## 3 Results and Discussion
### ssDNA and GNPs  
In the first stage of the study, we researched in detail the adsorption of a set of ssDNA on GNPs (concentrations of GNPs: 0.5 nM) under standardized conditions (Figure 2, Table 2) and carried out a theoretical calculation (affinity-rating analysis) of relative affinity of all tested ssDNA for GNPs, similarly to [23]. The standardized conditions (24 h incubation at 25 \({}^{\circ}\)C) have previously been shown to be sufficient to achieve thermodynamic equilibrium in a heterophasic interaction of ssDNA with GNPs [40]). Figure 1: Schematic representation of DNAs used in the work, where F is 5\({}^{\prime}\)-CTAACTAACGTACATCATCATAC-3\({}^{\prime}\), and R is 5\({}^{\prime}\)-GATATGATGATGATG-3\({}^{\prime}\). The “main” DNA regions are highlighted in gray or black. The red, blue, and green colors indicate the “anchor” DNA regions. The base oligodeoxynucleotides (hereafter \"initial oligodeoxynucleotides\") F and R have similar characteristics regarding their affinity for GNPs (Figure 2). Langmuir constants (K\({}_{\rm L}\)) and surface capacity of GNPs are almost identical between these ssDNA, which is important to consider below. As expected, the introduction of one high-affinity hexameric L motif at the 3\({}^{\prime}\) end of the F oligonucleotide led to a significant increase in the efficiency of adsorption of FL on GNPs. If we compare F with its extended version, FL, the surface capacity of GNPs increased from 36 to 56 molecules of DNA per nanoparticle; this increase is inversely proportional to a decrease in equilibrium interaction constant K\({}_{\rm L}\) (Table 2), which characterizes the stability of ssDNA/GNP associates. Making the anchor L motif longer--from hexa- to dodeca- and tetracosenucleotides--caused a significant decrease in the capacity of GNPs for oligonucleotides FL2 and FL4 (capacity for FL2: 38 molecules per GNP, and for FL4: 17). The efficiency of binding of ssDNA to GNPs changed approximately by the same factor (2.2), judging by the K\({}_{\rm L}\) value. Therefore, one of possible determinants of this imbalance is an increase in electrostatic repulsion between elongated DNAs adsorbed on the surface of metal nanoparticles. We have reported a high probability of this type of phenomenon earlier, in a detailed analysis of an interaction of charged molecules with a metal nanoparticle [41]. The second possible determinant is elevated likelihood of long oligonucleotides forming secondary structures (imperfect hairpins or intermolecular complexes, their stability was assessed by means of [42]) that possess weaker affinity for GNPs [39] (Figures S1 and S2, Table S3). There is no doubt that, in this case, ssDNA somewhat loses its ability to bind to GNPs because it is the implementation of a network of direct ssDNA/GNP contacts that primarily determines the stability of the nanoassociates in question [4; 23]. We could not resist the temptation to evaluate the influence of the nucleotide sequence of the \"anchor\" motif in ssDNA on the efficiency of its adsorption on the surface of GNPs. The presence of L motifs (TTGTTG sequence) within ssDNA (FLn series) should significantly enhance the interaction of the oligonucleotide with GNPs [23]. On the other hand, the use of a longer ssDNA can raise the probability of formation of its secondary structures that have lower affinity for GNPs and can increase electrostatic repulsion of DNA molecules between themselves and from the surface of citrate GNPs [39; 43]. That