ИСТИНА

Hydrogen peroxide is recognized as one of important analytes, being a chemical threat agent and a key metabolite of life pathways. Moreover, it is a side product of oxidases, included as terminal enzymes in more than 90% of the existing enzyme-based biosensors. The low-potential detection of H2O2 is the most progressive procedure for operation of the oxidase-based biosensors providing both high sensitivity and selectivity in the presence of easily oxidizable compounds. Prussian Blue (FeHCF or PB) is known to be the most advantageous low-potential H2O2 transducer [1]. While Prussian Blue serves as a superior electrocatalyst for hydrogen peroxide reduction, there is rather contradictory and non-satisfactory information concerning other transition metal hexacyanoferrates, which are PB structural analogues. We note that NiHCF, CoHCF and CuHCF, which are PB analogues, are completely inactive in H2O2 reduction electrocatalysis: Ni, Co and Cu HCFs-mediated H2O2 reduction is due to the presence of FeHCF, presented as defects in their structure. Electrocatalysis of H2O2 reduction is thus PB exceptional property [2]. Nevertheless, non-iron HCFs perform high mechanical and chemical stability and were used for the superior electrocatalyst entrapment. The method of PB stabilization with NiHCFs was elaborated. The approach of layer-by-layer deposition of the PB catalytic and transition metal layer was shown to be preferable [3]. The method was adapted for mass production: screen printed electrodes were modified with PB-NiHCF bilayers in the open circuit regime (chemically). The sensors modified with composite material of PB and NiHCF were completely stable in continuous flow of 1 mM H2O2 within more than 1 h, whereas common PB based sensors lose half of their response within 20 min. Furthermore, a new microscope-free pure electrochemical tool for evaluation of transition metal HCFs films continuity was elaborated. The decrease of HCFs films’ resistance upon material amount increase can be referred to as an apparent anti-Ohmic trend since the amount of the deposited film usually presumes film thickness. Nevertheless, assigning charge transfer resistance to the resistance of the electrode|film interface, its observed decrease with subsequent saturation is explained in terms of an increase of the interface area until the entire electrode is covered with the film. The dependence of charge transfer resistance on the amount of HCF deposited thus provides a microscopy-free estimation of the electroactive inorganic polymer film continuity [4]. Finally, we proposed a new approach of Prussian Blue-based (bio)sensors operation in power generation mode, providing advanced analytical performance characteristics. PB based (bio)sensors were successfully operated without a potentiostat by a simple short-circuiting the working and the reference electrodes. The noise of Prussian Blue-based (bio)sensors in power generation mode is an order of magnitude lower compared to it in a conventional three-electrode regime. Such approach simplifies elaboration of the controlling electronics and would have a potential for low voltage read-out methods, for example for printable electronics or wearable smart devices [5]. Financial support through Russian Science Foundation grant # 16-13-00010 is greatly acknowledged and Russian Foundation for Basic Research grant # 18-33-00392 is greatly acknowledged. References 1. Karyakin A.A. Advances of Prussian blue and its analogues in (bio)sensors // Current Opinion in Electrochemistry, 2017, 5(1), p. 92. 2. Sitnikova N.A., Komkova M.A., Karyakin A.A. et al. Transition Metal Hexacyanoferrates in Electrocatalysis of H2O2 Reduction: An Exclusive Property of Prussian Blue // Analytical Chemistry, 2014, 86 (9), p. 4131. 3. Sitnikova N.A., Borisova A.V., Komkova M.A., Karyakin A.A. Superstable Advanced Hydrogen Peroxide Transducer Based on Transition Metal Hexacyanoferrates // Analytical Chemistry, 2011, 83(6), p. 2359. 4. Komkova M.A., Karyakin A.A. et al. Estimation of continuity of electroactive inorganic films based on apparent anti-Ohmic trend in their charge transfer resistance // Electrochimica Acta, 2016, 219, p. 588. 5. Komkova M.A., Karyakina E.E., Karyakin A.A. Noiseless Performance of Prussian Blue Based (Bio)sensors through Power Generation // Analytical Chemistry, 2017, 89 (12), p. 6290.