Three-dimensional graphene networks as a new substrate for immobilization of laccase and dopamine and its application in glucose/O2 biofuel cell

Implementation of π-π interaction in AuNPs@GDY to boost the bioelectrocatalysis in enzymatic biofuel cells

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.

Effect of sucrose-based carbon foams as negative electrode additive on the performance of lead-acid batteries under high-rate partial-state-of-charge condition

Lead-acid batteries are noted for simple maintenance, long lifespan, stable quality, and high reliability, widely used in the field of energy storage. However, during the use of lead-acid batteries, the negative electrode is prone to irreversible sulfation, failing to meet the requirements of new applications such as maintenance-free hybrid vehicles and solar energy storage. In this study, in order to overcome the sulfation problem and improve the cycle life of lead-acid batteries, active carbon (AC) was selected as a foaming agent and foam fixing agent, and carbon foams (CF) with layered porous structure was prepared by mixing with molten sucrose. Sucrose as raw material is green and cheap, and the material preparation process is simple. The prepared CF material was then added as an additive to the negative electrode plate, and the electrochemical performance of the electrode plate and the battery was studied. The results proved that the addition of CF could effectively inhibit the sulfate formation of the negative electrode plate, with the 1.0 % CF negative electrode plate showing the best electrochemical performance. Specifically, according to the result of battery cycle testing, the simulated battery with CF had a cycle life of 3642 times, which was 2.87 times that of the blank group and 2.39 times of the AC group. Meanwhile, rate testing showed that the simulated battery with CF could maintain a high capacity even under high-rate discharge conditions.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Flexible and Stretchable Enzymatic Biofuel Cell with High Performance Enabled by Textile Electrodes and Polymer Hydrogel Electrolyte

Biofuel cells with good biocompatibility are promising to be used as the power source for flexible and wearable bioelectronics. We here report a type of highly flexible and stretchable biofuel cells, which are enabled by textile electrodes of graphene/carbon nanotubes (G/CNTs) composite and polymer hydrogel electrolyte. The CNT array covalently grown from a graphene layer not only can be served as a conducting substrate to immobilize enzyme molecules but also can provide efficient charge transport channels between the enzyme and graphene electrode. As a result, the developed biofuel cells deliver a high open-circuit voltage of 0.65 V and output power density of 64.2 μW cm^-2, which are much higher than previously reported results. Benefiting from the unique textile structure of electrodes and the polymer hydrogel electrolyte, the biofuel cells exhibit high retention of power density after 400 bending cycles and even stretched to a high strain of 60%.

Energy Harvesting Untethered Soft Electronic Devices

Advances in wearable and stretchable electronic technologies have yielded a wide range of electronic devices that can be conformably worn by, or implanted in humans to measure physiological signals. Moreover, various cutting-edge technologies for battery-free electronic devices have led to advances in healthcare devices that can continuously measure long-term biosignals for advanced human-machine interface and clinical diagnostics. This report presents the recent progress in battery-less, wearable devices using a wide range of energy harvesting sources, such as electromagnetic energy, mechanical energy, and biofuels. Additionally, this report also discusses the principles and working mechanisms of near/far-field communications, triboelectric, thermoelectric, and biofuel technologies.

Rational design of N-doped CNTs@C3N4 network for dual-capture of biocatalysts in enzymatic glucose/O2 biofuel cells

Carbonaceous materials are promising electrode materials for enzymatic biofuel cells (EBFCs) due to their excellent electrical conductivity, chemical and physical stability and biocompatibility. Design and preparation of carbon materials with a hollow structure and a rough surface are of great significance for immobilization of enzymes both inside and outside the carbon materials for EBFC applications. We report herein the synthesis of novel carbonaceous materials consisting of bamboo-shaped hollow N-doped carbon nanotubes (N-CNTs) and C3N4 nanosheets (denoted as N-CNTs@C3N4) as electrode materials for dual-capture of enzymes in glucose/O2 EBFCs. The combination of one-dimensional N-CNTs with an open structure and two-dimensional C3N4 nanosheets forms a three-dimensional crosslinking network that significantly enhances the immobilization of enzymes, electrode stability, and mass transfer of substrates, thus boosting the EBFC performance. As a result, EBFCs equipped with N-CNTs@C3N4 can generate a high open circuit potential of 0.93 V and output a maximum power density of 0.57 mW cm-2 at 0.47 V. Additionally, the as-fabricated glucose/O2 EBFCs are capable of directly harvesting energy from various soft drinks, which indicates the promising applications of the N-CNTs@C3N4 nanocomposite as an electrode material for EBFCs.

