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In this study, different flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenases (FADGDHs) were characterized electrochemically after “wiring” them with an osmium redox polymer [Os(4,4′-dimethyl-2,2′-bipyridine)2(PVI)10Cl]+ on graphite electrodes. One tested FADGDH was that recently discovered in Glomerella cingulata (GcGDH), another was the recombinant form expressed in Pichia pastoris (rGcGDH), and the third was a commercially available glycosylated enzyme from Aspergillus sp. (AspGDH). The performance of the Os-polymer “wired” GDHs on graphite electrodes was tested with glucose as the substrate. Optimal operational conditions and analytical characteristics like sensitivity, linear ranges and current density of the different FADGDHs were determined. The performance of all three types of FADGDHs was studied at physiological conditions (pH 7.4). The current densities measured at a 20 mM glucose concentration were 494 ± 17, 370 ± 24, and 389 ± 19 μA cm−2 for GcGDH, rGcGDH, and AspGDH, respectively. The sensitivities towards glucose were 2.16, 1.90, and 1.42 μA mM−1 for GcGDH, rGcGDH, and AspGDH, respectively. Additionally, deglycosylated rGcGDH (dgrGcGDH) was investigated to see whether the reduced glycosylation would have an effect, e.g., a higher current density, which was indeed found. GcGDH/Os-polymer modified electrodes were also used and investigated for their selectivity for a number of different sugars.FigureComparison of different parameters for GDHs/Os-polymer modified electrodes

A new extracellular flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase from Glomerella cingulata (GcGDH) was electrochemically studied as a recognition element in glucose biosensors. The redox enzyme was recombinantly produced in Pichia pastoris and homogeneously purified, and its glucose-oxidizing properties on spectrographic graphite electrodes were investigated. Six different Os polymers, the redox potentials of which ranged in a broad potential window between +15 and +489 mV versus the normal hydrogen electrode (NHE), were used to immobilize and "wire" GcGDH to the spectrographic graphite electrode's surface. The GcGDH/Os polymer modified electrodes were evaluated by chronoamperometry using flow injection analysis. The current response was investigated using a stepwisely increased applied potential. It was observed that the ratio of GcGDH/Os polymer and the overall loading of the enzyme electrode significantly affect the performance of the enzyme electrode for glucose oxidation. The best-suited Os polymer [Os(4,4'-dimethyl-2,2'-bipyridine)(2)(PVI)Cl](+) had a potential of +309 mV versus NHE, and the optimum GcGDH/Os polymer ratio was 1:2 yielding a maximum current density of 493 μA·cm(-2) at a 30 mM glucose concentration.

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The intervening barrier to produce hydrogen from water is the frustratingly slow kinetics of the water splitting reaction. In addition, insufficient understanding of the key obstacle of the oxygen evolution reaction (OER) is an obstruction to perceptive design of efficient OER electrocatalysts. In this research, we present synthesis, characterization, and electrochemical evaluation of nickel oxide/nickel sulfide (NiO/NiS) heterostructures and its counterparts nickel oxide (NiO) and nickel sulfide (NiS) as low-cost electrocatalysts for electrochemical water splitting. These electrocatalysts have been characterized using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The NiO/NiS is found to be highly efficient and stable electrocatalyst, which initiates the OER at an amazingly low potential of 1.42 V (vs RHE). The NiO/NiS electrocatalyst provides a current density of 40 mA cm–2 at 209 mV overpotential for OER in 1.0 M KOH with a Tafel slope of 60 mV dec–1, outperforming its counterparts (NiO and NiS) under same electrochemical conditions. These results are better than those of benchmark Ni-based and even noble metal-based electrocatalysts. The continued oxygen generation for several hours with an applied potential of 1.65 V (vs RHE) reveals the long-term stability and activity of NiO/NiS electrocatalyst toward OER. This development provides an attractive non-noble metal, highly efficient, and stable electrocatalyst toward OER.