NADH FLIM is based on the separation of the fluorescence decay components of the bound and the unbound fraction of NAD(P)H. The amplitudes and the decay times of the components are used to derive information on the metabolic state of the cells or the tissue. The separation of the decay components and the accuracy of the amplitudes and lifetimes improves substantially by using the ultra-fast HPM-100-06 and HPM-100-07 hybrid detectors. The IRF width in combination with the SPC-150N and SPC-150NX TCSPC modules is less than 20 ps, see bh news 2017/04. An IRF this fast does not interfere with the fluorescence decay. The usual deconvolution process in the data analysis virtually becomes a simple curve fitting, and the decay parameters are obtained at unprecendented accuracy.
A lifetime image of the amplitude-weighted lifetime of a double-exponential fit is shown below, upper row. The decay data in a selected spot of 9×9 pixels is shown on the right. Due to the fast response of the detector-TCSPC combination the rise of the fluorescence occurs almost instantaneously. Images of the amplitude ratio, a1/a2 (unbound/bound ratio), and of the fast (t1, unbound NADH) and the slow decay component (t2, bound NADH) are shown in the second row.
For details please see application note ‘Ultra-fast detectors improve NAD(P)H FLIM’.