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Biotium offers a wide selection of synaptic vesicle dyes, neuronal tracers, dyes for amyloid and neurotoxicity, fluorescent indicators for calcium, other ions, membrane potential, and more. Jump to a section below:

Neurotoxins & Fluorescent Toxin-Based Receptor Probes

α-Bungarotoxin (BTX) & Bungarotoxin Conjugates

α-Bungarotoxin is a potent inhibitor for the nicotinic acetylcholine receptor with sub-nanomolar affinity. Fluorescent conjugates of α-bungarotoxin can be used for labeling motor endplates in tissue sections. We offer pure α-bungarotoxin as well as conjugates with a selection of our CF® dyes and other labels. CF® dyes offer advantages in brightness and photostability compared to Alexa Fluor® dyes and other next generation fluorescent dyes. Learn more about CF® Dyes, or download the CF® Dye Selection Guide.


Figure 1. Neuromuscular junction endplate in a rat skeletal muscle cryosection stained with CF®594 α-bungarotoxin (red). Nuclei are stained with DAPI (blue).

Tetrodotoxin (TTX)

Tetrodotoxin (TTX) reversibly blocks excitable sodium channels and has been a widely used tool for studies of excitable membranes of nerve and muscle cells. Available lyophilized in citrate buffer, or citrate-free.

TTX, With or Without Citrate

Catalog numberSizeProduct
000601 mgTetrodotoxin, Citrate-Free
000611 mgTetrodotoxin, with Citrate

Cholera Toxin Subunit B

Cholera toxin is the symptom-causing toxin produced by the bacteria Vibrio cholerae during cholera infection. The toxin is composed of two subunits, A and B. Subunit A is the toxic enzymatic subunit present in one copy per toxin. Cholera toxin subunit B (CT-B) is the receptor binding subunit that is found as a pentamer in each toxin and is relatively non-toxic, making it useful for cell biological studies.

CT-B has been used as a neuronal tracer and has also been shown to bind to GM1 gangliosides that are found in lipid rafts on the surface of mammalian cells. Therefore, fluorescently labeled conjugates of CT-B have been used as lipid raft markers and endocytic tracers for live imaging or on fixed cells. Cholera Toxin Subunit B is available with a wide selection of our bright and photostable CF® dyes.

α-Bungarotoxin & Conjugates

Catalog No.SizeProductEx/Em
00010-11 mgα-BungarotoxinN/A
00002100 ug or 0.5 mgCF®405S α-Bungarotoxin404/431 nm
00005100 ug or 0.5 mgCF®488A α-Bungarotoxin490/515 nm
00026100 ug or 0.5 mgCF®543 α-Bungarotoxin541/560 nm
00018100 ug or 0.5 mgCF®555 α-Bungarotoxin555/565 nm
00006100 ug or 0.5 mgCF®568 α-Bungarotoxin562/583 nm
00007100 ug or 0.5 mgCF®594 α-Bungarotoxin596/614 nm
00009100 ug or 0.5 mgCF®633 α-Bungarotoxin630/650 nm
00004100 ug or 0.5 mgCF®640R α-Bungarotoxin642/662 nm
00003100 ug or 0.5 mgCF®680R α-Bungarotoxin680/701 nm
000170.5 mgBiotin-XX-α-BungarotoxinN/A
10×50 ug
0.5 mg
Fluorescein (FITC) α-Bungarotoxin494/518 nm
10×50 ug
0.5 mg
Tetramethylrhodamine α-Bungarotoxin553/577 nm
10×50 ug
0.5 mg
Sulforhodamine-101 (Texas Red®) α-Bungarotoxin593/613 nm
Texas Red is a registered trademark of Thermo Fisher Scientific.

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Nerve Terminal Dyes

SynaptoRed™ & SynaptoGreen™

SynaptoGreen™ and SynaptoRed™ nerve terminal probes (originally called FM® dyes) are membrane dyes used to trace endocytic vesicles. They are a series of fluorescent cationic styryl dyes developed to follow synaptic activity at neuromuscular junctions or synapses. The dyes label synaptic vesicles in neuronal tissues and cultured neurons in an activity-depending fashion. They also can be used to label endocytic vesicles in other cell types.

Nerve terminal dyes have highly hydrophilic, cationically charged head group at one end with lipophilic tails at the other end. They are virtually non-fluorescent in aqueous solution, but become intensely fluorescent in membranes. Following nerve stimulation, the dye molecules are internalized in newly formed endocytic vesicles. During exocytosis, the dyes are released from the vesicles along with neurotransmitters, causing a decrease in fluorescence signal. As a result, the change in fluorescent intensity reflects the amount of endocytosis/exocytosis or synaptic activity. The rate of fluorescence increase during endocytosis (on-rate), and the rate of fluorescence decrease during exocytosis (off-rate) vary from dye to dye. AM dyes and HM dyes are fixable nerve terminal dyes. After staining with these dyes, cells can be fixed and permeabilized for subsequent immunostaining. See the table below for a list of nerve terminal dyes and their properties.

