Interaction of G-quadruplex Forming DNA Aptamers with PAMAM Dendrimers Studied by Dynamic Light Scattering and UV-VIS Spectrophotometry**

The complexes of G-quadruplex forming DNA thrombin binding aptamers (TBA) and polyamidoamine dendrimers (PAMAM) were studied with the aim to form a model targeted drug delivery system. Hydrodynamic diameter, zeta potential and melting temperature (T_m) were investigated by dynamic light scattering and UV-VIS spectrophotometry. Non-covalent adsorption by means of electrostatic interaction between positively charged amino groups of dendrimers (+) and negatively charged phosphate groups of aptamers (−) has driven the formation of aggregates. The size of complexes was in the range of 0.2–2 μm and depended on the type of dispersant, charge ratio (+/−) and temperature. Raising the temperature increased the polydispersity, new smaller size distributions were observed indicating the G-quadruplex unfolding. The melting transition temperature of TBA aptamer was affected by the presence of amino-terminated PAMAM rather than carboxylated succinic acid PAMAM−SAH dendrimer, thus supporting the electrostatic nature of interaction that disturbed denaturation of target-specific quadruplex aptamer structure.