Radiosensitization by Gold Nanoparticles: Comparison of DNA Damage Induced by Low and High-Energy Electrons

Our previous studies on high energy (60 keV) electron bombardment of thin films of pGEM-3Zf(-) plasmid DNA with and without bound gold nanoparticles (GNP) showed that the presence of these particles greatly increases the formation of single- (SSB) and double-strand (DSB) breaks. To study the basic mechanisms underlying this DNA sensitization, we performed similar experiments with low energy (1, 10, 100 eV) and 60 keV electrons. The exposure response curves were recorded for the formation of SSB, DSB and loss of supercoiled DNA. The yields of SSB and DSB for pure DNA, salted DNA and GNP-DNA complexes with a molecular ratio of 1:1 were measured by agarose gel electrophoresis. The yields recorded for the GNP-DNA complexes were consistently enhanced by a factor of about 2 or more compared to those obtained with the salted DNA sample. Furthermore, the yields for low-energy electron damage were at least one order of magnitude larger than those produced by high-energy electrons. The results suggest that the radiosensitizing action of GNP takes place via two mechanisms: (1) an increase of the absorption of ionizing radiation close to the DNA, which in turns leads to a considerable increase in the production of short range secondary electrons that have a high probability of damaging DNA, and (2) an increase in the sensitivity of DNA to fragmentation induced by low energy electron impact near the site of binding of the GNP