Shop All Labels & Labeling Kits

4-Acetamido-4'-((iodoacetyl)amino)Stilbene-2,2'-Disulfonic Acid, Disodium Salt (Invitrogen™)

The iodoacetamide derivative of stilbene (4-acetamido-4'-((iodoacetyl) amino)stilbene-2,2'-disulfonic acid, disodium salt) is readily conjugated to thiols. The combination of high polarity and membrane impermeability makes this polysulfonated dye useful for determining whether thiol-containing proteins and polypeptide chains are exposed at the extracellular or cytoplsamic membrane surface. Stilbene protein adducts are charged and can be detected by gel or capillary electrophoresis.

4-Acetamido-4'-Maleimidylstilbene-2,2'-Disulfonic Acid, Disodium Salt (Invitrogen™)

Our 4-acetamido-4'-maleimidylstilbene-2,2'- disulfonic acid is a thiol-reactive reagent that is water soluble, with high polarity and membrane impermeability. This polysulfonated dye is useful for determining whether thiol-containing proteins and polypeptide chains are exposed at the extracellular or cytoplasmic membrane surface.

Rhodamine Green™ Carboxylic Acid, Succinimidyl Ester, Hydrochloride (5(6)-CR 110, SE), mixed isomers (Invitrogen™)

This mixed isomer preparation of the amine-reactive Rhodamine Green carboxylic acid, succinimidyl ester yields bright and photostable conjugates. Rhodamine Green dye—labeled probes have been frequently used for Fluorescence Correlation Spectroscopy (FCS).

Rhodamine Green™-X, Succinimidyl Ester, Hydrochloride, mixed isomers (Invitrogen™)

The thiol-reactive Rhodamine Green®-X, succinimidyl ester can be used to create green-fluorescent bioconjugates with excitation/emission maxima ~502/527 nm. This dye is the nonsulfonated analog of the Alexa Fluor® 488 dye.

Qtracker™ 565 Vascular Labels (Invitrogen™)

Qtracker® non-targeted quantum dots are designed to be injected into the tail vein of mice for the study of vascular structure using small animal in vivo imaging (SAIVI) techniques. These nanocrystals exhibit intense fluorescence with red-shifted emission for increased tissue penetration, and have a PEG surface coating specially developed to minimize nonspecific interactions and reduce immune response by the tissue. Because the PEG surface coating does not contain reactive functional groups, the Qtracker® non-targeted quantum dots are retained in circulation longer and can be imaged for up to 3 hours with a single injection or for longer periods of time with additional injections.

Need a different emission spectrum or longer tracking? View our other mammalian cell tracking products.

Key Attributes:

Qtracker® 565 label has Ex/Em (405-525/565) nm
Designed for small animal in vivo imaging
Introduced via tail vein injection, can be imaged for up to 3 hours after injection
Available in four colors—565 nm, 655 nm, 705 nm, or 800 nm emission

Read more about SAIVI and about applications for Qdot® nanocrystals.

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

Rhodamine Red™-X, Succinimidyl Ester, 5-isomer (Invitrogen™)

The amine-reactive Rhodamine Red™-X, succinimidyl ester can be used to create red-fluorescent bioconjugates with excitation/emission maxima ~560/580 nm. This reactive dye contains an additional seven-atom aminohexanoyl spacer ("X") between the fluorophore and the succinimidyl ester group. This spacer helps to separate the fluorophore from its point of attachment, potentially reducing the interaction of the fluorophore with the biomolecule to which it is conjugated.

ATTO-TAG™ FQ Derivatization Reagent (FQ; 3-(2-Furoyl)quinoline-2-Carboxaldehyde) (Invitrogen™)

The ATTO-TAG FQ reagent allows the ultrasensitive detection of primary amines. This reagent is available as a standalone product or as a component of an amine-derivatization kit (A-2334). Because ATTO-TAG FQ is nonfluorescent in the unreacted state and reacts specifically with amines to form highly fluorescent conjugates, it is particularly well-suited to the derivatization of peptides, amino acids, aminated sugars and other amine-containing molecules for detection by capillary electrophoresis with laser-induced fluorescence (LIF). Recently, researchers described a simple method in which the ATTO-TAG FQ reagent was used to derivatize very dilute solutions (10-8 M) of peptides.

pHrodo™ iFL Green STP Ester (amine-reactive) (Invitrogen™)

The amine-reactive pH-sensitive pHrodo iFL Green STP Ester dye is an improved version of pHrodo Green dye optimized for the creation of bioconjugates to be used in the study of antibody internalization, endocytosis, and phagocytosis. pHrodo iFL Green dye dramatically increases fluorescence as the pH of its surroundings become more acidic. It is more soluble than the original pHrodo Green dye, making it more useful for the labeling of antibodies that may otherwise precipitate out of solution during conjugation.

