Russian Chemical Bulletin, International Edition, Vol. 68, No. 2, pp. 431—437, February, 2019 431 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 0431—0437, February, 2019. 1066-5285/19/6802-0431 © 2019 Springer Science+Business Media, Inc. Electrochemical DNA sensors on the basis of electropolymerized thionine and Azure B with addition of pillar[5]arene as an electron transfer mediator D. I. Stoikov, A. V. Porfir´eva, D. N. Shurpik, I. I. Stoikov, and G. A. Evtyugin Alexander Butlerov Institute of Chemistry, Kazan Federal University, 18 ul. Kremvlevskaya, 420008 Kazan, Russian Federation. Fax: +7 (843) 233 7416. E-mail: porfireva-a@inbox.ru; Ivan.Stoikov@mail.ru A DNA sensor was developed on the basis of glassy carbon electrode coated with poly- meric forms of thionine and Azure B. Introduction of carbon black and pillar[5]arene into the electrode composition increases the efciency of polymerization and the oxidation peak currents of dyes due to the mediating efect of the macrocycle. The addition of DNA onto the sensor surface and into the reaction mixture diferently influences the electrochemical activity of poly(Azure B) and polythionine. The control of changes in current-voltage characteristics allowed us to identify the heat denaturation of DNA and its oxidation by reactive oxygen species generated upon the reaction of hydrogen peroxide and copper(II) salt. The DNA sensors can find application in the diagnosis of DNA damage on exposure to carcinogens and in screening of cytotoxic anticancer drugs. Key words: electropolymerization, biosensor, pillar[5]arene, polythionine, DNA damage. Electrochemical DNA sensors find wide application in bioanalysis and electroanalytical chemistry due to the capability of recognizing complex biomolecules, such as nucleic acid fragments, regulatory proteins, anticancer agents, and intercalating agents. 1—3 They are in demand as agents for disease diagnostics, 4 monitoring of carcino- genic pollutants in environment 5 and food products, 6 and in screening of cytostatic agents. 7 DNA sensors are applied in pure researches in the field of molecular biology and biochemistry. 8 Despite great advances in the design of electrochemi- cal DNA sensors, the improvement of methods for the measurement of their signals remains topical, especially upon detection of low-molecular-weight compounds or when nonspecific DNA damage (heat denaturation or oxidative damage on exposure to reactive oxygen species) should be determined. 9 The direct oxidation of DNA on an electrode requires high anode potentials to be applied, which is undesirable due to the efect of oxidizable com- ponents of a sample on the signal. In addition, this requires relatively high concentrations of nucleic acids and, con- sequently, the sensitivity of recording their damage will be low. For this reason, new approaches contemplating the use of covalently bound labels or the inclusion of DNA into the composition of surface complexes involving elec- trochemically active components are being extensively developed at the present time. Among electrochemically active components, a great attention is focused on polymer materials obtained on electrodes from monomer solutions in electropolymeriza- tion reactions. 10 Polymerization is typically initiated by the oxidation of a monomer on an electrode followed by condensation to deposit oligomers on the electrode. It is convenient to monitor the course of the reaction by cur- rent-voltage characteristics varying upon a change in the amount of the product on the electrode. When polymer- ization is performed in the presence of DNA, the biopoly- mer is trapped in a growing film; the negative charge of phosphate residues in the DNA helix favors polymerization due to accumulation of intermediate and final cationic products. The efect of DNA charge on polymerization and electrochemical properties of products is called tem- plate efect. It is manifested to the maximum extent in the case of polymerization of aniline. Polyaniline exhibits conductive properties and electrochemical activity as an electron transfer mediator predominantly in the acidic medium being in the semioxidized form of emeraldine. 11 Deoxyribonucleic acid as a polymeric counter-ion stabi- lizes this state favoring the retention of electrochemical activity in a weakly acidic or neutral regions, which are more suitable for recording biochemical interactions. 12—14 DNA has similar, but less pronounced efect on polymer- ization of pyrrole. 15 At the same time, the study of poly- * Dedicated to Academician of the Russian Academy of Sciences A. I. Konovalov on the occasion of his 85th birthday.