Direct production of DNA double strand break induced by two-photon absorption of 266-nm femtosecond pulses

Akamatsu, Ken; Murakami, Hiroshi; Yamada, Hidetaka*

We have investigated DNA strand breaks induced by 266-nm femtosecond (fs) laser pulses in the solid state. The amounts of open-circular (oc) and linear (L) forms produced from closed circular plasmid DNA (pUC18, 2686 base pairs) are quantified as a function of the laser intensity. The amount of L-form produced per pulse is proportional to the square of the intensity within 100 102 GW/cm region, while that of oc-form is almost proportional to the intensity. This indicates that the direct double strand break (DSB) formation occurs by the two-photon absorption corresponding to one-photon absorption in a vacuum ultraviolet (VUV) range (133 nm, 9.4 eV). The mechanism of the strand break is discussed on the basis of the ionization potential of DNA.