摘要
The effects of metal-enhanced fluorescence (MEF) of rhodamine dye by gold sub-micro hexagonal plates were studied. A multilayered avidin–biotin complex was designed and used as a spacer to connect the fluorophore and the sub-microplate. Fluorescence lifetime image microscopy (FLIM) combined with time-correlated single-photon counting was used to obtain lifetime images and intensities of dye on single particles. Gold hexagon plates ~900 nm were synthesized, and the avidin–biotin complexes were placed layer-by-layer for up to 4 layers onto the sub-microplates. All emission curves of fluorophore displayed biexponential decay with short lifetimes of 18–23 ps and long lifetimes of 249, 271, 304, and 348 ps for 1–4 layers on gold sub-microplates, respectively. Using the kinetic model of energy transfer between fluorophore and nanoparticles to explain the coupling mechanism, we found that the excited fluorophore transferred energy mostly to the high-order modes for the 1-layered avidin–biotin complexes enclosing gold nanospheres, consequently resulting in a non-emissive pathway. The 4-layered samples had the highest emission intensity because, at those distances, the enhancement by the gold sub-microplates during plasmonic excitation remained high and became comparable to the energy quenching rate. Using the composed complexes, the MEF effect achieved the maximal enhancement in this system.