Plasmon-enhanced total-internal-reflection fluorescence by momentum-mismatched surface nanostructures

We investigate optimum plasmon-enhanced total-internal-reflection fluorescence imaging by metallic thin films and nanostructures. The enhancement is based on the mismatch between the conditions of plasmon resonance and maximal near-field intensity. We have calculated plasmon-associated near-field and far-field characteristics using rigorous coupled-wave analysis. Near-field intensity was experimentally measured with fluorescent beads on silver thin films, nanogratings, and nanoislands. The results for nanostructurebased plasmon excitation confirm that momentum mismatching when exciting plasmons can increase the consequent emission of fluorescence substantially. The improvement can be critical depending on the specific structure.