TABLE 1.

Modern biosensors for neurotransmitters and neuromodulators.

FRET-based biosensors	FRET pair	Relative change of FRET ratio,ΔR/R (%)	Kd (μM)	Conditions used to measure ΔR/R and Kd	Substance (neurotransmitter or neuromodulator)	Template for sensing domain	In vivo use	References
SuperGluSnFR	ECFP-Citrine	44	2.5	Cultured neurons, 1P microscopy	Glutamate	GltI	Not tested	Hires et al., 2008
M1-cam5	ECFP-EYFP	10	Not determined	HEK293 cells, 1P microscopy	Acetylcholine	M1mAChR		Markovic et al., 2012
GlyFS	EGFP-Venus	20	20	Brain slices, 2P microscopy	Glycine	Atu2422 (AYW mutant)		Zhang et al., 2018
Single-FP-based biosensors	Circularly permuted FP	Relative change of fluorescence,ΔF/F (%)	Kd (μM)	Conditions used to measure ΔF/F and Kd	Substance (neurotransmitter or neuromodulator)	Template for sensing domain	In vivo use	References
iGluSnFR	cpGFP	103	4.9	Cultured neurons, 1P microscopy	Glutamate	GltI	Imaging of dendritic spines	Marvin et al., 2013
SF-iGluSnFR A184V	sfGFP	69	0.6					Marvin et al., 2018
SF-iGluSnFR S72A		250	34
SF-Azurite-iGluSnFR	Azurite	66	46
SF-Venus-iGluSnFR	Venus	66	2
SF-mTurquoise2-iGluSnFR	mTurquoise	90	41
iGABASnFR	sfGFP	250	9	Purified protein, fluorimeter	GABA	Pf622	Imaging of single neurons	Marvin et al., 2019
iGluf	EGFP	100	137	HEK293 cells, stopped-flow	Glutamate	GltI	Not tested	Helassa et al., 2018
iGluu		170	600
R-iGluSnFR1	mApple	−33	11	Purified protein, fluorimeter				Wu et al., 2018
R-ncp-iGluSnFR1			0.9
GACh	EGFP	90	2	HEK293 cells, 1P microscopy	Acetylcholine	M3R	Imaging of single neurons	Jing et al., 2018
GRABNE1m		230	1.9		Norepinephrine	α2AR	Aggregated fluorescence signal	Feng et al., 2019
GRABNE1h		150	0.093
Nb80-GFP		Not determined	Not determined	Not applicable		β2AR/Nb80	Not tested	Irannejad et al., 2013
OR-sensor	EGFP	Not determined	Not determined	Not applicable	Activation of μ and δ ORs	μ and δ ORs/Nb33	Not tested	Stoeber et al., 2018
iATPSnFR	spGFP	150	630	Cultured neurons, 1P microscopy	ATP	ε subunit of FOF1 ATPase from Bacillus PS3	Imaging of single astrocytes	Lobas et al., 2018
dLight1.1	EGFP	230	0.33	HEK293 cells, 1P microscopy	Dopamine	DRD1 (inserted into the ICL3)	Aggregated fluorescence signal	Patriarchi et al., 2018
dLight1.2		340	0.77
DA1m		90	0.13			DRD2 (inserted into the ICL3)		Sun et al., 2018
DA1h			0.01