Metallic bowtie nanostructures (BNSs) and their surface plasmon resonance (SPR) properties in the UV/Vis region, for Al and Au materials, have been investigated by employing discrete dipole approximation method. A crucial aspect for these applications is how SPR in BNS is affected after approach with DNA molecule. Our results reveal that SPR in Au nanostructure is redshifted by the DNA present. Au-based BNS have sensitivities about 0.055 and 0.018 to the vertical and horizontal DNA molecules, respectively. But sensitivity of Al-based BNS is very smaller than the Au. Moreover, DNA passage and its vertical and horizontal nature through the gap can be determined by the proposed method. Results provide useful indications for future characterization and monitoring of DNA molecules via SPR properties of nanostructures, as well as for the development of biosensing, trapping and sequencing devices.