• Use pH-sensitive pHrodo iFL Green STP Ester to make pH-sensitive bioconjugates of your choice
• Get faster, more accurate results than with any other endocytosis or phagocytosis assay—no need for wash steps or quenchers
• Multiplex with red fluorescent markers such as RFP, pHrodo iFL Red STP, and many others

The increase in fluorescence of pHrodo iFL Green dye as the pH changes from basic to acidic correlates with the acidification of intracellular vesicles, making it a valuable tool for the study of endocytosis or phagocytosis and their regulation by environmental factors, drugs, or pathogens. The spectral properties of pHrodo iFL Green dye make it useful for multi-color experiments. pHrodo iFL Green dye can be detected using most standard green-fluorescent filter sets and has been validated for use in a variety of applications, including flow cytometry, fluorescent microscopy, and high content screening (HCS). The lack of fluorescence of pHrodo iFL Green dye in a typical extracellular environment eliminates the need for wash steps or quencher dyes in the experimental workflow.

pHrodo iFL Green STP Ester is an amine-reactive dye that can be used to make pHrodo iFL Green STP bioconjugates in aqueous buffer. The STP ester will react with primary amines on a protein, cell, or virus to create a stable conjugate that can be used in live cell assays or stored for later use.

DACM, N-(7-Dimethylamino-4-Methylcoumarin-3-yl))Maleimide (Invitrogen™)

The thiol reactive coumarin, DACM can be used to create blue-fluorescent bioconjugates. When compared with AMCA conjugates, conjugates of the UV light-excitable 7-dialkylaminocoumarin fluorophore have slightly longer-wavelength emission spectra (~470 nm). The unreacted reagent is nonfluorescent and can also be used to quantitate free thiols.

CellTrace™ Calcein Green, AM - Special Packaging (Invitrogen™)

CellTrace calcein green AM is a cell-permeant dye that can be used to determine cell viability in most eukaryotic cells. In live cells the nonfluorescent CellTrace calcein green AM is converted to a green-fluorescent calcein after intracellular esterases remove the acetoxymethyl (AM) esters. This dye is also available as 1 mg of the solid (C-1430) and resuspended in DMSO (C-3099). For a longer wavelength version of this dye, check out our CellTrace calcein red-orange AM (C-34851).

Qtracker™ 705 Vascular Labels (Invitrogen™)

Qtracker® non-targeted quantum dots are designed to be injected into the tail vein of mice for the study of vascular structure using small animal in vivo imaging (SAIVI) techniques. These nanocrystals exhibit intense fluorescence with red-shifted emission for increased tissue penetration, and have a PEG surface coating specially developed to minimize nonspecific interactions and reduce immune response by the tissue. Because the PEG surface coating does not contain reactive functional groups, the Qtracker® non-targeted quantum dots are retained in circulation longer and can be imaged for up to 3 hours with a single injection or for longer periods of time with additional injections.

Need a different emission spectrum or longer tracking? View our other mammalian cell tracking products.

Key Attributes:

Qtracker® 705 label has Ex/Em (405-665/705) nm
Designed for small animal in vivo imaging
Introduced via tail vein injection, can be imaged for up to 3 hours after injection
Available in four colors—565 nm, 655 nm, 705 nm, or 800 nm emission

Read more about SAIVI and about applications for Qdot® nanocrystals.

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

SAMSA Fluorescein, 5-((2-(and-3)-S-(acetylmercapto) succinoyl) amino) Fluorescein, mixed isomers (Invitrogen™)

SAMSA fluorescein is a useful reagent for forming fluorescent protein conjugates and for assaying maleimide and iodoacetamide moieties on proteins with fluorescein. SAMSA fluorescein is activated with base to remove the acetyl protecting group, thereby generating a thiol-containing fluorescein.

