Electrophoresis examination of strand breaks in plasmid DNA induced by low-energy nitrogen ion irradiation

To study the effect on plasmid DNA of heavy ion in the energy range of keV where nuclear stopping interaction becomes more important or even predominant, thin film of plasmid pGEM-3Zf(-) DNA was prepared on aluminum surface and irradiated in vacuum (<10-3 Pa) by low-energy nitrogen ions with energy of 30 keV (LET=285 keV/μm) at various fluence ranging from 2 x 1010 to 8.2 x 1013 ions/cm2. DNA strand breaks were analyzed by neutral electrophoresis followed by quantification with image analysis software. Low-energy nitrogen ion irradiation induced single-, double- and multiple double-strand breaks (DSB) and multiple DSB as the dominating form of DNA damages. Moreover, the linear fluence-response relationship at a low fluence range suggests that DSBs are induced predominantly by single ion track. However, strand break production is limited to a short range in the irradiated samples