This work describes a novel method by which the homogeneous kinetics for an ErevCirrev system can be deduced using only the forward scan of second harmonic FTACV. We show that ratio of the heights of the two lobes of the 2nd harmonic voltammograms readily provides this information by fitting data to a working curve modelled by the simple equation ilobe,right/ilobe,left=1/(1+kτs), where τs is the characteristic voltammetric timescale. The validity of the relationship was tested by comparison with both simulated and experimental data. This novel approach offers the advantage of quick and easy determination of kf, while increasing accuracy by omitting the ambiguity in determining a baseline and minimising the effects of electrode passivation. We also show that these changes can be explained by considering the change in surface concentration of the [Ox] and [Red] species over the course of a scan, which are more profoundly expressed in the FTACV response compared with CV.

Ubiquinone (UQ) is a lipophilic compound present in most living organisms, where UQ's interesting but complex electrochemistry serves an important role in the transfer of electrons and protons within and across the mitochondrial membrane. We briefly review the electrochemical characteristics of UQ and its reduced state, ubiquinol, in solution and immobilized on electrodes, together with its application in electrochemical sensing and detection systems, for example, measuring redox status with reference to reactive oxidative species. The importance of the local environment, solvent, electrolyte, organic membrane, and pH, on the electrochemical behavior of UQ, is also discussed. We discuss techniques used for the direct detection of UQ such as liquid chromatography-electrochemistry. Mediated electrochemistry of UQ allows for quantitative measurements of ions, small molecules, and other analytes such as glucose via chemical sensors and biosensors.

Genipin is used to simultaneously crosslink chitosan, amine-containing osmium redox complex and glucose oxidase on graphite disks to produce enzyme-based electrodes for glucose oxidation. The enzyme electrodes produce glucose oxidation current densities of 730 mu A cm(-2) in 50 mM phosphate buffered saline (150 mM NaCl, pH 7.4, 37 degrees C) containing 100 mM glucose at an applied potential of 0.45 V (vs. Ag/AgCl), higher than the 440 mu A cm(-2) for conventional poly(ethylene glycol) diglycidyl ether (PEGDGE) epoxy ring-opening cross-linked films. Addition of multiwalled carbon nanotubes results in current response as high as 4.9 +/- 0.3 mA cm(-2) in 100 mM glucose. The genipin cross-linked hydrogels deliver a 3 fold increase in stability for continuous amperometric current production over a 20 h period when compared to PEGDGE cross-linked hydrogels. Genipin provides an effective route for simultaneous crosslinking glucose oxidase, chitosan and the redox complex while further optimisation of the crosslinking process holds promise for application of the enzyme electrodes as fuel cell and sensor devices.

Surface chemistry is known to influence the formation, composition, and electroactivity of electron-conducting biofilms. However, understanding of the evolution of microbial composition during biofilm development and its impact on the electrochemical response is limited. Here we present voltammetric, microscopic and microbial community analysis of biofilms formed under fixed applied potential for modified graphite electrodes during early (90 h) and mature (340 h) growth phases. Electrodes modified to introduce hydrophilic groups (-NH2, -COOH and -OH) enhance early-stage biofilm formation compared to unmodified or electrodes modified with hydrophobic groups (-C2H5). In addition, early-stage films formed on hydrophilic electrodes are dominated by the gram-negative sulfur-reducing bacterium Desulfuromonas acetexigens while Geobacter sp. dominates on -C2H5 and unmodified electrodes. As biofilms mature, current generation becomes similar, and D. acetexigens dominates in all biofilms irrespective of surface chemistry. Electrochemistry of pure culture D. acetexigens biofilms reveal that this microbe is capable of forming electroactive biofilms producing considerable current density of > 9 A/m2 in a short period of potential-induced growth (~19 h following inoculation) using acetate as an electron donor. The inability of D. acetexigens biofilms to use H2 as a sole source electron donor for current generation shows promise for maximizing H2 recovery in single-chambered microbial electrolysis cell systems treating wastewaters.

