Fluorescence lifetime imaging for biomedicine and spectroscopy

Summary form only. The determination of fluorescence lifetime requires only relative intensity measurements and so is especially useful for biomedical samples in which the heterogeneous nature of tissue and autofluorescence present significant problems. Since fluorescence lifetime is dependent upon both radiative and nonradiative decay rates, it may be used to distinguish between different fluorophore molecules (with different radiative decay rates) and to monitor local environmental perturbations that affect the nonradiative decay rate. Fluorescence lifetime imaging (FLIM) can be applied to almost any optical imaging modality, including microscopy and potentially to noninvasive optical biopsy. Fluorescence lifetime data may be acquired in the time or frequency domains. The recent development of user-friendly and relatively portable ultrafast laser technology and the availability of ultrafast gated optical image intensifiers (GOI) enable the development of relatively inexpensive time domain FLIM instruments that may be deployed outside specialist laser laboratories. We report a time domain FLIM system that incorporates an all-solid-state diode-pumped Cr:LiSGAF oscillator-amplifier system combined with a GOI. This laser system requires only four 500 mW pump diodes and will run off a domestic power outlet with minimal water-cooling requirements.