TABLE 4.
Commonly used GEVIs.
| Class | Indicator | Fluorescence reporter (Emission wavelength nm) | Description | References |
| Ion Channel-FPs | Shaker Kv-based FlaSH | FLaSH-GFP (505) | Slow, cannot resolve APs. Potential co-assembly with native channel subunits. Low fluorescence change. | Jin et al., 2011; Kostyuk et al., 2019 |
| SPARC | GFP (505) | Faster than FLaSH-based sensors, reports pulses as low as 2ms. Does not inactivate during extended depolarizations. Low fluorescence change. | Ataka and Pieribone, 2002; Kostyuk et al., 2019 | |
| FlaSH with split FP | Depends on FP | Low fluorescence change; slow kinetics. | Jin et al., 2011 | |
| FRET | VSFP1/2s, CR | CFP (477) YFP (529) citrine (529) |
Reliable membrane targeting. Limited by slower response kinetics compared to VSFP butterflies. | Sakai et al., 2001; Dimitrov et al., 2007; Lundby et al., 2008; Mutoh et al., 2009; Lam et al., 2012; Mishina et al., 2014 |
| Chimeric VSFP butterflies | Citrine (542) mKate2 (594) |
Faster than previous VSFPs. Reports membrane voltage oscillations up to 200 Hz. | Mishina et al., 2014 | |
| Nabi | Nabi1: mKO (559), UKG (499); Nabi2: Clover (515), mRuby2 (600) | Better SNR, faster than VSFP butterflies and VSFP-CR. | Sung et al., 2015 | |
| Mono-chromatic FPs | VSFP3s | Citrine (529) mOrange (562) TagRFP (584) mKate2 (633) | VSFP3 faster than VSFP2.3. Red-shifted VSFP3 available. | Lundby et al., 2008; Perron et al., 2009 |
| Arclight | GFP (507) | Robustly reports AP and subthreshold events and reveals electrical signals in neurite branches. | Cao et al., 2013; Borden et al., 2017 | |
| Bongwoori | s.e.pHluorin A227D (509) | Faster kinetics than Arclight. Resolves 60 Hz APs. | Piao et al., 2015 | |
| CpFP-based VSFPs | Depends on the FP | Weaker fluorescence than red shifted indicators. However, the red shifted indicators are still slower and weaker compared to other VSFPs. | Gautam et al., 2009 | |
| FlicR | cpmApple (560) | Bright and fast-read voltage indicator. Brighter than ArcLight Q239, similar kinetics to ArcLight Q239. | Abdelfattah et al., 2016 | |
| ASAP family | CpGFP (509) | ASAP1 has on-off kinetics of ∼2ms, detects APs and subthreshold changes. Tracks AP trains up to 200 Hz. ASAP2 more sensitive, suited for 2p imaging. | St-Pierre et al., 2014; Chamberland et al., 2017 | |
| Rhodopsin fluorescent probes | Arch | Arch (687nm), Arch (D95N; 687nm) | Fast and sensitive voltage sensor but it is very dim. | Kralj et al., 2011 |
| QuasArs | QuasAr1 (H95Q) 715 nm | Both QuasAr1 and QuasAr2 have enhanced fluorescence compared to Arch (D95N). | Hochbaum et al., 2014 | |
| Archons | Archon 1 retinal cofactor (637 nm) | Archon1 follows small, high-speed voltage changes in cultured neurons; brighter than QuasArs | Piatkevich et al., 2018 | |
| Opsin/FRET | Ace-mNeon | mNeonGreen (517 nm) | Responds five to six times as fast as MacQ-mCitrine and ASAP1 indicator; more photostable. | Gong et al., 2015 |
| VARNAM | MRuby3 N81S (565 nm) | Resolves APs with sensitivity and kinetics comparable to Ace-mNeon. | Kannan et al., 2018 | |
| MacQ-m Citirine | mCitirine (529nm) | Faster kinetics than Arclight. Not brighter than Arclight but with a comparable or better SNR. | Gong et al., 2014 | |
| QuasAr2-mOrange2 | Retinal cofactor (715 nm) | Outperforms red-shifted ASAP1 and eFRET GEVIs in sensitivity, speed, SNR and photostability, but requires intense laser illumination. | Zou et al., 2014 | |
| Fret-Dye | Voltron | JF525 (532 nm) | Brighter than Ace2N-mNeon and ASAP2f in cell culture. Improved photostability compared to Ace2N-mNeon. In mice, allows single-trial recording of spikes and subthreshold voltage signals from dozens of neurons simultaneously for 15 min. | Abdelfattah et al., 2019 |
| Other | hVOS | EGFP-F + DPA (505 nm) | Improved sensitivity and temporal resolution compared to previous GFP based probes. | Chanda et al., 2005 |
| VoltageSpy | (546 nm) | Robust, single-trial optical detection of APs at soma. Reports APs in axons and dendrites. | Grenier et al., 2019 |
AP, action potential; SNR, signal-to-noise ratio. Knöpfel and Song (2019).