Pyranose dehydrogenase (PDH) is a quinone-dependent extracellular flavoglycoprotein mainly produced by litter-decomposing fungi and contributes to the degradation of lignocellulose. PDH in terms of structure and catalytic features pertains to the glucose methanol-choline oxidoreductase family and oxidizes a wide substrate range of aldopyranoses including hexoses, pentoses, disaccharides and oligosaccharides with a high degree of regioselectivity. The purpose of this study was to rationalize the preference of PDH immobilized on an electrode with the structural features of various substrates and thus the kinetic constants were measured for various sugars. PDH was co-immobilized on the electrode with an osmium redox polymer. Response currents for different sugars were measured using flow injection amperometry at +0.3 V vs. Ag vertical bar AgCl, KCl (0.1 M). The Michaelis-Menten constants, the turnover numbers and the catalytic efficiency were calculated and revealed that type, orientation and configuration of the substituent play a major role on substrate preference. An OH-group at C-1 and C-6 are not essential and substrate specificities are little affected by the substitution at C-1. The presence and orientation of OH- at C-2 and C-3 are relevant for reactivity. Orientation of OH- at the C-4 position has little effect, and sugars with a substitution below the plane at C-5 are not suitable as substrate. Highest activity for oxidation of glucose, mannose and sucrose was detected at pH 8.5.

Wireless potentiostats capable of cyclic voltammetry and amperometry that connect to the Internet are emerging as key attributes of future point-of-care devices. This work presents an "integrated microfluidic electrochemical detector" (iMED) three-electrode multi-potentiostat designed around operational amplifiers connected to a powerful WiFi-based microcontroller as a promising alternative to more expensive and complex strategies reported in the literature. The iMED is integrated with a microfluidic system developed to be controlled by the same microcontroller. The iMED is programmed wirelessly over a standard WiFi network and all electrochemical data is uploaded to an open-source cloud-based server. A wired desktop computer is not necessary for operation or program uploading. This method of integrated microfluidic automation is simple, uses common and inexpensive materials, and is compatible with commercial sample injectors. An integrated biosensor platform contains four screen-printed carbon arrays inside 4 separate microfluidic detection chambers with Pt counter and pseudo Ag/AgCl reference electrodes in situ. The iMED is benchmarked with K3[Fe(CN)6] against a commercial potentiostat and then as a glucose biosensor using glucose-oxidising films of [Os(2,2'-bipyridine)2(polyvinylimidazole)10Cl] prepared on screen-printed electrodes with multi walled carbon nanotubes, poly(ethylene glycol) diglycidyl ether and flavin adenine dinucleotide-dependent glucose dehydrogenase. Potential application of this cost-effective wireless potentiostat approach to modern bioelectronics and point-of-care diagnosis is demonstrated by production of glucose oxidation currents, under pseudo-physiological conditions, using mediating films with lower redox potentials.

The Cover Feature shows the enhancement effect of a second poly(acrylic acid) coating layer on the catalytic response and operational stability of a lactate oxidase/Os redox polymer modified electrode. More information can be found in the Article by X. Xiao et al. on page 1344 in Issue 5, 2019 (DOI: 10.1002/celc.201800983).

The successful use of biosensors requires that the sensor can operate over abroad enough linear range that encompasses the physiological concentration of the substrate of interest. A polymer coating layer functioning as a mass-transport barrier is typically used to expand the linear range of biosensors with, however, the concomitant disadvantage of a reduction in the response. Effects of a poly(acrylic acid) coating layer on the response of a glassy carbon electrode modified with an Os redox polymer and lactate oxidase were evaluated. The coating layer resulted in an expanded linear range from 7 to 15 mM, doubled catalytic response towards the oxidation of 35 mM lactate, and improved operational stability. Detailed voltammetry studies revealed that the coating layer can improve the amount of the redox polymer that is available as a mediator, leading to the increased catalytic response at high concentrations of substrate. Similar results were obtained with other polymer layers [polystyrene sulfonate,poly(diallyldimethyl-ammonium chloride), and poly(3,4-ethylenedioxythiophene)] and with the enzymes glucose oxidase and bilirubin oxidase, demonstrating the general nature of the method.

