Cathodic Biocatalyst Research Articles

Employing Laccase-Producing Aspergillus sydowii NYKA 510 as a Cathodic Biocatalyst in Self-Sufficient Lighting Microbial Fuel Cell.

In the present work, we isolated and identified Aspergillus sydowii NYKA 510 as the most potent laccase producer. Its medium constituents were optimized to produce the highest possible amount of laccase, which was after 7 days at 31°C and pH 5.2. Banana peel and peptone excelled in inducing laccase production at concentrations of 15.1 and 2.60 g/l, respectively. Addition of copper sulfate elevated enzyme yield to 145%. The fungus was employed in a microbial fuel cell (MFC). The best performance was obtained at 2000 Ω achieving 0.76 V, 380 mAm-2, 160 mWm-2, and 0.4 W. A project to design a self-sufficient lighting unit was implemented by employing a system of 2 sets of 4 MFCs each, connected in series, for electricity generation. A scanning electron microscopy image of A. sydowii NYKA 510 was utilized in algorithmic form generation equations for the design. The mixed patterning and patterned customized mass approach were developed by the authors and chosen for application in the design.

Bioelectricity generation using sulphate-reducing bacteria as anodic and microalgae as cathodic biocatalysts

ABSTRACTBecause microalgal species carry out oxygenic photosynthesis, they can be employed in the cathode chamber of microbial fuel cells, thus negating the need for mechanical aeration for oxygen reduction reactions. A conventional H-shaped configuration is used for comparative analysis of bioelectricity generation using pure and mixed microalgal cultures. Three reactors are simultaneously inoculated with sulphate-reducing bacteria as anodic and mixed culture of microalgae (MA#1) and two pure species in the cathodic chamber in separate reactors (MA#2; MA#3). Maximum open circuit potentials of 670, 476 and 529 mV are achieved with MA#3, MA#2 and MA#1, respectively. Power densities on the order of 442.5, 69 and 135 mW/m3 are obtained for microalgal cultures MA#3, MA#2 and MA#1, respectively. The highest power and current density values are obtained with MA#3 inoculated with pure algal species. The algal species are also examined for their lipid content with the use of Fourier transform infrared spectroscopy, Nile red spectroscopy and lipid content analysis. A good amount of lipid content is shown in spectroscopy images. Biomass content is highest for the algal consortium (MA#1) whereas lipid content is best in the case of pure algal species (MA#2).

Cathodic biocatalyst consisting of laccase and gold nanoparticle for improving oxygen reduction reaction rate and enzymatic biofuel cell performance

New catalyst for promoting oxygen reduction reaction (ORR) and enzymatic biofuel cell (EBC) performance is suggested. The catalyst consist of laccase (LAC) and gold nanoparticle (GNP)-naphthalenethiol (NPT), which are linked to polyethyleneimine (PEI) and carbon nanotube (CNT) (CNT/PEI/[GNP-NPT]/LAC). Its onset potential and ORR rate are improved due to adoptions of PEI and GNP-NPT. Namely, CNT/PEI induces more immobilization of LACs and GNP-NPT acts as electron relay between CNP and NPT by thiol-gold bond and between CNT/PEI and LACs by electron collection effect. Even in EBC measurement, maximum power density of EBC using CNT/PEI/[GNP-NPT]/LAC is highest as 13μWcm−2.

Evolving stability and pH-dependent activity of the high redox potential Botrytis aclada laccase for enzymatic fuel cells

Fungal high redox potential laccases are proposed as cathodic biocatalysts in implantable enzymatic fuel cells to generate high cell voltages. Their application is limited mainly through their acidic pH optimum and chloride inhibition. This work investigates evolutionary and engineering strategies to increase the pH optimum of a chloride-tolerant, high redox potential laccase from the ascomycete Botrytis aclada. The laccase was subjected to two rounds of directed evolution and the clones screened for increased stability and activity at pH 6.5. Beneficial mutation sites were investigated by semi-rational and combinatorial mutagenesis. Fourteen variants were characterised in detail to evaluate changes of the kinetic constants. Mutations increasing thermostability were distributed over the entire structure. Among them, T383I showed a 2.6-fold increased half-life by preventing the loss of the T2 copper through unfolding of a loop. Mutations affecting the pH-dependence cluster around the T1 copper and categorise in three types of altered pH profiles: pH-type I changes the monotonic decreasing pH profile into a bell-shaped profile, pH-type II describes increased specific activity below pH 6.5, and pH-type III increased specific activity above pH 6.5. Specific activities of the best variants were up to 5-fold higher (13 U mg−1) than BaL WT at pH 7.5.

