Table 1. Properties of sarcosine VF dyes, PEGylated intermediates and VoltageSpy indicators.

dye	isomer	R	PEG units	λmax (abs)[a]	λmax (em)[a]	Φ[a]	cellular bright- ness[b]	Contrast [b][c]	%ΔF/F [b][d]	effective sensitivity [e]
11	5	-H	---	525	541	2.7	10	---	27.2 ±0.2	7
12	5	-OMe	---	525	540	5.5	1	---	12.2 ±0.4	1
13	6	-H	---	525	540	3.9	40	---	22.7 ±0.1	12
14	6	-OMe	---	524	540	0.8	6	---	29.3 ±0.8	6
15	6	-H	3	526	545	5.8	---	---	---	---
16	6	-H	11	526	544	10.9	---	---	3.2 ±0.1	---
17	6	-H	23	526	540	9.8	---	---	---	---
18	6	-H	35	526	540	11.2	---	---	---	---
19	6	-H	3	527	544	10.9	---	5.6 ±3.8	12.5 ±0.2 [f]	---
20	6	-H	11	526	544	7.9	---	12.6 ±8.6	13.1 ±0.2 [f][g]	---
21	6	-H	23	526	546	13.9	---	17.8 ±9.7	11.6 ±0.2 [f]	---
22	6	-H	35	526	546	8.7	---	34.6 ±29.3	12.7 ±0.1 [f]	---

^[a]Acquired in PBS, pH 7.4 with 0.1% Triton X-100.

^[b]measured in HEK cells.

^[c]ratio of fluorescence intensity of SpyCatcher expressing cells and median fluorescence intensity of untransfected cells loaded with 5 nM dye. Data is mean ±SD for 49 to 77 cells.

^[d]Per 100 mV step, optically sampled at 500 Hz.

^[e]Relative product of square root of cellular brightness and ΔF/F.

^[f]Values are measured in HEK cells expressing cell-surface SpyCatcher.

^[g]In cells that do not express SpyCatcher, voltage sensitivity is 9.1 ±0.1%.