This proposal will develop an assay to map genomic DNA, at the single molecule level and in a nanodevice, for oxidative DNA damage arising from radiation exposure; this will result in a highly quantitative approach to real-time health monitoring, dose response studies, studies of cancer progression, and systematic analyses of immunologically compromised cells. Exposure to radiation damages DNA. Reactive oxygen species (ROS) are liberated, causing oxidative damage to DNA bases. The major consequence of this damage is misincorporation of bases during replication, leading to irreversible cell damage, cancer or compromised cell function. Oxidatively damaged genomic DNA is tagged at the lesions using specific antibodies, and the resultant DNA is scanned in a linear manner by our single molecule nanodevice. The locations, amount, and type of lesions are recorded for each DNA molecule. Megabase pair DNA is scanned by the reader in milliseconds, at ultra-sensitive single molecule detection limits. The technology is highly practical based on our significant experiences in developing single molecule scanning technologies. The potential nanoscale device and analysis speed create new possibilities for routine implementation. This addresses a current unmet need since there are no existing technologies that allow comprehensive assessment of DNA oxidative damage.