ИСТИНА

Nowadays, hydrogen peroxide (H2O2) is recognized as one of the most important analytes, being a chemical threat agent, a key metabolite of life pathways and acting as oxidases’ side product. Biosensors based on transducing principles containing enzymes oxidases and operated due to hydrogen peroxide detection with the Prussian Blue based transducer are shown to be the most advantageous ones [1]. Prussian Blue (PB) is considered to be the most advantageous low-potential transducer for hydrogen peroxide over all known systems, demonstrating both high sensitivity (ca. 1 A•M/cm2) and selectivity in relation to oxygen reduction of more than three orders of magnitude higher, than for platinum electrodes, which are most widely used. Developed by A. Karyakin’s scientific group method of selective hydrogen peroxide detection by its electroreduction in the presence of oxygen [2] provoked an extensive work at Prussian Blue analogues. Here we confirm that Ni, Co and Cu hexacyanoferrates-mediated H2O2 reduction is due to the presence of Fe hexacyanoferrate (Prussian Blue), presented as defects in their structure. Prussian Blue demonstrates high electrocatalytic activity with the half-wave potential of the H2O2 reduction almost coincided with the Prussian Blue|Prussian White redox potential [3]. Nevertheless, electrocatalytic potential windows for the non-iron hexacyanoferrates in H2O2 reduction are separated from the redox activity window (at much more anodic potentials). Whereas H2O2 reduction with Ni, Co and Cu hexacyanoferrates occurs in the potential region similar to Prussian Blue and electrocatalytic activities are in average two orders of magnitude less compared to Prussian Blue. The observed activity is assigned to Prussian Blue entrapped as defects in non-iron cyanoferrates’ lattice. The presence of Prussian Blue in the polycrystalline structure is sustained with differential pulse voltammetry data as well. Electrocatalysis of H2O2 reduction is attributed to Prussian Blue and is its exceptional property. Despite of the highest electrocatalytic activity towards H2O2 reduction of Prussian Blue, other transition metal hexacyanoferrates-analogues are of great interest for analytical application as suitable matrixes for superior electrocatalyst entrapment (for instance, Prussian Blue stabilization with layer-by-layer deposition [4]) or construction of oxidase-based biosensors with improved characteristics. References: [1] A.A. Karyakin, Prussian Blue and Its Analogues: Electrochemistry and Analytical Applications, Electroanalysis, 13 (2001), 813-819. [2] A.A. Karyakin, O.V. Gitelmacher, E.E. Karyakina, Prussian Blue-Based First-Generation Biosensor. A Sensitive Amperometric Electrode for Glucose. Analytical сhemistry, 67 (1995), pp. 2419- 2423 [3] A.A. Karyakin, E.E. Karyakina, L. Gorton, On the mechanism of H2O2 reduction at prussian blue modified electrodes, Electrochemistry Communications, 1 (1999), 78-82. [4] N.A. Sitnikova, A.V. Borisova, M.A. Komkova, A.A. Karyakin, Superstable Advanced Hydrogen Peroxide Transducer Based on Transition Metal Hexacyanoferrates, Analytical chemistry, 83 (2011), 2359-2363.