Table 3.

Selected genetically encoded voltage indicators (GEVIs)

GEVI	ΔF/F −70 to +30 mVa	Brightness at −70 mV (mM−1 cm−1)b	Brightness at +30 mV (mM−1 cm−1)b	Activationc τfast (ms), fast fraction, τslow (ms)	Inactivationd τfast (ms), fast fraction, τslow (ms)	ΔF/F per APe	Refs.
VSFP2.3	−0.06 (Cerulean)	8.6f	ND	3.0, 27%, 69	92, 100%	−0.005	131−133
	+0.03 (Citrine)	10f	ND			+0.003
Butterfly1.2	−0.05* (Citrine)	36g	ND	1.0, 41%, 12*	90, 100%*	−0.007e*	24
	+0.03* (mKate2)	12g	ND			+0.003e*
Mermaid2	−0.24* (seCFP2)	NDh	ND	0.92, 79%, 13*	10, 100%*	−0.066e*	69
	+0.12* (YFP)	NDh	ND			+0.033e*
ArcLight Q239	−0.35*	22i	14	9.0, 50%, 48*	17, 79%, 60*	−0.022	134
	−0.32	22	15	104, 61%, 283	28, 39%, 271	−0.082	68
ASAP1	−0.18	4.2j	3.4	2.0, 60%, 72	2.0, 44%, 51	−0.048	18,25
	−0.29	4.2	3.0	3.0, 67%, 29	2.3, 88%, 39	−0.178	68
ASAP2f	−0.22	3.2i	2.5	2.8, 81%, 135	2.4, 71%, 155	−0.090	18
Archer1	+0.80	0.028k	0.050	~3, ND, ND	~5, ND, ND	+0.3	63
Mac-Citrine	−0.20	≤59l	≤22	2.8, 71%, 74	5.4, 77%, 67	−0.048	67
Ace2N-mNeon	−0.18	≤90l	≤74	0.36, 74%, 4.2	0.42, 64%, 5.2	−0.12	5
Ace2N-4aa-mNeon	−0.09	≤90l	≤82	0.37, 58%, 5.5	0.50, 60%, 5.9	−0.050	5

GEVIs with reported single-AP responses in neuronal culture and usage in live animals are included.

^aFluorescence change from −70 to +30 mV in long-lasting voltage steps in HEK293 cells at the emission peak of each channel. This number is empirically measured and, for the acceptor fluorophore in FRET sensors, is influenced by cross-excitation and bleed-through. As event detection is often optimized by single-channel imaging of FRET indicators^23,83, the two channels are shown separately.

^bEstimated molar brightness produced by each fluorophore. For FRET sensors, brightness for the donor channel at −70 mV is calculated as the product of donor peak extinction coefficient and donor quantum yield multiplied by 1 − E, where E is FRET efficiency at −70 mV. Brightness for the acceptor channel at −70 mV is calculated as the product of donor peak extinction coefficient and acceptor quantum yield multiplied by E. Values for specific parameters are noted below. Values do not account for any cross-excitation or bleed-through, but provide an estimate of the contribution of each fluorophore to indicator brightness. Brightness values for FRET indicators at +30 mV are not shown, as emission spectra at +30 mV have not been published. However, as the measured ΔF/F in each channel is small, brightness will not change much at +30 mV.

^cDuring steps from −70 to +30 mV.

^dDuring steps from +30 to −70 mV.

^eIn mouse or rat cortical or hippocampal neurons.

^fPeak Cerulean extinction coefficient is 28 mM⁻¹ cm⁻¹ at 433 nm, Cerulean quantum yield is 0.51 (ref. 135), Citrine quantum yield is 0.76 (ref. 130), and E at −70 mV is 0.40 as derived from the published emission spectrum as previously described^131,132.

^gCitrine extinction coefficient is 77 mM⁻¹ cm⁻¹ (ref. 130), mKate2 quantum yield is 0.40 (ref. 136), and E at −70 mV is 0.39 as derived from the published emission spectrum.

^hNot determined, as relevant emission spectra were not published.

ⁱBased on ArcLight reaching maximal fluorescence at −70 mV with the brightness of SEP from Table 1.

^jCalculated from the relative brightness of the indicator at −70 mV vs. a similar construct with sfGFP instead of cpsfGFP, and the measured brightness of sfGFP.

^kCalculated as 5 × the previously measured brightness of wild-type Archaerhodopsin⁶².

^lFRET efficiency at −70 mV is unknown, so brightness is indicated as less than or equal to the brightness of the fluorescent protein alone. Measurements were performed at room temperature unless otherwise indicated. Up to two significant digits are used; some values measured from published graphs are less precise.

^*Measurements were performed at 33–35 °C. ND, not determined.