Shop All Ion Indicators & Ionophores

4-Bromo A-23187, Free Acid (Invitrogen™)

The Ca2+ ionophore 4-bromo A-23187 is commonly used for in situ calibrations of fluorescent Ca2+ indicators, to equilibrate intracellular and extracellular Ca2+ concentrations and to permit Mn2+ to enter the cell to quench intracellular dye fluorescence. Unlike A-23187, brominated A-23187 is essentially nonfluorescent and can be used with UV-excitable calcium indicators like fura-2, indo-1 and quin-2 as well as the visible light-excitable indicators, including fluo-4, fluo-3, Calcium Green and rhod-2. 4-bromo A-23187 can also be used to equilibrate extracelular and intrcellular Mg2+ concentrations, making it useful for calibrating Mg2+ indicators.

Sodium Green™, Tetra (Tetramethylammonium) Salt, cell impermeant (Invitrogen™)

This cell-impermeant form of Sodium Green™, tetra(tetramethylammonium) salt is a visible light-excitable Na+ indicator.

Oregon Green™ 488 BAPTA-5N, Hexapotassium Salt, cell impermeant (Invitrogen™)

The cell-impermeant visible light—excitable, low affinity Ca2+ indicator,

Oregon Green® 488 BAPTA-5N, hexapotassium salt

has a Kd for Ca2+ ~20 µM and absorption/emission maxima ~492/517 nm.

Sodium Green™ Tetraacetate, cell permeant - Special Packaging (Invitrogen™)

This cell-permeant form of Sodium Green™ tetraacetate is a visible light-excitable Na+ indicator.

Nigericin, Free Acid (Invitrogen™)

Intracellular calibration of the fluorescence response of cytosolic pH indicators is typically performed using the K+/H+ ionophore nigericin, which causes equilibration of intracellular and extracellular pH in the presence of a depolarizing concentration of extracellular K+.

Newport Green™ DCF, Dipotassium Salt, cell impermeant (Invitrogen™)

The Newport Green™ DCF indicator has moderate zinc-binding affinity (Kd for Zn2+ ~1 µM) but is essentially insensitive to Ca2+ (Kd for Ca2+ >100 µM), making this a valuable probe for detecting Zn2+ influx into neurons through voltage- or glutamate-gated channels. When used alongside dyes with dual Ca2+ / Zn2+ sensitivity such as fura-2 and mag-fura-2, Newport Green™ DCF provides confirmation that changes in Zn2+ levels, and not Ca2+ or Mg2+, are being detected. The response of Newport Green™ DCF to transition metals, including Zn, Mn, Fe, Co, Cu(I), Cu(II), Ni and Cd, has been characterized.

Newport Green™ PDX has a higher Zn2+ dissociation constant (Kd for Zn2+ ~30 µM) and a larger Zn2+-free to Zn2+-saturated fluorescence intensity increase than the Newport Green™ DCF indicators.

Fluorescent Zinc Indicators Specifications:
• Label (Ex/Em): Newport Green™ DCF (~505/535 nm)
• Kd (Zn2+) (in buffer):~1 µM
• Lyophilized product may be dissolved in distilled water or aqueous buffer for use
• Product is typically loaded into cells using microinjection or diffusion from patch pipette


Find Fluorescent Indicators for Zinc and Other Metal Ions
We offer a number of fluorescent indicators to determine polyvalent cation concentrations inside cells, to follow metal ion transport through ion channels, to make measurements in environmental samples, and more. Review Fluorescent Indicators for Zn2+ and Other Metal Ions—Section 19.7 in the Molecular Probes® Handbook for more information on these products.

For Research Use Only. Not for human or animal therapeutic or diagnostic use.

Dextran, SNARF™-1, 70,000 MW, Anionic (Invitrogen™)

Labeled dextrans are hydrophilic polysaccharides most commonly used in microscopy studies to monitor cell division, track the movement of live cells, and to report the hydrodynamic properties of the cytoplasmic matrix. The labeled dextran is commonly introduced into the cells via microinjection.

Dextran Specifications:

Label (Ex/Em): SNARF®-1 (563/639)
Size: 70,000 MW
Charge: Anionic
Fixable: Nonfixable

High Manufacturing Standards of Molecular Probes® Dextrans
We offer more than 50 fluorescent and biotinylated dextran conjugates in several molecular weight ranges. Dextrans are hydrophilic polysaccharides characterized by their moderate-to-high molecular weight, good water solubility, and low toxicity. They also generally exhibit low immunogeniticy. Dextrans are biologically inert due to their uncommon poly-(α-D-1,6-glucose) linkages, which render them resistant to cleavage by most endogenous cellular glycosidases.

