Surface plasmon resonance (SPR) has been applied to sensing biomolecular and drug interactions because it allows real-time monitoring and label-free detection. Traditional thin film based SPR biosensing suffers from moderate detection sensitivity. In this research, we investigate sensitivity enhancement by target colocalized SPR using various subwavelength nanostructures. The nanostructures were designed by calculating near-field distribution based on rigorous coupled-wave analysis. Experimentally, angled shadow evaporation was performed to fabricate the nanostructures for target colocalization and measured resonance shifts using angle scanning SPR. The feasibility was tested by measuring DNA hybridization. Experimental results confirm significantly enhanced detection sensitivity over traditional SPR techniques to be feasible. The results are expected to open a new approach to biomolecular detection based on SPR.