Figure 2. General structure of SynaptoGreen™ and SynaptoRed™ dyes.
Figure 3. General structure of AM fixable nerve terminal dyes.

Background Reducers & Nerve Terminal Staining Kits

A common problem encountered with nerve terminal dyes is background fluorescence due to residual membrane staining, even after extensive washing. To reduce this background fluorescence, we offer three quencher or dye-clearing agents. ADVASEP-7, a sulfonated β-cyclodextrin, forms a water soluble inclusion complex with SynaptoGreen™ C4 that can be removed more effectively by washing. Biotium’s unique quencher, SCAS, reduces background fluorescence as soon as it is added to the preparation without the need for washing. Sulforhodamine 101 quenches SynaptoGreen™ background staining via fluorescent resonance energy transfer (FRET). We offer these reagents as individual products and in kits with dyes and the quencher/dye-clearing agents.

Figure 4. Neurons in mouse dorsal root ganglia (DRG) labeled with AM1-43. Image courtesy of Dr. David Corey, Harvard Medical School. Also see Figure 6.

Properties of Nerve Terminal Dyes

Nerve Terminal Dyem*n*Ex/Em in membranesFixable?Catalog No.Size
SynaptoGreen™ C101~480/600 nmNo70042, 700435 mg, 5 x 1 mg
SynaptoGreen™ C2 (equivalent to FM®2-10)11No70044, 70045
SynaptoGreen™ C321No70023, 70026
SynaptoGreen™ C4 (equivalent to FM®1-43)31No70020, 70022
SynaptoGreen™ C5 (equivalent to FM®1-84)41No70046, 70047
SynaptoGreen™ C18 (equivalent to FM®3-25)171No70048, 70049
AM1-4331Yes700241 mg
SynaptoRed™ C103~510/750 nmNo70040, 700415 mg, 5 x 1 mg
SynaptoRed™ C2 (equivalent to FM®4-64)13No70021, 70027
SynaptoRed™ C2M** (equivalent to FM®5-95)13No70019, 70028
AM4-6413Yes700251 mg
*m is the number of carbons in the lipophilic tail and n is the number of double bonds linking the two aromatic rings in the dye.
**The positively-charged end of SynaptoRed C2M is a trimethylammonium group.
FM is a registered trademark of Thermo Fisher Scientific.

Nerve Terminal Staining Kits

Nerve Terminal Staining KitNerve Terminal DyeBackground ReducerCatalog no.
Nerve Terminal Staining Kit ISynaptoGreen™ C4 (5 x 1 mg )ADVASEP-7 (250 mg)70030
Nerve Terminal Staining Kit II (A)AM1-43 (1 mg)ADVASEP-7 (100 mg)70031
Nerve Terminal Staining Kit II (B)AM1-43 (1 mg)SCAS (100 mg)70031-1
Nerve Terminal Staining Kit IIISynaptoGreen™ C4 (5 x 1 mg)Sulforhodamine 101 (100 mg)70032
Nerve Terminal Staining Kit IVSynaptoRed™ C2 (5 x 1 mg)ADVASEP-7 (250 mg)70034

Also see our selection of fast- and slow-responding potentiometric membrane potential dyes.

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Amyloid Stains & Neurodegeneration Dyes

Amyloid Stains

Congo Red is commonly used to detect amyloid protein aggregates associated with Alzheimer’s disease, Bovine Spongiform Encephalopathy, and related diseases. The staining can be detected by either colorimetric or fluorescence imaging (Ex/Em 497/614 nm).

DCDAPH is a far-red fluorescent probe (Ex/Em 597/665 nm) with high affinity (Kd=27 nM) to Aβ1-42 aggregates. It has been used for fluorescent staining of brain sections, as well as in vivo small animal near-IR imaging.

Thioflavin T is a cell-permeable benzothiazole dye that exhibits enhanced fluorescence (Ex/Em 450/482 nm) upon binding to amyloid fibrils. Thioflavin T has also been used in histology and for protein characterization.

Amyloid & Neurodegeneration Stains

ProductCatalog numberEx/Em
Congo Red, High Purity 80028 497/614 nm
DCDAPH80030597/665 nm
Thioflavin T, High Purity80033450/482 nm
PathoGreen™ Histofluorescent Stain, 1000X in Water80027497/520 nm

PathoGreen™ Histofluorescent Stain for Neurodegeneration

PathoGreen™ is an anionic green fluorescent dye functionally similar to Fluoro-Jade® dyes. These dyes stain degenerating neurons and their processes in brain sections and cell culture. The mechanism of staining by this class of dyes has not been determined, but the negatively charged dyes may bind to positively charged polyamines generated in dying neurons.

We also offer a wide selection of cell viability and apoptosis assays.

Figure 5. Section of mouse hippocampus stained with PathoGreen™. Degenerating neurons are stained green.

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Anterograde & Retrograde Axonal Tracers

Retrograde Tracers

Hydroxystilbamidine (also called Fluoro-Gold™) has been used extensively as a retrograde tracer for neurons and also a histochemical stain. Fluoro-Gold™ is used for retrograde tracing and dendrite filling.

