ИСТИНА

Nowadays, H2O2 is recognized as one of important analytes, being a chemical threat agent and a key metabolite of life pathways. Moreover, H2O2 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 was found to be 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 (PB) is inorganic coordination polymer, which is known to be the most advantageous low-potential H2O2 transducer1). The only disadvantage of the PB based sensing layers in respect to long-term monitoring is their inherent instability. We report on highly stable electrocatalytic layers based on transition metal hexacyanoferrates (HCFs) for advanced biosensors elaboration. 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 (PB), presented as defects in their structure. Electrocatalysis of H2O2 reduction is thus PB exceptional property2). Nevertheless, non-iron HCFs perform high mechanical and chemical stability and were used for the superior electrocatalyst entrapment. The method of PB stabilization with transition metals HCFs (Ni or Co) was elaborated. The approach of layer-by-layer deposition of the PB catalytic and transition metal layer was shown to be preferable3). 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 continuity4). Concluding, PB based glucose and lactate biosensors were successfully operated without a potentiostat by a simple short-circuiting the working and the reference electrodes. The noise of Prussian Blue-based sensors in power generation mode is an order of magnitude lower compared to it in a conventional three-electrode regime, which would have a potential for low voltage read-out methods, for example for printable electronics or wearable smart devices5). Financial support through Russian Science Foundation grant # 16-13-00010 is greatly acknowledged. References 1) Karyakin A.A. // Electroanalysis, 2001, 13(10), p. 813. 2) Sitnikova N.A., Komkova M.A., Karyakin A.A. et al.// Anal. Chem, 2014, 86 (9), p. 4131. 3) Sitnikova N.A., Borisova A.V., Komkova M.A., Karyakin A.A.// Anal. Chem. 2011, 83(6), p. 2359. 4) Komkova M.A., Karyakin A.A. et al.// Electrochimica Acta,2016, 219, p. 588. 5) Komkova M.A., Karyakina E.E., Karyakin A.A.// Anal. Chem, 2017, 89 (12), p. 6290.