Strong Strand Breaks in DNA Induced by Thermal Energy Particles, and Their Electrostatic Inhibition by Na+ Nanostructures.

Low-power laser pulses of 6 ns duration (1064 nm wavelength) have been used to create plasma in an aqueous solution of plasmid DNA (pUC19). Thermal-energy electrons and .OH-radicals in the plasma induce strand breakages in DNA, including double strand breaks (DSBs) and possible base oxidation/base degradation. The time-evolution of these modifications shows that it takes barely 30 s for damage to DNA to occur. Addition of physiologically relevant concentrations of a salt (NaCl) significantly inhibits such damage. We rationalize such inhibition using simple electrostatic considerations. The observation that DNA damage is induced by plasma-induced photolysis of water suggests implications beyond studies of DNA, and opens new vistas for using simple nanosecond lasers to probe how ultra-low energy radiation may affect living matter under physiological conditions.