Molecular Probes® Cell Imaging Kit (Invitrogen™)

Fluorescence imaging protocols are sometimes complicated and tedious, with more time spent preparing samples and reagents than acquiring images and data. To help researchers focus more on biology and get results faster, we have developed a set of imaging reagents that emphasize user friendliness and workflow convenience.

The Molecular Probes® Cell Imaging Kit contains the following products:

NucBlue™ Live ReadyProbes™ Reagent (Cat. No. R37605)
NucRed™ Live 647 ReadyProbes™ Reagent (Cat. No. R37106)
ReadyProbes™ Cell Viability Imaging Kit, Blue/Green (Cat. No. R37609)
Goat Anti-Rabbit IgG (H+L) Secondary Antibody, Alexa Fluor™ 594 conjugate (Cat. No. R37117)
Goat Anti-Mouse lgG Secondary Antibody, Alexa Fluor™ 488 conjugate (Cat. No. R37120)
Image-iT™ FX Signal Enhancer ReadyProbes™ Reagent (Cat. No. R37107)

5-ROX, SE (5-Carboxy-X-Rhodamine, Succinimidyl Ester), single isomer (Invitrogen™)

The isomeric 5-ROX, SE is an amine-reactive form of carboxy-X-rhodamine and is widely used for oligonucleotide labeling and automated DNA sequencing applications.

SiteClick™ Qdot™ 625 Antibody Labeling Kit (Invitrogen™)

Create a perfectly labeled antibody with the SiteClick™ Qdot® 625 Antibody Labeling Kit. This kit replaces the conventional Qdot® 625 Antibody Conjugation Kit (A10197). Unlike the conventional amine-thiol crosslinker method, SiteClick™ labeling specifically attaches the label to the heavy chains of an IgG antibody, ensuring that the antigen-binding domains remain available for binding to your antigen target. This site selectivity is achieved by targeting the carbohydrate domains present on essentially all IgG antibodies regardless of isotype and host species. In addition, no harsh reduction steps are required, and the labeling is consistent and reproducible each time it is performed. Depending upon the label, the resulting SiteClick™ -labeled antibody can be used in flow cytometry, fluorescence imaging, or Western blot detection.

Important Features of the SiteClick™ Qdot® 625 Antibody Labeling Kit:

• Contains everything required to label 100 µg of IgG antibody
• Easy to follow step-by-step protocol
• Highly efficient, site-specific, reproducible labeling chemistry results in high quality antibody conjugate.
• Qdot® 625 labels can be used in confocal or traditional fluorescence microscopy.
• In flow cytometry, Qdot® 625 can be excited by the 488 nm line of the argon-ion laser, or alternatively via excitation at 405 nm. This is true of all Qdot® fluorophores.

Qdot® Fluorophores are Our Brightest Labels
Antibody conjugates made with Qdot® fluorophores produce fluorescence output that surpasses that of traditional organic dyes. Paired with the correct optical filters, Qdot® nanocrystals are as much as 50 times brighter. Read more about Qdot® nanocrystals or review additional product details in Qdot® Nanocrystals—Section 6.6 in the Molecular Probes® Handbook.

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits (see Antibody Labeling from A to Z). To learn more about our various kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in the Molecular Probes® Handbook.

Custom SiteClick™ Antibody Labeling Services
If you have an antibody that is considered "difficult to label" or has lost activity after labeling using a conventional method, please contact our custom service representatives to determine whether the SiteClick™ Antibody Labeling Service would be right for your antibody. We offer complete custom SiteClick™ antibody labeling services with the option of multiple detection molecules including biotin, Alexa Fluor® dyes, Qdot® fluorophores, R-PE, and others.

pHrodo™ iFL Red Microscale Protein Labeling Kit (Invitrogen™)

The pHrodo iFL Red Microscale Protein Labeling Kit provides the reagents needed to easily label 3 microscale purified protein or antibody samples (20–100 µg) with pHrodo iFL Red dye.

