Fiber Photometry is a rapidly advancing field, with biosensors for more analytes and with better sensitivity being announced almost every month. We would like to share information about sensors that should be compatible with fiber photometry when using excitation with blue (~480 nm) light and measuring green (~525 nm) fluorescence. This is the most commonly used wavelength pair and is the one offered with TeleFipho wireless fiber photometry.

We will update this guide as more information becomes available.

Overview of Fluorescent indicators: Structure and considerations for use.

Genetically encoded fluorescent indicators (GEFIs) are used in conjunction with fiber photometry to report on changes in concentrations of molecules in vivo in real-time.

Most fluorescent biosensors consist of a fluorescent protein yoked to an analyte binding protein, constructed so that binding of the analyte causes a dramatic increase in fluorescence.

Akerboom, Rivera, Guilbe, Malavé, Hernandez, Tian, Hires, Marvin, Looger, Schreiter ER / CC BY (https://creativecommons.org/licenses/by/3.0)

When used with fiber photometry in behaving animals, the sensors are usually introduced by injecting viral expression vectors. The virus is used to both express the sensor and to control its location: targeting sequences allow the researcher to choose a specific cellular subtype, and even the cellular localization, such as axon or soma, where the sensor will be expressed. Anterograde and retrograde localization can also be used to target only a specific projection or circuit in a target region. Transgenic animals are also available for expressing some GEFIs.

Binding kinetics help determine the range of concentrations the sensor will respond to, as well as its ability to report fast events. A sensor with high affinity (low Kd) and a long dissociation time can measure very low concentrations of a molecule, but this happens at the expense of being able to resolve more frequent events and a narrower useful range of concentrations. Fast dissociation improves time resolution, but sensitivity usually suffers.

The brightness of the sensor, partially expressed as the ratio of the increase in fluorescence when bound to the analyte compared to baseline (∆F/F or ∆F/F0 ), is the other major factor to consider. Brighter sensors can generate a useful signal when expressed at lower levels or when used with less illumination when compared to less bright sensors.

Most biosensors are already available from AddGene: some as plasmids, others as aliquots of ready to use viral vectors. The newest biosensors listed here can be sourced directly from the laboratories which invented them. We included the best source we could find, as well as the original publication describing the sensor in the table below.

Calcium

Calcium SensorsAffinity (Kd or EC50)dissociation
Kinetics (Mean life,
1/Koff)
∆F/F0 (% increase)Source for vector or plasmidReference
GCaMP6s147 nM1796 ms1680
Addgene
Chen, 2013
GCaMP6f375 nM400 ms1314
Addgene
Chen, 2013
jGCaMP7s68 nM1260 ms
Janelia
Dana, 2019
jGCaMP7f270 ms
Janelia
Dana, 2019
GCaMP-X
Addgene
Yang, 2018
The GCaMP6 series of genetically encoded Ca2+ indicators (GECIs) are the most popular tools for examining action potentials and have been used extensively with TeleFipho photometry. GCaMP6f is optimized for fast decay kinetics, necessary for monitoring very fast events, while GCaMP6s has higher sensitivity and slower decay kinetics. If you are starting a new project consider the latest generation – jGCaMP7 – which offers higher sensitivity and a larger range of kinetics.

jGCaMP7 is the latest generation of GCaMP sensors, introduced in 2019 as a collaborative effort between Loren Looger at Janelia as well as other research institutes. The jGCaMP7 GECIs have several-fold higher ∆F/F0 and a wider range of kinetics when compared to the earlier GCaMP6 sensors. Some GCaMP7 variants that will be of interest to fiber photometry users include jGCaMP7s (highest sensitivity, but slower kinetics), and jGCaMP7f which has the fastest kinetics. We hope to have calcium data generated using jGCaMP7s and TeleFipho wireless fiber photometry soon.

GCaMP-X The calmodulin GCaMP based calcium sensors have been shown to cause side effects during some in-vivo uses, such as interference with the function of L-type calcium channels, nuclear accumulation, and cytotoxicity. These issues are largely addressed by changes to the design of GCaMP-X.

Dopamine

Dopamine is rapidly becoming the second most common target for imaging and photometry in neuroscience thanks to two sensors introduced in 2018, dLight and GRABDA. The intensity of illumination used with dLight and GRABDA is typically 20 – 30 μW, the same range as is used with GCaMP6.