3D Graphene Materials: From Understanding to Design and Synthesis Control

Carbon materials, with their diverse allotropes, have played significant roles in our daily life and the development of material science. Following 0D C₆₀ and 1D carbon nanotube, 2D graphene materials, with their distinctively fascinating properties, have been receiving tremendous attention since 2004. To fulfill the efficient utilization of 2D graphene sheets in applications such as energy storage and conversion, electrochemical catalysis, and environmental remediation, 3D structures constructed by graphene sheets have been attempted over the past decade, giving birth to a new generation of graphene materials called 3D graphene materials. This review starts with the definition, classifications, brief history, and basic synthesis chemistries of 3D graphene materials. Then a critical discussion on the design considerations of 3D graphene materials for diverse applications is provided. Subsequently, after emphasizing the importance of normalized property characterization for the 3D structures, approaches for 3D graphene material synthesis from three major types of carbon sources (GO, hydrocarbons and inorganic carbon compounds) based on GO chemistry, hydrocarbon chemistry, and new alkali-metal chemistry, respectively, are comprehensively reviewed with a focus on their synthesis mechanisms, controllable aspects, and scalability. At last, current challenges and future perspectives for the development of 3D graphene materials are addressed.

Optimization of rGO-PEI/Naph-SH/AgNWs/Frt/GOx nanocomposite anode for biofuel cell applications

The present study reports a new nanocomposite design using surface modified silver nanowires decorated on the surface of polyethyleneimine (PEI), a cationic polymer acting as glue for anchoring nanowires and reduced graphene oxide (rGO). The synthesized nanocomposite was employed as a promising electrode material for immobilization of biomolecules and effective transportation of electron, in enzymatic biofuel cell (EBFCs) application. The synthesized nanocomposite was confirmed by analytical techniques, for instance, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The electrochemical behaviour of the nanobioelectrocatalysts rGO-PEI/Frt/GOx, rGO-PEI/AgNWs/Frt/GOx, and rGO-PEI/Naph-SH/AgNWs/Frt/GOx was determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). The maximum current density obtained by the modified bioanode was found to be 19.9 mA cm⁻² at the limiting glucose concentration of 50 mM in PBS (pH 7.0) as supporting electrolyte at a scan rate of 100 mVs⁻¹.

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.

Three-dimensional macroporous gold electrodes superior to conventional gold disk electrodes in the construction of an electrochemical immunobiosensor for Staphylococcus aureus detection

Herein, a three-dimensional macroporous gold (3DMG) electrode is demonstrated to be a better choice than a conventional gold disk electrode in the construction of an electrochemical immunobiosensor for Staphylococcus aureus (S. aureus) detection. The 3DMG electrode was prepared on a gold disk electrode by one-step electrodeposition using hydrogen bubbles as dynamic templates. The 3DMG electrode has a high electrochemically active surface area with pore sizes ranging from 20 to 50 μm, and these unique features are conducive to the immobilization of primary antibodies and the capture of S. aureus. Secondary antibodies (Ab2) and alkaline phosphatase (ALP) were immobilized on mesoporous silica nanospheres (MSNs), and the resulting ALP-MSNs-Ab2 composites were utilized as signal tags to construct a sandwich-type electrochemical immunobiosensor. S. aureus was measured based on alkaline phosphatase-catalyzed silver deposition and differential pulse voltammetric detection. The linear range is from 5 to 109 CFU mL-1, and the detection limit is 2 CFU mL-1 for S. aureus detection. Due to the signal amplification of the 3DMG electrode, the sensitivity of the immunobiosensor constructed on the 3DMG electrode is 9 times that of an immunobiosensor constructed on a gold disc electrode. The proposed biosensor was successfully applied for detecting S. aureus in milk samples.

