## 3 Results and Discussion  
### Design of the Oligonucleotides  
Spherical GNPs 13 \(\pm\) 2 nm in diameter were used, as were model oligodeoxyribonucleotides that form the simplest duplex (i.e., the initial blunt-ended duplex designated as F-R) and duplexes carrying a 3\({}^{\prime}\) single-stranded overhang of various nucleotide compositions and lengths (designated as FLn-R and FTn-R) (Figure 1). FLn oligonucleotidesides (n = 1, 2, and 4) contained different numbers of an L motif (TTGTTG), which possesses enhanced affinity for the surface of GNPs [23]. Oligonucleotides from the FTn series served as controls, in which, instead of the L motif, we used hexatimidylate; it has weaker affinity for the surface of GNPs [23]. Single-stranded L motifs, as explained above, should play the role of DNA regions that predetermine the enhanced affinity of DNA molecules for GNPs, that is, they should act as \"anchor\" regions.  
We studied in detail effects of the length of the L and T motifs on the affinity of the respective ssDNA and dsDNA for the surface of GNPs and on the capacity of GNPs for these DNAs (i.e., the highest possible number of bound DNA molecules per GNP). By the affinity of DNA for GNPs, we mean the energy of interaction of nucleotide units and of their motifs with the surface of GNPs. In this context, the multipoint nature of the interaction of DNA strands with GNPs should be taken into account. This phenomenon implies that the formation of several (many) contacts with a GNP by one DNA molecule reduces the area of the GNP available for adsorption of other identical molecules of DNA. Consequently, the capacity of GNPs for a DNA having stronger affinity for GNPs is less than that for a DNA having weaker affinity. It is the details addressed by this study (on the basis of principles of material balance) that allow us to elucidate the mechanism of (and problems with) the formation of noncovalent associates of DNA with GNPs (DNA/GNP). In our study, the 3\({}^{\prime}\)-terminal single-stranded motifs 6, 12, and 24 nucleotides long in the oligonucleotides of the L and T series underlie the comparative analysis of the formation of noncovalent associates of ssDNA or dsDNA with GNPs. It is important to emphasize again that (1) all formed duplexes bearing an overhang have a 3\({}^{\prime}\)-terminal single-stranded motif, and (2) for the assembly of all duplexes, the same oligonucleotide R was used, which is completely complementary to the F segment within oligonucleotides of any series (Figure 1). At the same time, sequences F and R were chosen so as to minimize the likelihood of both intra- and intermolecular interactions [38]. The last requirement was imposed because of evidence that the formation of secondary structures of DNA, that is, hairpins or duplexes, lowers the efficiency of the formation of DNA/GNP associates [23; 39].  
We deliberately employed 5\({}^{\prime}\)-32P-labeled (radioactive) strands of ssDNA to exclude the effect of fluorescent labels on the interaction of DNAs with GNPs; this phenomenon has been documented by us earlier [14]. For dsDNA, the 32P label was introduced into either one or the other strand (consecutively) to quantify the interaction of each strand with GNPs.