Dopamine sensorsAffinity (Kd or EC50)dissociation
Kinetics (residence time, τ = 1/Koff)
∆F/F0 (% increase)Source for vector or plasmidReference
dLight1.1330 nMNA230
Addgene
Patriarchi, 2018
dLight1.2770 nM90 ms340
Addgene
Patriarchy, 2018
GRABDA1m130 nM700 ms90
Addgene
Sun, 2018
GRABDA2m90 nMNA340
Yulong Li Lab
Sun, 2020
GRABDA1h10 nm2500 ms90
Addgene
Sun, 2018
GRABDA2h7 nMNA280
Yulong Li Lab
Sun, 2020

dLight1.1 and dLight1.2, developed by the Tian lab, have both been used extensively with fiber photometry, with settings similar to those used for GCaMP6.

GRABDA DA2M, DA2H

GRABDA (GPCR-Activation Based DA) was first introduced by Yulong Li’s lab in 2018 and has just been updated to increase Δf/f and increase the range of kinetics. The new versions are DA2H (high affinity) and DA2M (medium affinity). Both GRABDA2m and GRABDA2H have already been used with fiber photometry, but so far results have only been communicated via preprints.

Norepinephrine and Serotonin

More from the Yulong Li lab, though as of yet their characterization is only available through preprints. GRABNE1m and GRAB5-HT1.0 have both already been used to measure norepinephrine and serotonin via fiber photometry in mice.

SensorsAnalyteAffinity
(Kd or EC50)
dissociation Kinetics
( τ = 1/Koff))
∆F/F0 (% increase)Source for vector or plasmidReference
GRABNE1hNorepinephrine83 nM2000 ms130
Yulong Li Lab
Feng, 2019
GRABNE1mNorepinephrine930 nM750 ms250
Yulong Li Lab
Feng, 2019
GRAB-5HT1.0Serotonin22 nM3.1 s280
Yulong Li Lab
Wan, 2020

Biosensors for endocannabinoids (GRABeCB), ATP, cholecystokinin (CCK), vasoactive intestinal peptide (VIP), somatostatin (SST), vasopressin/oxytocin, ghrelin, and orexin were also announced by the Li lab at Neuroscience 2019, and are still being validated. The best way to keep up with the Li lab may be checking #GRABSensors on Twitter!

GABA

GABA SensorsAffinity (Kd or EC50dissociation
Kinetics
(τ = 1/Koff)
∆F/F0 (% increase)SourceReference
iGABASnFR9 μM250
Addgene
Marvin, 2019

Glutamate

There are two main sensor types available for monitoring glutamate: iGluSnFR and iGlu. The original iGluSnFR has slower kinetics, while iGluf (fast) and iGluu (ultrafast) are much faster. The new SF-iGluSnFR variants offer higher brightness and a range of different kinetics compared to the original.

Glutamate SensorsAffinity (Kd or EC50dissociation
Kinetics
(τ = 1/Koff)
>∆F/F0 (% increase)SourceReference
iGluSnFR4.9 μM92 ms100
Addgene
Marvin, 2018
iGluf137 μM2.1 ms
Addgene
Helassa, 2018
iGluu600 μM0.7
Addgene
Helassa, 2018

Acetylcholine

Acetylcholine SensorsAffinity (Kd or EC50dissociation
Kinetics
(τ = 1/Koff)
∆F/F0 (% increase)SourceReference
iACHSnFR1.3 µM1200
Addgene
Borden, 2020
ACh3.02
μM
3.7s
Yulong Li Lab
Jing, 2019
ACh4.3
Yulong Li Lab

iACHSnFR is one of the most recent GEFIs created by the Loren Looger lab at Janelia, along with collaborators.

GACH and GRABACh3.0
While the initial version of the GRAB type acetylcholine indicator (GACH) was not sensitive enough for measuring physiological levels of ACh using fiber photometry (personal communication), the version described in a preprint from Dec. 2019 (ACh3.0) has been used successfully with fiber photometry. The Li lab is also supplying researchers with an even newer version, ACh4.3.

Please lets us know if you have any corrections or additions for this list!

TeleFipho is the world’s first commercially available wireless fiber photometry system. It is a turnkey system tested in both mice and rats. If you would like to know more:

Both TeleFipho and the Teleopto Wireless Optogenetics system now accept standard Ø2.5 mm FC cannulae, commonly used with patchcord-connected optogenetics and fiber photometry systems allowing you to use the same implanted fiber-optic cannula with either system.