Re-direction of surface plasmon-coupled emission using metallic nanoparticles

Fluorophores within near-field distances of thin metal films are known to be coupled with plasmonic states thereby resulting in a narrow angular distribution of emissions from the bottom of the structure. This phenomenon of surface plasmon-coupled emission (SPCE) has become widely used in immunoassays and diagnostics. The coupled emission is typically measured through a prism under the slide, which can be difficult for microplate readers and other instruments designed for rapid testing, or high-throughput screening. We show that SPCE can be re-directed upwards into the free-space direction using a layer of silver particles. This result enables fluorescence to be measured from the top or bottom of the sample. This capability may expand the range of assays using plasmon-controlled fluorescence (PCF).