Variation of strand break yield for plasmid DNA irradiated with high-Z metal nanoparticles

Using agarose gel electrophoresis, we measured the effectiveness of high-Z metal particles of different sizes on SSB and DSB yields for plasmid DNA irradiated with 160 kVp X rays. For plasmid samples prepared in Tris-EDTA buffer, gold nanoparticles were shown to increase G'(SSB) typically by a factor of greater than 2 while G'(DSB) increased by a factor of less than 2. Similar dose-modifying effects were also observed using gold microspheres. Addition of 10(-1) M DMSO typically decreased damage yields by a factor of less than 0.5. Plasmid samples prepared in PBS showed significantly different damage yields compared to those prepared in Tris-EDTA (P < 0.001) with G'(SSB) and G'(DSB) increasing by factors of 100 and 48, respectively. Furthermore, addition of gold nanoparticles to samples prepared in PBS decreased G'(SSB) and G'(DSB) by factors of 0.2 and 0.3, respectively. The results show plasmid damage yields to be highly dependent on differences in particle size between the micro- and nanometer scale, atomic number (Z) of the particle, and scavenging capacity of preparation buffers. This study provides further evidence using a plasmid DNA model system for the potential of high-Z metal nanoparticles as local dose-modifying agents.