Electrochemically active microorganisms from an acid mine drainage-affected site promote cathode oxidation in microbial fuel cells

The limited database of acidophilic or acidotolerant electrochemically active microorganisms prevents advancements on microbial fuel cells (MFCs) operated under low pH. In this study, three MFCs were used to enrich cathodic biofilms using acid mine drainage (AMD) sediments as inoculum. Linear sweep voltammetry showed cathodic current plateaus of 5.5 (±0.7) mA at about −170mV vs Ag/AgCl and 8.5 (±0.9) mA between −500mV to −450mV vs Ag/AgCl for biofilms developed on small graphite fiber brushes. After gamma irradiation, biocathodes exhibited a decrease in current density approaching that of abiotic controls. Electrochemical impedance spectroscopy showed six-fold lower charge transfer resistance with viable biofilm. Pyrosequencing data showed that Proteobacteria and Firmicutes dominated the biofilms. Acidithiobacillus representatives were enriched in some biocathodes, supporting the potential importance of these known iron and sulfur oxidizers as cathodic biocatalysts. Other acidophilic chemolithoautotrophs identified included Sulfobacillus and Leptospirillum species. The presence of chemoautotrophs was consistent with functional capabilities predicted by PICRUSt related to carbon fixation pathways in prokaryotic microorganisms. Acidophilic or acidotolerant heterotrophs were also abundant; however, their contribution to cathodic performance is unknown. This study directs subsequent research efforts to particular groups of AMD-associated bacteria that are electrochemically active on cathodes.

Self-Powered Arsenic Biosensor Based on the Inhibition of Laccase By As3+ and As5+

Laccase is a multi-copper center enzyme that is able to oxidize phenolic substrates and undergo a four electron reduction of O2 to H2O. The interaction of laccase with different environmental toxins has been reported, whereby laccase can either oxidize pollutants (polyphenols, polyamines and paradiphenols) as fuels or be inhibited by the toxin (mercury and azide).[1] Laccase is also commonly employed within enzymatic fuel cells (EFCs) yielding a biocathode that bioelectrocatalytically reduces O2 to H2O. Self-powered biosensors are advantageous in terms of portability because they are not reliant on external power sources. In the past, glucose/O2 EFCs have been widely used as self-powered biosensors utilizing laccase as the cathodic biocatalyst.[2] Self-powered biosensors that sense based on enzymatic inhibition by an analyte are an important category of self-powered biosensors and have been extensively studied.[3] This study reports the first experimental evidence on the inhibition of laccase by two arsenic species (arsenite and arsenate). The mechanism for both inhibitors was determined to follow an uncompetitive inhibition model via UV-Vis assays using 2,2'azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as the oxidant/indicator. Enzymatic inhibition was also studied electrochemically via amperometric i-t experiments. Furthermore, laccase cathodes were employed as part of a conceptual self-powered arsenite/arsenate biosensor, demonstrating sensitivities of 0.91 ± 0.07 mV/mM for arsenite and 0.98 ± 0.02 mV/mM for arsenate. [1] S. R. Couto, J. L. T. Herrera, Biotechnology advances 2006, 24, 500-513. [2] E. Katz, A. F. Bückmann, I. Willner, Journal of the American Chemical Society 2001, 123, 10752-10753. [3] D. Wen, L. Deng, S. Guo, S. Dong, Analytical chemistry 2011, 83, 3968-3972. Figure 1

Transparent and flexible, nanostructured and mediatorless glucose/oxygen enzymatic fuel cells

Here we detail transparent, flexible, nanostructured, membrane-less and mediator-free glucose/oxygen enzymatic fuel cells, which can be reproducibly fabricated with industrial scale throughput. The electrodes were built on a biocompatible flexible polymer, while nanoimprint lithography was used for their nanostructuring. The electrodes were covered with gold, their surfaces were visualised using scanning electron and atomic force microscopies, and they were also studied spectrophotometrically and electrochemically. The enzymatic fuel cells were fabricated following our previous reports on membrane-less and mediator-free biodevices in which cellobiose dehydrogenase and bilirubin oxidase were used as anodic and cathodic biocatalysts, respectively. The following average characteristics of transparent and flexible biodevices operating in glucose and chloride containing neutral buffers were registered: 0.63 V open-circuit voltage, and 0.6 μW cm−2 maximal power density at a cell voltage of 0.35 V. A transparent and flexible enzymatic fuel cell could still deliver at least 0.5 μW cm−2 after 12 h of continuous operation. Thus, such biodevices can potentially be used as self-powered biosensors or electric power sources for smart electronic contact lenses.

