The direct use of enzymatic biofuel cells as functional bioelectronics

Enzymatic biofuel cells (EBFCs) are a subgroup of fuel cells that use enzymes as catalysts. EBFCs that utilizephysiological substrates such as glucose or lactate are of great interest as implantable or wearable power sourcesto activate medical devices. This contribution introduces the working principles of EBFCs and summarizes recentprogress in EBFC-enabled biosensors, pulse generators, and therapy. Biosensors with self-powered characteristicenjoy 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 theapplication in medical related electrostimulation. By providing the direct electrical stimulation, or controllablyreleasing 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.

Amine axial ligand-coordinated cobalt phthalocyanine-based catalyst for flow-type membraneless hydrogen peroxide fuel cell or enzymatic biofuel cell

In this study,an amine-coordinated cobalt phthalocyanine(CoPc)-based anodic catalyst was fabricated by a facile process,to enhance the performance of hydrogen peroxide fuel cells(HPFCs) and enzymatic biofuel cells(EBCs).For this purpose,polyethyleneimine(PEI) was added onto the reduced graphene oxide and CoPc composite(RGO/CoPc) to create abundant NH2 axial ligand groups,for anchoring the Co core within the CoPc.Owing to the PEI addition,the onset potential of the hydrogen peroxide oxidation reaction was shifted by 0.13 V in the negative direction(0.02 V) and the current density was improved by 1.92 times(1.297 mA cm^(-2)),compared to those for RGO/CoPc(0.15 V and 0.676 mA cm^(-2),respectively),due to the formation of donor-acceptor dyads and the prevention of CoPc from leaching out.The biocatalyst using glucose oxidase(GOx)([RGO/CoPc]/PEI/GOx) showed a better onset potential and catalytic activity(0.15 V and 318.7 μA cm^(-2)) than comparable structures,as well as significantly improved operational durability and long-term stability.This is also attributed to PEI,which created a favorable microenvironment for the enzyme.The maximum power densities(MPDs) and open-circuit voltages(OCVs) obtained for HPFCs and EBCs using the suggested catalyst were 105.2±1.3 μW cm^(-2)(0.317±0.003 V) and 25.4±0.9 μW cm^(-2)(0.283±0.007 V),respectively.This shows that the amine axial ligand effectively improves the performance of the actual driving HPFCs and EBCs.

Effect of the protection layer formed by cross-linked gelatin on the stability and performance of glucose and oxygen fuel cells

A glucose oxidation catalyst comprising carbon nanotube,tetrathiafulvalene(TTF),gelatin,glutaraldehyde(GA)and glucose oxidase(GOx)(CNT/[TTF-GOx]/Gelatin+GA)is suggested to enhance the reactivity of glucose oxidation reaction(GOR),and the performance and stability of enzymatic biofuel cells(EBCs)using this catalyst.In this catalyst,TTF is used as mediator to transfer electron effectively,while GA is crosslinked to gelatin to form non-soluble network.The structure prevents the dissolution of gelatin from aqueous electrolyte and reduces the leaching-out of GOx and TTF molecules.To confirm the crosslinking effect of GA and gelatin,Fourier-transform infrared spectroscopy(FT-IR)and electrochemical evaluations are utilized.According to FT-IR analysis,it was observed that the amide I peak shifted after crosslinking.This is evidence showing the appropriate network formation and the reactivity of CNT/[TTFGOx]/Gelatin+GA is well preserved even after multiple potential cycling.In addition,its GOx activity is regularly monitored for one month and the measurements prove that the structure prevents the leaching out of GOx molecules.Based on that,EBC using the anodic catalyst shows excellent performances,such as open circuit voltage of 0.75 V and maximum power density of 184μW/cm^(2).

Screen-Printable Functional Nanomaterials for Flexible and Wearable Single-Enzyme-Based Energy-Harvesting and Self-Powered Biosensing Devices

Developing flexible bioelectronics is essential to the realization of artificial intelligence devices and biomedical applications, such as wearables, but their potential is limited by sustainable energy supply. An enzymatic biofuel cell(BFC) is promising for power supply, but its use is limited by the challenges of incorporating multiple enzymes and rigid platforms. This paper shows the first example of screen-printable nanocomposite inks engineered for a single-enzyme-based energy-harvesting device and a self-powered biosensor driven by glucose on bioanode and biocathode. The anode ink is modified with naphthoquinone and multiwalled carbon nanotubes(MWCNTs), whereas the cathode ink is modified with Prussian blue/MWCNT hybrid before immobilizing with glucose oxidase. The flexible bioanode and the biocathode consume glucose. This BFC yields an open circuit voltage of 0.45 V and a maximum power density of 266 μW cm-2. The wearable device coupled with a wireless portable system can convert chemical energy into electric energy and detect glucose in artificial sweat. The self-powered sensor can detect glucose concentrations up to 10 mM. Common interfering substances,including lactate, uric acid, ascorbic acid, and creatinine, have no effect on this self-powered biosensor. Additionally, the device can endure multiple mechanical deformations. New advances in ink development and flexible platforms enable a wide range of applications, including on-body electronics, self-sustainable applications, and smart fabrics.