The pHrodo iFL Red Microscale Labeling Kit is:
Convenient—labeling typically takes 2 hours with less than 30 min hands-on time
Versatile—label proteins with molecular weights between 12 and 150 kDa
Customizable—create your own probes for studying antibody internalization, phagocytosis, and endocytosis

This kit contains amine-reactive pH-sensitive pHrodo iFL Red STP ester dye that covalently binds to free lysines anywhere they occur in an antibody or protein. pHrodo iFL Red dye is an improved version of pHrodoRed dye optimized for the creation of bright and soluble bioconjugates to be used in the study of antibody internalization, endocytosis, and phagocytosis. It is more soluble than the original pHrodo Red dye, making it useful for the labeling of antibodies that may otherwise precipitate out of solution during conjugation. pHrodo iFL Red dye dramatically increases fluorescence as the pH of its surroundings become more acidic. It is non-fluorescent outside the cell, but fluoresces bright red in phagosomes and endosomes.

MDCC, 7-Diethylamino-3-((((2-Maleimidyl)ethyl)amino)carbonyl)coumarin (Invitrogen™)

The thiol reactive coumarin, MDCC can be used to create blue-fluorescent bioconjugates. When compared with AMCA conjugates, conjugates of the UV light-excitable 7-dialkylaminocoumarin fluorophore have slightly longer-wavelength emission spectra (~470 nm).

CellTrace™ Calcein Blue, AM - Special Packaging (Invitrogen™)

CellTrace calcein blue AM is a proven short-term, blue-fluorescent tracer for cell labeling. The probe possesses acetoxymethyl (AM) esters that allow its passive diffusion across cell membranes. Upon cleavage of the AM esters by intracellular esterases, the molecule that remains (absorption/emission maxima ~360/449 nm) is relatively polar and is retained by cells for several hours.

View a selection guide for all Nonfixable Viability Dyes for Flow Cytometry.

Iodoacetamide Alkyne (Invitrogen™)

Conjugates prepared with the thiol-reactive alkyne, succinimidyl ester can be detected with an azide-containing molecule in a click chemistry reaction. Click chemistry describes a class of chemical reactions that use bio-orthogonal or biologically unique moities to label and detect a molecule of interest using a two-step procedure. The two-step reaction procedure involves a copper-catalyzed triazole formation of an azide and an alkyne. Click reactions have several characteristics: the reaction between the detection moieties is efficient; no extreme temperatures or solvents are required; the reaction product is stable; the components of the reaction are bioinert; and perhaps most importantly, no side reactions occur – the label and detection tags react selectively and specifically with one another. Unlike traditional chemical reactions utilizing succinimidyl esters or maleimides that target amines and sulfhydryls – functional groups that are not unique – click chemistry-labeled molecules can be applied to complex biological samples and be detected with unprecedented sensitivity due to extremely low background.

Qtracker™ 800 Vascular Labels (Invitrogen™)

Qtracker® non-targeted quantum dots are designed to be injected into the tail vein of mice for the study of vascular structure using small animal in vivo imaging (SAIVI) techniques. These nanocrystals exhibit intense fluorescence with red-shifted emission for increased tissue penetration, and have a PEG surface coating specially developed to minimize nonspecific interactions and reduce immune response by the tissue. Because the PEG surface coating does not contain reactive functional groups, the Qtracker® non-targeted quantum dots are retained in circulation longer and can be imaged for up to 3 hours with a single injection or for longer periods of time with additional injections.

Need a different emission spectrum or longer tracking? View our other mammalian cell tracking products.

Key Attributes:

Qtracker® 800 label has Ex/Em (405-760/800) nm
Designed for small animal in vivo imaging
Introduced via tail vein injection, can be imaged for up to 3 hours after injection
Available in four colors—565 nm, 655 nm, 705 nm, or 800 nm emission

Read more about SAIVI and about applications for Qdot® nanocrystals.

