## 1 Introduction  
The development of delivery systems for therapeutic nucleic acids (NAs) and of sensors containing NAs as disease markers begins with research on fundamental aspects of the binding of NAs to the carrier surface. There are many promising carriers, including gold nanoparticles (GNPs). GNPs have low toxicity [1] and chemical inertness [2] as well as the ability to bind (on their surface) biomolecules (containing or not containing thio groups) via strong covalent and noncovalent adsorption [3; 4; 5; 6]. It should be noted that the process of even covalent attachment of biomolecules to the surface of GNPs [7; 8; 9; 10] is initiated by noncovalent adsorption [11]. Therefore, understanding the patterns of noncovalent adsorption of biomolecules on the surface of GNPs is important for the creation of carriers containing NAs. It is known that the adsorption of single-stranded DNAs (ssDNAs or oligonucleotides) on GNPs proceeds more efficiently than the adsorption of double-stranded DNAs (dsDNAs or DNA duplexes) [12]. ssDNA forms multipoint contacts with a GNP, and the nucleotide sequence, its length, the presence of modifications in the DNA, ionic strength and pH of the medium during the incubation, temperature, and association reaction time significantly affect the efficiency of observed adsorption of ssDNA to the surface of GNPs [4; 13; 14]. It has been shown that the adsorption of various DNA structures (dsDNAs, ssDNA with a hairpin structure, and self-complementary ssDNA) on GNPs indeed substantially varies if we compare values of the association constant of the NAs toward the surface of inorganic nanoparticles [15]. It should be mentioned that the effects of differences in the primary structure of model DNAs were not discussed in the work just cited. It is important to understand that DNA forms secondary structures in which the most hydrophilic polyanion residues (the phosphate backbone) protect the hydrophobic portions of the duplexes (i.e., the DNA bases) from direct contact with the gold surface. Therefore, nitrogenous bases of dsDNA can be exposed to the gold surface only on the side of the major and minor grooves or as terminal base pairs of the duplex, which are in a state of dynamic equilibrium between open and closed forms. This mechanism was first demonstrated by analysis of the interaction of DNA with the flat surface of a gold layer [16]. There are two main differences between ssDNA and dsDNA in the context of their interaction with GNPs [17]. First, heterocyclic bases of ssDNA, being spatially accessible, are capable of forming hydrogen bonds and/or hydrophobic contacts with atoms on the surface of GNPs; these processes are severely impeded for heterocycles within dsDNA [18]. According to a number of studies (including our data), it is this interaction that determines the strength of binding between NAs and GNPs [4; 19; 20]. The second difference is that ssDNA has a much more mobile structure, whereas dsDNA has a rigid structure that hinders the direct interaction of nitrogenous bases with the surface of nanoparticles. This statement is supported by data obtained by circular dichroism spectroscopy, indicating that the interaction of dsDNA with GNPs leads to a forced change in dsDNA's spatial structure [21]. According to [PERSON] and coauthors [22], molecules of dsDNA tend to have planar positioning relative to the gold surface. It is this circumstance that forces researchers to look for approaches ensuring the effective interaction of dsDNA with nanoparticles, including approaches involving duplexes with single-stranded overhangs, the affinity of which for the surface of inorganic nanoparticles can be predetermined [23; 24]. Such an approach was first demonstrated via binding of dsDNA containing a single-stranded homoA overhang to the surface of a gold film and subsequent dehybridization/hybridization of the DNA complex on the surface of GNPs [25].