Probing low-energy electron induced DNA damage using single photon ionization mass spectrometry

Single photon ionization mass spectrometry (SPI MS) followed by gel electrophoresis was developed for investigation of low-energy electron (LEE) induced DNA damage. This method detects neutral species generated from DNA molecules during LEE irradiation. The neutral yields are then correlated with single strand breaks (SSBs) and double strand breaks (DSBs) as a function of incident electron energy. Specifically, fragments with masses of m/z = 27, 68 and 69 show resonance structure between 6–12 and 15–25 eV which is similar to that observed in the SSB and DSB probabilities. These fragments are likely associated with sugar damage and dissociative electron attachment (DEA) channels. Other fragments with masses of m/z = 45, 56, 67 and 70 show a monotonic increase at threshold energies around 10–12 eV, indicating the possible role of direct dissociative excitation or ionization. Resonance structure above the 10–12 eV threshold for fragments with masses of m/z = 43, 44, 67 and 70 are also observed and can be associated with compound states in the continuum and core-excited excitations. The results support the contention that DEA resonances localized on DNA sub-units can lead to damage, especially at energies below the ionization threshold. Damage also occurs due to direct dissociative excitation and dissociative ionization.