Wide-field time-correlated single-photon counting (TCSPC) lifetime microscopy with microsecond time resolution.

A 1 MHz frame rate complementary metal-oxide semiconductor (CMOS) camera was used in combination with an image intensifier for wide-field time-correlated single-photon counting (TCSPC) imaging. The system combines an ultrafast frame rate with single-photon sensitivity and was employed on a fluorescence microscope to image decays of ruthenium compound Ru(dpp) with lifetimes from around 1 to 5 μs. A submicrowatt excitation power over the whole field of view is sufficient for this approach, and compatibility with live-cell imaging was demonstrated by imaging europium-containing beads with a lifetime of 570 μs in living HeLa cells. A standard two-photon excitation scanning fluorescence lifetime imaging (FLIM) system was used to independently verify the lifetime for the europium beads. This approach brings together advantageous features for time-resolved live-cell imaging such as low excitation intensity, single-photon sensitivity, ultrafast camera frame rates, and short acquisition times.