Whole-field fluorescence lifetime imaging with picosecond resolution for biomedicine

Summary form only given. Fluorescence lifetime measurements permit both detection of specific fluorophores and monitoring of their local environment for biomedical and other applications including microscopy, biotechnology, and process monitoring. Fluorescence lifetime imaging (FLIM) is particularly exciting because it can provide noninvasive functional/diagnostic imaging by exploiting the sensitivity of fluorescence lifetime to the local environment (e.g. [Ca/sup 2+/], pH etc.). The recent development of user-friendly and relatively portable ultrafast laser technology and the availability of ultrafast gated optical image intensifiers (GOIs) mean that this technology can be readily applied to almost any optical imaging modality including microscopy and endoscopy. The authors report a FLIM system based on a GOI (Kentech Gated Optical Imager) with a temporal response of 90 ps, which uses pulses of /spl sim/1 /spl mu/J energy. This is compatible with the authors´ all-solid-state diode-pumped Cr:LiSAF oscillator-amplifier system, potentially providing a portable and relatively inexpensive instrument. Using the apparatus shown in a figure, fluorescent samples were excited by /spl sim/10 ps pulses at 415 nm. A FLIM map is produced by recording images of the fluorescence at different delays after excitation, and performing a least-squares fit to each point in the field of view. For simple fluorophore distributions the authors have demonstrated near-real-time FLIM with an update time of <3 s. In order to investigate the minimum detectable fluorescence lifetime difference, the authors prepared a phantom consisting of 4 pipettes containing the laser dye DASPI in different ethanol/glycerol solutions. Changing the viscosity of the solvent changes the fluorescence lifetime of the dye.