GEVIBench › All sensors › VARNAM2
VARNAM2
Second-generation red-shifted eFRET voltage indicator derived from VARNAM with improved voltage sensitivity for low-power in vivo imaging in behaving animals.
- Category: eFRET GEVI
- Published: 2022-11-04 — Science 2022
- Derived from: VARNAM
- Response polarity: negative-going (fluorescence decreases on depolarization)
- Spectrum: excitation peak 558 nm, emission peak 592 nm (VARNAM2)
- Plasmid: Addgene #195520
- Tags: Ace opsin, mRuby3, Red, FRET
Headline values (as shown in the GEVIBench table)
| Metric | Value | Definition |
|---|---|---|
| Brightness (B/B_EGFP) | 0.85× EGFP | Molecular brightness relative to EGFP (extinction coefficient × quantum yield, or a measured ratio). Sensors not measured against EGFP directly are placed through a chain of pairwise brightness comparisons, combined by geometric mean. |
| Kinetics τ_on / τ_off (ms) | 0.95 / 1.2 ms | Activation / decay time constants in ms (amplitude-weighted mean τ for multi-exponential fits). The value shown averages the measurements made at physiological temperature (≥33 °C); if there are none, it is the measurement closest to 33 °C. |
| ΔF/F per 100 mV | -19.1% (median of 2 measurements: −22.9%) | Steady-state fluorescence change for a 100 mV depolarization step (−70 → +30 mV); the sign gives the polarity. The table shows the first listed measurement; the median across measurements (one-photon preferred) is used for sorting. |
| ΔF/F per mV | 0.23% (estimated from the F–V curve) | Subthreshold sensitivity: fluorescence change per mV near rest (−90 to −50 mV). Where no value is reported directly, it is estimated from the F–V curve. |
| ΔF/F per AP | 7.3% (median of 2 measurements: 8.15%) | Fluorescence change per single action potential in neurons. The table shows the first listed measurement; the median across measurements (one-photon preferred) is used for sorting. |
| AP width (FWHM, ms) | 5.3 ms | Full width at half maximum of the optical spike waveform. |
| Photostability t75% @ 100 mW/mm² | 1.7 min | Time for fluorescence to fall to 75% of its initial value under one-photon illumination, linearly dose-scaled to 100 mW/mm² (t50% is used where the 75% crossing falls inside a fast initial transient). Two-photon curves are not dose-scaled and are excluded. |
| Papers using it (N_used) | 3 | Number of published research papers, tracked by GEVIBench, that used the sensor for an experiment (a popularity / track-record measure). |
Measurements and sources
Kinetics
- τ_on 0.95 ms, τ_off 1.21 ms at 22°C — Kannan 2022, Table S1
ΔF/F per 100 mV
- -19.1%, 1P — Kannan 2022, Table S1
- -26.7%, 1P — Han 2023, Fig. 1B
ΔF/F per action potential
- 7.3%, 1P — Kannan 2022, Fig. 1I
- 9%, 1P — Han 2023, Fig. 1C
AP width (FWHM)
- 2.7 ms at 400 Hz sampling, Mouse, V1 VIP+ interneurons, awake, in vivo, 1P, 37°C — Kannan 2022, Fig. 1I
- 8 ms at 484 Hz sampling, cultured rat hippocampal neurons, in vitro, 1P — Han 2023, Fig. 1D
Brightness comparisons
- 1× the brightness of VARNAM — Kannan 2022, Fig. S11A
- 1.4285714285714286× the brightness of pAceR — Kannan 2022, Fig. S11A
Photobleaching
- t75% = 421 s at 15.9 mW/mm², 1P — Han 2023, Fig. S6A
- t50% = 552 s, 1P — Kannan 2022, Fig. S11B
Fluorescence–voltage (F–V) curve
ΔF/F (%) at each membrane potential, normalized to 0 at −70 mV: -150 mV: 17%; -130 mV: 14%; -110 mV: 11%; -90 mV: 5%; -70 mV: 0%; -50 mV: -4%; -30 mV: -10%; -10 mV: -14%; 10 mV: -18%; 30 mV: -21%; 50 mV: -23% — Kannan 2022, Fig. 1D
Research papers using VARNAM2 (3)
- Dual-polarity voltage imaging of the concurrent dynamics of multiple neuron types — Kannan M, Vasan G, Haziza S, Huang C, Chrapkiewicz R, Luo J, Cardin JA, Schnitzer MJ, Pieribone VA, Science 2022 (HEK cells, in vitro; Drosophila PPL1-α'2α2 dopaminergic neurons, in vivo; mouse hippocampus CA1 EC-projecting pyramidal neurons, in vivo)
- Imaging high-frequency voltage dynamics in multiple neuron classes of behaving mammals — Haziza S, Chrapkiewicz R, Zhang Y, Kruzhilin V, Li J, Delamare G, Swanson R, Buzsáki G, Kannan M, Vasan G, Lin MZ, Zeng H, Daigle T, Schnitzer MJ, Cell 2025 (Mouse, visual cortex (pyramidal neurons) and hippocampus, in vivo; dual-cell-type TEMPO imaging with VARNAM2 in pyramidal cells and ASAP3 in PV cells)
- Prefrontal gamma oscillations engage dynamic cell type-specific configurations to support flexible behavior — Phensy AJ, Hagopian LL, Costello CM, Haziza S, Ghenand O, Zhang Y, Schnitzer MJ, Sohal V, bioRxiv 2025 (Mouse, medial prefrontal cortex, in vivo; VARNAM2 expressed in PFC→MD projection neurons (dual-color with Ace-mNeon2 in PV interneurons))
Data and citation
- llms.txt — summary for language models
- llms-full.txt — every sensor in full (Markdown)
- gevis.json — all values and measurements with sources (JSON)
- gevis.csv — one row per sensor (CSV)
Cite GEVIBench as: Adam E. Cohen and Daozheng Gong (2026). Voltage imaging: A practical guide. Neuron. https://doi.org/10.1016/j.neuron.2026.08.002
Generated from the GEVIBench database on 2026-10-12.