Superstable advanced hydrogen peroxide transducer based on transition metal hexacyanoferrates.

We report on a superstable hydrogen peroxide (H(2)O(2)) transducer made by sequential deposition of the iron- and nickel-hexacyanoferrate (NiHCF) layers. Both chemical and mechanical stability of the latter, as well as similarity of its structure to Prussian Blue (PB) provide a substantial stabilization of the most advantageous H(2)O(2) transducer. The electrochemically deposited five bilayers of PB-NiHCF exhibit a complete stability under the continuous wall-jet flow of 1 mM of H(2)O(2) during more than 2 h, maintaining current at a level of 0.2 mA cm(-2), whereas common Prussian Blue loses half of its response within the first 20-25 min. Even being deposited in the open circuit regime on screen-printed electrodes, PB-NiHCF bilayers dramatically improve tolerance of the resulting transducer to alkaline solutions and iron ligands. Despite their 2-2.5 times decreased sensitivity (compared to common Prussian Blue), the sequentially deposited bilayers of PB-NiHCF provide a similar dynamic range of the transducer due to the decreased noise level.

Sol-gel immobilization of lactate oxidase from organic solvent: toward the advanced lactate biosensor.

We report on the novel protocol for enzyme immobilization into gel of siloxanes using water-organic mixtures with the high content of organic solvent as a reaction medium. Hydrolysis of alkoxysilanes carried out without excessive dilution with water resulted in more active and stable enzyme containing membranes. Immobilization of an inherently labile lactate oxidase according to the proposed sol-gel protocol over Prussian Blue modified electrode resulted in an advanced lactate biosensor characterized with a sensitivity of 0.18 A M(-1) cm(-2) in the flow injection analysis (FIA) mode over a wide dynamic range. A comparison with the known sensors has shown that analytical performances of the elaborated lactate biosensor are advantageous over both published systems and commercialized devices. The biosensor shows an appropriate stability and is suitable for clinical analysis (including noninvasive diagnostics) and food quality control.

Kinetic approach for evaluation of total antioxidant activity.

We propose a novel approach for assessment of total antioxidant activity by monitoring kinetics of hydrogen peroxide (H(2)O(2)) scavenging after its injection into liquid sample under study. H(2)O(2) is known to be the strongest oxidant, really presented in human body in contrast to the majority of the model oxidative systems used for evaluation of antioxidant activity. In addition, kinetic approach, being more informative than the commonly used determination of the final product, obviously provides better discrimination of potential antioxidants. Prussian Blue based sensor due to its high sensitivity and operational stability allowed to monitor kinetics of hydrogen peroxide consumption in turbid and colored samples. The pseudo-first order kinetic constants of hydrogen peroxide scavenging in the presence of different food additives correlated with total antioxidant activity of these samples evaluated via standard procedure based on lipid peroxidation. However, in contrast to the standard method, the proposed kinetic approach is expressed and does not require fresh biological tissues.