Plasmonic nanoantennas enable forbidden FRET

FRET is highly sensitive to the mutual orientation of donor and acceptor dipoles, and can be strongly prohibited for perpendicularly oriented dipoles. However, all previous studies combining FRET with nanophotonics largely overlooked this orientation effect. In a recent Nano Letters article "Plasmonic Nanoantennas Enable Forbidden Förster Dipole–Dipole Energy Transfer and Enhance the FRET Efficiency", we show for the first time how to exploit the orientation dependence in FRET using plasmonic nanoantennas.

Significance:

- Nanoantennas can allow FRET even for perpendicularly oriented donor and acceptor pairs. This provides a new strategy using nanophotonics to reveal FRET interactions that would otherwise be impossible to probe with diffraction-limited microscopy.

- While all previous work were dominated by the plasmonic losses which compete with FRET and decrease the FRET efficiency, our approach exploiting the dipolar orientation effect overcomes the losses. We report the first gain in FRET efficiency using nanophotonics, which even reaches up to 50%.

- Numerical simulations elucidate this new FRET enhancement and reveal the crucial role of the simultaneous presence of electric field components along all three directions of space inside the nanogap. This bridges the gap between FRET orientation effects and near-field optics.