images for measuring the donor quenching or donor lifetime for estimating
energy transfer efficiency (E %) [86, 87]. The figure illustrates images comparing
C-FRET, 2p-FRET, and FLIM-FRET. C-FRET and 2p-FRET images of the
quenched donor (a, c) and the PFRET images (b, d) are shown. The respective
efficiency (E ) and the distance (r) are shown in the table below the figure.
The distance between donor and acceptor molecules appears to be higher for
2p-FRET than for C-FRET. This may be due to the difference in methodology
of acquisition of photons. Both C-FRET and 2p-FRET signals were collected in
the same cell and optics using the Biorad Radiance2100 confocal/multiphoton
microscopy system. For the same cell, the donor lifetime images were acquired
in the ...