbon nanoscaffolds. The immobilization of ADH using both MADQUAT and carbon nanoscaffolds exhibited strong potential for the development of an efficient bio-anode for ethanol powered biofuel cells.