Hydrogenase as the basis for green hydrogen production and utilization

Hydrogenase is a paradigm of highly efficient biocatalyst for H_(2) production and utilization evolved in nature. A dilemma is that despite the high activity and efficiency expected for hydrogenases as promising catalysts for the hydrogen economy, the poor oxygen tolerance and low yield of hydrogenases largely hinder their practical application. In these years, the enigmas surrounding hydrogenases regarding their structures, oxygen tolerance, mechanisms for catalysis, redox intermediates, and proton-coupled electron transfer schemes have been gradually elucidated;the schemes, which can well couple hydrogenases with other highly efficient(in)organic and biological catalysts to build novel reactors and drive valuable reactions, make it possible for hydrogenases to find their niches. To see how scientists put efforts to tackle this issue and design novel reactors in the fields where hydrogenases play crucial roles, in this review,recent advances were summarized, including different strategies for protecting enzyme molecules from oxygen, enzyme-based assembling systems for H_(2) evolution in the photoelectronic catalysis, enzymatic biofuel cells for H_(2) utilization and storage and the efficient electricity-hydrogen-carbohydrate cycle for high-purity hydrogen and biofuel automobiles. Limitations and future perspectives of hydrogenasebased applications in H_(2) production and utilization with great impact are discussed. In addition, this review also provides a new perspective on the use of biohydrogen in healthcare beyond energy.

Could hydrogen gas be produced using human cells?

Although fossil fuels are widely used to meet energy needs,intensive research has been carried out in recent years on hydrogen production from renewable sources due to their decrease over time and environmental pollution concerns.Biofuel cell technology is one of the promising current technologies.It has been proven that various microorganisms produce energy through their natural metabolism,and that energy production is produced in biofuel cells by exoelectrogenic microorganisms that can transfer electrons to an electrode surface.Although it has been stated that employing human cells to generate energy is feasible,it is unknown whether doing so would enable the production of hydrogen.Within the scope of this perspective article,the issue of hydrogen production in bioelectrolysis cells using human cells will be discussed for the first time.Optimizing hydrogen production in bioelectrolysis cells using human cells is important in terms of contributing to hydrogen technologies.Within the scope of the article,promising human cell lines for hydrogen production are emphasized and hydrogen production potentials in bioelectrolysis cells using these cell lines are discussed.In conclusion,some human cells can be used for hydrogen gas production in bioelectrolysis cells due to their bioelectrochemical and metabolic properties.

Epidermal self-powered sweat sensors for glucose and lactate monitoring

Sweat could be a carrier of informative biomarkers for health status identification;therefore,wearable sweat sensors have attracted significant attention for research.An external power source is an important component of wearable sensors,however,the current power supplies,i.e.,batteries,limit further shrinking down the size of these devices and thus limit their application areas and scenarios.Herein,we report a stretchable self-powered biosensor with epidermal electronic format that enables the in situ detec-tion of lactate and glucose concentration in sweat.Enzymatic biofuel cells serve as self-powered sensing modules allowing the sweat sensor to exhibit a determination coefficient(R2)of 0.98 with a sensitivity of 2.48 mV/mM for lactate detection,and R2 of 0.96 with a sensitivity of 0.11 mV/μM for glucose detection.The microfluidic channels developed in an ultra-thin soft flexible polydimethylsiloxane layer not only enable the effective collection of sweat,but also provide excellent mechanical properties with stable performance output even under 30%stretching.The presented soft sweat sensors can be integrated at nearly any location of the body for the continuous monitoring of lactate and glucose changes during normal daily activities such as exercise.Our results provide a promising approach to develop next-generation sweat sensors for real-time and in situ sweat analysis.