In most cases, Molecular Probes® fluorescent dextrans are much brighter and have higher negative charge than dextrans available from other sources. Furthermore, we use rigorous methods for removing as much unconjugated dye as practical, and then assay our dextran conjugates by thin-layer chromatography to help ensure the absence of low molecular weight contaminants.

A Wide Selection of Substituents and Molecular Weights
Molecular Probes® dextrans are conjugated to biotin or a wide variety of fluorophores, including seven of our Alexa Fluor® dyes (Molecular Probes dextran conjugates–Table 14.4) and are available in these nominal molecular weights (MW): 3,000; 10,000; 40,000; 70,000; 500,000; and 2,000,000 daltons.

Dextran Net Charge and Fixability
We employ succinimidyl coupling of our dyes to the dextran molecule, which, in most cases, results in a neutral or anionic dextran. The reaction used to produce the Rhodamine Green™ and Alexa Fluor® 488 dextrans results in the final product being neutral, anionic, or cationic. The Alexa Fluor®, Cascade Blue®, lucifer yellow, fluorescein, and Oregon Green® dextrans are intrinsically anionic, whereas most of the dextrans labeled with the zwitterionic rhodamine B, tetramethylrhodamine, and Texas Red® dyes are essentially neutral. To produce more highly anionic dextrans, we have developed a proprietary procedure for adding negatively charged groups to the dextran carriers; these products are designated "polyanionic" dextrans.

Some applications require that the dextran tracer be treated with formaldehyde or glutaraldehyde for subsequent analysis. For these applications, we offer "lysine-fixable" versions of most of our dextran conjugates of fluorophores or biotin. These dextrans have covalently bound lysine residues that permit dextran tracers to be conjugated to surrounding biomolecules by aldehyde-mediated fixation for subsequent detection by immunohistochemical and ultrastructural techniques. We have also shown that all of our 10,000 MW Alexa Fluor® dextran conjugates can be fixed with aldehyde-based fixatives.

Key Applications Using Labeled Dextrans
There are a multitude of citations describing the use of labeled dextrans. Some of the most common uses include:

Neuronal tracing (anterograde and retrograde) in live cells
Cell lineage tracing in live cells
Neuroanatomical tracing
Examining intercellular communications (e.g., in gap junctions, during wound healing, and during embryonic development)
Investigating vascular permeability and blood–brain barrier integrity
Tracking endocytosis
Monitoring acidification (some dextran–dye conjugates are pH-sensitive)
Studying the hydrodynamic properties of the cytoplasmic matrix

For Research Use Only. Not intended for any animal or human therapeutic or diagnostic use.

Premo™ Halide Sensor (Invitrogen™)

The Premo™ Halide Sensor is based on a yellow fluorescent protein (YFP) molecule sensitive to halide ions. The combination of the YFP (Venus) biosensor with efficient and non-cytopathic BacMam delivery and expression gives researchers a highly sensitive, robust and easy-to-use tool to efficiently screen halide ion channels and transporter modulators in their cellular models of choice. No specialized instruments are needed, as the sensor works on standard HTS platforms. - Cl– channel–specific—measure halide ion flux in voltage- and ligand-gated chloride channels and transporters - Fast—measure chloride flux in high-throughput mode with highly reproducible results - Robust—reliably high expression of the bright and fast maturating Venus sensor gives an excellent signal window - Convenient—study chloride flux in your cellular model by efficient and non-cytopathic delivery of Premo™ Halide Sensor by BacMam technology - Pharmacologically relevant—known modulators show dose-dependent quenching and BacMam delivery enables assays in primary cells The assay combines the YFP Venus halide sensor with a surrogate ion for chloride (iodide); upon stimulation of the chloride channel or transporter, iodide ions flow down the concentration gradient into the cells and quench YFP fluorescence upon binding; the amount of quench is directly proportional to the ion flux (chloride channel or transporter activity). Due to the bright Venus fluorescence, the Premo™ Halide Sensor signal window is excellent. We have demonstrated the utility and efficiency of the Premo™ Halide Sensor as a robust and true “no wash" HTS chloride assay. Premo™ Halide Sensor is pre-packaged and ready for immediate use. It contains all components required for cellular delivery and expression. Screening can be conducted in complete medium and without any wash steps. To uncouple cell maintenance and preparation from screening, simply freeze transduced cells and bring out as little as 4 h before the screen. Both stable cell lines and human primary cells can be prepared frozen and “assay-ready".