Challenges and Opportunities of Carbon Nanomaterials for Biofuel Cells and Supercapacitors: Personalized Energy for Futuristic Self-Sustainable Devices

Various carbon allotropes are fundamental components in electrochemical energy-conversion and energy-storage devices, e.g., biofuel cells (BFCs) and supercapacitors. Recently, biodevices, particularly wearable and implantable devices, are of distinct interest in biomedical, fitness, academic, and industrial fields due to their new fascinating capabilities for personalized applications. However, all biodevices require a sustainable source of energy, bringing widespread attention to energy research. In this review, we detail the progress in BFCs and supercapacitors attributed to carbon materials. Self-powered biosensors for futuristic biomedical applications are also featured. To develop these energy devices, many challenges needed to be addressed. For this reason, there is a need to: optimize the electron transfer between the enzymatic site and electrode; enhance the power efficiency of the device in fluctuating oxygen conditions; strengthen the efficacy of enzymatic reactions at the carbon-based electrodes; increase the electrochemically accessible surface area of the porous electrode materials; and refine the flexibility of traditional devices by introducing a mechanical resiliency of electrochemical devices to withstand daily multiplexed movements. This article will also feature carbon nanomaterial research alongside opportunities to enhance energy technology and address the challenges facing the field of personalized applications. Carbon-based energy devices have proved to be sustainable and compatible energy alternatives for biodevices within the human body, serving as attractive options for further developing diverse domains, including individual biomedical applications.

Dual Engineering Interface-Driven Complementary Graphene Oxide-Protein Dimer Supramolecular Architecture Enables Nucleus Imaging and Therapy

Seeking a versatile nanoplatform for multimodal nucleus imaging and therapy is a challenging task. General complementary bottom-up bionanotechnology for controlling a 3D supramolecular coassembly is proposed. The dual engineering interface proof-of-concept of the supramolecular architecture can be demonstrated via a genetically engineered protein dimer and plasmonically engineered graphene oxide (GO). Incorporation of anisotropic plasmonic nanoparticles as an intercalation layer among the GO 3D supramolecular architecture can provide covalent conjugation sites and simultaneously endow tunable optical properties of GO, ranging from the ultraviolet-to-near-infrared region. Interestingly, the precise design of a specific two-site mutation of the plasmid is favorable for giving an organized coassembly instead of random networks of GO, which contributes to giving continuous distinguishable enhanced Raman imaging for tracking cancer cells. Unexpectedly, penetration into the cell nucleus via the submicro 3D supramolecular coassembly exhibits an excellent nucleus therapeutic potential of cancer cells.

Kraton based polymeric nanocomposite bioanode for the application in a biofuel cell

The objective of this work is to introduce a nanocomposite based bioanode for biofuel cell application. The as-prepared Kraton/MWCNTs nanocomposite was used as a current enhancer and ferritin (Frt) as a mediator between glucose oxidase (GOx) and the electrode surface. The hybrid anode achieved enzymatic oxidation of glucose by the nanocomposite reflecting an efficient energy conversion from glucose. The resulting Kraton/MWCNTs/Frt/GOx bioande exhibited good catalytic activity towards glucose oxidation along with excellent stability. The maximum current density attained by the bioanode is 1.14 mA cm^-2 at the optimum glucose concentration of 60 mM. This enzymatic strategy can be employed to develop other polysaccharide or oligosaccharide fuel cells in which glucose oxidation is involved.

A shriveled rectangular carbon tube with the concave surface for high-performance enzymatic glucose/O2 biofuel cells

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/O₂, 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.

Three-Dimensional Graphene Foams: Synthesis, Properties, Biocompatibility, Biodegradability, and Applications in Tissue Engineering

Presently, clinical nanomedicine and nanobiotechnology have impressively demanded the generation of new organic/inorganic analogues of graphene (as one of the intriguing biomedical research targets) for stem-cell-based tissue engineering. Among different shapes of graphene, three-dimensional (3D) graphene foams (GFs) are highly promising candidates to provide conditions for mimicking in vivo environments, affording effective cell attachment, proliferation,and differentiation due to their unique properties. These include the highest biocompatibility among nanostructures, high surface-to-volume ratio, 3D porous structure (to provide a homogeneous/isotropic growth of tissues), highly favorable mechanical characteristics, and rapid mass and electron transport kinetics (which are required for chemical/physical stimulation of differentiated cells). This review aims to describe recent and rapid advances in the fabrication of 3D GFs, together with their use in tissue engineering and regenerative nanomedicine applications. Moreover, we have summarized a broad range of recent studies about the behaviors, biocompatibility/toxicity,and biodegradability of these materials, both in vitro and in vivo. Finally, the highlights and challenges of these 3D porous structures, compared to the current polymeric scaffold competitors, are discussed.

