Three-dimensional localisation of fluorescence resonance energy transfer in living cells under two-photon excitation

Three-dimensional (3-D) imaging of fluorescence resonance energy transfer ( FRET) in human cells under two-photon excitation was demonstrated in this s tudy. A sample was prepared by expressing a donor and an acceptor in living cells and using an antibody to secure the proximity of contact between the donor and the acceptor. The quenching of fluorescence emission of a donor in the double-labelled cells indicates the presence of FRET that occurred i n these living cells. Because of the quadratic relation of the excitation p ower, 3-D localisation of FRET becomes possible.