Controlling the fluorescence lifetime of dyes in nanostructured geometries

Controlled surface plasmon enhanced fluorescence from 1D gold gratings via azimuth rotations

We demonstrate a method to maximise the fluorescence enhancement from a dye using gold coated diffraction gratings. Rotations about the azimuth provides a convenient approach to maximise the coupling between the grating and excitation source while achieving enhancements comparable to traditional optical configurations where the grating and in plane light vectors are parallel. This approach yields a 30 fold enhancement in the fluorescence signal over metal free substrates, while opening up the range of possible orientations and configurations suitable for fluorescence enhancement applications.

Manipulation of the local density of photonic states to elucidate fluorescent protein emission rates

We present experiments to determine the quantum efficiency and emission oscillator strength of exclusively the emitting states of the widely used enhanced green fluorescent protein (EGFP). We positioned the emitters at precisely defined distances from a mirror to control the local density of optical states, resulting in characteristic changes in the fluorescence decay rate that we monitored by fluorescence lifetime microscopy. To the best of our knowledge, this is the first emission lifetime control of a biological emitter. From the oscillation of the observed emission lifetimes as a function of the emitter to mirror distance, we determined the radiative and nonradiative decay rates of the fluorophore. Since only the emitting species contribute to the change in emission lifetimes, the rates determined characterize specifically the quantum efficiency and oscillator strength of the on-states of the emitter, in contrast to other methods that do not differentiate between emitting and dark states. The method reported is especially interesting for photophysically complex systems like fluorescent proteins, where a range of emitting and dark forms has been observed. We have validated the analysis method using Rhodamine 6G dye, obtaining results in very good agreement with the literature. For EGFP we determine the quantum efficiency of the on-states to be 72%. As expected for this complex system, our value is higher than that determined by methods that average over on- and off-states.