Improved Electrical Wiring of Glucose Oxidase Enzyme with an in-Situ Immobilized Mn(1,10-Phenanthroline)2Cl2-Complex/Multiwalled Carbon Nanotube-Modified Electrode Displaying Superior Performance to Os-Complex for High-Current Sensitivity Bioelectrocatalytic and Biofuel Cell Applications

The search for a new and efficient transducer that can electrically connect enzyme active sites, like flavin adenine dinucleotide in glucose oxidase (GOx), with the electrode surface is a cutting-edge research area. Currently, Os(bpy)-complex pendent polyvinylpyridine/polyvinyl imidazole/pyridinium hydrogel based chemically modified electrodes have been widely used for this purpose (bpy = 2,2'-bipyridine). Herein, we report, a [Mn₂^III(phen)₄(O)(Cl)₂]²⁺ complex/Nafion-immobilized carboxylic acid-functionalized multiwalled carbon nanotube modified glassy carbon electrode (GCE/f-MWCNT@Mn₂(Phen)₄O(Cl)₂-Nf, phen = 1,10-phenanthroline), prepared by an in-situ electrochemical method using the precursor, Mn(phen)₂Cl₂, as an efficient and low cost alternate to the Os-complex transducer, for the glucose oxidase enzyme (GOx) based bio-electro-catalytic system. The existence of the key active site, [Mn₂^III(phen)₄(O)(Cl)₂]²⁺, on the modified electrode was confirmed by physicochemical characterizations using transmission electron microscope, Raman, infrared, and UV-vis spectroscopes and electrospray ionization mass spectrometry techniques. The Mn-complex modified electrode showed a redox peak at E°' = 0.55 V vs Ag/AgCl in neutral solution with a surface excess (Γ_Mn) value of 5.6 × 10^-9 mol cm^-2. The GOx enzyme bioanode prepared by adsorbing GOx on the Mn-complex modified electrode has shown an efficient bioelectrocatalytic oxidation of glucose with a Tafel slope value of 111 mV dec^-1. Amperometric i-t analysis of glucose showed a calibration plot in a linear range of 50-550 μM and with current sensitivity of 316.7 μA mM^-1 cm^-2. The current sensitivity value obtained here is about 2-80 000 times higher than that of the Os(bpy)-complex based transducers used for GOx based bio-electro-catalytic applications. Utilizing this new bioanode system along with a Pt-based oxygen reduction electrode, a new biofuel cell was constructed and achieved a power density value 7.5 μW cm^-2.

In Situ Immobilized Sesamol-Quinone/Carbon Nanoblack-Based Electrochemical Redox Platform for Efficient Bioelectrocatalytic and Immunosensor Applications

