The research focuses on optimization of a leaky metal-insulator-metal (MIM) nanopillar array design for the detection of sub-100 nm viruses. Here we have explored different MIM nanopillar and array geometries along with the insulator layer material to tune the plasmonic field leakage. For the optimized design, we observe a sensitivity of the surface refractive index change of -101.68 nm RIU-1. Using 100 nm diameter polystyrene particles, a sensitivity of 17.66 nm/decade was achieved with a detection limit of one particle. The optimized structures thus demonstrate a homogeneous surface sensitivity over a large active sensing area for sub-100 nm virus detection.