FIGURE 2.

Classification of FRET biosensors. Based on whether the donor and the acceptor are on the same molecule, FRET biosensors can be classified into intramolecular (A) or intermolecular FRET biosensors (B). The intramolecular FRET biosensor could be further classified into distance change-based FRET biosensor or FP property change-based FRET biosensors, based on the mechanism of FRET ratio change. (C) Multicolor FRET biosensors usually contain more than two FPs and could be used for imaging of different cellular events in the same live cell.