Cholera toxin subunit B binds GM1 ganglioside in lipid rafts, and is used as a retrograde neuronal tracer. Available with a wide selection of bright and photostable CF® dyes. See Cholera Toxin Conjugates.

Retrograde & Anterograde Tracers

WGA is a glycoprotein-binding lectin that has been used for retrograde and anterograde neuronal tracing. We offer WGA CF® dye conjugates with fluorescence from UV to near-IR, plus HRP. See WGA Conjugates.

Labeled dextran amine can be used for both retrograde and anterograde tracing. CF® dye dextrans are anionic with an aldehyde-fixable free amine group, and are available with a wide selection of colors and a range of molecular weights. See Dextran Conjugates.

Biotin ethylenediamine is equivalent to Neurobiotin™, a useful anterograde and transneuronal tracer.

Anterograde & Retrograde Tracers

ProductEx/EmCatalog number 
Hydroxystilbamidine (Fluoro-Gold™)361/536 nm80014
Hydroxystilbamidine (Fluoro-Gold™), 4% in H2O361/536 nm80023
Biotin ethylenediamine, hydrobromide (Neurobiotin™)N/A90057
Biotin ethylenediamine, hydrochlorideN/A90075
Cholera Toxin ConjugatesChoice of 10 colors
Wheat Germ Agglutinin ConjugatesChoice of 13 colors, plus HRP
Dextran ConjugatesChoice of 11 colors & 5 molecular weights

Cytosolic Tracers for Cell Morphology & Gap Junctions

Biotin derivatives

Formaldehyde-fixable biocytin and biocytin hydrazide are widely used microinjectable polar tracers. Biocytin has been used as an anterograde tracer and gap junction probe. Biotin derivatives can be detected with labeled streptavidin or anti-biotin antibodies. Biotin ethylenediamine is equivalent to Neurobiotin™, a useful anterograde and transneuronal tracer. We also offer fluorescent CF® dye biotin and biocytin conjugates.

Lucifer Yellow and Related Dyes

Lucifer Yellow is a classic cell-impermeant cytosolic and gap junction dye. We also offer Lucifer Yellow Cadaverine and Lucifer Yellow CH with aldehyde-fixable groups.

Membrane-Permeant Cytosolic Stains

Calcein-AM is a membrane-permeant, non-fluorescent compound that can be loaded into cultured cells by incubation. Once inside the cytoplasm, it is hydrolyzed inside viable cells to release the green fluorescent, membrane impermeant dye calcein, which fills the entire cell. Calcein-AM can be used to assess cell viability, and for short term cytoplasmic labeling.

ViaFluor® SE Cell Proliferation Dyes are membrane-permeant compounds that are hydrolyzed in the cytoplasm to release amine-reactive fluorescent dyes. The staining fills the entire cell, is stable for several days to weeks, and can withstand fixation and permeabilization. Available with blue and green fluorescence.

CF® Dye Hydrazides

Hydrazides are non-toxic, highly water soluble membrane-impermeant tracers that can be used to fill cells by microinjection. See our large selection of bright, photostable CF® dye hydrazides.

Figure 6. Cultured rat hippocampal neurons microinjected with CF®647 hydrazide (red) and stained with SynaptoGreen™ C4 (green). Image courtesy of Professor Guosong Liu, Tsinghua University.

Cytosolic Tracers & Fluid Phase Markers

CF® Hydrazides• Microinjectable, fixable fluorescent tracers
• Wide selection of bright & photostable CF® dyes
Calcein • Water soluble green fluorescent tracer for microinjection
Calcein AM• Membrane-permeable compound is hydrolyzed in live cells to release water soluble green fluorescent dye
• Uniform intracellular labeling
• Dead cells don’t retain dye, for true endpoint viability assay
ViaFluor® SE Dyes• Membrane-permeable compound is hydrolyzed in live cells to release amine-reactive dye
• Covalent, fixable intracellular labeling
• Choice of blue or green fluorescence
Lucifer Yellow Derivatives• Widely used green fluorescent tracers for neuronal morphology and gap junction studies
• Fixable Lucifer Yellow CH and Lucifer Yellow Cadaverine
• Lucifer Yellow Cadaverin Biotin-X for secondary detection with streptavidin
Hydroxystilbamidine (equivalent to Fluoro-Gold™)• Widely used UV-excitable green fluorescent retrograde neuronal tracer
• Available in solid and 4% solution in water
Biotin Derivatives• Biotin-based tracers for secondary detection with streptavidin
CF® Dye Biotin• Biotin conjugates of our bright & photostable CF® dyes
CF® Dye Biocytin• Aldehyde-fixable biocytin conjugated with bright & photostable CF® dyes.

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More Probes for Neuronal Research

Ion indicators

  • Fluorescent indictators calcium & other ions
  • Chelators, calibrations buffers, & ionophores

 Cellular stains

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