Abstract
Abstract Since about a decade, metal-induced energy transfer (MIET) has become a tool to measure the distance of fluorophores to a metal-coated surface with nanometer accuracy. The energy transfer from a fluorescent molecule to surface plasmons within a metal film results in the acceleration of its radiative decay rate. This can be observed as a reduction of the molecule’s fluorescence lifetime which can be easily measured with standard microscopy equipment. The achievable distance resolution is in the nanometer range, over a total range of about 200 nm. The method is perfectly compatible with biological and even live cell samples. In this review, we will summarize the theoretical and technical details of the method and present the most important results that have been obtained using MIET. We will also show how the latest technical developments can contribute to improving MIET, and we sketch some interesting directions for its future applications in the life sciences.
Highlights
The emission process of almost all fluorescent molecules can be excellently described by the classical theory of an electric dipole emitter
Since about a decade, metal-induced energy transfer (MIET) has become a tool to measure the distance of fluorophores to a metal-coated surface with nanometer accuracy
The situation becomes even more complex for structured environments, such as interfaces [2, 3], cylindrical nanocavities [4, 5], or spherical nanocavities [6, 7]. Another well-known example is Förster resonance energy transfer (FRET) [8, 9], where the electromagnetic near-field coupling between a donor and an acceptor molecule leads to a dramatic change of the radiative decay rate of the donor
Summary
The emission process of almost all fluorescent molecules can be excellently described by the classical theory of an electric dipole emitter. In the 1960s and 1970s, a series of remarkable and elegant experiments by Kuhn and Drexhage demonstrated the striking effect of a reflecting mirror on the fluorescence of molecules in close proximity [10,11,12,13,14,15,16,17] They observed changes in the angular distribution of emission as well as in the spontaneous decay rate of the fluorescent molecules. Two techniques that perform even better are interferometric PALM [28] and 4pi-STORM [29] They reach nanometer axial single-molecule localization accuracy, but for the prize of extreme technical complexity and difficult applicability for routine biological research. The principle of MIET imaging is based on the energy transfer from a fluorescent molecule to surface plasmons within a thin metal film on a glass surface, which results in the acceleration of its spontaneous decay rate This can be observed as a reduction of the molecule’s fluorescence lifetime. Within this distance range, a measured fluorescence lifetime can be uniquely converted into a distance between the emitter and the surface
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