QuasAr1

First-generation QuasAr with extremely fast response times.

Category: Opsin GEVI
Published: 2014-06-22 — Nature Methods 2014
Derived from: Arch
Response polarity: positive-going (fluorescence increases on depolarization)
Spectrum: excitation peak 590 nm, emission peak 715 nm (QuasAr1)
Plasmid: Addgene #51629
Tags: Archaerhodopsin, Far-red

Headline values (as shown in the GEVIBench table)

Metric	Value	Definition
Brightness (B/B_EGFP)	0.0028× 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)	0.24 / 0.29 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	+32%	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	0.25% (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	21%	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)	2.6 ms	Full width at half maximum of the optical spike waveform.
Photostability t75% @ 100 mW/mm²	—	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)	1	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 0.24 ms, τ_off 0.29 ms at 23°C — Hochbaum 2014, Table S2

ΔF/F per 100 mV

+32%, 1P — Hochbaum 2014, Fig. 1c

ΔF/F per action potential

21%, 1P — Hochbaum 2014, Fig. 1e

AP width (FWHM)

2.6 ms at 2000 Hz sampling, Cultured rat hippocampal neurons, in vitro, 1P, 23°C — Hochbaum 2014, Fig. 1f

Brightness comparisons

15.2× the brightness of Arch — Hochbaum 2014, Table S2
20× the brightness of Arch — Monakhov 2020, Table 1

Fluorescence–voltage (F–V) curve

ΔF/F (%) at each membrane potential, normalized to 0 at −70 mV: -100 mV: -11%; -90 mV: -7%; -80 mV: -3%; -70 mV: 0%; -60 mV: 2%; -50 mV: 5%; -40 mV: 8%; -30 mV: 12%; -20 mV: 15%; -10 mV: 18%; 0 mV: 20%; 10 mV: 22%; 20 mV: 25%; 30 mV: 26%; 40 mV: 30%; 50 mV: 31% — Hochbaum 2014, Fig. 1c

Research papers using QuasAr1 (1)

All-optical electrophysiology in mammalian neurons using engineered microbial rhodopsins — Hochbaum DR, Zhao Y, Farhi SL, Klapoetke NC, Werley CA, Kapoor V, Zou P, Kralj JM, Maclaurin D, Smedemark-Margulies N, Saulnier JL, Boulting GL, Straub C, Cho YK, Melkonian M, Wong GKS, Harrison DJ, Murthy VN, Sabatini BL, Boyden ES, Campbell RE, Cohen AE, Nature Methods 2014 (HEK293 cells, cultured rat hippocampal neurons, in vitro)

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.