Radiosensitization of condensed plasmid DNA by co-aggregation with gold nanoparticles and a tetra-arginine peptide

The basic peptide N-acetyl-tetra-L-arginine-amide has been reported to act as a DNA condensing agent. This peptide also aggregated lipoate coated gold nanoparticles (AuNPs). In the absence of the peptide, the anionic DNA and AuNPs showed no evidence of interaction with one another. However, when a solution containing both DNA and AuNPs was treated with the peptide, the sedimentation behavior, UV-visible spectroscopy, scanning electron microscopy, and atomic force microscopy all revealed that they can be co-aggregated. Dynamic light scattering and the sedimentation behavior of these co-aggregated particles both indicated a mean particle size of ca. 3 mu m. The DNA could be released and assayed for damage after increasing the ionic strength. This constitutes a convenient model system with which to quantify radiosensitization by AuNPs. Using these co-aggregates as targets for gammas and X-rays, the presence of AuNPs resulted in a 1.3- to 1.6-fold increase in the DNA single strand break (SSB) yield produced by these ionizing radiations.