Effect of monovalent and divalent ionic environments on the in-lattice nanoparticle-grafted single-stranded DNA.

Polyelectrolyte polymers (PEs) are sensitive to change in environment around them such as pH, temperature, presence of different type of salt, type of solvent etc., which affect the chain morphology and its conformation in the solution. Although much work is done on the free PEs morphology in the presence of the different salts and concentrations but not much work has been done when the movement of the chains are constricted when they are attached on the spherical surface. Our work investigates, using in-situ small-angle x-ray scattering (SAXS), the morphology of PEs (single-stranded DNA) chains grafted onto a surface of spherical gold nanoparticles assembled in a lattice in the presence of monovalent and divalent salts. Our experiments reveal that when DNA chains are present in the divalent salt the chain length decreases at faster rate when compared to the monovalent salts. Power law and modified Daoud Cotton has been used to get insight about the behaviour of the DNA chains in different ionic environments. It has been found that for monovalent salts electrostatic interaction is leading to the decrease of the DNA chain length whereas for divalent salts both electrostatic interactions and the ion-bridging contributes leading to faster decrease of the DNA chain length.