Interfacial interactions between DNA and polysaccharide-coated magnetic nanoparticles: Insight from simulations and experiments.

In this work we examine the structural and energetic stability and the interactions between dextran-coated magnetic nanoparticles (MNPs) and a DNA oligonucleotide at ionic strength conditions that are relevant to physiological gene delivery processes. All-atom Molecular Dynamics simulations provided information at the atomic-level regarding the mechanisms responsible for the physical adsorption of Dextran on the magnetic surface and the conditions under which a successful DNA-Dextran complexation can be accomplished. Coulombic interactions were found to play the main role for the formation of the Dextran interfacial layer onto the magnetic surface while hydrogen bonding between the Dextran molecules enhanced the structural integrity of this layer. The Dextran-DNA complexation was also driven by electrostatic interactions between the two moieties. An increase of the salt concentration was found to promote DNA complexation with the DX-coated magnetic nanoparticles, through the modification of the Coulombic interactions between the DX and DNA chains, which worked synergistically with the increase in hydrogen bonding between the two macromolecules. Comparison of the behavior of the coated with the uncoated magnetic nanoparticles, highlighted the significant role of the DX interfacial layer on the DNA association to the magnetic surface. Relevant experimental results provided complementary information for the coated nanoparticle/DNA interactions at different (larger) length scales. A good qualitative agreement was found between the simulation and experimental findings. This study demonstrates that tailoring the nanoparticle coating and ionic strength can optimize the delivery of DNA by fine-tuning the favorable interfacial forces and thus the DNA/MNP binding stability.