VSFP2.1

VSFP variant tuned to operate near resting membrane potential.

Category: VSD-FRET GEVI
Published: 2007-05-09 — PLoS ONE 2007
Derived from: VSFP1
Response polarity: positive-going (fluorescence increases on depolarization)
Spectrum: excitation peak 433 nm, emission peak 529 nm (VSFP2.1)
Tags: Ci-VSP, Cerulean/Citrine, FRET

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)	15 / 75 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	+2.7%	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	0.086%	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	—	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)	2	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 15 ms, τ_off 75 ms at 35°C — Dimitrov 2007, Table 1

ΔF/F per 100 mV

+2.7%, 1P — Dimitrov 2007, Fig. 3B

ΔF/F per mV (subthreshold)

0.086%/mV (Maximal slope of the ΔR/R–V curve at V½ = 8.6%/100 mV = 0.086 %/mV (Dimitrov 2007 Table 1, VSFP2.1 at 35°C). VSFP2.1 was engineered (Ci-VSP R217Q) to place V½ (−68.4 mV) near the resting potential, maximizing near-rest voltage sensitivity — its defining feature. 1P.) — Dimitrov 2007, Table 1

Fluorescence–voltage (F–V) curve

ΔF/F (%) at each membrane potential, normalized to 0 at −70 mV: -140 mV: -3%; -120 mV: -2.8%; -100 mV: -2.1%; -80 mV: -0.8%; -70 mV: 0%; -60 mV: 0.8%; -40 mV: 2%; -20 mV: 2.5%; 0 mV: 2.6%; 20 mV: 2.7%; 40 mV: 2.7% — Dimitrov 2007, Fig. 3B

Research papers using VSFP2.1 (2)

Engineering and characterization of an enhanced fluorescent protein voltage sensor — Dimitrov D, He Y, Mutoh H, Baker BJ, Cohen L, Akemann W, Knöpfel T, PLoS ONE 2007 (PC12 cells (neuroendocrine), in vitro)
Second and third generation voltage-sensitive fluorescent proteins for monitoring membrane potential — Perron A, Mutoh H, Akemann W, Ghimire Gautam S, Dimitrov D, Iwamoto Y, Knöpfel T, Frontiers in Molecular Neuroscience 2009 (PC12 cells (neuroendocrine), primary 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.