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.

Graphite electrodes are modified with a redox polymer, [Os(4,4-dimethoxy-2,2-bipyridine)(2)(polyvinylimidazole)(10)Cl](+) (E degrees=-0.02V vs Ag/AgCl (3M KCl), crosslinked with a flavin adenine dinucleotide glucose dehydrogenase and multi-walled carbon nanotubes for electrocatalytic oxidation of glucose. The enzyme electrodes provide 52% higher current density, 1.22 +/- 0.10mAcm(-2) in 50mM phosphate-buffered saline at 37 degrees C containing 5mM glucose, when component amounts are optimised using a design of experiments approach compared to one-factor-at-a-time. Current densities of 0.84 +/- 0.15mAcm(-2) were achieved in the presence of oxygen for these enzyme electrodes. Further analysis of the model allowed for altering of the electrode components while maintaining similar current densities, 0.78 +/- 0.11mAcm(-2) with 34% less enzyme. Application of the cost-effective anodes in membrane-less enzymatic fuel cells is demonstrated by connection to cathodes prepared by co-immobilisation of [Os(2,2-bipyridine)(2)(polyvinylimidazole)(10)Cl+] redox polymer, Myrothecium verrucaria bilirubin oxidase and multi-walled carbon nanotubes on graphite electrodes. Power densities of up to 285Wcm(-2), 146Wcm(-2) and 60Wcm(-2) are achieved in pseudo-physiological buffer, artificial plasma and human plasma respectively, showing promise for invivo or ex vivo power generation under these conditions.

Pyranose Dehydrogenase 1 from the basidiomycete Agaricus meleagris (AmPDH1) is an oxidoreductase capable of oxidizing a broad variety of sugars. Due to this and its ability of dioxidation of substrates and no side production of hydrogen peroxide, it is studied for use in enzymatic bio-fuel cells. In-vitro deglycosylated AmPDH1 as well as knock-out mutants of the N-glycosylation sites N75 and N175, near the active site entrance, were previously shown to improve achievable current densities of graphite electrodes modified with AmPDH1 and an osmium redox polymer acting as a redox mediator, up to 10-fold. For a better understanding of the role of N-glycosylation of AmPDH1, a systematic set of N-glycosylation site mutants was investigated in this work, regarding expression efficiency, enzyme activity and stability. Furthermore, the site specific extend of N-glycosylation was compared between native and recombinant wild type AmPDH1. Knocking out the site N252 prevented the attachment of significantly extended N-glycan structures as detected on polyacrylamide gel electrophoresis, but did not significantly alter enzyme performance on modified electrodes. This suggests that not the molecule size but other factors like accessibility of the active site improved performance of deglycosylated AmPDH1/osmium redox polymer modified electrodes. A fourth N-glycosylation site of AmPDH1 could be confirmed by mass spectrometry at N319, which appeared to be conserved in related fungal pyranose dehydrogenases but not in other members of the glucose-methanol-choline oxidoreductase structural family. This site was shown to be the only one that is essential for functional recombinant expression of the enzyme.

