Table 1.

Major modes of genetically encoded fluorescent protein biosensors (FPBs) with specific examples

Fluorescence mode	FPB type	Specific examples	Reference(s)
Intrinsic fluorescence	Engineered fluorescent proteins
	Fluorescent proteins	GFP	118
	Spectral variants	Cerulean & mCherry	119
	Ca++	Pericam, Cameleons	53, 73, 120
	pH	pHluorins, EGFP	121, 122
	Fluorescent protein fusions
	Complementation	BiFC*	123
	Modified fluorescent proteins	cpFP†	123
	FRET photoconvertible	CFP → YFP FRET	52
	Intracellular localization	PAFPs‡, FRAP, P-PIB§	8, 31, 50, 124
	Intracellular chloride	Clomeleon	125
	Optogenetic biosensors
	Action potential modulation	Halorhodopsins	65
		Channel rhodopsins	63, 126
		Archaerhodopsins	65
	Voltage sensitive	Mermaid	69
	Calcium indicators	GECI	66, 127
Extrinsic fluorescence	Antibody-based systems	FAP**	128
		Quench bodies	129
	Covalent labels	SNAP-tag, HaloTag	130,131
		FlAsH	9
		Inteins	132
		Biotinylation	132,133

^*Bimolecular fluorescence complementation.

^†Circularly permuted fluorescence protein.

^‡Photoactivatable fluorescence proteins.

^§Protein–protein interaction biosensor.

^**Fluorogen-activating protein.