Time‐domain whole‐field fluorescence lifetime imaging with optical sectioning

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Abstract
A whole‐field time‐domain fluorescence lifetime imaging (FLIM) microscope with the capability to perform optical sectioning is described. The excitation source is a mode‐locked Ti:Sapphire laser that is regeneratively amplified and frequency doubled to 415 nm. Time‐gated fluorescence intensity images at increasing delays after excitation are acquired using a gated microchannel plate image intensifier combined with an intensified CCD camera. By fitting a single or multiple exponential decay to each pixel in the field of view of the time‐gated images, 2‐D FLIM maps are obtained for each component of the fluorescence lifetime. This FLIM instrument was demonstrated to exhibit a temporal discrimination of better than 10 ps. It has been applied to chemically specific imaging, quantitative imaging of concentration ratios of mixed fluorophores and quantitative imaging of perturbations to fluorophore environment. Initially, standard fluorescent dyes were studied and then this FLIM microscope was applied to the imaging of biological tissue, successfully contrasting different tissues and different states of tissue using autofluorescence. To demonstrate the potential for real‐world applications, the FLIM microscope has been configured using potentially compact, portable and low cost all‐solid‐state diode‐pumped laser technology. Whole‐field FLIM with optical sectioning (3D FLIM) has been realized using a structured illumination technique.