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

Alexa Fluor™ 700 NHS Ester (Succinimidyl Ester) (Invitrogen™)

Alexa Fluor® 700 is a bright and photostable near-IR dye that can be excited with a xenon-arc lamp, far-red diode lasers, or dye pumped lasers operating in the 675–700 nm range. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 700 dye is water soluble and pH-insensitive from pH 4 to pH 10. Fluorescence of this long-wavelength Alexa Fluor® dye is not visible to the human eye but is readily detected by most imaging systems. In addition to reactive dye formulations, we offer Alexa Fluor® 700 dye conjugated to a variety of antibodies, peptides, proteins, tracers, and amplification substrates optimized for cellular labeling and detection.The NHS ester (or succinimidyl ester) of Alexa Fluor® 700 is the most popular tool for conjugating this dye to a protein or antibody. NHS esters can be used to label to the primary amines (R-NH2) of proteins, amine-modified oligonucleotides, and other amine-containing molecules. The resulting Alexa Fluor® conjugate will exhibit brighter fluorescence and greater photostability than the conjugates of other spectrally similar fluorophores.

Detailed information about this AlexaFluor® NHS ester:

Fluorophore label: Alexa Fluor® 700 dye
Reactive group: NHS ester
Reactivity: Primary amines on proteins and ligands, amine-modified oligonucleotides
Ex/Em of the conjugate: 702/723 nm
Extinction coefficient: 205,000 cm-1M-1
Molecular weight: ~1400

Typical Conjugation Reaction
You can conjugate amine-reactive reagents with virtually any protein or peptide (the provided protocol is optimized for IgG antibodies). You can scale the reaction for any amount of protein, but the concentration of the protein should be at least 2 mg/mL for optimal results. We recommend trying three different degrees of labeling, using three different molar ratios of the reactive reagent to protein.

The Alexa Fluor® NHS ester is typically dissolved in high-quality anhydrous dimethylformamide (DMF) or dimethylsulfoxide (DMSO) (D12345), and the reaction is carried out in 0.1–0.2 M sodium bicarbonate buffer, pH 8.3, at room temperature for 1 hour. Because the pKa of the terminal amine is lower than that of the lysine epsilon-amino group, you may achieve more selective labeling of the amine terminus using a buffer closer to neutral pH.

Conjugate Purification
Labeled antibodies are typically separated from free Alexa Fluor® dye using a gel filtration column, such as Sephadex™ G-25, BioGel® P-30, or equivalent. For much larger or smaller proteins, select a gel filtration media with an appropriate molecular weight cut-off or purify by dialysis. We offer several purification kits optimized for different quantities of antibody conjugate:
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

D-Biotin (Invitrogen™)

D-biotin binds with high affinity to streptavidin, avidin and NeutrAvidin® biotin-binding proteins. This solution can be used in conjunction with unlabeled streptavidin or avidin in procedures to block endogenous biotin.

Click-IT™ GalNAz Metabolic Glycoprotein Labeling Reagent (Tetraacetylated N-Azidoacetylgalactosamine) (Invitrogen™)

The Click-iT® GalNAz metabolic glycoprotein labeling reagent provides the first part of a simple and robust two-step technique to identify and characterize cell surface O-linked glycoproteins. In step one, cultured cells are incubated with the azide-modified galactosamine (GalNAz). The azido-sugar is metabolically incorporated into cell surface O-linked glycoproteins through the permissive nature of the oligosaccharide biosynthesis pathway. In step two, via the chemoselective ligation or click reaction between an azide and an alkyne, the azido-labeled glycoproteins can then be detected with a Click-iT® Glycoprotein Detection Kit for gels (TAMRA or Dapoxyl® alkyne) or Western blots (biotin alkyne). These Click-iT® products are compatible with LC-MS⁄MS and Multiplexed Proteomics™ technologies for in-depth analyses of the glycoproteome.

Alexa Fluor™ 405 NHS Ester (Succinimidyl Ester) (Invitrogen™)

Alexa Fluor® 405 is a blue-fluorescent dye optimal for use with the 405 nm violet laser. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 405 dye is water soluble and pH-insensitive from pH 4 to pH 10. In addition to reactive dye formulations, we offer Alexa Fluor® 405 dye conjugated to a variety of antibodies, peptides, proteins, tracers, and amplification substrates optimized for cellular labeling and detection (learn more).

The NHS ester (or succinimidyl ester) of Alexa Fluor® 405 is the most popular tool for conjugating this dye to a protein or antibody. NHS esters can be used to label to the primary amines (R-NH2) of proteins, amine-modified oligonucleotides, and other amine-containing molecules. The resulting Alexa Fluor® conjugate will exhibit brighter fluorescence and greater photostability than the conjugates of other spectrally similar fluorophores.

