Abstract
Label-free biosensing based on extraordinary optical transmission (EOT) through metallic nanoaperture arrays is a highly promising application of nanoplasmonics. The optical properties of these nanostructures, however, are complex due to the coupling between propagating and localized plasmon resonances, and some important features of the sensing mechanism have not been fully exploited. In this paper, in contrast to most previous studies that focused on the optimization of sensor response to bulk refractive index changes, we investigate the sensor response upon biomolecule bindings at different sensor positions inside or outside the nanoapertures. By properly tuning the geometric parameters of a gold nanoslit array, we show that the enhanced optical field in this EOT-based sensor can be spatially tailored to increase its interaction volume with the binding target biomolecules and improve the sensor performance. The results presented deepen the current understanding of the EOT-based sensor properties and open up new opportunities to further optimize their sensing performance.