GEVIBench › All sensors › ASAP4b
ASAP4b
Bright-optimized ASAP4 variant with superior brightness and photostability for extended two-photon recordings.
- Category: VSD-cpGFP GEVI
- Published: 2023-07-06 — Nature Methods 2023
- Derived from: ASAP3
- Response polarity: positive-going (fluorescence increases on depolarization)
- Spectrum: excitation peak 375 nm, emission peak 522 nm (ASAP4b)
- Two-photon compatible: yes
- Plasmid: Addgene #201030
- Tags: cpGFP, Positive-going, Two-photon
Headline values (as shown in the GEVIBench table)
| Metric | Value | Definition |
|---|---|---|
| Brightness (B/B_EGFP) | 0.20× 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) | 5.6 / 7.0 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 | +180% (median of 2 measurements: +174%) | 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 | 1.3% (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 | 35% (median of 6 measurements: 28%) | 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) | 8.7 ms | Full width at half maximum of the optical spike waveform. |
| Photostability t75% @ 100 mW/mm² | 59 s | 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) | 5 | 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 17.66 ms, τ_off 22.85 ms at 22°C — Evans 2023, Table S1
- τ_on 5.56 ms, τ_off 7 ms at 37°C — Evans 2023, Table S1
ΔF/F per 100 mV
- +180%, 1P — Evans 2023, Table 1
- +168%, 1P — Lee 2024, Table S1
ΔF/F per action potential
- 35%, 1P — Evans 2023, Table 1
- 30%, 1P — Evans 2023, Ext. Fig. 5c
- 31%, 1P — Lee 2024, Table S1
- 13%, 1P — Liu 2025, Table S2
- 19%, 1P — Evans 2023, Ext. Fig. 5a
- 26%, 1P — Evans 2023, Ext. Fig. 5a
AP width (FWHM)
- 7.4 ms at 1000 Hz sampling, HEK293A cells, whole-cell voltage clamp, hippocampal-neuron AP command waveform scaled to 2-ms FWHM (−70 → +30 mV), 1P, 22°C — Evans 2023, Ext. Fig. 5a
- 10 ms at 1000 Hz sampling, HEK293A cells, whole-cell voltage clamp, hippocampal-neuron AP command waveform scaled to 4-ms FWHM (−70 → +30 mV), 1P, 22°C — Evans 2023, Ext. Fig. 5a
Brightness comparisons
- 0.4468× the brightness of ASAP3 — Evans 2023, Ext. Fig. 3d
Photobleaching
- t75% = 59 s at 100 mW/mm², 1P — Evans 2023, Fig. 2b
- curve only (did not reach 75% within the measured window) at 888 mW/mm², 2P — Evans 2023, Ext. Fig. 4b
- t75% = 71 s at 960 mW/mm², 2P — Evans 2023, Ext. Fig. 4c
Fluorescence–voltage (F–V) curve
ΔF/F (%) at each membrane potential, normalized to 0 at −70 mV: -120 mV: -24%; -100 mV: -17%; -80 mV: -10%; -70 mV: 0%; -60 mV: 15%; -40 mV: 34%; -20 mV: 66%; 0 mV: 96%; 30 mV: 168%; 50 mV: 201%; 70 mV: 222%; 90 mV: 235%; 120 mV: 246% — Evans 2023, Fig. 1B
Research papers using ASAP4b (5)
- A positively tuned voltage indicator for extended electrical recordings in the brain — Evans SW, Shi DQ, Chavarha M, et al., Nature Methods 2023 (HEK293A cells (voltage clamp), mouse hippocampus and striatum, in vivo (origin paper introducing ASAP4b))
- Improving positively tuned voltage indicators for faster kinetics and higher contrast — Lee S, Zhang G, Hao YA, et al., bioRxiv 2024 (HEK293A cells, voltage clamp and AP-waveform characterization of ASAP4b)
- Positive-going hybrid indicators for voltage imaging in excitable cells and tissues — Liu S, et al., Science Advances 2025 (Cultured rat hippocampal neurons, ASAP4b used as a green positive-going reference (484 Hz, 1P))
- Voltage imaging reveals hippocampal inhibitory dynamics shaping pyramidal memory-encoding sequences — Taxidis J, et al., Nature Neuroscience 2025 (Mouse, dorsal CA1 hippocampus, SST+ interneurons, in vivo 1P widefield (AAV8-EF1α-DiO-ASAP4b-Kv, 2 mice; ASAP4e-Kv in 3 more, ASAP3-Kv in the main cohort))
- Imaging sensory transmission and neuronal plasticity in primary sensory neurons with a positively tuned voltage indicator — Zhang Y, et al., Nature Communications 2025 (Mouse, L5 dorsal root ganglia, in vivo (the paper's sensor is named ASAP4.4-Kv; the text never says ASAP4b, and no ASAP4.4 appears in the ASAP4 paper - identity vs ASAP4b UNCONFIRMED))
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.