Microbial Electroreduction: Screening for New Cathodic Biocatalysts

AbstractCathodic microbial electrocatalysis, where microorganisms consume electrons from a cathode to perform biochemical reductions, is currently of high interest. For an effective electrochemical screening of potential new cathode biocatalysts, we developed a time‐saving medium‐throughput potentiostatic BES system to evaluate microbial ability to accept reducing equivalents from an electrode in pure cultures. Of nine tested physiologically and phylogenetically different strains, five promising cathode‐active strains were identified: Acidithiobacillus ferrooxidans (jmax=−50 μA cm−2), Desulfosporosinus orientis (jmax=−4 μA cm−2), Thiobacillus denitrificans and Sulfurimonas denitrificans (jmax=−2 μA cm−2 for both), and Desulfovibrio piger (jmax=−1.5 μA cm−2). From this screening, hypotheses were formulated on possible electron consumption and utilization processes. This work serves as a foundation for deeper investigation and characterization of the identified cathode biocatalysts.

Biofilms in Water-Energy-Nexus

Biofilms are used to clean wastewater, convert chemical energy in wastewater to electrical energy, and are ubiquitous in water bodies. Therefore they play a crucial role in the water-energy nexus. In addition, biofilms on electrodes acting as anodic or cathodic biocatalysts can be used to improve water quality. This section invites papers describing the use of biofilms relevant to the water-energy nexus. Specifically, we welcome papers describing 1) the use of biofilms to clean water, 2) the use of biofilms to convert chemical energy in wastewater to electrical energy, 3) the use of biofilms on electrodes to enhance water treatment, 4) the use of biofilms in energy producing devices in natural waters (i.e. sediment/benthic microbial fuel cells), 5) the use of biofilms on electrodes for water desalination, and 6) biofilms used to monitor water quality. Basic science approaches describing mass and electron fluxes operating inside these biofilms that are within the context of the water-energy nexus are especially welcome. We also welcome innovative applications of biofilms not explicitly described above that may be of interest to biofilm researchers.

Effect of Contaminants and Bacteria Presence on Bilirubin Oxidase Based Cathode Operation

Effect of Contaminants and Bacteria Presence on Bilirubin Oxidase Based Cathode Operation

A novel biofuel cell based on electrospun collagen-carbon nanotube nanofibres

The paper demonstrates a novel glucose/O2 biofuel cell (BFC) based on the electrospun collagen-SWNTs nanofibres with the glucose oxidase (GOD) as the anodic biocatalysts and the laccase as the cathodic biocatalysts. With an average diameter of about (260±95) nm, the electrospun collagen-SWNTs nanofibres exhibited smooth surfaces. The collagen-SWNTs nanofibres modified electrode showed good electron transfer behavior, because of the properties of SWNTs and the three-dimensional reticular structure of the electrospun nanofibers. The GOD and laccase, immobilized in the collagen-SWNTs nanofibres, exhibited good catalytic activity towards glucose oxidation and oxygen reduction through mediators of ferrocene monocarboxylic acid (FMCA) and 2,2'-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS), respectively. The maximum power density of the assembled glucose/O2 BFC based on the electrospun collagen-SWNTs nanofibres was ca. 14.3 μW/cm2. Moreover, more than 50% of the initial value remained after continuous operation of 100 h. The results indicated the potential to apply the electrospun collagen-SWNTs nanofibres for novel BFC device.

Microaerophilic microenvironment at biocathode enhances electrogenesis with simultaneous synthesis of polyhydroxyalkanoates (PHA) in bioelectrochemical system (BES)

Microaerophilic microenvironment at biocathode was evaluated for electrogenesis along with the polyhydroxyalkanoates (PHA) accumulation in bio-electrochemical system (BES). The electrogenic activity (512mV; 15.2mW/m2) was extended for longer periods (144h) which might be attributed to the lowering of losses due to the controlled microbial metabolism. Growth limiting stress at cathode due to lower oxygen levels and its effective utilization by the protons and electrons coming from anode, might have diverted the microbial metabolism towards PHA synthesis instead of oxidation. PHA accumulation (19% of dry cell weight (DCW)) was observed with higher hydroxy butyrate (HB) (89%) concentration at 48thh in the cathodic biocatalyst and was re-utilized by the end of experiment. Bio-electro kinetics studied through voltammetry and Tafel analysis further supported the observed electrogenesis in microaerophilic reduction microenvironment, in terms of redox catalytic currents, Tafel slopes, exchange current densities and polarization resistance.

