## 3 Results and Discussion
### Adsorption of OGNs on the MNPs  
The adsorption of DNA-20 at the surface of all three synthesized MNPs was tested. Co-polymeric coatings have a zwitterionic character; thus, IE and HI mode were investigated. In the first mode, the solution of analyte was mixed with water or 10 mM solution of NH\({}_{4}\)OAc at pH 3.5. 4.5, 5.5, or 6.5 before mixing with the conditioned adsorbent. After the OGN adsorption step, the supernatants were collected and analyzed. The detailed adsorption conditions and the obtained results are presented in Table 2.  
Results shows that adsorption of OGN in IE mode strongly depends on co-polymer structure, pH, and the presence of salt. In the case of MNP-Ac, partial adsorption was possible from water solution without buffer addition or pH change. However, almost full adsorption was possible only when the analyte solution was mixed with buffer at pH \(<\) 4.5 (Table 2). Nearly full adsorption of DNA-20 on MNP-Sul and MNP-Mal was possible only on pH = 3.5. In other conditions, adsorption was impossible or significantly low (Table 2). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Extraction Mode**} & \multirow{2}{*}{**Conditions**} & \multicolumn{3}{c}{**Amount of Adsorbed OGN**} \\ \cline{3-5}  & & **MNP-Ac** & **MNP-Sul** & **MNP-Mal** \\ \hline \multirow{5}{*}{Ion-exchange} & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 50 \(\mu\)L H\({}_{2}\)O & 63.2 \(\pm\) 3.5\% & 0 & 0 \\  & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 50 \(\mu\)L NH\({}_{4}\)OAc pH = 6.5 & 36.5 \(\pm\) 1.3\% & 0 & 0 \\  & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 50 \(\mu\)L NH\({}_{4}\)OAc pH = 5.5 & 33.8 \(\pm\) 1.0\% & 0 & 0 \\  & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 50 \(\mu\)L NH\({}_{4}\)OAc pH = 4.5 & 94.5 \(\pm\) 3.8\% & 0 & 27.2 \(\pm\) 3.6\% \\  & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 50 \(\mu\)L NH\({}_{4}\)OAc pH = 3.5 & 93.3 \(\pm\) 2.1\% & 93.1 \(\pm\) 0.8\% & 93.1 \(\pm\) 2.3\% \\ \hline \multirow{5}{*}{Hydrophilic interactions} & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 50 \(\mu\)L ACN & 89.3 \(\pm\) 2.3\% & 45.1 \(\pm\) 1.3\% & 68.9 \(\pm\) 2.1\% \\  & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 450 \(\mu\)L ACN & 59.5 \(\pm\) 3.4\% & 64.1 \(\pm\) 2.7\% & 50.5 \(\pm\) 1.9\% \\ \cline{1-1}  & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 50 \(\mu\)L ACE & 83.6 \(\pm\) 0.7\% & 43.3 \(\pm\) 1.7\% & 37.4 \(\pm\) 2.5\% \\ \cline{1-1}  & 50 \(\mu\)L DNA-20 5 \(\mu\)M + 450 \(\mu\)L ACE & 65.2 \(\pm\) 1.5\% & 62.7 \(\pm\) 1.1\% & 80.1 \(\pm\) 2.9\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Amounts of DNA-20 adsorbed on tested MNPs in different modes. Abbreviations: OGN—oligonucleotide; ACN—acetonitrile; ACE—acetone. In further studies, the adsorption of OGNs on MNP-Ac was performed at pH = 4.5, while, on MNP-Sul and MNP-Mal, adsorption was performed at pH = 3.5. Investigated analytes are highly polar compounds with multiple negative charges. On the other hand, at the surface of the copolymer coated MNPs, there are positives charges on imidazolium rings and negative charges connected with the presence of carboxyl or sulphonate group. At low pH values, the negative charge on the surface of the adsorbent can be neutralized, and the negative charged OGNs can interact electrostatically with imidazolium rings. These interactions play a dominant role in analyte adsorption. Differences in adsorption effectiveness between three adsorbents can relate to different structures and differences in ligands protonation. As can be seen in the case of MNP-Ac, the addition of salt causes the increase of ionic strength of the solution and the lowering of the amount of adsorbed OGN. Considering the structures of OGNs and MNPs coatings, other possible interactions can be indicated, such as \(\pi\) interactions (between imidazolium rings and benzene rings of co-polymer and aromatic rings of nucleobases) or hydrogen bonding (between the carboxyl group and polar groups of nucleic acid bases). For adsorption of OGN on MNPs in HI mode, the standard solution was mixed with an appropriate volume (50 or 450 \(\mu\)L) of organic solvent (ACN or ACE).