ИСТИНА

Nucleic acids are the biompolymers which carry genetic information for protein production essential to all known forms of life. Deoxyribonucleic acids (DNA) are promising subjects for a point-of-need testing as markers of environmental contamination or human deseases. In a search for robust, portable, and sensitive DNA detection systems for in situ applications, the development of electrochemical sensing principles for nucleic acids is of high interest [1]. DNA are known to be electoactive through their nitrogenous bases: guanine, adenine, cytosine, and thymine [2, 3]. However, the direct electrochemistry of DNA characterizes by high oxidation/reduction potentials and low values of registered currents. Guanine possessing the lowest electrooxidation potential among nucleobases oxidizes at 0.6–0.8 V (vs. Ag/AgCl) [2]. Electroreduction of nucleobases takes place at the potentials over –1.5 V [3]. The signals of DNA are severely affected by the molecular weight of biopolymer [4] and the formation of double helix – nucleobases linked together by hydrogen bonds inside the DNA double helix become hardly accessible for electrode reactions [1]. To overcome this problem, we are suggesting a novel strategy for detection of double stranded DNA (dsDNA) through the tyrosine (Tyr) oxidation. As it was shown previously, there is an intercalative interaction between tyrosine and dsDNA with the binding constant of 4 × 103 mol−1 L [5]. In this work, oxidation of free Tyr in the presence of native DNA and Zn(II) ions was studied by square wave voltammetry on carbon screen printed electrodes. The addition of DNA to the Tyr or Tyr + Zn(II) samples induced the significant decrease of the oxidation signal at 0.6 V, especially in the presence of Zn(II) ions. The calibration curves in coordinates ‘Ip (Tyr), μA – lg(c(DNA), M)’ were linear from 2 to 500 μM of herring sperm DNA with different slopes in the absence and in the presents of Zn(II) ions. At the same time, direct electrochemical detection of the DNA through the oxidation of guanine residue (Gua) at the potential of about 0.8 V gave a linear calibration curve in coordinates ‘Ip (Gua), μA – c(DNA), M’ from 10 to 500 μM. Other amino acids tested, namely cysteine (Cys) and tryptophan (Trp), which electrochemical oxidation occurs in the same potential range as Tyr (0.5–0.7 V), demonstrated no pronounced effect of DNA on their signals both in the absence and the presence of Zn(II) ions. The oxidation signals of Cys or Trp just slightly decreased and shifted to more positive potentials in the presence of DNA. Interesting, that these amino acids demonstrated unequal responses to addition of Zn(II) ions (DNA free controls): oxidation peaks of Tyr and Trp decreased, while the signal of Cys became more developed. To detect DNA, instead of Tyr, well-known redox indicator K3Fe(CN)6 was studied as well, but found less sensitive to the presence of DNA than free Tyr. Finally, two possible mechanisms of registered decrease of Tyr oxidation peak may be suggested: (i) a formation of the complex between Tyr, DNA, and Zn(II) ions; (ii) the blockage of Tyr oxidation by the DNA adsorption on electrode surface, enhanced by Zn(II) ions. This work was financially supported by the Russian Science Foundation, grant 19-14-00247. 1. M. Trotter, N. Borst, R. Thewes, F. von Stetten, Electrochemical DNA sensing – Principles, commercial systems, and applications, Biosens. Bioelectron. (2020) 112069. 2. A. M. Oliveira-Brett, Electrochemical DNA Assays, in: P. N. Bartlett (Ed.), Bioelectrochemistry: Fundamentals, Experimental Techniques and Applications, John Wiley & Sons, 2008, pp. 411–442. 3. J. Špaček, A. Daňhel, S. Hasoň, M. Fojta, Label-free detection of canonical DNA bases, uracil and 5-methylcytosine in DNA oligonucleotides using linear sweep voltammetry at a pyrolytic graphite electrode, Electrochem. Commun. 82 (2017) 34. 4. V. Brabec, J. Koudelka, Oxidation of deoxyribonucleic acid at carbon electrodes. The effect of the quality of the deoxyribonucleic acid sample, J. Electroanal. Chem. Interfacial Electrochem. 116 (1980) 793. 5. L. Fotouhi, R. Tabatabaee, A study of the interaction tyrosine and DNA using voltammetry and spectroscopy methods, Spectrochim. Acta A Mol. Biomol. Spectrosc. 121 (2014) 152.