Most of the common redox mediators such as organic dyes and cyanide ligand-associated metal complex systems that have been used for various electrochemical applications are hazardous nature. Sesamol, a vital nutrient that exists in natural products like sesame seeds and oil, shows several therapeutic benefits including anticancer, antidiabetic, cardiovascular protective properties, etc. Herein, we introduce a new electrochemical redox platform based on a sesamol derivative, sesamol-quinone (Ses-Qn; oxidized sesamol), prepared by the in situ electrochemical oxidation method on a carbon nanoblack chemically modified glassy carbon electrode surface (GCE/CB@Ses-Qn) in pH 7 phosphate buffer solution, for nontoxic and sustainable electrochemical, electroanalytical, and bioelectroanalytical applications. The new Ses-Qn-modified electrode showed a well-defined redox peak at E ^o = 0.1 V vs Ag/AgCl without any surface-fouling behavior. Following three representative applications were demonstrated with this new redox system: (i) simple and quick estimation of sesamol content in the natural herbal products by electrochemical oxidation on GCE/CB followed by analyzing the oxidation current signal. (ii) Utilization of the GCE/CB@Ses-Qn as a transducer, bioelectrocatalytic reduction, and sensing of H₂O₂ after absorbing the horseradish peroxidase (HRP)-based enzymatic system on the underlying surface. The biosensor showed a highly selective H₂O₂ signal with current sensitivity and detection limit values 0.1303 μA μM^-1 and 990 nM, respectively, with tolerable interference from the common biochemicals like dissolved oxygen, cysteine, ascorbic acid, glucose, xanthine, hypoxanthine, uric acid, and hydrazine. (iii) Electrochemical immunosensing of white spot syndrome virus by sequentially modifying primary antibody, antigen, secondary antibody (HRP-linked), and bovine serum albumin on the redox electrode, followed by selective bioelectrochemical detection of H₂O₂.

Enzymatic Fuel Cell-Based Self-Powered Homogeneous Immunosensing Platform via Target-Induced Glucose Release: An Appealing Alternative Strategy for Turn-On Melamine Assay

Enzymatic fuel cell (EFC)-based self-powered biosensors have attracted considerable attention because of their unique feature of no need for extra power sources during the entire detection process, which endows them with the merits of simplicity, rapidness, low cost, anti-interference, and ease of use. Herein, we proposed, for the first time, an EFC-based self-powered homogeneous immunosensing platform by integrating the target-induced biofuel release and bioconjugate immunoassay for ultrasensitive melamine (ME) detection. In this design, the biofuel, i.e., glucose molecules, was entrapped in the pores of positively charged mesoporous silica nanoparticles and capped by the biogate AuNPs-labeled anti-ME antibody (AuNPs-Ab). The presence of the target ME triggered the entrapped glucose release due to the removal of the biogate via immunoreaction, which resulted in the transfer of electrons produced by glucose oxidation at the bioanode to the biocathode, and thus, the open-circuit voltage of the EFC-based self-powered immunosensor dramatically increased, realizing the ultrasensitive turn-on assay for ME. The limit of detection for ME assay was down to 2.1 pM (S/N = 3), superior to those previously reported in the literature. Notably, real milk samples need no special sample pretreatment for the detection of ME because of the good anti-interference ability of EFC-based self-powered biosensors and the excellent selectivity of the homogeneous immunoassay. Therefore, this appealing self-powered homogeneous immunosensing platform holds great promise as a successful prototype of portable and on-site bioassay in the field of food safety.

Improved Performance of Glucose Bioanodes Using Composites of (7,6) Single-Walled Carbon Nanotubes and a Ferrocene-LPEI Redox Polymer

The effect of incorporating different types of carbon nanotubes into composite films of a redox polymer (FcMe₂-C₃-LPEI) and glucose oxidase (GOX) was investigated. The composite films were constructed by first forming a high-surface area network film of either single-walled carbon nanotubes (SWNTs) or multiwalled carbon nanotubes (MWNTs) on a glassy carbon electrode (GCE) by solution casting of a suspension of Triton-X-100 dispersed SWNTs. Next a glucose responsive redox hydrogel was formed on top of the nanotube-modified electrode by cross-linking FcMe₂-C₃-LPEI with glucose oxidase via ethylene glycol diglycidyl ether (EGDGE). Electrochemical and enzymatic measurements showed that composite films made with (7,6) SWNTs produced a higher response (3.3 mA/cm²) to glucose than films made with (6,5) SWNTs (1.8 mA/cm²) or MWNTs (1.2 mA/cm²) or films made without SWNTs (0.7 mA/cm²). We also show that the response of the composite films could be systematically varied by fabricating SWNT films with different weight ratios of (7,6) and (6,5) SWNTs. Optimization of the (7,6) SWNTs loading and the redox polymer-enzyme film produced a glucose response of 11.2 mA/cm². Combining the optimized glucose films with a platinum oxygen breathing cathode into a biofuel cell produced a maximum power density output of 343 μW/cm².

