Novel detectors for fluorescence lifetime imaging on the picosecond time scale

Simultaneous acquisition of time and space information on the picosecond time scale became feasible with a recent advance in microchannel-plate photomultiplier-tube (MCP-PMT) technology: we present two novel MCP-PMT detectors for time- and space-correlated single-photon counting (TSCSPC), featuring a space-sensitive delay-line (DL) anode and quadrant anode (QA), respectively. The linear DL-MCP-PMT is characterized by a spatial instrument response function (IRF) of 100-Μm FWHM, resulting in 200 space channels, whereas the QA-MCP-PMT is a 2D imager with 400 x 400 pixels at 40-Μm resolution. The detectors have a temporal IRF of 75 ps (DL) and 80 ps (QA) FWHM, sufficient for 10 ps time resolution, at a dynamic range of 10⁵ of the uncooled detector. A throughput of 10⁵ cps is possible; in the imaging mode without timing, the QA-detector can achieve 10⁶ cps. We present time-resolved spectroscopy of DNA probes (DAPI, TOTO, C350) in solution, in micelles, complexed to DNA, protein, and fixed cells. Aging of DAPI stock solutions is reported. A polarity model for the photophysics of DAPI is proposed. First microscope lifetime images on the picosecond time scale show a clear potential for dynamic stray-light rejection and kinetic discrimination of probe-protein and probe-DNA complexes.