Small-size biofuel cell on paper

In this work, we demonstrated a novel paper-based mediator-less and compartment-less biofuel cell (BFC) with small size (1.5cm×1.5cm). Ionic liquid functionalized carbon nanotubes (CNTs-IL) nanocomposite was used as support for both stably confining the anodic biocatalyst (i.e., NAD+-dependent glucose dehydrogenase, GDH) for glucose electrooxidation and for facilitating direct electrochemistry of the cathodic biocatalyst (i.e., bilirubin oxidase, BOD) for O2 electroreduction. Such BFC provided a simple approach to fabricate low-cost and portable power devices on small-size paper, which can harvest energy from a wide range of commercial beverages containing glucose (e.g., Nescafe instant coffee, Maidong vitamin water, Watermelon fresh juice, and Minute Maid grape juice). These made the low-cost paper-based biodevice potential for broad energy applications.

Self-Powered Sensor for Trace Hg2+ Detection

A self-powered electrochemical sensor has been facilely designed for sensitive detection of Hg(2+) based on the inhibition of biocatalysis process of enzymatic biofuel cell (BFC) for the first time. The as-prepared one-compartment BFC, which was consisted of alcohol dehydrogenase supported on single-walled carbon nanohorns-based mediator system as the anode and bilirubin oxidase as the cathodic biocatalyst, generated an open circuit potential (V(oc)) of 636 mV and a maximum power density of 137 μW cm(-2). It was interestingly found that the presence of Hg(2+) would affect the performance of the constructed BFC (e.g., V(oc)). Taking advantage of the inhibitive effect of Hg(2+), a novel self-powered Hg(2+) sensor has been developed, which showed a linear range of 1-500 nM (R(2) = 0.999) with a detection limit of 1 nM at room temperature. In addition, this BFC-type sensor exhibited good selectivity for Hg(2+) against other common environmental metal ions, and the feasibility of the method for Hg(2+) detection in actual water samples (i.e., tap, ground, and lake water) was demonstrated with satisfactory results.

A glucose/O 2 biofuel cell base on nanographene platelet-modified electrodes

This study demonstrated a novel nanographene platelets (NGPs)-based glucose/O 2 biofuel cell (BFC) with the glucose oxidase (GOD) as the anodic biocatalysts and the laccase as the cathodic biocatalysts. The GOD/NGPs-modified electrode exhibited good catalytic activity towards glucose oxidation and the laccase/NGPs-modified electrode exhibited good catalytic activity towards O 2 electroreduction. The maximum power density was ca. 57.8 μW cm − 2 for the assembled glucose/O 2 NGPs-based BFC. These results indicated that the NGPs were very useful for the future development of novel carbon-based nanomaterials BFC device.

Carbon nanotube–hydroxyapatite nanocomposite: A novel platform for glucose/O2 biofuel cell

This study demonstrates a novel carbon nanotubes-hydroxyapatite (CNTs–HA) nanocomposite-based compartment-less glucose/O2 biofuel cell (BFC) with the glucose oxidase (GOD) as the anodic biocatalysts and the laccase as the cathodic biocatalysts. CNTs–HA nanocomposite prepared by the self-assembly method via an aqueous solution reaction has been used as the co-immobilization matrix to incorporate biocatalysts, i.e. GOD and laccase successfully. Moreover, the three-dimensional configuration of the CNTs–HA films electrode would be advantageous to the glucose oxidation on the bioanode and O2 electroreduction on the biocathode of BFC. The maximum power density delivered by the assembled glucose/O2 BFC could reach 15.8μWcm−2 at a cell voltage of 0.28V with 10mM glucose. The results indicate that the CNTs–HA nanocomposite is believed to be very useful for the development of novel BFC device.

Air diffusion biocathode with CueO as electrocatalyst adsorbed on carbon particle-modified electrodes

The current density of biofuel cells which use dissolved O 2 as electron acceptor is limited by O 2 supply to the electrode surface due to the low solubility and small diffusion coefficient of O 2 in the electrolyte solution. In order to increase the current density, we constructed an air diffusion biocathode which uses O 2 directly from the air. As cathodic biocatalyst, we utilized CueO from Escherichia coli, which belongs to the family of multi-copper oxidases. O 2 reduction was catalyzed by CueO adsorbed on Ketjen black-modified carbon paper electrodes. The hydrophobic electrode surface was obtained by optimizing the weight ratio of polytetrafluoroethylene binder to Ketjen black. The current density of O 2 reduction reached values as high as 20 mA cm − 2 at 0 V vs. Ag|AgCl, KCl(sat.) in a citrate buffer (1.0 M, pH 5.0, 25 °C).