Detailed information about this AlexaFluor® NHS ester:

Fluorophore label: Alexa Fluor® 405 dye
Reactive group: NHS ester
Reactivity: Primary amines on proteins and ligands, amine-modified oligonucleotides
Ex/Em of the conjugate: 400/424 nm
Extinction coefficient: 35,000 cm-1M-1
Spectrally similar dyes: Pacific Blue
Molecular weight: 1028.3

Typical Conjugation Reaction
You can conjugate amine-reactive reagents with virtually any protein or peptide (the provided protocol is optimized for IgG antibodies). You can scale the reaction for any amount of protein, but the concentration of the protein should be at least 2 mg/mL for optimal results. We recommend trying three different degrees of labeling, using three different molar ratios of the reactive reagent to protein.

The Alexa Fluor® NHS ester is typically dissolved in high-quality anhydrous dimethylformamide (DMF) or dimethylsulfoxide (DMSO) (D12345), and the reaction is carried out in 0.1–0.2 M sodium bicarbonate buffer, pH 8.3, at room temperature for 1 hour. Because the pKa of the terminal amine is lower than that of the lysine epsilon-amino group, you may achieve more selective labeling of the amine terminus using a buffer closer to neutral pH.

Conjugate Purification
Labeled antibodies are typically separated from free Alexa Fluor® dye using a gel filtration column, such as Sephadex™ G-25, BioGel® P-30, or equivalent. For much larger or smaller proteins, select a gel filtration media with an appropriate molecular weight cut-off or purify by dialysis. We offer several purification kits optimized for different quantities of antibody conjugate:
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

DyLight™ 680-4xPEG NHS Ester (Thermo Scientific™)

Thermo Scientific DyLight 680-4xPEG Amine-Reactive Dye is a derivative of our high-performance DyLight 680 Dye that can be used to fluorescently label antibodies and other proteins.

The DyLight 680-4xPEG dye contains 4 polyethylene glycol (PEG) chains that are non-cytotoxic, enhance fluorescence and reduce nonspecific binding of conjugates made with them. Conjugates made with DyLight 680-4xPEG Dye can be used as molecular probes for cellular imaging and other fluorescence detection methods. The far-red to NIR fluorescence properties of DyLight 680-4xPEG Dye make it especially useful in a variety of biological, chemical, and pharmaceutical applications, including in vivo imaging. The PEG chains also improve solubility of the dyes and labeled molecules in aqueous solution, aid in cell permeability and improve tissue retention.

Features of the DyLight 680-4xPEG NHS Ester:

High fluorescence intensity—significantly brighter fluorescence than Alexa Fluor™ 680
PEGylated—improves solubility in aqueous solution, aids in cell permeability and improves tissue retention in in vivo applications

Applications:
• Fluorescence microscopy
In vivo or ex vivo imaging
• Cell-based assays
• Flow cytometry/fluorescence-activated cell sorting (FACS)

DyLight 680-4xPEG Amine-Reactive Dye is activated with an N-hydroxysuccinimide (NHS) ester moiety to react with exposed N-terminal α-amino groups or the ε-amino groups of lysine residues to form stable amide bonds. Learn more about NHS ester chemistry.

Typical labeling reactions require the dye to first be dissolved in anhydrous dimethyl formamide (DMF) or another suitable organic solvent before adding a specific molar amount of dye to an amine-free buffer containing the protein to be labeled. However, the high solubility of DyLight Fluors permits protein solutions to be added directly to the labeling reagent. This feature allows DyLight 680-4xPEG Amine-Reactive Dye to be provided in multiple formats with flexible protocols to achieve efficient degrees of labeling.

We also offer Standard and Microscale DyLight 680-4xPEG Antibody Labeling Kits for fast and efficient fluorescent labeling of antibodies. The standard size kit contains all necessary components to perform three separate labeling reactions using 1 mg IgG or similar quantities of other proteins. The microscale kit contains all of the necessary components to perform five separate labeling reactions using 100 µg IgG. Both kit sizes include the Amine-Reactive DyLight 680-4xPEG NHS-ester in convenient single-use vials as well as purification resin and spin columns for the preparation of ready-to-use conjugate.

