Smart Design of Zero-Mode Waveguide Nanodevices for Effective Detection of Single-Molecule Fluorescence

The spontaneous decay rate of an excited molecule placed near a circular nanoaperture in a metal film of finite thickness and finite conductivity lying on a dielectric substrate (zero-mode waveguide, ZMW) is investigated. A significant influence of the molecule position and the presence of the substrate on the spontaneous emission rate of the molecule is shown. The asymptotes, which can be used to describe this process, are found. Total, radiative, and nonradiative channels of spontaneous decay rates of the excited molecule are extracted and analyzed. It is shown that a special choice of the substrate and the material of metal film leads to the appearance of "leaky" surface plasmon waves and substantial enhancement of the radiative decay rate. The results can be useful in the design of alternative ZMW optical nanodevices for effective detection of single-molecule fluorescence.