Influence of sulfate and phosphate on the deposition of plasmid DNA on silica and alumina-coated surfaces

The influence of sulfate and phosphate on the deposition kinetics of plasmid DNA on solid surfaces was examined at a constant 300 mM ionic strength in both NaCl–Na₂SO₄ and NaCl–NaH₂PO₄–Na₂HPO₄mixing solutions with varied sulfate and phosphate concentrations at pH 6.0 by utilizing a quartz crystal microbalance with dissipation (QCM-D). Two representative solid surfaces, both silica and alumina-coated surfaces, were concerned in this study. To better understand the effects of sulfate and phosphate on plasmid DNA deposition, QCM-D data were complemented by diffusion coefficients and zeta potentials of DNA as a function of examined solution conditions. The presence of sulfate and phosphate in solutions decreased the deposition efficiencies of plasmid DNA on both silica and alumina-coated surfaces. Moreover, the deposition efficiencies decreased with increasing concentrations of sulfate/phosphate. With sulfate/phosphate ions present in solutions, the deposition kinetics of plasmid DNA on both silica and alumina-coated surfaces were mainly controlled by classic Derjaguin–Landau–Verwey–Overbeek (DLVO) interactions.