What is the difference between fluorescence lifetime imaging and time-gated imaging?
If a sample has both long-lived and short-lived fluorescence (or phosphorescence etc.) it is often desirable to distinguish between these. For example, a long-lived fluorescent label can be detected with high sensitivity against a highly fluorescent background if the latter has a short lifetime. One simple way to accomplish this is to use a ‘gated’ detector synchronised to the excitation source. If the detector is insensitive during and immediately after excitation but is turned on rapidly thereafter, then only long-lived emission is measured. If a similar measurement is made without ‘gating’, all emission is seen. The difference between the measurements with and without ‘gating’ gives primarily the short-lived component of emission. If the detector is a camera of some type, then a time-gated image can be measured. A fluorescence lifetime image is one where contrast is directly proportional to some function of fluorescence decay time. For example, the image contrast might represent the
