Nanoimprint lithography is used to fabricate 200 nm-10 mu m wide SU-8 channels reversal imprinted onto Si substrates. The immobilization and stretching of double stranded lambda-DNA molecules within the micro-and nanochannels are demonstrated and controlled by varying the hydrophobicity of SU-8 using oxygen plasma exposure. Site-directed immobilization of DNA is achieved by the integration of 10 mu m wide SU-8 patterns with 6 mu m gaps into 100 mu m wide and 1 mu m deep Si channels. (c) 2007 American Vacuum Society.