Ultrasensitive Self-Powered Aptasensor Based on Enzyme Biofuel Cell and DNA Bioconjugate: A Facile and Powerful Tool for Antibiotic Residue Detection

Herein, we reported a novel ultrasensitive one-compartment enzyme biofuel cells (EBFCs)-based self-powered aptasensing platform for antibiotic residue detection. By taking full advantage of the unique features of both EBFCs-based self-powered sensors and aptamers, the as-proposed aptasensing platform has the merits of simple instrumentation, anti-interference ability, high selectivity, and low cost. In this study, DNA bioconjugate, i.e., SiO₂@gold nanoparticles-complementary strand of aptamer (SiO₂@AuNPs-csDNA), was elaborately designed and played a key role in blocking the mass transport of glucose to the bioanode. While in the presence of the target antibiotic, SiO₂@AuNPs-csDNA bioconjugate broke away from the bioanode due to the aptamer recognition of the target. Without the blocking of glucose by the DNA bioconjugate, a significantly elevated open circuit voltage of the EBFCs-based aptasensor was obtained, whose amplitude was dependent on the antibiotic concentration. In addition, this proposed aptasensor was the first reported self-powered aptasensing platform for antibiotic determination and featured high sensitivity owing to the elaborate design of the DNA bioconjugate modified bioanode of EBFC, which was superior to those previously reported in the literature. Furthermore, due to the anti-interference ability and the excellent selectivity of the aptasensor, no special sample pretreatment was needed for the detection of antibiotics in milk samples. Therefore, the proposed EBFCs-based self-powered aptasensor has a great promise to be applied as a powerful tool for on-site assay in the field of food safety.

Al-Based porous coordination polymer derived nanoporous carbon for immobilization of glucose oxidase and its application in glucose/O2 biofuel cell and biosensor

Herein, we report the first example of using the Al-based porous coordination polymers (Al-PCP) as a template for preparation of nanoporous carbon through a two-step carbonized method.

Nanostructured material-based biofuel cells: recent advances and future prospects

The review provides comprehensive discussions about electrode materials of BFCs and prospects of this technology for real-word applications.

Direct electrochemistry and bioelectrocatalysis of glucose oxidase in CS/CNC film and its application in glucose biosensing and biofuel cells

Due to their unique physicochemical properties, carbon nanochips (CNCs) have been used for studies of the direct electrochemical and electrocatalytic properties of oxidoreductase.

Dominant Factors Governing the Electron Transfer Kinetics and Electrochemical Biosensing Properties of Carbon Nanofiber Arrays

Carbon-based electrodes have been widely used in electroanalysis for more than half a century, but the factors governing the heterogeneous electron-transfer (HET) rate are still unclear. The effects of the exposed edge plane site density, inherent resistance of the carbon electrode, and adjustable resistors on the HET kinetics of several outer- and inner-sphere redox couples including [Fe(CN)₆]^3-/4-, Ru(NH₃)₆^3+/2+, Fe^3+/2+, dopamine, ascorbic acid, and uric acid are investigated using three kinds of carbon electrodes composed of core-shell quasi-aligned nanofiber arrays (QANFAs). The internal resistance is found to be a key factor affecting the HET kinetics and electrochemical biosensing properties. The electrodes exhibit high selectivity and sensitivity in dopamine detection in the presence of ascorbic acid and uric acid. In addition to the promising application to electrochemical biosensing, the core-shell TiC/C QANFAs encompassing a highly electroactive carbon shell and conductive TiC core provide insights into the design and construction of the ideal carbon electrode.

Enzymatic Biofuel Cells on Porous Nanostructures

Biofuel cells (BFCs) that utilize enzymes as catalysts represent a new sustainable and renewable energy technology. Numerous efforts have been directed to improve the performance of the enzymatic BFCs (EBFCs) with respect to power output and operational stability for further applications in portable power sources, self-powered electrochemical sensing, implantable medical devices, etc. The latest advances in EBFCs based on porous nanoarchitectures over the past 5 years are detailed here. Porous matrices from carbon, noble metals, and polymers promote the development of EBFCs through the electron transfer and mass transport benefits. Some key issues regarding how these nanostructured porous media improve the performance of EBFCs are also discussed.