Fura-2 Calcium Imaging Calibration Kit (Zero to 10 mM CaEGTA, 50 µM Fura-2) (Invitrogen™)

The Fura-2 Calcium Imaging Calibration Kit is designed to facilitate rapid calibration and standardization of digital imaging microscopes. The kit contains 11 pre-diluted buffers supplemented with 50 µM fura-2 (F-1200) as well as 15 µm—diameter microspheres.

Fluo-5N, AM, cell permeant - Special Packaging (Invitrogen™)

Labeled calcium indicators are molecules that exhibit an increase in fluorescence upon binding Ca2+. Fluo-5F, fluo-5N, and fluo-4ff are analogs of fluo-4 with lower Ca2+-binding affinity, making them suitable for detecting intracellular calcium levels in the 1 µM to 1 mM range that would saturate the response of fluo-3 and fluo-4. Cells may be loaded with the AM ester forms of these calcium indicators by adding the dissolved indicator directly to dishes containing cultured cells. These indicators are compatible with excitation at 488 nm by argon-ion laser sources, making them useful for confocal microscopy, flow cytometry, and microplate screening applications.

Calcium Indicator (AM Ester) Specifications:
• Label (Ex/Em of Ca2+–bound form): Fluo-5N (494/516 nm)
• Fluorescence intensity increase upon binding Ca2+: >100 fold
• Kd for Ca2+ in buffer: ~90 µM
• Exhibit fluorescence increase upon binding Ca2+ with little shift in wavelength


Using TPEN to Control Heavy Metal Cations
In addition, BAPTA-based indicators such as these bind various heavy metal cations (e.g., Mn2+, Zn2+, Pb2+) with substantially higher affinity than Ca2+. Perturbations to calcium measurements caused by presence of these ions can be controlled using the heavy metal-selective chelator TPEN.

More Choices for Fluorescent Calcium Indicators
We offer a large selection of Molecular Probes® calcium indicators for use in various experimental scenarios. For more information, review Fluorescent Ca2+ Indicators Excited with Visible Light—Section 19.3 in the Molecular Probes® Handbook.

For UV-excitable Ca2+ indicators, protein-based Ca2+ indicators, conjugates of Ca2+ indicators, and for fluorescence-based indicators of other metal ions (i.e., Mg2+, Zn2+) review Indicators for Ca2+, Mg2+, Zn2+ and Other Metal Ions—Chapter 19 in the Molecular Probes® Handbook.

For Research Use Only. Not for human or animal therapeutic or diagnostic use.

Newport Green™ DCF Diacetate, cell permeant (Invitrogen™)

The Newport Green™ DCF indicator has moderate zinc-binding affinity (Kd for Zn2+ ~1 µM) but is essentially insensitive to Ca2+ (Kd for Ca2+ >100 µM), making this a valuable probe for detecting Zn2+ influx into neurons through voltage- or glutamate-gated channels. When used alongside dyes with dual Ca2+ / Zn2+ sensitivity such as fura-2 and mag-fura-2, Newport Green™ DCF provides confirmation that changes in Zn2+ levels, and not Ca2+ or Mg2+, are being detected. The response of Newport Green™ DCF to transition metals, including Zn, Mn, Fe, Co, Cu(I), Cu(II), Ni and Cd, has been characterized.

Newport Green™ PDX has a higher Zn2+ dissociation constant (Kd for Zn2+ ~30 µM) and a larger Zn2+-free to Zn2+-saturated fluorescence intensity increase than the Newport Green™ DCF indicators.

Fluorescent Zinc Indicators Specifications:
• Label (Ex/Em): Newport Green™ DCF (~505/535 nm)
• Kd (Zn2+) (in buffer): ~1 µM
• Lyophilized product may be dissolved in DMSO for use
• Product is typically loaded into cells by adding the dissolved indicator to medium containing cells


Find Fluorescent Indicators for Zinc and Other Metal Ions
We offer a number of fluorescent indicators to determine polyvalent cation concentrations inside cells, to follow metal ion transport through ion channels, to make measurements in environmental samples, and more. Review Fluorescent Indicators for Zn2+ and Other Metal Ions—Section 19.7 in the Molecular Probes® Handbook for more information on these products.

For Research Use Only. Not for human or animal therapeutic or diagnostic use.

