Atomic force microscopy investigation of electron and neutron-induced DNA double-strand breaks

This dissertation reports an investigation of radiation-induced DNA double-strand breaks (DSBs), using the method of Atomic Force Microscopy. Electrons and neutrons were employed as examples of low-LET and high-LET radiation. Using the capacity of the AFM to measure individual DNA fragments as short as a few nanometers, we obtained the fragment distributions of the irradiated pUC19 plasmid DNA as a function of radiation dose. From these distributions we determined quantities that are most reflective of radiation-induced DSB: the fraction of unbroken DNA molecules, the fraction of DNA molecules with one break only, the average number of DSBs per DNA, and the average number of DSBs per broken DNA. Comparing these quantities for electrons and neutrons, we evaluated the quantitative similarities and differences in the DNA damage caused by these two types of radiation. We found that electrons produce DSBs that are more uniformly distributed, whereas neutrons produce DSBs that are much more locally and densely distributed. Furthermore, we found that electron-induced DSBs satisfy a random DSB model, whereas neutron-induced DSBs do not.