Highly ordered mesoporous carbons-based glucose/O 2 biofuel cell

This study demonstrates a novel compartment-less glucose/O 2 biofuel cell (BFC) based on highly ordered mesoporous carbons (OMCs) with three-dimensionally (3D) interconnected and ordered pore structures. OMCs are used as supports for both stably confining the electrocatalyst (i.e., meldola's blue, MDB) for NADH oxidation and the anodic biocatalyst (i.e., NAD +-dependent glucose dehydrogenase, GDH) for glucose oxidation, and for facilitating direct electrochemistry of the cathodic biocatalyst (i.e., laccase, LAC) for O 2 electroreduction. In 0.10 M pH 6.0 PBS containing 20 mM NAD + and 60 mM glucose under the air-saturated atmosphere, the open circuit voltage (0.82 V) and the maximum power output (38.7 μW cm −2 (at 0.54 V)) of the assembled compartment-less OMCs-based BFC are both higher than those of carbon nanotubes (CNTs)-based BFC (0.75 V and 2.1 μW cm −2 (at 0.46 V)). These may make OMCs to be another kind of robust and advanced carbon electrode material besides CNTs for BFCs applications.

A Miniature Glucose/O2 Biofuel Cell With a High Tolerance Against Ascorbic Acid

AbstractThis study demonstrates a miniature glucose/O2 biofuel cell (BFC) with a high tolerance against physiological level of ascorbic acid (AA) by immobilising ascorbate oxidase (AAox) on both the bioanode and the biocathode. Single‐walled carbon nanotube (SWNT)‐modified carbon fiber microelectrodes (CFMEs) are employed as the substrate electrode for the bioanode and biocathode. Glucose dehydrogenase (GDH) and bilirubin oxidase (BOD) are used as the biocatalysts for the electro‐oxidation of glucose and for the electro‐reduction of oxygen, respectively. SWNTs are used as the support for the both, stably confining the electrocatalyst (i.e. polymerised methylene blue, polyMB) for the oxidation of NADH co‐factor for GDH and efficiently facilitating direct electrochemistry of the cathodic biocatalyst (i.e. BOD) for O2 reduction. The prepared micro‐sized GDH‐based bioanode and BOD‐based biocathode employed for the bioelectrocatalytic oxidation of glucose and reduction of oxygen, respectively, are further over‐coated with AAox to give a miniature glucose/O2 BFC with a high tolerance against AA. The maximum power density and the open circuit voltage (OCV) of the assembled glucose/O2 BFC are 52 μW cm–2 and 0.60 V, respectively. These values remain unchanged with the presence of AA in solution. In the human serum containing 10 mM NAD+ and under ambient air, the maximum power density and the OCV of the assembled glucose/O2 BFC with AAox immobilisation on both the bioanode and the biocathode are 35 μW cm–2 and 0.39 V, respectively. These values are remarkably larger than those of the glucose/O2 BFC without AAox immobilisation on both the bioanode and the biocathode. This study could offer a new route to the development of enzymatic BFCs with promising application in real biological systems.

A Miniature glucose/O 2 biofuel cell with single-walled carbon nanotubes-modified carbon fiber microelectrodes as the substrate

This study demonstrates a new kind of miniature glucose/O 2 biofuel cells (BFCs) based on carbon fiber microelectrodes (CFMEs) modified with single-walled carbon nanotubes (SWNTs). SWNTs are used as a support both for stably confining the electrocatalyst (i.e., methylene green, MG) for the oxidation of NADH and the anodic biocatalyst (i.e., NAD +-dependent glucose dehydrogenase, GDH) for the oxidation of glucose and for efficiently facilitating direct electrochemistry of the cathodic biocatalyst (i.e., laccase) for the O 2 reduction. The prepared micro-sized GDH-based bioanode and laccase-based biocathode exhibit good bioelectrocatalytic activity toward the oxidation of glucose and the reduction of oxygen, respectively. In 0.10 M phosphate buffer containing 10 mM NAD + and 45 mM glucose under ambient air, the power density of the assembled miniature compartment-less glucose/O 2 BFC reaches 58 μW cm −2 at 0.40 V. The stability of the miniature glucose/O 2 BFC is also evaluated.