Design of plasmonic nanostructures for single molecule detection based on fluorescence dependent surface Plasmon coupled emission

Abstract

Surface plasmon-coupled emission (SPCE) is the complementary phenomenon of surface plasmon resonance (SPR), where the light emitted from a fluorescent molecule couples into the adjacent thin metal layer resulting in highly directional emission in the SPR angle. In addition to the high directionality of emission, SPCE has the added advantage of surface selectivity, high spectral and spatial resolution. This effect can be exploited in bioassays with high signal to noise ratio. However, SPCE based detection is still not used to image single molecule due to large detection volume, which results in low resolution imaging.

Single molecule detection requires much smaller detection volume than that is provided by typical SPCE based structure. This thesis mainly focuses on designing nanostructures to address this issue. In this work, we propose a new structure that replaces the thin metal layer – used in typical SPCE design – with a nanostructured metal layer, which contains periodic nanoholes. We use finite difference time domain (FDTD) analysis to solve Maxwell’s equations and calculate detection volume, excitation field intensity, coupled power to detection side, and peak SPCE intensity for different sizes of nanoholes with varying periodicity. We use particle swarm algorithm to find the optimum combination of periodicity and diameter of the nanoholes so that the proposed structure provides minimum detection volume. Our proposed structure not only reduces the detection volume by 84 percent but also significantly improves the excitation field intensity, coupled power to detection side, and peak SPCE intensity.