Gluconobacter oxydans (G. oxydans) cells together with an osmium redox polymer (ORP) [Osmium (2,2'-bipyridine) 2(poly-vinylimidazole) 10Cl] Cl were combined with a glassy carbon paste electrode (GCPE) to form a bioanode for a microbial fuel cell (MFC) based on G. oxydans. Although there are G. oxydans/ORP combined bioanode in the literature, as far as it is known, this system is the first one where G. oxydans/ORP bioanode is combined with a cathode and a MFC is formed. After the optimization of experimental parameters, analytical characteristics of ORP/G. oxydans/GCPE bioanode were investigated. ORP/G. oxydans/GCPE showed two linear ranges for ethanol substrate as 1.0-30 mM (R-2 = 0.902) and 30-500 mM (R-2 = 0.997) and analytical range as 1.0-1000 mM. Limit of detection (3.0 s/m) and limit of quantification (10 s/m) values were calculated as 1.29 mM and 4.30 mM respectively where the RSD value was 1.16% for n=5. Combining the developed bioanode in the presence of 5.0 mM K3Fe(CN) 6 mediator with a Pt wire cathode a double compartment MFC was obtained via a salt bridge. G. oxydans/GCPE bioanode based MFC had maximum power density of 0.133 mW cm(-2) (at 33.5 mV), maximum current density as 8.73 mA cm(-2) and OCP value of 156 mV. On the other hand, ORP/G. oxydans/GCPE based MFC showed maximum power density as 0.26 mW cm(-2) (at 46.8 mV), maximum current density as 15.079 mA cm(-2) and OCP value of 176 mV.

The cover picture shows the use of nanoporous gold electrodes to immobilize glucose dehydrogenase (Glomorella cingulata) and bilirubin oxidase (Myrothecium verrucaria) for use in a biofuel cell. The enzymes can penetrate completely through, are accessible within the porous network, and are stabilized inside the pores. More details can be found in the Full Paper by E. Magner and co-workers on page 553 in Issue 4, 2017 (DOI: 10.1002/cplu.201600455).

In this work, a carbon felt electrode (CFE) was modified with a multiwalled carbon nanotube-gold-platinum (MWCNT-Au-Pt) hybrid nanomaterial and integrated with an osmium redox polymer (OsRP, [Os(2,2'-bipyridine)(2)(poly-vinylimidazole)(10)Cl]Cl) and Gluconobacter oxydans DSM 2343 (G. oxydans) cells. The developed electrode was used as the bioanode in a 5.0mM K3Fe(CN)(6) mediator containing phosphate buffer (pH6.5) anolyte and combined with a Pt wire cathode in phosphoric acid medium (pH3.5). As a result, a two chamber microbial fuel cell (MFC) was formed, in which an activated Nafion membrane was used as a proton exchange membrane. The OsRP/G.oxydans/MWCNT-Au-Pt/CFE based bioanode was electrochemically examined in differently deoxygenated bioanode chambers and additionally the amounts of hybrid nanomaterial and OsRP were optimized. In terms of MFC characteristics, it was found that an anaerobic OsRP/G.oxydans/MWCNT-Au-Pt/CFE bioanode based MFC had a maximum power density of 32.1 mW m(-2) (at 90mV), a maximum current density of 1032mA m(-2) and a charge transfer efficiency (E%) value of 22.30 (open circuit potential 180mV).

Enzymatic biofuel cells can generate electricity directly from the chemical energy of biofuels in physiological fluids, but their power density is significantly limited by the performance of the cathode which is based on oxygen reduction for in vivo applications. An oxygen-independent and membrane-less glucose biobattery was prepared that consists of a dealloyed nanoporous gold (NPG) supported glucose dehydrogenase (GDH) bioanode, immobilised with the assistance of conductive polymer/Os redox polymer composites, and a solid-state NPG/MnO2 cathode. In a solution containing 10mM glucose, a maximum power density of 2.3µWcm-2 at 0.21V and an open circuit voltage (OCV) of 0.49V were registered as a biobattery. The potential of the discharged MnO2 could be recovered, enabling a proof-of-concept biobattery/supercapacitor hybrid device. The resulting device exhibited a stable performance for 50 cycles of self-recovery and galvanostatic discharge as a supercapacitor at 0.1mAcm-2 over a period of 25h. The device could be discharged at current densities up to 2mAcm-2 supplying a maximum instantaneous power density of 676 μW cm-2, which is 294 times higher than that from the biobattery alone. A mechanism for the recovery of the potential of the cathode, analogous to that of RuO2 (Electrochim. Acta 42(23), 3541-3552) is described.