Molecular engineering of Ni-/Co-porphyrin multilayers on reduced graphene oxide sheets as bifunctional catalysts for oxygen evolution and oxygen reduction reactions

Ni- and Co-porphyrin multilayers on reduced graphene oxide (rGO) sheets are reported as novel bifunctional catalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). After binding with organic porphyrin molecules, the catalytically-active Ni2+ and Co2+ ions are periodically constructed onto the rGO surfaces via the layer-by-layer (LBL) assembly technique. The resulting catalysts exhibit good performance towards both OER and ORR, which is achieved with accurate control of the composition and thickness of the multilayer structures. This work highlights the potential for the fabrication of efficient electrocatalysts via molecular design.

A polyaniline wrapped aminated graphene composite on nickel foam as three-dimensional electrodes for enzymatic microfuel cells

Ni foam coated with a NH₂-G/PAni composite is reported as a promising 3D electrode material for enzymatic microfuel cells for the first time.

An atom-scale interfacial coordination strategy to prepare hierarchically porous Fe3O4-graphene frameworks and their application in charge and size selective dye removal

A novel atom-scale interfacial coordination assisted synthesis method for the textural engineering of three-dimensional (3D) Fe3O4-graphene oxide frameworks with hierarchical macro- and meso-porous structures is developed.

Graphene based enzymatic bioelectrodes and biofuel cells

The excellent electrical conductivity and ease of functionalization make graphene a promising material for use in enzymatic bioelectrodes and biofuel cells. Enzyme based biofuel cells have attracted substantial interest due to their potential to harvest energy from organic materials. This review provides an overview of the functional properties and applications of graphene in the construction of biofuel cells as alternative power sources. The review covers the current state-of-the-art research in graphene based nanomaterials (physicochemical properties and surface functionalities), the role of these parameters in enhancing electron transfer, the stability and activity of immobilized enzymes, and how enhanced power density can be achieved. Specific examples of enzyme immobilization methods, enzyme loading, stability and function on graphene, functionalized graphene and graphene based nanocomposite materials are discussed along with their advantages and limitations. Finally, a critical evaluation of the performance of graphene based enzymatic biofuel cells, the current status, challenges and future research needs are provided.

Three-dimensional graphene-based composites for energy applications

Three-dimensional (3D) graphene-based composites have drawn increasing attention for energy applications due to their unique structures and properties. By combining the merits of 3D graphene (3DG), e.g., a porous and interconnected network, a high electrical conductivity, a large accessible surface area, and excellent mechanical strength and thermal stability, with the high chemical/electrochemical activities of active materials, 3DG-based composites show great promise as high-performance electrode materials in various energy devices. This article reviews recent progress in 3DG-based composites and their applications in energy storage/conversion devices, i.e., supercapacitors, lithium-ion batteries, dye-sensitized solar cells, and fuel cells.

Membrane/mediator-free rechargeable enzymatic biofuel cell utilizing graphene/single-wall carbon nanotube cogel electrodes

Enzymatic biofuel cells (EBFCs) utilize enzymes to convert chemical energy present in renewable biofuels into electrical energy and have shown much promise in the continuous powering of implantable devices. Currently, however, EBFCs are greatly limited in terms of power and operational stability with a majority of reported improvements requiring the inclusion of potentially toxic and unstable electron transfer mediators or multicompartment systems separated by a semipermeable membrane resulting in complicated setups. We report on the development of a simple, membrane/mediator-free EBFC utilizing novel electrodes of graphene and single-wall carbon nanotube cogel. These cogel electrodes had large surface area (∼ 800 m(2) g(-1)) that enabled high enzyme loading, large porosity for unhindered glucose transport and moderate electrical conductivity (∼ 0.2 S cm(-1)) for efficient charge collection. Glucose oxidase and bilirubin oxidase were physically adsorbed onto these electrodes to form anodes and cathodes, respectively, and the EBFC produced power densities up to 0.19 mW cm(-2) that correlated to 0.65 mW mL(-1) or 140 mW g(-1) of GOX with an open circuit voltage of 0.61 V. Further, the electrodes were rejuvenated by a simple wash and reloading procedure. We postulate these porous and ultrahigh surface area electrodes will be useful for biosensing applications, and will allow reuse of EBFCs.