Anthraquinone Derivative Chiral Schiff Base Copper（Ⅱ） Complexes for Enzyme Type Bio-Fuel Cell Mediators

Electrochemically, laccase, a family of multi-copper oxidase, has specificity for performing not only one-electron oxidation of phenolic-related compounds but also four-electron reduction of oxygen, which is expected to be a cathode of biofuel ceils. We have prepared three amino-acid derivatives （for enhancing affinity to laccase） and one control （just for determining redox behavior of ligands and Cu（II/I）） copper（lI） complexes 0-3 having phenolic-related ligands involving anthraquinone moiety. Enhancing current density of electron transfer between the cathode （composed of electron conducting materials such as Nation and carbon nanotube） and laccase could be observed for all 1-3 acting as good mediators according to （spectro）electrochemical results.

Live microalgal cells modified by L-cys/Au@carbon dots/bilirubin oxidase layers for enhanced oxygen reduction in a membrane-less biofuel cell

Electrochemical oxygen reduced reaction(ORR)is a critical element in clean energy development.Despite efforts to enhance gas transfer to the reaction interface,the low solubility of O_(2)molecules and slow diffusion rate in liquid electrolyte is still a significant challenge.Herein,we design an artificial outer membrane on microalgal cells,which consists of a carbon dots/bilirubin oxidase(CDs/BOD)ORR catalyst layer and a L-cystine/Au nanoporous O_(2)supply layer.O_(2)generated by photosynthesis from microalgal cells then can be directly transported to the CDs/BOD catalytic interfaces,overcoming the sluggish gas transfer in the electrolyte.Thus,the cathode constructed by the fabricated microalgal cells realizes an ORR current density of 655.2μA/cm^(2) with fast ORR kinetics,which is 2.68 times higher than that of a BOD cathode fed with pure O_(2).A membrane-less glucose/O_(2)biofuel cell is further developed using the hybrid artificial cells as the cathode,and the power density is 2.39 times higher than that of a BOD cathode biofuel cell in O_(2)saturated solution.This biomimetic design supplies O_(2)directly to the carbon dots/BOD catalyst layer from the microalgae membrane through a nanoporous L-cys/Au layer,providing an alternative solution for the transfer barrier of O_(2)in the electrolyte.

Uniform ordered mesoporous ZnCo2O4 nanospheres for super-sensitive enzyme-free H2O2 biosensing and glucose biofuel cell applications

Uniform, ordered mesoporous ZnCo2O4 （meso-ZnCo2O4） nanospheres were successfully synthesized using a sacrificing template method. The meso-ZnCo2O4 nanospheres were used for the first time for H2O2 biosensing and in glucose biofuel cells （GBFCs） as an enzyme mimic. The meso-ZnCo2O4 nanospheres not only exhibited excellent catalytic performance in the H2O2 sensor, achieving a high sensitivity （658.92 μA.mM-1.cm-2） and low detection limit （0.3 nM at signal-to-noise ratio （S/N） = 3）, but also performed as an excellent cathode material in GBFCs, resulting in an open circuit voltage of 0.83 V, maximum power density of 0.32 mW.cm-2, and limiting current density of 1.32 mA.cm-2. The preeminent catalytic abilities to H2O2 and glucose may be associated with the large specific surface area of the mesoporous structure in addition to the intrinsic catalytic activity of ZnCo2O4. These significant findings provide a successful basis for developing methods for the supersensitive detection of H2O2 and enriching catalytic materials for biofuel cells.

Preparation of Close-Packed Silver Nanoparticles on Graphene to Improve the Enzyme Immobilization and Electron Transfer at Electrode in Glucose/O2 Biofuel Cell

In this study, chemical reduced graphene-silver nanoparticles hybrid （AgNPs@CR-GO） with close-packed AgNPs structure was used as a conductive matrix to adsorb enzyme and facilitate the electron transfer between im- mobilized enzyme and electrode. A facile route to prepare AgNPs@CR-GO was designed involving in β-cyclodextrin （β-CD） as reducing and stabilizing agent. The morphologies of AgNPs were regulated and controlled by various experimental factors. To fabricate the bioelectrode, AgNPs@CR-GO was modified on glassy carbon electrode followed by immobilization of glucose oxidase （GOx） or laccase. It was demonstrated by electrochemical testing that the electrode with close-packed AgNPs provided high GOx loading （Г=4.80 × 10^- l0 mol·cm^-2） and fast electron transfer rate （ks=5.76 s^-1）. By employing GOx based-electrode as anode and laccase based-electrode as cathode, the assembled enzymatic biofuel cell exhibited a maximum power density of 77.437 μW·cm^-2 and an open-circuit voltage of 0.705 V.