Metal-Enhanced Fluorescence from Silver−SiO₂−Silver Nanoburger Structures

Multilayers of nanoburger structures of silver island films−SiO₂−silver island films (SIFs−SiO₂−SIFs) were used as substrates to study the fluorescence of close-proximity fluorophores. Compared to single-layered SIFs, multilayer nanoburgers exhibit several distinctive properties including a significantly enhanced fluorescence intensity, decreased lifetimes, and increased fluorphore photostability by simply varying the dielectric layer thickness while the SIF layer is kept constant. Finite-difference time-domain (FDTD) calculations show that the maximum electric field intensity can be tuned by varying the distance between the silver particles. Enhanced fluorescence emission coupled with a reduced fluorophore lifetime suggests that both an electric field and plasmon-coupling component are the underlying mechanisms for nanoburger-based metal-enhanced fluorescence (MEF). This tunable multilayer nanoburger structure holds great potential for applications in biology, microscopy, imaging, and biomedical research, given the current uses of MEF.