Positron2

Positive-going Ace2N-HaloTag variant optimized for stronger spike and subthreshold responses in cultured neurons.

Category: Chemigenetic GEVI
Published: 2022-11-10 — Janelia Figshare 2022
Derived from: Positron; also related to pAce
Response polarity: positive-going (fluorescence increases on depolarization)
Spectrum: excitation peak 534 nm, emission peak 554 nm (Positron2 (JF525))
Plasmid: Addgene #239079
Tags: Ace opsin, HaloTag, Positive-going, JF525

Headline values (as shown in the GEVIBench table)

Metric	Value	Definition
Brightness (B/B_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)	—	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	+37%	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	0.38% (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	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)	—	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

ΔF/F per 100 mV

+37%, 1P, dye JF525 — Hasseman 2022, Fig. 1

ΔF/F per action potential

15%, 1P, dye JF525 — Hasseman 2022, Fig. 2

Fluorescence–voltage (F–V) curve

ΔF/F (%) at each membrane potential, normalized to 0 at −70 mV: -110 mV: -12%; -90 mV: -7%; -70 mV: 0%; -50 mV: 8%; -30 mV: 16%; -10 mV: 24%; 10 mV: 32%; 30 mV: 37%; 50 mV: 41% — Hasseman 2022, Fig. 1

Research papers using Positron2 (1)

Optimization of genetically encoded voltage and calcium indicators for in vivo imaging — Hasseman J, Abdelfattah AS, Arthur B, et al., Janelia Figshare 2022 (Rat, cortical/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.