FIDA fluorescence intensity distribution

FIDA Fluorescence Intensity Distribution Analysis. Uses the distribu-... 

Fluorescence-based detection methods are the most commonly used readouts for HTS as these readouts are sensitive, usually homogeneous and can be readily miniaturised, even down to the single molecule level.7,8 Fluorescent signals can be detected by methods such as fluorescence intensity (FI), fluorescence polarisation (FP) or anisotropy (FA), fluorescence resonance energy transfer (FRET), time-resolved fluorescence resonance energy transfer (TR-FRET) and fluorescence intensity life time (FLIM). Confocal single molecule techniques such as fluorescence correlation spectroscopy (FCS) and one- or two-dimensional fluorescence intensity distribution analysis (ID FID A, 2D FIDA) have been reported but are not commonly used. 

Due to the use of a confocal volume, FCS is particularly suited for miniaturization in HTS and relatively insensitive to auto fluorescent test compounds. Moreover, in compound testing, the small path length of the confocal volume greatly limits any filter effects on fluorescence intensity. As in FP, the requirement for large differences in mass in the assay design is a limitation to the applicability of FCS. However, it can be overcome by methods like Fluorescence Intensity Distribution Analysis (FIDA) or two-colour cross correlation derived from the original FCS concept. 

Reviews listed in Further Reading provide excellent introductions to PCS. Related techniques have been developed to detect other molecular properties. These properties include fluorescence cross-correlation spectroscopy (FCCS) (28) to detect codiffusing fluorophores and photon-counting histograms (PCH) (29), or fluorescence intensity distribution analysis (FIDA) (29) to distinguish fluorescent species according to their brightness. 

Photon-Counting Histogram. Contains the distribution of the fluorescence intensity of a small number of molecules measured within consecutive time bins. The PCH is the basis of Fluorescence Intensity Distribution Analysis (FIDA). 

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