Inclusion of silver nanoparticles into condensed DNA

Abstract

Ionizing radiation is widely used as a therapeutic tool. There is interest in the use of metallic nanoparticles in the role of radiation sensitizer. We have previously described an experimental system in which plasmid DNA condensed with basic oligopeptides functions as a model for chromatin. This system reproduces well the yields of DNA radiation damage observed in mammalian cells. We aimed here to extend this model system by including silver nanoparticles. Spectroscopy, light scattering, gel electrophoresis, sedimentation, and atomic force microscopy all indicate that anionic lipoate-coated silver nanoparticles can be co-aggregated with DNA by using a tetra-arginine peptide. The resulting co-aggregates are micron sized, of the same order as the nuclei of mammalian cells. Increasing the ionic strength results in disaggregation enabling recovery of the freed DNA after which it can be subjected to a wide variety of assays to characterize the radiosensitizing effects of the silver nanoparticles. This self-assembled system of three ionically bound components (nanoparticle, DNA, and peptide) offers the advantage of avoiding the complexity of forming and breaking covalent bonds between the nanoparticles and DNA.