(269g) Plasmid DNA Adhesion on Silica: Kinetics and Conformational Changes in Mono and Divalent Salts

We use a quartz crystal microbalance with dissipation (QCM-D) to determine the adhesion rate of a supercoiled plasmid DNA onto a quartz surface and the structure of the resulting adsorbed DNA layer. To better understand the DNA adhesion mechanisms and the adhered layer physicochemical properties, the QCM-D data are complemented by dynamic light scattering measurements of diffusion coefficients of the DNA molecules as a function of solution ionic composition. The data from simultaneous monitoring of variations in frequency and dissipation energy with the QCM-D suggest that the adsorbed DNA layer is more rigid in the presence of divalent cations compared to monovalent cations. Adhesion rates are significantly higher in the presence of divalent cations, attaining a transport limited rate at about 1 mM Ca2+. Results further suggest that in low ionic strength solutions containing 1 mM Ca2+ or Mg2+, and in moderately high ionic strength solutions containing 300 mM NaCl, the plasmid DNA adhesion to negatively charged mineral surfaces is irreversible.