Under the photoirradiation, DNA works as both template and reducing agent to drive the formation of metallic nanomaterials. In this study the plasmid DNA with different base pairs was applied as biotemplate to synthesize Ag nanoparticles (NPs) by using photoirradiation approach. The evolution of DNA dimension changed during the synthesis process, and their effect on the morphology of the synthesized Ag NPs was studied by UV-Vis spectra, FT-IR spectra, Raman spectra, AFM, and TEM. It is found that the plasmid DNA shrinked twice during the synthesis, the first time happened when the Ag (I) cations neutralized the negative charge along the DNA chain, and the second time happened when plasmid DNA reduced Ag (I) induced by the ultraviolet C (254 nm) irradiation. The size of the synthesized Ag NPs showed approximately linear relationship with the dimension of plasmid DNA scaffolds under this photo-induce condition. The compaction degree of the plasmid DNA during the Ag formation was shown by the slope of the linear relationship.
