Structure of Adsorbed and Grafted Single-Stranded DNA Fragments on Aminated Latex Particles: A Small-Angle Neutron Scattering Study

Adsorption and covalent binding of polythymidylic acid (dT 35 ) on aminated polystyrene latex particles have been studied. Both the electrostatic interactions between negative charges of the dT 35 and the positive charges of the cationic latex particles and hydrophobic interactions are the driving forces for the adsorption. Small-angle neutron scattering (SANS) has been used to determine the structure of the adsorbed or grafted dT 35 layers. The thickness of the adsorbed oligonucleotide layer on the latex particles is small with respect to the extended length of dT 35 molecules (∼120 Å) indicating that the adsorbed molecules lay close in a flat conformation on the surface, irrespective of the pH and ionic strength. In contrast, the covalently grafted dT 35 molecules at basic pH and high surface coverage extends more radially into the solvent, giving rise to a thicker layer in comparison to the case of adsorption.