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<INF>35</INF>) on aminated polystyrene latex particles have been studied. Both the electrostatic interactions between negative charges of the dT<INF>35</INF> 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<INF>35</INF> layers. The thickness of the adsorbed oligonucleotide layer on the latex particles is small with respect to the extended length of dT<INF>35</INF> 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<INF>35</INF> 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.