The integration of supercapacitors with enzymatic biofuel cells (BFCs) can be used to prepare hybrid devices in order to harvest significantly higher power output. In this study, a supercapacitor/biofuel cell hybrid device was prepared by the immobilisation of redox enzymes with electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) and the redox polymer [Os(2,2'-bipyridine)2(polyvinylimidazole)10Cl]+/2+(Os(bpy)2PVI) on dealloyed nanoporous gold. The thickness of the deposition layer can be easily controlled by tuning the deposition conditions. Once charged by the internal BFC, the device can be discharged as a supercapacitor at a current density of 2mAcm-2 providing a maximum power density of 608.8μWcm-2, an increase of a factor of 468 when compared to the power output from the BFC itself. The hybrid device exhibited good operational stability for 50 charge/discharge cycles and ca. 7h at a discharge current density of 0.2mAcm-2. The device could be used as a pulse generator, mimicking a cardiac pacemaker delivering pulses of 10μA for 0.5ms at a frequency of 0.2Hz.

Coimmobilization of pyranose dehydrogenase as an enzyme catalyst, osmium redox polymers [Os(4,4'-dimethoxy-2,2'-bipyridine)2(poly(vinylimidazole))10Cl](+) or [Os(4,4'-dimethyl-2,2'-bipyridine)2(poly(vinylimidazole))10Cl](+) as mediators, and carbon nanotube conductive scaffolds in films on graphite electrodes provides enzyme electrodes for glucose oxidation. The recombinant enzyme and a deglycosylated form, both expressed in Pichia pastoris, are investigated and compared as biocatalysts for glucose oxidation using flow injection amperometry and voltammetry. In the presence of 5 mM glucose in phosphate-buffered saline (PBS) (50 mM phosphate buffer solution, pH 7.4, with 150 mM NaCl), higher glucose oxidation current densities, 0.41 mA cm(-2), are obtained from enzyme electrodes containing the deglycosylated form of the enzyme. The optimized glucose-oxidizing anode, prepared using deglycosylated enzyme coimmobilized with [Os(4,4'-dimethyl-2,2'-bipyridine)2(poly(vinylimidazole))10Cl](+) and carbon nanotubes, was coupled with an oxygen-reducing bilirubin oxidase on gold nanoparticle dispersed on gold electrode as a biocathode to provide a membraneless fully enzymatic fuel cell. A maximum power density of 275 μW cm(-2) is obtained in 5 mM glucose in PBS, the highest to date under these conditions, providing sufficient power to enable wireless transmission of a signal to a data logger. When tested in whole human blood and unstimulated human saliva maximum power densities of 73 and 6 μW cm(-2) are obtained for the same fuel cell configuration, respectively.

Nanoporous gold (NPG) electrodes were prepared by dealloying sputtered gold:silver alloys. Electrodes of different thicknesses and pore sizes areas were prepared by varying the temperature and duration of the dealloying procedure; these were then used as supports for FAD-dependent glucose dehydrogenase (GDH) (Glomorella cingulata) and bilirubin oxidase (BOx) (Myrothecium verrucaria). Glucose dehydrogenase was immobilized by drop-casting a solution of the enzyme with an osmium redox polymer together with a crosslinked polymer, whereas bilirubin oxidase was attached covalently through carbodiimide coupling to a diazonium-modified NPG electrode. The stability of the bilirubin-oxidase-modified NPG electrode was significantly improved in comparison with that of a planar gold electrode. Enzyme fuel cells were also prepared; the optimal response was obtained with a BOx-modified NPG cathode (500 nm thickness) and a GDH-modified anode (300 nm), which generated power densities of 17.5 and 7.0 μW cm-2 in phosphate-buffered saline and artificial serum, respectively.