Recently, commercial home electric appliances with bactericidal/viral inactivation function of room air have been widely available. Most of these home appliances equip discharge devices which possibly generate reactive oxygen and nitrogen oxides. However, these effects are still controversial problem. To elucidate the inactivation effect of these devices at molecular level, we have been considering large DNA molecules as a biomarker to be used. By exposing DNA solution to the gas containing the chemical species, oxidative damage to DNA such as strand breaks can be induced. We have conducted the single-molecule-based evaluation method of DNA strand break using large linear DNA molecules. The obtained breakage rate could possibly be used for evaluation of reactivity of radicals generated by the discharge devices.