Related Products
DyLight™ 680-4xPEG Antibody Labeling Kit
DyLight™ 680-4xPEG Microscale Antibody Labeling Kit

Alexa Fluor™ 568 NHS Ester (Succinimidyl Ester) (Invitrogen™)

Alexa Fluor® 568 is a bright orange dye. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 568 dye is water soluble and pH-insensitive from pH 4 to pH 10. In addition to reactive dye formulations, we offer Alexa Fluor® 568 dye conjugated to a variety of antibodies, peptides, proteins, tracers, and amplification substrates optimized for cellular labeling and detection (learn more).

The NHS ester (or succinimidyl ester) of Alexa Fluor® 568 is the most popular tool for conjugating this dye to a protein or antibody. NHS esters can be used to label to the primary amines (R-NH2) of proteins, amine-modified oligonucleotides, and other amine-containing molecules. The resulting Alexa Fluor® conjugate will exhibit brighter fluorescence and greater photostability than the conjugates of other spectrally similar fluorophores.

Detailed information about this AlexaFluor® NHS ester:

Fluorophore label: Alexa Fluor® 568 dye
Reactive group: NHS ester
Reactivity: Primary amines on proteins and ligands, amine-modified oligonucleotides
Ex/Em of the conjugate: 578/602 nm
Extinction coefficient: 88,000 cm-1M-1
Spectrally similar dyes: Rhodamine Red
Molecular weight: 791.8

Typical Conjugation Reaction
You can conjugate amine-reactive reagents with virtually any protein or peptide (the provided protocol is optimized for IgG antibodies). You can scale the reaction for any amount of protein, but the concentration of the protein should be at least 2 mg/mL for optimal results. We recommend trying three different degrees of labeling, using three different molar ratios of the reactive reagent to protein.

The Alexa Fluor® NHS ester is typically dissolved in high-quality anhydrous dimethylformamide (DMF) or dimethylsulfoxide (DMSO) (D12345), and the reaction is carried out in 0.1–0.2 M sodium bicarbonate buffer, pH 8.3, at room temperature for 1 hour. Because the pKa of the terminal amine is lower than that of the lysine epsilon-amino group, you may achieve more selective labeling of the amine terminus using a buffer closer to neutral pH.

Conjugate Purification
Labeled antibodies are typically separated from free Alexa Fluor® dye using a gel filtration column, such as Sephadex™ G-25, BioGel® P-30, or equivalent. For much larger or smaller proteins, select a gel filtration media with an appropriate molecular weight cut-off or purify by dialysis. We offer several purification kits optimized for different quantities of antibody conjugate:
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

EZ-Link™ PFP-Biotin (Thermo Scientific™)

Thermo Scientific EZ-Link PFP-biotin is a pentafluorophenyl-ester biotinylation reagent that has similar properties to NHS-biotin but is more reactive and will target both primary and secondary amines for biotinylation.

Features of EZ-Link PFP-Biotin:

Molecular labeling—biotinylate proteins and nucleic acids for avidin-biotin methods
Membrane-permeable—can be used to label inside cells (intracellular)
Amine-reactive—reacts with primary and secondary amines of proteins and other molecules (unlike typical NHS reagents, which react with primary amines only)
Irreversible—forms permanent amide bonds; spacer arm cannot be cleaved
Solubility—must be dissolved in DMSO or DMF before further dilution in aqueous buffers
Very short—spacer arm (total length added to target) is 9.6 angstroms; it consists of the native biotin valeric acid group only

PFP-Biotin is an amine-reactive biotinylation reagent based on activation as as a pentafluorophenyl ester (PFP ester) rather than the usual N-hydroxysuccinimide (NHS) ester. The compound has properties similar to those of NHS-Biotin (Part No. 20217) but exhibits greater reactivity toward amino groups. Unlike NHS-Biotin, PFP-Biotin will react with both secondary amines and primary amines, enabling it to be used to label nucleic acids as well as proteins. The reaction occurs spontaneously at pH 7 to 9.

We manufacture biotin reagents to ensure the highest possible overall product integrity, consistency and performance for the intended research applications.

