Rapid optimisation of a lactate biosensor design using soft probes scanning electrochemical microscopy

We report the mapping of biocatalytically active surfaces, particularly on an express search for optimal immobilization conditions of the enzyme lactate oxidase by means of scanning electrochemical microscopy (SECM). With this aim, soft stylus SECM probes containing a carbon paste ultramicroelectrode were modified with Prussian Blue yielding reproducible hydrogen peroxide (H2O2) sensors with a sensitivity of 1.6 ± 0.5 A·M–1·cm–2 for screening applications. The ultramicroelectrode response was stable under harsh conditions of 1 mM H2O2 during the first hour, while the response decay during the second hour was less than 4 % providing sensor suitability for long-term experiments. SECM imaging in contact mode of different lactate oxidase spots containing membranes allowed for a straightforward optimization of the enzyme immobilization conditions on rough screen-printed carbon paste substrates. The resulting lactate biosensor was characterized by improved analytical performance characteristics: a four times enhanced sensitivity (up to 0.3 A·M–1·cm–2) in comparison to previous reports and a remarkably increased operational stability

Ultramicrosensors based on transition metal hexacyanoferrates for scanning electrochemical microscopy

We report here a way for improving the stability of ultramicroelectrodes (UME) based on hexacyanoferrate-modified metals for the detection of hydrogen peroxide. The most stable sensors were obtained by electrochemical deposition of six layers of hexacyanoferrates (HCF), more specifically, an alternating pattern of three layers of Prussian Blue and three layers of Ni–HCF. The microelectrodes modified with mixed layers were continuously monitored in 1 mM hydrogen peroxide and proved to be stable for more than 5 h under these conditions. The mixed layer microelectrodes exhibited a stability which is five times as high as the stability of conventional Prussian Blue-modified UMEs. The sensitivity of the mixed layer sensor was 0.32 A·M−1·cm−2, and the detection limit was 10 µM. The mixed layer-based UMEs were used as sensors in scanning electrochemical microscopy (SECM) experiments for imaging of hydrogen peroxide evolution

Turning cellulose waste into electricity: hydrogen conversion by a hydrogenase electrode.

Hydrogen-producing thermophilic cellulolytic microorganisms were isolated from cow faeces. Rates of cellulose hydrolysis and hydrogen formation were 0.2 mM L(-1) h(-1) and 1 mM L(-1) h(-1), respectively. An enzymatic fuel cell (EFC) with a hydrogenase anode was used to oxidise hydrogen produced in a microbial bioreactor. The hydrogenase electrode was exposed for 38 days (912 h) to a thermophilic fermentation medium. The hydrogenase activity remaining after continuous operation under load was 73% of the initial value

Evaluation of the Lattice Energy of the Two-Component Molecular Crystals Using Solid-State Density Functional Theory

The lattice energy <i>E</i>_latt of the two-component crystals (three co-crystals, a salt, and a hydrate) is evaluated using two schemes. The first one is based on the total energy of the crystal and its components computed using the solid-state density functional theory method with the plane-wave basis set. The second approach explores intermolecular energies estimated using the bond critical point parameters obtained from the Bader analysis of crystalline electron density or the pairwise potentials. The <i>E</i>_latt values of two-component crystals are found to be lower or equal to the sum of the absolute sublimation enthalpies of the pure components. The computed energies of the supramolecular synthons vary from ∼80 to ∼30 kJ/mol and decrease in the following order: acid–amide > acid–pyridine > hydroxyl–acid > amide–amide > hydroxyl–pyridine. The contributions from different types of noncovalent interactions to the <i>E</i>_latt value are analyzed. We found that at least 50% of the lattice energy comes from the heterosynthon and a few relatively strong H-bonds between the heterodimer and the adjacent molecules

Electron micrograph of the cellulose.

<p><b>T</b>he isolated microorganisms immersed in exopolysaccharide matrix on the surface of cellulosic fibers (7 days of cultivation).</p

Hydrogen production by the selected microbial consortium using different types of substrates.

<p>1 – glossy white paper; 2 – glossy paper with print; 3 – glossy colour printed paper; 4 – white newsprint paper; 5 – newsprint with print; 6 – colour newsprint paper; 7 – wheat bran; 8 – kitchen waste; 9 – grains; 10 – yeast; 11 – wood sawdust; 12 – straw; 13 – pretreated filter paper; 14 – filter paper. The cultivation time was 7 days.</p

Dynamic of changes in the open circuit potential values.

<p>The cultivation time of hydrogen-producing bacteria in the bioreactor cell was 25 days (overpressure in the bioreactor – 0.5 atm, pH 6.7–7.0, 60 °C).</p

Scheme of the developed bioreactor cell.

<p>MPDBP - pyrrole derivative N-methyl-N’-(12-pyrrol-1-yldodecyl)-4,4’-bipyridinium ditetrafluoroborate.</p