Critical low-energy Ar-ion beam conditions to induce direct DNA double strand break

Ultra-low-energy ion interaction with naked DNA has been an interesting research topic as it can reveal fundamentals involved in charged particle irradiation effect on life as well as biological evolution. This study was a detailed investigation on ultra-low-energy argon ion bombardment effects on naked DNA. Argon ion beam was decelerated by a deceleration lens to ultra low energy ranging from about 1 keV down to a few tens of eV to bombard naked DNA plasmid pGFP to fluences of 1, 2 and 4 × 1015 ions/cm2. After ion bombardment, gel electrophoresis analyzed changes in the DNA topological form. The result showed that the DNA form changed, including from original supercoiled to damaged relaxed and linear forms, certainly depending on the ion energy and fluence. The DNA form changes as functions of the ion energy and fluence were quantified. It was found that the critical Ar-ion beam conditions were the energy 750 eV to be the lowest with the fluence 2 × 1015 ions/cm2 which could induce the linear DNA form, indicating direct double strand breaks, a more severe damage of DNA which might lead to mutation.