  Single molecule F\"orster resonance energy transfer (smFRET) is widely used
to monitor conformations and interactions dynamics at the molecular level.
However, conventional smFRET measurements are ineffective at donor-acceptor
distances exceeding 10 nm, impeding the studies on biomolecules of larger size.
Here, we show that zero-mode waveguide (ZMW) apertures can be used to overcome
the 10 nm barrier in smFRET. Using an optimized ZMW structure, we demonstrate
smFRET between standard commercial fluorophores up to 13.6 nm distance with a
significantly improved FRET efficiency. To further break into the classical
FRET range limit, ZMWs are combined with molecular constructs featuring
multiple acceptor dyes to achieve high FRET efficiencies together with high
fluorescence count rates. As we discuss general guidelines for quantitative
smFRET measurements inside ZMWs, the technique can be readily applied for
monitoring conformations and interactions on large molecular complexes with
enhanced brightness.
