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Final Report Summary - NANORADAM (Probing DNA Radiation Damage by DNA Nanotechnology)

It is well-known that high-energy radiation is harmful for biological organisms since the carrier of genetic information, DNA, can be severely damaged. This is employed routinely in tumor radiation therapy to reduce cancer tissue. However, it is barely explored how the DNA damage induced by low-energy secondary electrons depends on the nucleotide sequence due to a lack of suitable experimental techniques. The aim of the “NanoRadam” project is to apply DNA nanostructures for the investigation of low-energy-electron induced DNA strand breaks. DNA origami platforms provide specific oligonucleotide target structures and the electron induced damage of the target structures is probed on a single-molecule level using atomic force microscopy (AFM). Within the first funding period of “NanoRadam” an electron irradiator was assembled to irradiate target structures on DNA origami platforms with low-energy electrons. With this approach it is possible to obtain absolute cross sections for DNA strand breakage, which represent benchmark values that can directly be compared to cross sections of other radiation induced processes. Within first experiments a pronounced nucleotide sequence dependence of the strand break cross sections was found, and especially the incorporation of therapeutically used radiosensitizers leads to a considerable increase of strand break cross sections. Furthermore, novel experimental approaches have been tested, such as the use of DNA origami templates as substrates for surface-enhanced Raman scattering (SERS), and the analysis of DNA radiation damage by SERS using gold nanoparticles. The research was carried out by the newly established junior research group “Optical spectroscopy and Chemical Imaging” at the University of Potsdam and the Federal Institute of Materials Research and Testing (BAM), Germany. Within the second funding period of “NanoRadam” this technique has been applied to a broad range of DNA sequences including G rich telomeric DNA, and oligonucleotides that are sensitized by incorporation of halogenated nucleobases. Specifically, the efficiency of the potential radiosensitizer 2-Fluoroadenine to enhance electron induced DNA strand breaks has been demonstrated and the underlying mechanisms have been studied in detail. Furthermore, the experiments on laser-irradiated nucleobases have been extended to study damage of DNA model systems in solution by using gold and silver nanoparticles. Damage products have been observed by UV-Vis absorption spectroscopy and surface-enhanced Raman scattering (SERS) and the effect of electrons and plasmonically generated heat has been disentangled.

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