DyLight™ 405 Maleimide (Thermo Scientific™)

Thermo Scientific DyLight 405 Sulfhydryl-Reactive Dye is a maleimide-activated derivative of high-performance DyLight 405 used to fluorescently label sulfhydryl-containing peptides, proteins and other biomolecular probes.

DyLight 405 has high fluorescence intensity over a broad pH range (pH 4-9) and is more photostable than Alexa Fluor™ 405, Cascade™ Blue and AMCA dyes in many applications. The high water solubility of DyLight Fluors means that a high dye-to-protein ratio can be attained without causing precipitation of the conjugates.

Features of DyLight 405 Maleimide:

High performance—DyLight 405 shows brighter fluorescence than Alexa Fluor 405, Cascade Blue and AMCA
Specific—maleimide-activated dye labels proteins and other molecules at reduced sulfhydryls (-SH)
Efficient labeling methods—well-characterized chemistry and optimized protocols provide for reliable, high-quality labeling
Optimized antibody labeling procedure—complete protocol for IgG reduction and labeling and calculating the labeling efficiency

Applications:
• Antibody labeling for immunofluorescence applications, including immunocytochemistry (ICC), immunohistochemistry (IHC), Western blotting and ELISA assay
• Target macromolecule labeling for in vitro and in vivo fluorescent detection strategies

DyLight 405 Sulfhydryl-Reactive Dye is activated with a maleic acid imide (maleimide) moiety to form a reactive alkylation reagent. Labeling occurs through reaction of the maleimide-activated dye with reduced sulfhydryl groups (-SH) to form stable thioether bonds. Maleimides are specific for sulfhydryl groups between pH 6.5-7.5. Learn more about maleimide chemistry.

6-ROX, SE (6-Carboxy-X-Rhodamine, Succinimidyl Ester), single isomer (Invitrogen™)

The isomeric 6-ROX, SE is an amine-reactive form of carboxy-X-rhodamine and is widely used for oligonucleotide labeling and automated DNA sequencingapplications.

SiteClick™ Qdot™ 655 Antibody Labeling Kit (Invitrogen™)

Create a perfectly labeled antibody with the SiteClick™ Qdot® 655 Antibody Labeling Kit. This kit replaces the conventional Qdot® 655 Antibody Conjugation Kit (Q22021MP). Unlike the conventional amine-thiol crosslinker method, SiteClick™ labeling specifically attaches the label to the heavy chains of an IgG antibody, ensuring that the antigen-binding domains remain available for binding to your antigen target. This site selectivity is achieved by targeting the carbohydrate domains present on essentially all IgG antibodies regardless of isotype and host species. In addition, no harsh reduction steps are required, and the labeling is consistent and reproducible each time it is performed. Depending upon the label, the resulting SiteClick™ -labeled antibody can be used in flow cytometry, fluorescence imaging, or Western blot detection.

Important Features of the SiteClick™ Qdot® 655 Antibody Labeling Kit:

• Contains everything required to label 100 µg of IgG antibody
• Easy to follow step-by-step protocol
• Highly efficient, site-specific, reproducible labeling chemistry results in high quality antibody conjugate.
• Qdot® 655 labels can be used in confocal or traditional fluorescence microscopy.
• In flow cytometry, Qdot® 655 can be excited by the 488 nm line of the argon-ion laser, or alternatively via excitation at 405 nm. This is true of all Qdot® fluorophores.

Qdot® Fluorophores are Our Brightest Labels
Antibody conjugates made with Qdot® fluorophores produce fluorescence output that surpasses that of traditional organic dyes. Paired with the correct optical filters, Qdot® nanocrystals are as much as 50 times brighter. Read more about Qdot® nanocrystals or review additional product details in Qdot® Nanocrystals—Section 6.6 in the Molecular Probes® Handbook.

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits (see Antibody Labeling from A to Z). To learn more about our various kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in the Molecular Probes® Handbook.

Custom SiteClick™ Antibody Labeling Services
If you have an antibody that is considered "difficult to label" or has lost activity after labeling using a conventional method, please contact our custom service representatives to determine whether the SiteClick™ Antibody Labeling Service would be right for your antibody. We offer complete custom SiteClick™ antibody labeling services with the option of multiple detection molecules including biotin, Alexa Fluor® dyes, Qdot® fluorophores, R-PE, and others.