Mag-Fura-2, Tetrapotassium Salt, cell impermeant (Invitrogen™)

Mag-fura-2, tetrapotassium salt is an intracellular magnesium indicator that is ratiometric and UV light-excitable. This water-soluble salt form is useful for intracellular loading by microinjection, infusion from patch pipette or uptake induced by our Influx pinocytic cell-loading reagent (I14402).

Mag-Fluo-4, Tetrapotassium Salt, cell impermeant (Invitrogen™)

The cell-impermeant mag-fluo-4 potassium salt is an analog of fluo-4 with a Kd for Mg2+ of 4.7 mM and a Kd for Ca2+ of 22 µM, making it useful as an intracellular Mg2+ indicator as well as a low-affinity Ca2+ indicator.

FluoZin™-3, Tetrapotassium Salt, cell impermeant (Invitrogen™)

The FluoZin™-3 indicator is a Zn2+-selective indicator with a structure that resembles fluo-4. FluoZin™-3 exhibits high Zn2+-binding affinity that is unperturbed by Ca2+ concentrations up to at least 1 µM. In addition, FluoZin™-3 exhibits a >50-fold increase in fluorescence in response to saturating levels of Zn2+. Although imaging applications of FluoZin™-3 are predominant, cell-based microplate assays and flow cytometry protocols have also been developed. FluoZin™-3 indicator is available in a cell-permeant and a cell-impermeant form.

Fluorescent Zinc Indicators Specifications:
• Label (Ex/Em): FluoZin™-3 (~494/516 nm)
• Kd (Zn2+) (in buffer): ~15 nM
• Lyophilized product may be dissolved in distilled water or aqueous buffer for use
• Product is typically loaded into cellsusing microinjection or diffusion from patch pipette


Find Fluorescent Indicators for Zinc and Other Metal Ions
We offer a number of fluorescent indicators to determine polyvalent cation concentrations inside cells, to follow metal ion transport through ion channels, to make measurements in environmental samples, and more. Review Fluorescent Indicators for Zn2+ and Other Metal Ions—Section 19.7 in the Molecular Probes® Handbook for more information on these products.

For Research Use Only. Not for human or animal therapeutic or diagnostic use.

SBFI, AM, cell permeant (Invitrogen™)

SBFI is a sodium-sensitive molecule used to estimate Na+ gradients in isolated mitochondria, to measure intracellular NA+ levels, to measure Na+ efflux in cells, and, in combination with other fluorescent indicators used to correlate changes in intracellular Na+ with Ca2+ and Mg2+ concentrations, intracellular pH, and membrane potential. Although the selectivity of SBFI for Na+ is less than that of calcium indicators such as fura-2, it is sufficient for the detection of physiological concentrations of Na+ in the presence of other monovalent cations. The spectral response of SBFI upon ion binding permit excitation ratio measurements, and this indicator can be used with the same optical filters and equipment used for fura-2.

Fluorescent Ion Indicators Specifications:
• Label (Ex/Em): SBFI (~340,380/500 nm)
• Lyophilized product may be dissolved in DMSO for use
• Product is typically loaded into cells by adding the dissolved indicator to medium containing cells


Selectivity Considerations and Cell Loading Strategies
The dissociation constant (Kd) of SBFI for Na+ is 3.8 mM in the absence of K+, and 11.3 mM in solutions with a combined Na+ and K+ concentration of 135 mM (which approximates physiological ionic strength). SBFI is ~18-fold more selective for Na+ than for K+.

SBFI is available as both cell-impermeant acid salt (S1262) and as cell-permeant acetoxymethyl (AM) esters (S1263, S1264). The anionic acid forms can be loaded into cells using our Influx™ pinocytic cell-loading reagent (I14402, Chelators, Calibration Buffers, Ionophores and Cell-Loading Reagents—Section 19.8), or by microinjection, patch-pipette infusion or electroporation. For AM ester loading (Loading and Calibration of Intracellular Ion Indicators—Note 19.1), addition of the Pluronic® F-127 (P3000MP, P6866, P6867) or PowerLoad™ (P10020) dispersing agents as well as relatively long incubation times—up to four hours—are typically necessary.

Find Fluorescent Indicators for Na+ and K+
We offer a number of fluorescent indicators for measuring Na+ and K+. Review Fluorescent Na+ and K+ Indicators—Section 21.1 in the Molecular Probes® Handbook for more information on these products.

For Research Use. Not for human or animal therapeutic or diagnostic use.