Maria A. Komkova

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.

Transition metal hexacyanoferrates in electrocatalysis of H2O2 reduction: an exclusive property of Prussian Blue.

The ability of Prussian Blue, ferric hexacyanoferrate (FeHCF), to sensitively and selectively detect hydrogen peroxide by its reduction in the presence of oxygen is of high importance for analytical chemistry. Success with Prussian Blue (PB) provided an appearance of contradictory reports concerning electrocatalysis of the other transition metal hexacyanoferrates (HCFs) in H2O2 reduction. Investigating thermodynamics of the catalyzed reactions as well as electrochemical properties of the hexacyanoferrates, we are able to conclude that the noniron hexacyanoferrates themselves are completely electrocatalytically inactive, except for a minor electrocatalysis in the opposite reaction, hydrogen peroxide oxidation, registered for NiHCF. Concerning the most important reaction, H2O2 reduction, the observed electrocatalytic activity (by the way, 100 times decreased compared to PB) is due to the presence of FeHCF (Prussian Blue) as defects in the structure of noniron hexacyanoferrates. This finding, considering other unique properties of transition metal HCFs, will provide a systematic search for sensing materials with improved analytical performance characteristics.

Hydrogen Peroxide Detection in Wet Air with a Prussian Blue Based Solid Salt Bridged Three Electrode System

We report on a novel electroanalytical system for hydrogen peroxide (H2O2) detection in humidity or droplets of aerosol, formed by air bubbling through a washing chamber; the resulting flow mimics the exhaled human breath. The system is based on a planar three-electrode structure (with a Prussian Blue based H2O2 transducer modified working electrode) bridged by a solid salt-saturated filament material (filter paper, cotton textile). Respective to the hydrogen peroxide content in the washing valve, the response of the aerosol-sensing system is linear in the concentration range of 0.1-10 μM, which overlaps the generally accepted H2O2 content in exhaled breath condensate (EBC), with the sensitivity of 8 A M(-1) cm(-2). The response to the upper limit of the calibration range is stable for more than 50 injection cycles recorded within 3 days. Both the stability and the suitable calibration range allow one to consider the reported aerosol-sensing system as a prototype for a simple (avoiding intermediate EBC collection) noninvasive diagnostic tool for pulmonary patients.

Ultramicrosensors based on transition metal hexacyanoferrates for scanning electrochemical microscopy

Summary 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.

Catalytically Synthesized Prussian Blue Nanoparticles Defeating Natural Enzyme Peroxidase

We synthesized Prussian Blue (PB) nanoparticles through catalytic reaction involving hydrogen peroxide (H2O2) activation. The resulting nanoparticles display the size-dependent catalytic rate constants in H2O2 reduction, which are significantly improved compared to natural enzyme peroxidase: for PB nanoparticles 200 nm in diameter, the turnover number is 300 times higher; for 570 nm diameter nanoparticles, it is 4 orders of magnitude higher. Comparing to the known peroxidase-like nanozymes, the advantages of the reported PB nanoparticles are their true enzymatic properties: (1) enzymatic specificity (an absence of oxidase-like activity) and (2) an ability to operate in physiological solutions. The ultrahigh activity and enzymatic specificity of the catalytically synthesized PB nanoparticles together with high stability and low cost, obviously peculiar to noble metal free inorganic materials, would allow the substitution of natural and recombinant peroxidases in biotechnology and analytical sciences.

Electrochemical detection of Penicillium chrysogenum based on increasing conductivity of polyaminophenylboric acid

Electrochemical detection of the Penicillium chrysogenum mold is carried out in aqueous solution using decreasing resistance of conducting polyaminophenylboric acid. Polymer resistance is calculated on the basis of the data of electrochemical impedance spectroscopy of polymer-modified interdigitated gold microelectrodes with the interelectrode distance of 10 μm. Polymer degradation and the background signal are directed towards an increase in resistance counter to the change in the polymer properties in the presence of microorganisms. Thus, the developed sensor is applicable in practice, as it allows distinguishing the signal of specific binding from nonspecific background processes. The lower limit of microorganism detection was 600 colony-forming units per 1 mL (CFU/mL).