Optical control of DNA-base radio-sensitivity

{\bf Purpose}: Manipulation of the radio-sensitivity of the nucleotide-base driven by the spin blockade mechanism of diffusive free radicals against ionizing radiation. {\bf Materials and methods}: We theoretically propose a mechanism which uses the simultaneous application of circularly polarized light and an external magnetic field to control the polarization of the free radicals and create S=1 electron-hole spin excitations (excitons) on nucleotide-base. We deploy an ab-initio molecular dynamics model to calculate the characteristic parameters of the light needed for optical transitions. {\bf Results}: As a specific example, we present the numerical results calculated for a Guanine, in the presence of an OH free radical. To increase the radio-resistivity of this system, a blue light source for the optical pumping and induction of excitons on guanine can be used. {\bf Conclusions}: The effect of spin-injection on the formation of a free energy barrier in diffusion controlled chemical reaction pathways leads to the control of radiation-induced base damage. The proposed method allows us to manipulate and partially suppress the damage induced by ionizing radiation.